00001 ;*******************************************************************************
00002 ;*                                                                             *
00003 ;*                           S T A R   R A I D E R S                           *
00004 ;*                                                                             *
00005 ;*                  for the Atari 8-bit Home Computer System                   *
00006 ;*                                                                             *
00007 ;*       Reverse-engineered and documented assembly language source code       *
00008 ;*                                                                             *
00009 ;*                                     by                                      *
00010 ;*                                                                             *
00011 ;*                                Lorenz Wiest                                 *
00012 ;*                                                                             *
00013 ;*                            (lo.wiest(at)web.de)                             *
00014 ;*                                                                             *
00015 ;*                                First Release                                *
00016 ;*                                 22-SEP-2015                                 *
00017 ;*                                                                             *
00018 ;*                                 Last Update                                 *
00019 ;*                                 15-MAR-2016                                 *
00020 ;*                                                                             *
00021 ;*                STAR RAIDERS was created by Douglas Neubauer                 *
00022 ;*                  STAR RAIDERS was published by Atari Inc.                   *
00023 ;*                                                                             *
00024 ;*******************************************************************************
00025
00026 ; I wrote this document out of my own curiosity. When STAR RAIDERS was released
00027 ; in 1979 it became the killer app for the Atari 8-bit Home Computer System.
00028 ; Since then I have always been wondering what made it tick and how its (at that
00029 ; time) spectacular 3D graphics worked, especially the rotating star field.
00030 ; Impressed by "The Atari BASIC Source Book" I decided to reverse-engineer the
00031 ; STAR RAIDERS 8KB ROM cartridge to recreate a fully documented assembly
00032 ; language source code file. I had no access to the original source code, so the
00033 ; only way to succeed was a combination of educated guesses, trial-and-error,
00034 ; and patience. Eventually, I made it.
00035 ;
00036 ; Essential in preparing this document were three programs I wrote:
00037 ;
00038 ; (1) A 6502-cross-assembler based on the syntax of the MAC/65 assembler for the
00039 ;     Atari 8-bit Home Computer System to create the binary file that I verified
00040 ;     against the binary of the original ROM cartridge.
00041 ;
00042 ; (2) A text formatter to layout the source code file with its copious comment
00043 ;     sections. This was a big time saver, because as the documentation grew the
00044 ;     source code had to be reformatted over and over again.
00045 ;
00046 ; (3) A symbol checker to verify that the ubiquitous symbol-value pairs in the
00047 ;     documentation match the corresponding symbol values produced by the
00048 ;     assembler.
00049 ;
00050 ; This assembly language source code file is compatible with the MAC/65
00051 ; assembler for the Atari 8-bit Home Computer System. I was able to assemble it
00052 ; on an emulated Atari running MAC/65, producing the identical binary of the ROM
00053 ; cartridge. 
00054 ;
00055 ; Your feedback is welcome! Send feedback to lo.wiest(at)web.de.
00056 ;
00057 ; Enjoy! -- Lorenz
00058
00059 ;*******************************************************************************
00060 ;*                                                                             *
00061 ;*                               N O T A T I O N                               *
00062 ;*                                                                             *
00063 ;*******************************************************************************
00064
00065 ; BITS AND BYTES
00066 ;
00067 ; o   A "byte" consists of 8 bits. They are numbered B7..0. Bit B0 is the least
00068 ;     significant bit.
00069 ;
00070 ; o   A "word" consists of 16 bits. They are numbered B15..B0. Bit B0 is the
00071 ;     least significant bit. A word is stored in low-order then high-order byte
00072 ;     order.
00073 ;
00074 ; o   The high-order byte ("high byte") of a word consists of bits B15..8 of the
00075 ;     word.
00076 ;
00077 ; o   The low-order byte ("low byte") of a word consists of bits B7..0 of the
00078 ;     word.
00079 ;
00080 ; NUMBERS
00081 ;
00082 ; o   The dollar sign ($) prefixes hexadecimal numbers.
00083 ;     Example: $101 is the decimal number 257.
00084 ;
00085 ; o   The percent sign (%) prefixes binary numbers.
00086 ;     Example: %101 is the decimal number 5.
00087 ;
00088 ; o   The asterisk (*) is a wildcard character for a single hexadecimal or
00089 ;     binary digit.
00090 ;     Example: $0*00 is a placeholder for the numbers $0000, $0100, ..., $0F00.
00091 ;
00092 ; o   The lowercase R (r) is a wildcard character for a single random
00093 ;     hexadecimal or binary digit. The random digit r is chosen by a random
00094 ;     number generator.
00095 ;     Example: %00r0 is a placeholder for the numbers %0000 or %0010.
00096 ;
00097 ; OPERATORS
00098 ;
00099 ; o   The exclamation mark (!) is the binary OR operator.
00100 ;     Example: $01!$02 is $03.
00101 ;
00102 ; o   The less-than sign (<) indicates bits B7..0 of a word.
00103 ;     Example: <$1234 is $34.
00104 ;
00105 ; o   The greater-than sign (>) indicates bits B15..8 of a word.
00106 ;     Example: >$1234 is $12.
00107 ;
00108 ; o   A pair of brackets ([]) groups mathematical expressions.
00109 ;     Example: [3-1]*4 is 8.
00110 ;
00111 ; ASSEMBLY LANGUAGE
00112 ;
00113 ; o   The uppercase A (A) indicates the accumulator register of the 6502 CPU.
00114 ;
00115 ; o   The uppercase X (X) indicates the X register of the 6502 CPU.
00116 ;
00117 ; o   The uppercase Y (Y) indicates the Y register of the 6502 CPU.
00118 ;
00119 ; o   The prefix uppercase L and dot (L.) indicates a local variable, a memory
00120 ;     location used temporarily in a subroutine.
00121 ;
00122 ; PSEUDO-FUNCTIONS
00123 ;
00124 ; o   The function ABS(<num>) returns the absolute value of <num>.
00125 ;     Example: ABS(3) returns 3.
00126 ;     Example: ABS(-3) returns 3.
00127 ;
00128 ; o   The function RND(<num1>..<num2>) returns a random integer in
00129 ;     <num1>..<num2>.
00130 ;     Example: RND(3..5) returns a random number out of 3, 4, or 5.
00131 ;
00132 ; o   The function MAX(<num1>,<num2>) returns the larger number of <num1> and
00133 ;     <num2>.
00134 ;     Example: MAX(2,4) returns 4.
00135 ;
00136 ; VECTORS
00137 ;
00138 ; o   The lowercase X (x) indicates the x-axis of the 3D coordinate system.
00139 ;
00140 ; o   The lowercase Y (y) indicates the y-axis of the 3D coordinate system.
00141 ;
00142 ; o   The lowercase Z (z) indicates the z-axis of the 3D coordinate system.
00143 ;
00144 ; o   Components of a position vector (called "coordinates") have the arbitrary
00145 ;     unit <KM> ("kilometers").
00146 ;
00147 ; o   Components of a velocity vector have the arbitrary unit <KM/H>
00148 ;     ("kilometers per hour").
00149 ;
00150 ; o   A positive component of a position vector (coordinate) in hexadecimal
00151 ;     notation is written in the form +$<hexNum> <KM>. <hexNum> is an unsigned
00152 ;     integer value.
00153 ;     Example: The starbase is +$1000 (or 4096) <KM> ahead of our starship.
00154 ;
00155 ; o   A negative component of a position vector (coordinate) in hexadecimal
00156 ;     notation is written in the form -($<hexNum>) <KM>. <hexNum> is an unsigned
00157 ;     integer value. To calculate the actual bit pattern of this coordinate
00158 ;     value compute the two's-complement of <hexNum>. See also "ON POSITION
00159 ;     VECTORS".
00160 ;     Example: The starbase is -($1000) (or -4096) <KM> behind our starship.
00161 ;
00162 ; o   An absolute component of a position vector (coordinate) in hexadecimal
00163 ;     notation is written in the form $<hexNum> <KM>. <hexNum> is an unsigned
00164 ;     integer value.
00165 ;     Example: The Zylon fighter fires when it is closer than $1000 (or 4096)
00166 ;              <KM>. 
00167 ;
00168 ; DISPLAY LIST
00169 ;
00170 ; o   The following notation is used for Display List instructions:
00171 ;
00172 ;     BLK<n>           = Display <n> blank video lines (<n> in 1..8)
00173 ;     GR1              = Display one GRAPHICS 1 row of 20 text characters
00174 ;     GR2              = Display one GRAPHICS 2 row of 20 text characters
00175 ;     GR7              = Display one GRAPHICS 7 row of 160 pixels
00176 ;     DLI              = Trigger a Display List Interrupt
00177 ;     ... @ <addr>     = Point to screen memory at address <addr>
00178 ;     JMP @ <addr>     = Jump to next Display List instruction at address <addr>
00179 ;     WAITJMP @ <addr> = Wait for vertical blank phase, then jump to next
00180 ;                        Display List instruction at address <addr>
00181 ;
00182 ; MISCELLANEOUS
00183 ;
00184 ; o   Probabilities are written in the form <percentage>% (<number of values out
00185 ;     of the possible values>:<number of possible values>).
00186 ;     Example: The probability to throw the number 3 with a die is 16% (1:6).
00187 ;
00188 ; o   A "game loop iteration" (or "game loop") is a single execution of the game
00189 ;     loop, the main program of the game.
00190 ;
00191 ; o   A "TICK" is the time span it takes to update the TV screen (1/60 s on an
00192 ;     NTSC TV system, 1/50 s on a PAL TV system).
00193 ;
00194 ; o   A pair of braces ({}) encloses color names.
00195 ;     Example: {BLACK}
00196 ;
00197 ; o   A pair of parentheses enclosing a question mark ((?)) indicates code that
00198 ;     is not well understood.
00199 ;
00200 ; o   A pair of parentheses enclosing an exclamation mark ((!)) indicates a
00201 ;     potential bug.
00202
00203 ;*******************************************************************************
00204 ;*                                                                             *
00205 ;*                               O V E R V I E W                               *
00206 ;*                                                                             *
00207 ;*******************************************************************************
00208
00209 ; ON POSITION VECTORS
00210 ;
00211 ; The program uses a 3D coordinate system with the position of our starship at
00212 ; its center and the following coordinate axes:
00213 ;
00214 ; o   The x-axis points to the right.
00215 ; o   The y-axis points up.
00216 ; o   The z-axis points in flight direction.
00217 ;
00218 ; By the way, this is called a "left-handed" coordinate system.
00219 ;
00220 ; The locations of all space objects (Zylon ships, meteors, photon torpedoes,
00221 ; starbase, transfer vessel, Hyperwarp Target Marker, stars, and explosion
00222 ; fragments) are described by a "position vector".
00223 ;
00224 ; A "position vector" is composed of an x, y, and z component. The values of the
00225 ; position vector components are called the x, y, and z "coordinates". They have
00226 ; the arbitrary unit <KM>.
00227 ;
00228 ; Each coordinate is a signed 17-bit integer number, which fits into 3 bytes:
00229 ;
00230 ;     Sign     Mantissa
00231 ;          B16 B15...B8 B7....B0
00232 ;            | |      | |      |
00233 ;     0000000* ******** ********
00234 ;
00235 ; o   B16 contains the sign bit. Used values are:
00236 ;       1 -> Positive sign
00237 ;       0 -> Negative sign
00238 ; o   B15..0 contain the coordinate value (or "mantissa") as a two's-complement
00239 ;     integer number.
00240 ;
00241 ; The range of a position vector component is -65536..+65535 <KM>.
00242 ;
00243 ; Examples:
00244 ;
00245 ;     00000001 11111111 11111111 = +65535 <KM>
00246 ;     00000001 00010000 00000000 =  +4096 <KM>
00247 ;     00000001 00001111 11111111 =  +4095 <KM>
00248 ;     00000001 00000001 00000000 =   +256 <KM>
00249 ;     00000001 00000000 11111111 =   +255 <KM>
00250 ;     00000001 00000000 00010000 =    +16 <KM>
00251 ;     00000001 00000000 00001111 =    +15 <KM>
00252 ;     00000001 00000000 00000001 =     +1 <KM>
00253 ;     00000001 00000000 00000000 =     +0 <KM>
00254 ;
00255 ;     00000000 11111111 11111111 =     -1 <KM>
00256 ;     00000000 11111111 11111110 =     -2 <KM>
00257 ;     00000000 11111111 11110001 =    -15 <KM>
00258 ;     00000000 11111111 11110000 =    -16 <KM>
00259 ;     00000000 11111111 00000001 =   -255 <KM>
00260 ;     00000000 11111111 00000000 =   -256 <KM>
00261 ;     00000000 11110000 00000001 =  -4095 <KM>
00262 ;     00000000 11110000 00000000 =  -4096 <KM>
00263 ;     00000000 00000000 00000000 = -65536 <KM>
00264 ;
00265 ; The position vector for each space object is stored in 9 tables:
00266 ;
00267 ; o   XPOSSIGN ($09DE..$0A0E), XPOSHI ($0A71..$0AA1), and XPOSLO ($0B04..$0B34)
00268 ; o   YPOSSIGN ($0A0F..$0A3F), YPOSHI ($0AA2..$0AD2), and YPOSLO ($0B35..$0B65)
00269 ; o   ZPOSSIGN ($09AD..$09DD), ZPOSHI ($0A40..$0A70), and ZPOSLO ($0AD3..$0B03)
00270 ;
00271 ; There are up to 49 space objects used in the program simultaneously, thus each
00272 ; table is 49 bytes long.
00273 ;
00274 ; o   Position vectors 0..4 belong to space objects represented by PLAYERs
00275 ;     (Zylon ships, meteors, photon torpedoes, starbase, transfer vessel, and
00276 ;     Hyperwarp Target Marker).
00277 ; o   Position vectors 5..48 belong to space objects represented by PLAYFIELD
00278 ;     pixels. Position vectors 5..16 (stars, explosion fragments) are used for
00279 ;     stars, position vectors 17..48 are used for explosion fragments and star
00280 ;     trails.
00281 ;
00282 ; INFO: The x and y coordinates of space objects are converted and displayed by
00283 ; the THETA and PHI readouts of the Control Panel Display in "gradons". The
00284 ; z-coordinate is converted and displayed by the RANGE readout in "centrons".
00285 ; The conversion takes place in subroutine SHOWDIGITS ($B8CD) where the high
00286 ; byte of a coordinate (with values $00..$FF) is transformed with lookup table
00287 ; MAPTOBCD99 ($0EE9) into a BCD value of 00..99 in "gradons" or "centrons".
00288 ;
00289 ;
00290 ; ON VELOCITY VECTORS
00291 ;
00292 ; The velocities of all space objects are described by a "velocity vector". The
00293 ; velocity vector is relative to our starship.
00294 ;
00295 ; A "velocity vector" is composed of an x, y, and z component. The values of the
00296 ; velocity vector components are called the x, y, and z "velocities". They have
00297 ; the arbitrary unit <KM/H>.
00298 ;
00299 ; Each velocity vector component is an 8-bit integer number, which fits into 1
00300 ; byte:
00301 ;
00302 ;     B7 Sign
00303 ;     |
00304 ;     |B6...B0 Mantissa
00305 ;     ||     |
00306 ;     ********
00307 ;
00308 ; o   B7 contains the sign bit. Used values are:
00309 ;     0 -> Positive sign, movement along the positive coordinate axis
00310 ;          (x-velocity: right, y-velocity: up, z-velocity: in flight direction)
00311 ;     1 -> Negative sign, movement along the negative coordinate axis
00312 ;          (x-velocity: left, y-velocity: down, z-velocity: in reverse flight
00313 ;          direction)
00314 ; o   B6..B0 contain the velocity value (or "mantissa"). It is an unsigned
00315 ;     number.
00316 ;
00317 ; The range of a velocity vector component is -127..+127 <KM/H>.
00318 ;
00319 ; Examples:
00320 ;
00321 ;     01111111 = +127 <KM/H>
00322 ;     00010000 =  +16 <KM/H>
00323 ;     00001111 =  +15 <KM/H>
00324 ;     00000001 =   +1 <KM/H>
00325 ;     00000000 =   +0 <KM/H>
00326 ;
00327 ;     10000000 =   -0 <KM/H>
00328 ;     10000001 =   -1 <KM/H>
00329 ;     10001111 =  +15 <KM/H>
00330 ;     10010000 =  +16 <KM/H>
00331 ;     11111111 = -127 <KM/H>
00332 ;
00333 ; The velocity vector for each space object stored in 3 tables:
00334 ;
00335 ; o   XVEL ($0B97..$0BC7)
00336 ; o   YVEL ($0BC8..$0BF8)
00337 ; o   ZVEL ($0B66..$0B96)
00338 ;
00339 ; There are up to 49 space objects used in the program simultaneously, thus each
00340 ; table is 49 bytes long.
00341 ;
00342 ; o   Velocity vectors 0..4 belong to space objects represented by PLAYERs
00343 ;     (Zylon ships, meteors, photon torpedoes, starbase, transfer vessel, and
00344 ;     Hyperwarp Target Marker).
00345 ; o   Velocity vectors 5..48 belong to space objects represented by PLAYFIELD
00346 ;     pixels. Velocity vectors 5..16 are used for stars, velocity vectors 17..48
00347 ;     are used for explosion fragments and star trails.
00348 ;
00349 ; INFO: The velocity of our starship is converted and displayed by the VELOCITY
00350 ; readout of the Control Panel Display in "metrons per second" units. The
00351 ; conversion takes place in subroutine SHOWDIGITS ($B8CD) where our starship's
00352 ; velocity VELOCITYL ($70) (with values $00..$FF) is transformed with lookup
00353 ; table MAPTOBCD99 ($0EE9) into a BCD value of 00..99 in "metrons per second".  
00354
00355 ;*******************************************************************************
00356 ;*                                                                             *
00357 ;*                             M E M O R Y   M A P                             *
00358 ;*                                                                             *
00359 ;*******************************************************************************
00360 ;
00361 ; The following variables are not changed by a SYSTEM RESET:
00362 ;
00363 ; $62      MISSIONLEVEL
00364 ;
00365 ;          Mission level. Used values are:
00366 ;            $00 -> NOVICE mission
00367 ;            $01 -> PILOT mission
00368 ;            $02 -> WARRIOR mission
00369 ;            $03 -> COMMANDER mission
00370 ;
00371 ; $63      FKEYCODE
00372 ;
00373 ;          Function key code. Used values are:
00374 ;            $00 -> No function key pressed
00375 ;            $01 -> START function key pressed
00376 ;            $02 -> SELECT function key pressed
00377 ;
00378 ; $64      ISDEMOMODE
00379 ;
00380 ;          Indicates whether the program is in game or demo mode. Used values
00381 ;          are:
00382 ;            $00 -> Game mode
00383 ;            $FF -> Demo mode
00384 ;
00385 ; $65      NEWTITLEPHR
00386 ;
00387 ;          New title phrase offset for the text in the title line. The new title
00388 ;          phrase is not immediately displayed in the title line but only after
00389 ;          the display time of the currently displayed title phrase has expired.
00390 ;          Thus, setting a value to NEWTITLEPHR ($65) "enqueues" the display of
00391 ;          new title phrase. Used values are:
00392 ;            $00..$7B -> Title phrase offset into PHRASETAB ($BBAA)
00393 ;            $FF      -> Hide title line
00394 ;
00395 ;          See also TITLEPHR ($D1).
00396 ;
00397 ; $66      IDLECNTHI
00398 ;
00399 ;          Idle counter (high byte). Forms a 16-bit counter together with
00400 ;          IDLECNTLO ($77), which is incremented during the execution of the
00401 ;          Vertical Blank Interrupt handler VBIHNDLR ($A6D1). IDLECNTHI ($66) is
00402 ;          reset to 0 when the joystick trigger or a keyboard key has been
00403 ;          pressed, or to 1..3 when a function key has been pressed. When
00404 ;          IDLECNTHI ($66) reaches a value of 128 (after about 10 min idle time)
00405 ;          the program enters demo mode.
00406 ;
00407 ; The following variables are set to 0 after a SYSTEM RESET:
00408 ;
00409 ; $67      ISVBISYNC
00410 ;
00411 ;          Indicates whether the Vertical Blank Interrupt handler VBIHNDLR
00412 ;          ($A6D1) is executed. Used to synchronize the execution of a new game
00413 ;          loop iteration in GAMELOOP ($A1F3) with the vertical blank phase.
00414 ;          Used values are:
00415 ;            $00 -> Halt execution at start of game loop and wait for VBI
00416 ;            $FF -> Continue execution of game loop
00417 ;
00418 ; $68..$69 MEMPTR
00419 ;
00420 ;          A 16-bit memory pointer.
00421 ;
00422 ;          Also used as a local variable.
00423 ;
00424 ; $6A..$6B DIVIDEND
00425 ;
00426 ;          A 16-bit dividend value passed in GAMELOOP ($A1F3) to subroutine
00427 ;          PROJECTION ($AA21) to calculate a division.
00428 ;
00429 ;          Also used as a local variable.
00430 ;
00431 ; $6C      Used as a local variable.
00432 ;
00433 ; $6D      JOYSTICKDELTA
00434 ;
00435 ;          Used to pass joystick directions from GAMELOOP ($A1F3) to subroutine
00436 ;          ROTATE ($B69B). Used values are:
00437 ;            $01 -> Joystick pressed right or up
00438 ;            $00 -> Joystick centered
00439 ;            $FF -> Joystick pressed left or down
00440 ;
00441 ;          Also used as a local variable.
00442 ;
00443 ; $6E      Used as a local variable.
00444 ;
00445 ; $70      VELOCITYLO
00446 ;
00447 ;          Our starship's current velocity (low byte) in <KM/H>. Forms a 16-bit
00448 ;          value together with VELOCITYHI ($C1). In subroutine UPDPANEL ($B804),
00449 ;          VELOCITYLO ($70) is mapped to a BCD-value in 00..99 and displayed by
00450 ;          the VELOCITY readout of the Control Panel Display. See also
00451 ;          NEWVELOCITY ($71).
00452 ;
00453 ; $71      NEWVELOCITY
00454 ;
00455 ;          Our starship's new velocity (low byte) in <KM/H>. It is set by
00456 ;          pressing one of the speed keys '0'..'9'. A pressed speed key is
00457 ;          mapped to the new velocity value with VELOCITYTAB ($BAB4).
00458 ;
00459 ; $72      COUNT8
00460 ;
00461 ;          Wrap-around counter. Counts from 0..7, then starts over at 0. It is
00462 ;          incremented every game loop iteration. It is used to change the
00463 ;          brightness of stars and explosion fragments more randomly in GAMELOOP
00464 ;          ($A1F3) and to slow down the movement of the hyperwarp markers of the
00465 ;          Galactic Chart in subroutine SELECTWARP ($B162).
00466 ;
00467 ; $73      EXPLLIFE
00468 ;
00469 ;          Explosion lifetime. It is decremented every game loop iteration. Used
00470 ;          values are:
00471 ;              $00 -> Explosion is over
00472 ;            < $18 -> Number of explosion fragment space objects is decremented
00473 ;            < $70 -> HITBADNESS ($8A) is reset
00474 ;              $80 -> Initial value at start of explosion
00475 ;
00476 ; $74      CLOCKTIM
00477 ;
00478 ;          Star date clock delay timer. Counts down from 40 to 0. It is
00479 ;          decremented every game loop iteration. When the timer falls below 0
00480 ;          the last digit of the star date of the Galactic Chart Panel Display
00481 ;          is increased and the timer is reset to a value of 40. 
00482 ;
00483 ; $75      DOCKSTATE
00484 ;
00485 ;          State of docking operation. Used values are:
00486 ;            $00 -> NOT DOCKED
00487 ;            $01 -> TRANSFER COMPLETE
00488 ;            $81 -> RETURN TRANSFER VESSEL
00489 ;            $FF -> ORBIT ESTABLISHED
00490 ;
00491 ; $76      COUNT256
00492 ;
00493 ;          Wrap-around counter. Counts from 0..255, then starts over at 0. It is
00494 ;          incremented every game loop iteration. It is used to make the
00495 ;          starbase pulsate in brightness in GAMELOOP ($A1F3) and to decide on
00496 ;          the creation of a meteor in subroutine MANEUVER ($AA79).
00497 ;
00498 ; $77      IDLECNTLO
00499 ;
00500 ;          Idle counter (low byte). Forms a 16-bit counter together with
00501 ;          IDLECNTHI ($66), which is incremented during the execution of the
00502 ;          Vertical Blank Interrupt handler VBIHNDLR ($A6D1).
00503 ;
00504 ;          NOTE: This variable is never properly initialized except at initial
00505 ;          cartridge startup (cold start).
00506 ;
00507 ; $78      ZYLONUNITTIM
00508 ;
00509 ;          Zylon unit movement timer. This delay timer triggers movement of
00510 ;          Zylon units on the Galactic Chart. At the start of the game, the
00511 ;          timer is initialized to a value of 100. It is decremented every 40
00512 ;          game loop iterations. When the timer falls below 0 the Zylon units
00513 ;          move on the Galactic Chart and the timer value is reset to 49. If a
00514 ;          starbase is surrounded the timer is reset to 99 to buy you some extra
00515 ;          time to destroy one of the surrounding Zylon units.
00516 ;
00517 ; $79      MAXSPCOBJIND
00518 ;
00519 ;          Maximum index of used space objects in the current game loop
00520 ;          iteration. Frequently used values are:
00521 ;            $10 -> During regular cruise (5 PLAYER space objects + 12 PLAYFIELD
00522 ;                   space objects (stars))
00523 ;            $30 -> During explosion or hyperwarp (5 PLAYER space objects + 12
00524 ;                   PLAYFIELD space objects (stars) + 32 PLAYFIELD space objects
00525 ;                   (explosion fragments or stars of star trails))
00526 ;
00527 ; $7A      OLDMAXSPCOBJIND
00528 ;
00529 ;          Maximum index of used space objects in the previous game loop
00530 ;          iteration. Frequently used values are:
00531 ;            $10 -> During regular cruise (5 PLAYER space objects + 12 PLAYFIELD
00532 ;                   space objects (stars))
00533 ;            $30 -> During explosion or hyperwarp (5 PLAYER space objects + 12
00534 ;                   PLAYFIELD space objects (stars) + 32 PLAYFIELD space objects
00535 ;                   (explosion fragments or stars of star trails))
00536 ;
00537 ; $7B      ISSTARBASESECT
00538 ;
00539 ;          Indicates whether a starbase is in this sector. Used values are:
00540 ;            $00 -> Sector contains no starbase
00541 ;            $FF -> Sector contains starbase
00542 ;
00543 ; $7C      ISTRACKCOMPON
00544 ;
00545 ;          Indicates whether the Tracking Computer is on or off. Used values
00546 ;          are:
00547 ;            $00 -> Tracking Computer is off
00548 ;            $FF -> Tracking Computer is on
00549 ;
00550 ; $7D      DRAINSHIELDS
00551 ;
00552 ;          Energy drain rate of the Shields per game loop iteration in energy
00553 ;          subunits. See also subroutine UPDPANEL ($B804). Used values are:
00554 ;            $00 -> Shields are off
00555 ;            $08 -> Shields are on
00556 ;
00557 ; $7E      DRAINATTCOMP
00558 ;
00559 ;          Energy drain rate of the Attack Computer per game loop iteration in
00560 ;          energy subunits. See also subroutine UPDPANEL ($B804). Used values
00561 ;          are:
00562 ;            $00 -> Attack Computer off
00563 ;            $02 -> Attack Computer on
00564 ;
00565 ; $7F      ENERGYCNT
00566 ;
00567 ;          Running counter of consumed energy subunits (256 energy subunits = 1
00568 ;          energy unit displayed by the 4-digit ENERGY readout of the Control
00569 ;          Panel Display). Forms an invisible fractional or "decimals" part of
00570 ;          the 4-digit ENERGY readout of the Control Panel Display. See also
00571 ;          subroutine UPDPANEL ($B804).
00572 ;
00573 ; $80      DRAINENGINES
00574 ;
00575 ;          Energy drain rate of our starship's Engines per game loop iteration
00576 ;          in energy subunits (256 energy subunits = 1 energy unit displayed by
00577 ;          the 4-digit ENERGY readout of the Control Panel Display). Values are
00578 ;          picked from table DRAINRATETAB ($BAD3). See also subroutine UPDPANEL
00579 ;          ($B804).
00580 ;
00581 ; $81      SHIELDSCOLOR
00582 ;
00583 ;          Shields color. Used values are: 
00584 ;            $00 -> {BLACK} (Shields are off)
00585 ;            $A0 -> {DARK GREEN} (Shields are on)
00586 ;
00587 ; $82      PL3HIT
00588 ;
00589 ;          Collision register of PLAYER3 (usually our starship's photon torpedo
00590 ;          0) with other PLAYERs. Used values are:
00591 ;              $00 -> No collision
00592 ;            > $00 -> PLAYER3 has collided with another PLAYER space object. See
00593 ;                     subroutine COLLISION ($AF3D) for details which PLAYER has
00594 ;                     been hit by PLAYER3.
00595 ;
00596 ; $83      PL4HIT
00597 ;
00598 ;          Collision register of PLAYER4 (usually our starship's photon torpedo
00599 ;          1) with other PLAYERs. Used values are:
00600 ;              $00 -> No collision
00601 ;            > $00 -> PLAYER4 has collided with another PLAYER space object. See
00602 ;                     subroutine COLLISION ($AF3D) for details which PLAYER has
00603 ;                     been hit by PLAYER4.
00604 ;
00605 ; $84      OLDTRIG0
00606 ;
00607 ;          Joystick trigger state. Used values are:
00608 ;            $00 -> Joystick trigger was pressed
00609 ;            $01 -> Joystick trigger was not pressed
00610 ;            $AA -> Joystick trigger was "virtually" pressed (will launch
00611 ;                   another of our starship's photon torpedoes, see subroutine
00612 ;                   TRIGGER ($AE29).
00613 ;
00614 ; $86      ISTRACKING
00615 ;
00616 ;          Indicates whether one of our starship's photon torpedoes is currently
00617 ;          tracking (homing in on) the target space object. Used values are:
00618 ;              $00 -> No target space object tracked. Our starship's photon
00619 ;                     torpedoes will fly just straight ahead.
00620 ;            > $00 -> Tracking a target space object. Our starship's photon
00621 ;                     torpedoes will home in on the tracked space object.
00622 ;
00623 ; $87      BARRELNR
00624 ;
00625 ;          Barrel from which our starship's next photon torpedo will be
00626 ;          launched. Used values are:
00627 ;            $00 -> Left barrel
00628 ;            $01 -> Right barrel
00629 ;
00630 ; $88      LOCKONLIFE
00631 ;
00632 ;          Lifetime of target lock-on. A target remains in lock-on while
00633 ;          LOCKONLIFE ($88) counts down from 12 to 0. It is decremented every
00634 ;          game loop iteration.
00635 ;
00636 ; $89      PLTRACKED
00637 ;
00638 ;          Index of currently tracked PLAYER. It is copied in subroutine TRIGGER
00639 ;          ($AE29) from TRACKDIGIT ($095C). Used values are:
00640 ;            $00 -> Track Zylon ship 0
00641 ;            $01 -> Track Zylon ship 1
00642 ;            $02 -> Track starbase during docking operations
00643 ;            $03 -> Track Hyperwarp Target Marker during hyperwarp
00644 ;
00645 ; $8A      HITBADNESS
00646 ;
00647 ;          Severeness of a Zylon photon torpedo hit. Used values are:
00648 ;            $00 -> NO HIT
00649 ;            $7F -> SHIELDS HIT
00650 ;            $FF -> STARSHIP DESTROYED
00651 ;
00652 ; $8B      REDALERTLIFE
00653 ;
00654 ;          Lifetime of red alert. It decreases from 255 to 0. It is decremented
00655 ;          every game loop iteration.
00656 ;
00657 ; $8C      WARPDEPRROW
00658 ;
00659 ;          Departure hyperwarp marker row number on the Galactic Chart. It is
00660 ;          given in Player/Missile pixels relative to the top Galactic Chart
00661 ;          border. It is initialized to a value of $47 (vertical center of
00662 ;          Galactic Chart). Divide this value by 16 to get the departure sector
00663 ;          row number. Used values are: $00..$7F.
00664 ;
00665 ; $8D      WARPDEPRCOLUMN
00666 ;
00667 ;          Departure hyperwarp marker column number on the Galactic Chart. It is
00668 ;          given in Player/Missile pixels relative to the left Galactic Chart
00669 ;          border and initialized to a value of $43 (horizontal center of
00670 ;          Galactic Chart). Divide this value by 8 to get the departure sector
00671 ;          column number. Used values are: $00..$7F.
00672 ;
00673 ; $8E      WARPARRVROW
00674 ;
00675 ;          Arrival hyperwarp marker row number on the Galactic Chart in
00676 ;          Player/Missile pixels relative to top Galactic Chart border. It is
00677 ;          initialized to a value of $47 (vertical center of Galactic Chart).
00678 ;          Divide this value by 16 to get the arrival sector row number. Used
00679 ;          values are: $00..$7F. 
00680 ;
00681 ; $8F      WARPARRVCOLUMN
00682 ;
00683 ;          Arrival hyperwarp marker column number on the Galactic Chart in
00684 ;          Player/Missile pixels relative to left Galactic Chart border. It is
00685 ;          initialized to a value of $43 (horizontal center of Galactic Chart).
00686 ;          Divide this value by 8 to get the arrival sector column number. Used
00687 ;          values are: $00..$7F. 
00688 ;
00689 ; $90      CURRSECTOR
00690 ;
00691 ;          Galactic Chart sector of the current location of our starship. At the
00692 ;          start of the game it is initialized to a value of $48. Used values
00693 ;          are: $00..$7F with, for example,
00694 ;            $00 -> NORTHWEST corner sector
00695 ;            $0F -> NORTHEAST corner sector
00696 ;            $70 -> SOUTHWEST corner sector
00697 ;            $7F -> SOUTHWEST corner sector
00698 ;
00699 ;          See also ARRVSECTOR ($92). 
00700 ;
00701 ; $91      WARPENERGY
00702 ;
00703 ;          Energy required to hyperwarp between the departure and arrival
00704 ;          hyperwarp marker locations on the Galactic Chart divided by 10.
00705 ;          Values are picked from table WARPENERGYTAB ($BADD). Multiply this
00706 ;          value by 10 to get the actual value in energy units displayed by the
00707 ;          Galactic Chart Panel Display.
00708 ;
00709 ; $92      ARRVSECTOR
00710 ;
00711 ;          Galactic Chart arrival sector of our starship after hyperwarp. Used
00712 ;          values are: $00..$7F with, for example,
00713 ;            $00 -> NORTHWEST corner sector
00714 ;            $0F -> NORTHEAST corner sector
00715 ;            $70 -> SOUTHWEST corner sector
00716 ;            $7F -> SOUTHWEST corner sector
00717 ;
00718 ;          See also CURRSECTOR ($90). 
00719 ;
00720 ; $93      HUNTSECTOR
00721 ;
00722 ;          Galactic Chart sector of the starbase toward which the Zylon units
00723 ;          are currently moving. Used values are: $00..$7F with, for example,
00724 ;            $00 -> NORTHWEST corner sector
00725 ;            $0F -> NORTHEAST corner sector
00726 ;            $70 -> SOUTHWEST corner sector
00727 ;            $7F -> SOUTHWEST corner sector
00728 ;
00729 ; $94      HUNTSECTCOLUMN
00730 ;
00731 ;          Galactic Chart sector column number of the starbase toward which the
00732 ;          Zylon units are currently moving. Used values are: 0..15.
00733 ;
00734 ; $95      HUNTSECTROW
00735 ;
00736 ;          Galactic Chart sector row number of the starbase toward which the
00737 ;          Zylon units are currently moving. Used values are: 0..7.
00738 ;
00739 ; $96..$9E NEWZYLONDIST
00740 ;
00741 ;          Table of distances between a Zylon unit and the hunted starbase when
00742 ;          the Zylon unit is tentatively moved in one of the 9 possible
00743 ;          directions NORTH, NORTHWEST, WEST, SOUTHWEST, SOUTH, SOUTHEAST, EAST,
00744 ;          NORTHEAST, CENTER. Used to decide into which sector the Zylon unit
00745 ;          should move.
00746 ;
00747 ; $9E      OLDZYLONDIST
00748 ;
00749 ;          Current distance between the Zylon unit and the hunted starbase.
00750 ;
00751 ; $9F      HUNTTIM
00752 ;
00753 ;          Delay timer for Zylon units to decide on which starbase to hunt. It
00754 ;          counts down from 7. It is decremented every game loop iteration. When
00755 ;          the timer falls below 0 the Zylon units re-decide toward which
00756 ;          starbase to move.
00757 ;
00758 ; $A0      BLIPCOLUMN
00759 ;
00760 ;          Top-left screen pixel column number of blip shape displayed in the
00761 ;          Attack Computer Display. Used in subroutine UPDATTCOMP ($A7BF). Used
00762 ;          values are: 120..142.
00763 ;
00764 ; $A1      BLIPROW
00765 ;
00766 ;          Top-left screen pixel row number of blip shape displayed in the
00767 ;          Attack Computer Display. Used in subroutine UPDATTCOMP ($A7BF). Used
00768 ;          values are: 71..81.
00769 ;
00770 ; $A2      BLIPCYCLECNT
00771 ;
00772 ;          Blip cycle counter. It controls drawing the blip shape in the Attack
00773 ;          Computer Display. Its value is incremented every game loop iteration.
00774 ;          Used in subroutine UPDATTCOMP ($A7BF). Used values are:
00775 ;            $00..$04 -> Draw 0..4th row of blip shape
00776 ;            $05..$09 -> Do not draw blip shape (delay)
00777 ;            $0A      -> Recalculate blip shape position, erase Attack Computer
00778 ;                        Display
00779 ;
00780 ; $A3      ISINLOCKON
00781 ;
00782 ;          Indicates whether the tracked space object is currently in full
00783 ;          lock-on (horizontally and vertically centered as well as in range) in
00784 ;          the Attack Computer Display. If so, all lock-on markers show up on
00785 ;          the Attack Computer Display and our starship's launched photon
00786 ;          torpedoes will home in on the tracked space object. Used values are:
00787 ;            $00 -> Not in lock-on
00788 ;            $A0 -> In lock-on
00789 ;
00790 ; $A4      DIRLEN
00791 ;
00792 ;          Used to pass the direction and length of a single line to be drawn in
00793 ;          the PLAYFIELD. Used in subroutines DRAWLINES ($A76F), DRAWLINE
00794 ;          ($A782), and UPDATTCOMP ($A7BF). Used values are:
00795 ;            Bit B7 = 0 -> Draw right
00796 ;            Bit B7 = 1 -> Draw down
00797 ;            Bits B6..0 -> Length of line in pixels.
00798 ;
00799 ;          See also PENROW ($A5) and PENCOLUMN ($A6).
00800 ;
00801 ; $A5      PENROW
00802 ;
00803 ;          Used to pass the start screen pixel row number of the line to be
00804 ;          drawn in the PLAYFIELD. Used in subroutines DRAWLINES ($A76F),
00805 ;          DRAWLINE ($A782), and UPDATTCOMP ($A7BF).
00806 ;
00807 ; $A6      PENCOLUMN
00808 ;
00809 ;          Used to pass the start screen pixel column number of the line to be
00810 ;          drawn in the PLAYFIELD. Used in subroutines DRAWLINES ($A76F),
00811 ;          DRAWLINE ($A782), and UPDATTCOMP ($A7BF).
00812 ;
00813 ; $A7      CTRLDZYLON
00814 ;
00815 ;          Index of Zylon ship currently controlled by the program. Used in
00816 ;          subroutine MANEUVER ($AA79). The value is toggled every other game
00817 ;          loop iteration. Used values are:
00818 ;            $00 -> Control Zylon ship 0.
00819 ;            $01 -> Control Zylon ship 1.
00820 ;
00821 ; $A8      ZYLONFLPAT0
00822 ;
00823 ;          Flight pattern of Zylon ship 0. Used in subroutine MANEUVER ($AA79).
00824 ;          Used values are:
00825 ;            $00 -> Attack flight pattern "0"
00826 ;            $01 -> Flight pattern "1"
00827 ;            $04 -> Flight pattern "4"
00828 ;
00829 ; $A9      ZYLONFLPAT1
00830 ;
00831 ;          Flight pattern of Zylon ship 1. Compare ZYLONFLPAT0 ($A8).
00832 ;
00833 ; $AA      MILESTTIM0
00834 ;
00835 ;          Delay timer of the milestone velocity indices of Zylon ship 0. Used
00836 ;          in subroutine MANEUVER ($AA79).
00837 ;
00838 ;          When Zylon ship 0 is active, this value is decremented every game
00839 ;          loop iteration. If it falls below 0 then the milestone velocity
00840 ;          indices of Zylon ship 0 are recalculated. When Zylon ship 0 is
00841 ;          controlled by the computer for the first time, the timer is set to an
00842 ;          initial value of 1, later to an initial value of 120.
00843 ;
00844 ; $AB      MILESTTIM1
00845 ;
00846 ;          Delay timer of the milestone velocity index vector of Zylon ship 1.
00847 ;          Compare MILESTTIM0 ($AA).
00848 ;
00849 ; $AC      MILESTVELINDZ0
00850 ;
00851 ;          Milestone z-velocity index of Zylon ship 0. Used in subroutine
00852 ;          MANEUVER ($AA79). The current z-velocity index of Zylon ship 0
00853 ;          ZYLONVELINDZ0 ($B2) is compared with this index and gradually
00854 ;          adjusted to it. Used values are: 0..15.
00855 ;
00856 ; $AD      MILESTVELINDZ1
00857 ;
00858 ;          Milestone z-velocity index of Zylon ship 1. Compare MILESTVELINDZ0
00859 ;          ($AC).
00860 ;
00861 ; $AE      MILESTVELINDX0
00862 ;
00863 ;          Milestone x-velocity index of Zylon ship 0. Used in subroutine
00864 ;          MANEUVER ($AA79). The current x-velocity index of Zylon ship 0
00865 ;          ZYLONVELINDX0 ($B4) is compared with this index and gradually
00866 ;          adjusted to it. Used values are: 0..15.
00867 ;
00868 ; $AF      MILESTVELINDX1
00869 ;
00870 ;          Milestone x-velocity index of Zylon ship 1. Compare MILESTVELINDX0
00871 ;          ($AE).
00872 ;
00873 ; $B0      MILESTVELINDY0
00874 ;
00875 ;          Milestone y-velocity index of Zylon ship 0. Used in subroutine
00876 ;          MANEUVER ($AA79). The current y-velocity index of Zylon ship 0
00877 ;          ZYLONVELINDY0 ($B6) is compared with this index and gradually
00878 ;          adjusted to it. Used values are: 0..15.
00879 ;
00880 ; $B1      MILESTVELINDY1
00881 ;
00882 ;          Milestone y-velocity index of Zylon ship 1. Compare MILESTVELINDY0
00883 ;          ($B0).
00884 ;
00885 ; $B2      ZYLONVELINDZ0
00886 ;
00887 ;          Current z-velocity index of Zylon ship 0. Used in subroutine MANEUVER
00888 ;          ($AA79). It indexes velocity values in ZYLONVELTAB ($BF99). Used
00889 ;          values are: 0..15.
00890 ;
00891 ; $B3      ZYLONVELINDZ1
00892 ;
00893 ;          Current z-velocity index of Zylon ship 1. Compare ZYLONVELINDZ0
00894 ;          ($B2).
00895 ;
00896 ; $B4      ZYLONVELINDX0
00897 ;
00898 ;          Current x-velocity index of Zylon ship 0. Compare ZYLONVELINDZ0
00899 ;          ($B2).
00900 ;
00901 ; $B5      ZYLONVELINDX1
00902 ;
00903 ;          Current x-velocity index of Zylon ship 1. Compare ZYLONVELINDZ0
00904 ;          ($B2).
00905 ;
00906 ; $B6      ZYLONVELINDY0
00907 ;
00908 ;          Current y-velocity index of Zylon ship 0. Compare ZYLONVELINDZ0
00909 ;          ($B2).
00910 ;
00911 ; $B7      ZYLONVELINDY1
00912 ;
00913 ;          Current y-velocity index of Zylon ship 1. Compare ZYLONVELINDZ0
00914 ;          ($B2).
00915 ;
00916 ; $B8      ISBACKATTACK0
00917 ;
00918 ;          Indicates whether Zylon ship 0 will attack our starship from the
00919 ;          back. Used in subroutine MANEUVER ($AA79). Used values are:
00920 ;            $00 -> Zylon ship 0 attacks from the front of our starship
00921 ;            $01 -> Zylon ship 0 attacks from the front and back of our starship
00922 ;
00923 ; $B9      ISBACKATTACK1
00924 ;
00925 ;          Indicates whether Zylon ship 1 will attack our starship from the
00926 ;          back. Compare ISBACKATTACK0 ($B8).
00927 ;
00928 ; $BA      ZYLONTIMX0
00929 ;
00930 ;          Delay timer of the x-velocity index of Zylon ship 0. Used in
00931 ;          subroutine MANEUVER ($AA79). It is decremented every game loop
00932 ;          iteration. When the timer value falls below 0 the current velocity
00933 ;          index ZYLONVELINDX0 ($B4) is adjusted depending on the current
00934 ;          joystick position. The new timer value is set depending on the
00935 ;          resulting new x-velocity index. Used values are: 0, 2, 4, ..., 14.
00936 ;
00937 ; $BB      ZYLONTIMX1
00938 ;
00939 ;          Delay timer of x-velocity index of Zylon ship 1. Compare ZYLONTIMX0
00940 ;          ($BA).
00941 ;
00942 ; $BC      ZYLONTIMY0
00943 ;
00944 ;          Delay timer of y-velocity index of Zylon ship 0. Compare ZYLONTIMX0
00945 ;          ($BA).
00946 ;
00947 ; $BD      ZYLONTIMY1
00948 ;
00949 ;          Delay timer of y-velocity index of Zylon ship 1. Compare ZYLONTIMX0
00950 ;          ($BA).
00951 ;
00952 ; $BE      TORPEDODELAY
00953 ;
00954 ;          After a Zylon photon torpedo has hit our starship this delay timer is
00955 ;          initialized to a value of 2. It is decremented every game loop
00956 ;          iteration and so delays the launch of the next Zylon photon torpedo
00957 ;          for 2 game loop iterations.
00958 ;
00959 ; $BF      ZYLONATTACKER
00960 ;
00961 ;          Index of the Zylon ship that launched the Zylon photon torpedo. It is
00962 ;          used in GAMELOOP ($A1F3) to override the current tracking computer
00963 ;          settings in order to track this Zylon ship first. Used values are:
00964 ;            $00 -> Zylon photon torpedo was launched by Zylon ship 0
00965 ;            $01 -> Zylon photon torpedo was launched by Zylon ship 1
00966 ;
00967 ; $C0      WARPSTATE
00968 ;
00969 ;          Hyperwarp state. Used values are:
00970 ;            $00 -> Hyperwarp not engaged
00971 ;            $7F -> Hyperwarp engaged
00972 ;            $FF -> In hyperspace
00973 ;
00974 ; $C1      VELOCITYHI
00975 ;
00976 ;          Our starship's velocity (high byte) in <KM/H>. Used values are:
00977 ;            $00 -> Not in hyperspace (regular cruise or accelerating to
00978 ;                   hyperspace velocity)
00979 ;            $01 -> Hyperspace velocity
00980 ;
00981 ;          See also VELOCITYLO ($70). 
00982 ;
00983 ; $C2      TRAILDELAY
00984 ;
00985 ;          Delay timer to create the next star trail. Its value is decremented
00986 ;          from 3 to 0 every game loop iteration during the hyperwarp STAR TRAIL
00987 ;          PHASE in subroutine INITTRAIL ($A9B4).
00988 ;
00989 ; $C3      TRAILIND
00990 ;
00991 ;          Position vector index of the star trail's first star. Used in
00992 ;          subroutine INITTRAIL ($A9B4) to initialize a star trail, which is
00993 ;          then displayed during the hyperwarp STAR TRAIL PHASE. Used values
00994 ;          are: 17..48 in wrap-around fashion.
00995 ;
00996 ; $C4      WARPTEMPCOLUMN
00997 ;
00998 ;          Temporary arrival column number of our starship on the Galactic Chart
00999 ;          at the begin of hyperspace. It is given in Player/Missile pixels
01000 ;          relative to the left Galactic Chart border. Divide this value by 8 to
01001 ;          get the sector column number. Used values are: $00..$7F. See also
01002 ;          WARPARRVCOLUMN ($8F).
01003 ;
01004 ; $C5      WARPTEMPROW
01005 ;
01006 ;          Temporary arrival row number of our starship on the Galactic Chart at
01007 ;          the begin of hyperspace. It is given in Player/Missile pixels
01008 ;          relative to top Galactic Chart border. Divide this value by 16 to get
01009 ;          the sector row number.  Used values are: $00..$7F. See also
01010 ;          WARPARRVROW ($8E).
01011 ;
01012 ; $C6      VEERMASK
01013 ;
01014 ;          Limits the veer-off velocity of the Hyperwarp Target Marker during
01015 ;          the hyperwarp ACCELERATION PHASE in subroutine HYPERWARP ($A89B).
01016 ;          Values are picked from table VEERMASKTAB ($BED7).
01017 ;
01018 ;          Also used as a local variable.
01019 ;
01020 ; $C7      VICINITYMASK
01021 ;
01022 ;          Mask to confine space objects' position vector components
01023 ;          (coordinates) in a sector into a certain interval around our starship
01024 ;          after its arrival from hyperspace. Values are picked from table
01025 ;          VICINITYMASKTAB ($BFB3).
01026 ;
01027 ; $C8      JOYSTICKX
01028 ;
01029 ;          Horizontal joystick direction. Values are picked from table
01030 ;          STICKINCTAB ($BAF5). Used values are:
01031 ;            $01 -> Right
01032 ;            $00 -> Centered
01033 ;            $FF -> Left
01034 ;
01035 ; $C9      JOYSTICKY
01036 ;
01037 ;          Vertical joystick direction. Values are picked from table STICKINCTAB
01038 ;          ($BAF5). Used values are:
01039 ;            $01 -> Up
01040 ;            $00 -> Centered 
01041 ;            $FF -> Down
01042 ;
01043 ; $CA      KEYCODE
01044 ;
01045 ;          Hardware keyboard code of the pressed key on the keyboard. Shift and
01046 ;          Control key bits B7..6 are always set.
01047 ;
01048 ; $CB..$CC SCORE
01049 ;
01050 ;          Internal 16-bit score of the game in low byte-high byte order
01051 ;
01052 ; $CD      SCOREDRANKIND
01053 ;
01054 ;          Scored Rank Index. It is translated with table RANKTAB ($BEE9) to a
01055 ;          title phrase offset pointing to the rank string. Used values are: 
01056 ;            $00 -> GALACTIC COOK
01057 ;            $01 -> GARBAGE SCOW CAPTAIN
01058 ;            $02 -> GARBAGE SCOW CAPTAIN
01059 ;            $03 -> ROOKIE
01060 ;            $04 -> ROOKIE
01061 ;            $05 -> NOVICE
01062 ;            $06 -> NOVICE
01063 ;            $07 -> ENSIGN
01064 ;            $08 -> ENSIGN
01065 ;            $09 -> PILOT
01066 ;            $0A -> PILOT
01067 ;            $0B -> ACE
01068 ;            $0C -> LIEUTENANT
01069 ;            $0D -> WARRIOR
01070 ;            $0E -> CAPTAIN
01071 ;            $0F -> COMMANDER
01072 ;            $10 -> COMMANDER
01073 ;            $11 -> STAR COMMANDER
01074 ;            $12 -> STAR COMMANDER
01075 ;
01076 ; $CE      SCOREDCLASSIND
01077 ;
01078 ;          Scored Class Index. It is translated into a class number with table
01079 ;          CLASSTAB ($BEFC). Used values are:
01080 ;            $00 -> Class 5
01081 ;            $01 -> Class 5
01082 ;            $02 -> Class 5
01083 ;            $03 -> Class 4
01084 ;            $04 -> Class 4
01085 ;            $05 -> Class 4
01086 ;            $06 -> Class 4
01087 ;            $07 -> Class 3
01088 ;            $08 -> Class 3
01089 ;            $09 -> Class 3
01090 ;            $0A -> Class 2
01091 ;            $0B -> Class 2
01092 ;            $0C -> Class 2
01093 ;            $0D -> Class 1
01094 ;            $0E -> Class 1
01095 ;            $0F -> Class 1
01096 ;
01097 ; $CF      TITLELIFE
01098 ;
01099 ;          Lifetime of title line. It is decremented every game loop iteration.
01100 ;          Used initial values are:
01101 ;            $3C -> When displaying regular title phrases
01102 ;            $FE -> When displaying "STARBASE SURROUNDED", "STARBASE DESTOYED",
01103 ;                   and "RED ALERT" messages
01104 ;            $FF -> Hide title line
01105 ;
01106 ; $D0      SHIPVIEW
01107 ;
01108 ;          Current view of our starship. Values are picked from table
01109 ;          VIEWMODETAB ($BE22). Used values are:
01110 ;            $00 -> Front view
01111 ;            $01 -> Aft view
01112 ;            $40 -> Long-Range Scan view
01113 ;            $80 -> Galactic Chart view
01114 ;
01115 ; $D1      TITLEPHR
01116 ;
01117 ;          Title phrase offset for text phrase in title line. Used values are:
01118 ;            $00..$7B -> Title phrase offset into PHRASETAB ($BBAA)
01119 ;            $FF      -> Hide title line
01120 ;
01121 ;          See also NEWTITLEPHR ($65). 
01122 ;
01123 ; $D2      BEEPFRQIND
01124 ;
01125 ;          Beeper sound pattern: Running index into frequency table BEEPFRQTAB
01126 ;          ($BF5C). See also BEEPFRQSTART ($D7). See also subroutines BEEP
01127 ;          ($B3A6) and SOUND ($B2AB).
01128 ;
01129 ; $D3      BEEPREPEAT
01130 ;
01131 ;          Beeper sound pattern: Number of times the beeper sound pattern is
01132 ;          repeated - 1. See also subroutines BEEP ($B3A6) and SOUND ($B2AB).
01133 ;
01134 ; $D4      BEEPTONELIFE
01135 ;
01136 ;          Beeper sound pattern: Lifetime of tone in TICKs - 1. See also
01137 ;          subroutines BEEP ($B3A6) and SOUND ($B2AB).
01138 ;
01139 ; $D5      BEEPPAUSELIFE
01140 ;
01141 ;          Beeper sound pattern: Lifetime of pause in TICKs - 1. Used values
01142 ;          are: 
01143 ;            < $FF -> Number of TICKs - 1 to play
01144 ;              $FF -> Skip playing pause
01145 ;
01146 ;          See also subroutines BEEP ($B3A6) and SOUND ($B2AB).
01147 ;
01148 ; $D6      BEEPPRIORITY
01149 ;
01150 ;          Beeper sound pattern: Pattern priority. Each beeper sound pattern has
01151 ;          a priority. When a pattern of higher priority is about to be played
01152 ;          the pattern that is currently playing is stopped. Used values are:
01153 ;              $00 -> No pattern playing at the moment
01154 ;            > $00 -> Pattern priority
01155 ;
01156 ;          See also subroutines BEEP ($B3A6) and SOUND ($B2AB).
01157 ;
01158 ; $D7      BEEPFRQSTART
01159 ;
01160 ;          Beeper sound pattern: Index to first byte of the pattern frequency in
01161 ;          table BEEPFRQTAB ($BF5C). See also BEEPFRQIND ($D2). See also
01162 ;          subroutines BEEP ($B3A6) and SOUND ($B2AB).
01163 ;
01164 ; $D8      BEEPLIFE
01165 ;
01166 ;          Beeper sound pattern: Lifetime of the current tone or pause in TICKs.
01167 ;          It is decremented every TICK. See also subroutines BEEP ($B3A6) and
01168 ;          SOUND ($B2AB). 
01169 ;
01170 ; $D9      BEEPTOGGLE
01171 ;
01172 ;          Beeper sound pattern: Indicates that either a tone or a pause is
01173 ;          currently played. Used values are:
01174 ;            $00 -> Tone
01175 ;            $01 -> Pause
01176 ;
01177 ;          See also subroutines BEEP ($B3A6) and SOUND ($B2AB).    
01178 ;
01179 ; $DA      NOISETORPTIM
01180 ;
01181 ;          Noise sound pattern: Delay timer for PHOTON TORPEDO LAUNCHED noise
01182 ;          sound pattern. It is decremented every TICK. See also subroutines
01183 ;          NOISE ($AEA8) and SOUND ($B2AB).
01184 ;
01185 ; $DB      NOISEEXPLTIM
01186 ;
01187 ;          Noise sound pattern: Delay timer for SHIELD EXPLOSION and ZYLON
01188 ;          EXPLOSION noise sound pattern. It is decremented every TICK. See also
01189 ;          subroutines NOISE ($AEA8) and SOUND ($B2AB).
01190 ;
01191 ; $DC      NOISEAUDC2
01192 ;
01193 ;          Noise sound pattern: Audio channel 1/2 control shadow register. See
01194 ;          also subroutines NOISE ($AEA8) and SOUND ($B2AB).
01195 ;
01196 ; $DD      NOISEAUDC3
01197 ;
01198 ;          Noise sound pattern: Audio channel 3 control shadow register. See
01199 ;          also subroutines NOISE ($AEA8) and SOUND ($B2AB).
01200 ;
01201 ; $DE      NOISEAUDF1
01202 ;
01203 ;          Noise sound pattern: Audio channel 1 frequency shadow register. See
01204 ;          also subroutines NOISE ($AEA8) and SOUND ($B2AB).
01205 ;
01206 ; $DF      NOISEAUDF2
01207 ;
01208 ;          Noise sound pattern: Audio channel 2 frequency shadow register. See
01209 ;          also subroutines NOISE ($AEA8) and SOUND ($B2AB).
01210 ;
01211 ; $E0      NOISEFRQINC
01212 ;
01213 ;          Noise sound pattern: Audio channel 1/2 frequency increment. See also
01214 ;          subroutines NOISE ($AEA8) and SOUND ($B2AB).
01215 ;
01216 ; $E1      NOISELIFE
01217 ;
01218 ;          Noise sound pattern: Noise sound pattern lifetime. It is decremented
01219 ;          every TICK. See also subroutines NOISE ($AEA8) and SOUND ($B2AB).
01220 ;
01221 ; $E2      NOISEZYLONTIM
01222 ;
01223 ;          Delay timer to trigger the ZYLON EXPLOSION noise sound pattern. It is
01224 ;          set in subroutine COLLISION ($AF3D) when an impact of one of our
01225 ;          starship's photon torpedoes into a target is imminent. The timer is
01226 ;          decremented every TICK during the execution of the Vertical Blank
01227 ;          Interrupt handler VBIHNDLR ($A6D1). When the timer value reaches 0
01228 ;          the ZYLON EXPLOSION noise sound pattern is played in subroutine SOUND
01229 ;          ($B2AB). 
01230 ;
01231 ; $E3      NOISEHITLIFE
01232 ;
01233 ;          Lifetime of STARSHIP EXPLOSION noise when our starship was destroyed
01234 ;          by a Zylon photon torpedo. It is set in routine GAMELOOP ($A1F3) to a
01235 ;          value of 64 TICKs. It is decremented every TICK during the execution
01236 ;          of the Vertical Blank Interrupt handler VBIHNDLR ($A6D1).
01237 ;
01238 ; $E4      PL0SHAPOFF
01239 ;
01240 ;          PLAYER0 offset into shape table PLSHAP2TAB ($B9B1)
01241 ;
01242 ; $E5      PL1SHAPOFF
01243 ;
01244 ;          PLAYER1 offset into shape table PLSHAP2TAB ($B9B1)
01245 ;
01246 ; $E6      PL2SHAPOFF
01247 ;
01248 ;          PLAYER2 offset into shape table PLSHAP1TAB ($B8E4)
01249 ;
01250 ; $E7      PL3SHAPOFF
01251 ;
01252 ;          PLAYER3 offset into shape table PLSHAP1TAB ($B8E4)
01253 ;
01254 ; $E8      PL4SHAPOFF
01255 ;
01256 ;          PLAYER4 offset into shape table PLSHAP1TAB ($B8E4)
01257 ;
01258 ; $E9      PL0LIFE
01259 ;
01260 ;          Lifetime of the space object represented by PLAYER0 (usually Zylon
01261 ;          ship 0). Any value other than $FF is decremented with every game loop
01262 ;          iteration. Used values are:
01263 ;            $00      -> Space object not alive (= not in use)
01264 ;            $01..$FE -> Values during lifetime countdown
01265 ;            $FF      -> Infinite lifetime (not counted down)
01266 ;
01267 ; $EA      PL1LIFE
01268 ;
01269 ;          Lifetime of a space object represented by PLAYER1 (usually Zylon ship
01270 ;          1). Compare PL0LIFE ($E9).
01271 ;
01272 ; $EB      PL2LIFE
01273 ;
01274 ;          Lifetime of a space object represented by PLAYER2 (usually the Zylon
01275 ;          photon torpedo). Compare PL0LIFE ($E9).
01276 ;
01277 ;          If this PLAYER represents a photon torpedo, its lifetime is
01278 ;          decremented from an initial value of $FF.
01279 ;
01280 ; $EC      PL3LIFE
01281 ;
01282 ;          Lifetime of a space object represented by PLAYER3 (usually our
01283 ;          starship's photon torpedo 0). Compare PL2LIFE ($EB).
01284 ;
01285 ;          If this PLAYER represents a photon torpedo, its lifetime is
01286 ;          decremented from an initial value of $FF.
01287 ;
01288 ; $ED      PL4LIFE
01289 ;
01290 ;          Lifetime of a space object represented by PLAYER4 (usually our
01291 ;          starship's photon torpedo 1). Compare PL2LIFE ($EB).
01292 ;
01293 ;          If this PLAYER represents a photon torpedo, its lifetime is
01294 ;          decremented from an initial value of $FF.
01295 ;
01296 ; $EE      PL0COLOR
01297 ;
01298 ;          Color of PLAYER0
01299 ;
01300 ; $EF      PL1COLOR
01301 ;
01302 ;          Color of PLAYER1
01303 ;
01304 ; $F0      PL2COLOR
01305 ;
01306 ;          Color of PLAYER2
01307 ;
01308 ; $F1      PL3COLOR
01309 ;
01310 ;          Color of PLAYER3
01311 ;
01312 ; $F2      PF0COLOR
01313 ;
01314 ;          Color of PLAYFIELD0
01315 ;
01316 ; $F3      PF1COLOR
01317 ;
01318 ;          Color of PLAYFIELD1
01319 ;
01320 ; $F4      PF2COLOR
01321 ;
01322 ;          Color of PLAYFIELD2
01323 ;
01324 ; $F5      PF3COLOR
01325 ;
01326 ;          Color of PLAYFIELD3
01327 ;
01328 ; $F6      BGRCOLOR
01329 ;
01330 ;          Color of BACKGROUND
01331 ;
01332 ; $F7      PF0COLORDLI
01333 ;
01334 ;          Color of PLAYFIELD0 after DLI
01335 ;
01336 ; $F8      PF1COLORDLI
01337 ;
01338 ;          Color of PLAYFIELD1 after DLI
01339 ;
01340 ; $F9      PF2COLORDLI
01341 ;
01342 ;          Color of PLAYFIELD2 after DLI
01343 ;
01344 ; $FA      PF3COLORDLI
01345 ;
01346 ;          Color of PLAYFIELD3 after DLI
01347 ;
01348 ; $FB      BGRCOLORDLI
01349 ;
01350 ;          Color of BACKGROUND after DLI
01351 ;
01352 ; $0280..$02E9 DSPLST
01353 ;
01354 ;              Display List
01355 ;
01356 ; $0300..$03FF PL4DATA
01357 ;
01358 ;              PLAYER4 data area
01359 ;
01360 ; $0400..$04FF PL0DATA
01361 ;
01362 ;              PLAYER0 data area
01363 ;
01364 ; $0500..$05FF PL1DATA
01365 ;
01366 ;              PLAYER1 data area
01367 ;
01368 ; $0600..$06FF PL2DATA
01369 ;
01370 ;              PLAYER2 data area
01371 ;
01372 ; $0700..$07FF PL3DATA
01373 ;
01374 ;              PLAYER3 data area
01375 ;
01376 ; $0800..$0863 PFMEMROWLO
01377 ;
01378 ;              Lookup table of start addresses (low byte) for each row of
01379 ;              PLAYFIELD memory, which is located at PFMEM ($1000). The table
01380 ;              contains 100 bytes for 100 rows (of which only 99 are shown by
01381 ;              the Display List, the PLAYFIELD is 160 x 99 pixels). The
01382 ;              addresses grow in increments of 40 (40 bytes = 160 pixels in
01383 ;              GRAPHICS7 mode = 1 PLAYFIELD row of pixels). See also PFMEMROWHI
01384 ;              ($0864).
01385 ;
01386 ; $0864..$08C7 PFMEMROWHI
01387 ;
01388 ;              Lookup table of start addresses (high byte) of each row of
01389 ;              PLAYFIELD memory. See also PFMEMROWLO ($0800).
01390 ;
01391 ; $08C9..$0948 GCMEMMAP
01392 ;
01393 ;              Galactic Chart memory map (16 columns x 8 rows = 128 bytes)
01394 ;
01395 ; $0949..$0970 PANELTXT
01396 ;
01397 ;              Memory of Control Panel Display (bottom text window) in Front
01398 ;              view, Aft view, and Long-Range Scan view (20 characters x 2 rows
01399 ;              = 40 bytes).
01400 ;
01401 ; $094A        VELOCD1
01402 ;
01403 ;              First digit (of 2) of the VELOCITY readout in Control Panel
01404 ;              Display memory.
01405 ;
01406 ; $0950        KILLCNTD1
01407 ;
01408 ;              First digit (of 2) of the KILL COUNTER readout in Control Panel
01409 ;              Display memory.
01410 ;
01411 ; $0955        ENERGYD1
01412 ;
01413 ;              First digit (of 4) of the ENERGY readout in Control Panel Display
01414 ;              memory.
01415 ;
01416 ; $095A        TRACKC1
01417 ;
01418 ;              Character of the TRACKING readout 'T' or 'C' in Control Panel
01419 ;              Display memory.
01420 ;
01421 ; $095C        TRACKDIGIT
01422 ;
01423 ;              Digit of the TRACKING readout in Control Panel Display memory. It
01424 ;              is used to store the index of the currently tracked space object.
01425 ;              Used values are:
01426 ;                $00 -> Track Zylon ship 0
01427 ;                $01 -> Track Zylon ship 1
01428 ;                $02 -> Track starbase
01429 ;                $03 -> Track Hyperwarp Target Marker
01430 ;
01431 ; $0960        THETAC1
01432 ;
01433 ;              First character of the THETA readout in Control Panel Display
01434 ;              memory.
01435 ;
01436 ; $0966        PHIC1
01437 ;
01438 ;              First character of the PHI readout in Control Panel Display
01439 ;              memory.
01440 ;
01441 ; $096C        RANGEC1
01442 ;
01443 ;              First character of the RANGE readout in Control Panel Display
01444 ;              memory.
01445 ;
01446 ; $0971..$09AC GCTXT
01447 ;
01448 ;              Memory of Galactic Chart Panel Display (bottom text window) of
01449 ;              Galactic Chart view (20 characters x 3 rows = 60 bytes).
01450 ;
01451 ; $097D        GCWARPD1
01452 ;
01453 ;              First digit (of 4) of the HYPERWARP ENERGY readout in Galactic
01454 ;              Chart Panel Display memory.
01455 ;
01456 ; $098D        GCTRGCNT
01457 ;
01458 ;              First target counter digit (of 2) in Galactic Chart Panel Display
01459 ;              memory.
01460 ;
01461 ; $0992        GCSTATPHO
01462 ;
01463 ;              Photon Torpedo status letter in Galactic Chart Panel Display
01464 ;              memory. Used values are:
01465 ;                %00****** -> OK
01466 ;                %10****** -> Destroyed
01467 ;                %11****** -> Damaged
01468 ;
01469 ; $0993        GCSTATENG
01470 ;
01471 ;              Engines status letter in Galactic Chart Panel Display memory.
01472 ;              Used values are:
01473 ;                %00****** -> OK
01474 ;                %10****** -> Destroyed
01475 ;                %11****** -> Damaged
01476 ;
01477 ; $0994        GCSTATSHL
01478 ;
01479 ;              Shields status letter in Galactic Chart Panel Display memory.
01480 ;              Used values are:
01481 ;                %00****** -> OK
01482 ;                %10****** -> Destroyed
01483 ;                %11****** -> Damaged
01484 ;
01485 ; $0995        GCSTATCOM
01486 ;
01487 ;              Attack Computer status letter in Galactic Chart Panel Display
01488 ;              memory. Used values are:
01489 ;                %00****** -> OK
01490 ;                %10****** -> Destroyed
01491 ;                %11****** -> Damaged
01492 ;
01493 ; $0996        GCSTATLRS
01494 ;
01495 ;              Long-Range Scan status letter in Galactic Chart Panel Display
01496 ;              memory. Used values are:
01497 ;                %00****** -> OK
01498 ;                %10****** -> Destroyed
01499 ;                %11****** -> Damaged
01500 ;
01501 ; $0997        GCSTATRAD
01502 ;
01503 ;              Subspace Radio status letter in Galactic Chart Panel Display
01504 ;              memory. Used values are:
01505 ;                %00****** -> OK
01506 ;                %10****** -> Destroyed
01507 ;                %11****** -> Damaged
01508 ;
01509 ; $09A3        GCSTARDAT
01510 ;
01511 ;              First (of 5) digits of the star date clock in the Galactic Chart
01512 ;              Panel Display memory.
01513 ;
01514 ; $09AD..$09DD ZPOSSIGN
01515 ;
01516 ;              Table containing the sign bit (B16) of position vector
01517 ;              z-components (z-coordinate) (49 bytes). Bytes 0..4 belong to
01518 ;              position vectors of PLAYER space objects (Zylon ships, photon
01519 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01520 ;              PLAYFIELD space objects (stars, explosion fragments). Used values
01521 ;              are:
01522 ;                $00 -> Negative sign (behind our starship)
01523 ;                $01 -> Positive sign (in front of our starship)
01524 ;
01525 ;              See also "ON POSITION VECTORS".
01526 ;
01527 ; $09AD        PL0ZPOSSIGN
01528 ;
01529 ;              Sign bit (B16) of position vector z-component (z-coordinate) of
01530 ;              PLAYER0. Compare ZPOSSIGN ($09AD). See also "ON POSITION
01531 ;              VECTORS".
01532 ;
01533 ; $09AE        PL1ZPOSSIGN
01534 ;
01535 ;              Sign bit (B16) of position vector z-component (z-coordinate) of
01536 ;              PLAYER1. Compare ZPOSSIGN ($09AD). See also "ON POSITION
01537 ;              VECTORS".
01538 ;
01539 ; $09AF        PL2ZPOSSIGN
01540 ;
01541 ;              Sign bit (B16) of position vector z-component (z-coordinate) of
01542 ;              PLAYER2. Compare ZPOSSIGN ($09AD). See also "ON POSITION
01543 ;              VECTORS".
01544 ;
01545 ; $09B0        PL3ZPOSSIGN
01546 ;
01547 ;              Sign bit (B16) of position vector z-component (z-coordinate) of
01548 ;              PLAYER3. Compare ZPOSSIGN ($09AD). See also "ON POSITION
01549 ;              VECTORS".
01550 ;
01551 ; $09B1        PL4ZPOSSIGN
01552 ;
01553 ;              Sign bit (B16) of position vector z-component (z-coordinate) of
01554 ;              PLAYER4. Compare ZPOSSIGN ($09AD). See also "ON POSITION
01555 ;              VECTORS".
01556 ;
01557 ; $09DE..$0A0E XPOSSIGN
01558 ;
01559 ;              Table containing the sign bit (B16) of position vector
01560 ;              x-components (x-coordinate) (49 bytes). Bytes 0..4 belong to
01561 ;              position vectors of PLAYER space objects (Zylon ships, photon
01562 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01563 ;              PLAYFIELD space objects (stars, explosion fragments). Used values
01564 ;              are:
01565 ;                $00 -> Negative sign (left)
01566 ;                $01 -> Positive sign (right)
01567 ;
01568 ;              See also "ON POSITION VECTORS".
01569 ;
01570 ; $09DE        PL0XPOSSIGN
01571 ;
01572 ;              Sign bit (B16) of position vector x-component (x-coordinate) of
01573 ;              PLAYER0. Compare XPOSSIGN ($09DE). See also "ON POSITION
01574 ;              VECTORS".
01575 ;
01576 ; $09DF        PL1XPOSSIGN
01577 ;
01578 ;              Sign bit (B16) of position vector x-component (x-coordinate) of
01579 ;              PLAYER1. Compare XPOSSIGN ($09DE). See also "ON POSITION
01580 ;              VECTORS".
01581 ;
01582 ; $09E0        PL2XPOSSIGN
01583 ;
01584 ;              Sign bit (B16) of position vector x-component (x-coordinate) of
01585 ;              PLAYER2. Compare XPOSSIGN ($09DE). See also "ON POSITION
01586 ;              VECTORS".
01587 ;
01588 ; $09E1        PL3XPOSSIGN
01589 ;
01590 ;              Sign bit (B16) of position vector x-component (x-coordinate) of
01591 ;              PLAYER3. Compare XPOSSIGN ($09DE). See also "ON POSITION
01592 ;              VECTORS".
01593 ;
01594 ; $09E2        PL4XPOSSIGN
01595 ;
01596 ;              Sign bit (B16) of position vector x-component (x-coordinate) of
01597 ;              PLAYER4. Compare XPOSSIGN ($09DE). See also "ON POSITION
01598 ;              VECTORS".
01599 ;
01600 ; $0A0F..$0A3F YPOSSIGN
01601 ;
01602 ;              Table containing the sign bit (B16) of position vector
01603 ;              y-components (y-coordinate) (49 bytes). Bytes 0..4 belong to
01604 ;              position vectors of PLAYER space objects (Zylon ships, photon
01605 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01606 ;              PLAYFIELD space objects (stars, explosion fragments). Used values
01607 ;              are:
01608 ;                $00 -> Negative sign (down)
01609 ;                $01 -> Positive sign (up)
01610 ;
01611 ;              See also "ON POSITION VECTORS".
01612 ;
01613 ; $0A0F        PL0YPOSSIGN
01614 ;
01615 ;              Sign bit (B16) of position vector y-component (y-coordinate) of
01616 ;              PLAYER0. Compare YPOSSIGN ($0A0F). See also "ON POSITION
01617 ;              VECTORS".
01618 ;
01619 ; $0A10        PL1YPOSSIGN
01620 ;
01621 ;              Sign bit (B16) of position vector y-component (y-coordinate) of
01622 ;              PLAYER1. Compare YPOSSIGN ($0A0F). See also "ON POSITION
01623 ;              VECTORS".
01624 ;
01625 ; $0A11        PL2YPOSSIGN
01626 ;
01627 ;              Sign bit (B16) of position vector y-component (y-coordinate) of
01628 ;              PLAYER2. Compare YPOSSIGN ($0A0F). See also "ON POSITION
01629 ;              VECTORS".
01630 ;
01631 ; $0A12        PL3YPOSSIGN
01632 ;
01633 ;              Sign bit (B16) of position vector y-component (y-coordinate) of
01634 ;              PLAYER3. Compare YPOSSIGN ($0A0F). See also "ON POSITION
01635 ;              VECTORS".
01636 ;
01637 ; $0A13        PL4YPOSSIGN
01638 ;
01639 ;              Sign bit (B16) of position vector y-component (y-coordinate) of
01640 ;              PLAYER4. Compare YPOSSIGN ($0A0F). See also "ON POSITION
01641 ;              VECTORS".
01642 ;
01643 ; $0A40..$0A70 ZPOSHI
01644 ;
01645 ;              Table containing the high byte (B15..8) of position vector
01646 ;              y-components (y-coordinate) (49 bytes). Bytes 0..4 belong to
01647 ;              position vectors of PLAYER space objects (Zylon ships, photon
01648 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01649 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01650 ;              "ON POSITION VECTORS".
01651 ;
01652 ; $0A40        PL0ZPOSHI
01653 ;
01654 ;              High byte (B15..8) of position vector z-component (z-coordinate)
01655 ;              of PLAYER0. Compare ZPOSHI ($0A40). See also "ON POSITION
01656 ;              VECTORS".
01657 ;
01658 ; $0A41        PL1ZPOSHI
01659 ;
01660 ;              High byte (B15..8) of position vector z-component (z-coordinate)
01661 ;              of PLAYER1. Compare ZPOSHI ($0A40). See also "ON POSITION
01662 ;              VECTORS".
01663 ;
01664 ; $0A42        PL2ZPOSHI
01665 ;
01666 ;              High byte (B15..8) of position vector z-component (z-coordinate)
01667 ;              of PLAYER2. Compare ZPOSHI ($0A40). See also "ON POSITION
01668 ;              VECTORS".
01669 ;
01670 ; $0A43        PL3ZPOSHI
01671 ;
01672 ;              High byte (B15..8) of position vector z-component (z-coordinate)
01673 ;              of PLAYER3. Compare ZPOSHI ($0A40). See also "ON POSITION
01674 ;              VECTORS".
01675 ;
01676 ; $0A44        PL4ZPOSHI
01677 ;
01678 ;              High byte (B15..8) of position vector z-component (z-coordinate)
01679 ;              of PLAYER4. Compare ZPOSHI ($0A40). See also "ON POSITION
01680 ;              VECTORS".
01681 ;
01682 ; $0A71..$0AA1 XPOSHI
01683 ;
01684 ;              Table containing the high byte (B15..8) of position vector
01685 ;              x-components (x-coordinate) (49 bytes). Bytes 0..4 belong to
01686 ;              position vectors of PLAYER space objects (Zylon ships, photon
01687 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01688 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01689 ;              "ON POSITION VECTORS".
01690 ;
01691 ; $0A71        PL0XPOSHI
01692 ;
01693 ;              High byte (B15..8) of position vector x-component (x-coordinate)
01694 ;              of PLAYER0. Compare XPOSHI ($0A71). See also "ON POSITION
01695 ;              VECTORS".
01696 ;
01697 ; $0A72        PL1XPOSHI
01698 ;
01699 ;              High byte (B15..8) of position vector x-component (x-coordinate)
01700 ;              of PLAYER1. Compare XPOSHI ($0A71). See also "ON POSITION
01701 ;              VECTORS".
01702 ;
01703 ; $0A73        PL2XPOSHI
01704 ;
01705 ;              High byte (B15..8) of position vector x-component (x-coordinate)
01706 ;              of PLAYER2. Compare XPOSHI ($0A71). See also "ON POSITION
01707 ;              VECTORS".
01708 ;
01709 ; $0A74        PL3XPOSHI
01710 ;
01711 ;              High byte (B15..8) of position vector x-component (x-coordinate)
01712 ;              of PLAYER3. Compare XPOSHI ($0A71). See also "ON POSITION
01713 ;              VECTORS".
01714 ;
01715 ; $0A75        PL4XPOSHI
01716 ;
01717 ;              High byte (B15..8) of position vector x-component (x-coordinate)
01718 ;              of PLAYER4. Compare XPOSHI ($0A71). See also "ON POSITION
01719 ;              VECTORS".
01720 ;
01721 ; $0AA2..$0AD2 YPOSHI
01722 ;
01723 ;              Table containing the high byte (B15..8) of position vector
01724 ;              y-components (y-coordinate) (49 bytes). Bytes 0..4 belong to
01725 ;              position vectors of PLAYER space objects (Zylon ships, photon
01726 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01727 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01728 ;              "ON POSITION VECTORS".
01729 ;
01730 ; $0AA2        PL0YPOSHI
01731 ;
01732 ;              High byte (B15..8) of position vector y-component (y-coordinate)
01733 ;              of PLAYER0. Compare YPOSHI ($0AA2). See also "ON POSITION
01734 ;              VECTORS".
01735 ;
01736 ; $0AA3        PL1YPOSHI
01737 ;
01738 ;              High byte (B15..8) of position vector y-component (y-coordinate)
01739 ;              of PLAYER1. Compare YPOSHI ($0AA2). See also "ON POSITION
01740 ;              VECTORS".
01741 ;
01742 ; $0AA4        PL2YPOSHI
01743 ;
01744 ;              High byte (B15..8) of position vector y-component (y-coordinate)
01745 ;              of PLAYER2. Compare YPOSHI ($0AA2). See also "ON POSITION
01746 ;              VECTORS".
01747 ;
01748 ; $0AA5        PL3YPOSHI
01749 ;
01750 ;              High byte (B15..8) of position vector y-component (y-coordinate)
01751 ;              of PLAYER3. Compare YPOSHI ($0AA2). See also "ON POSITION
01752 ;              VECTORS".
01753 ;
01754 ; $0AA6        PL4YPOSHI
01755 ;
01756 ;              High byte (B15..8) of position vector y-component (y-coordinate)
01757 ;              of PLAYER4. Compare YPOSHI ($0AA2). See also "ON POSITION
01758 ;              VECTORS".
01759 ;
01760 ; $0AD3..$0B03 ZPOSLO
01761 ;
01762 ;              Table containing the low byte (B7..0) of position vector
01763 ;              z-components (z-coordinate) (49 bytes). Bytes 0..4 belong to
01764 ;              position vectors of PLAYER space objects (Zylon ships, photon
01765 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01766 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01767 ;              "ON POSITION VECTORS".
01768 ;
01769 ; $0AD3        PL0ZPOSLO
01770 ;
01771 ;              Low byte (B7..0) of position vector z-component (z-coordinate) of
01772 ;              PLAYER0. Compare ZPOSLO ($0AD3). See also "ON POSITION VECTORS".
01773 ;
01774 ; $0AD4        PL1ZPOSLO
01775 ;
01776 ;              Low byte (B7..0) of position vector z-component (z-coordinate) of
01777 ;              PLAYER1. Compare ZPOSLO ($0AD3). See also "ON POSITION VECTORS".
01778 ;
01779 ; $0AD5        PL2ZPOSLO
01780 ;
01781 ;              Low byte (B7..0) of position vector z-component (z-coordinate) of
01782 ;              PLAYER2. Compare ZPOSLO ($0AD3). See also "ON POSITION VECTORS".
01783 ;
01784 ; $0AD6        PL3ZPOSLO
01785 ;
01786 ;              Low byte (B7..0) of position vector z-component (z-coordinate) of
01787 ;              PLAYER3. Compare ZPOSLO ($0AD3). See also "ON POSITION VECTORS".
01788 ;
01789 ; $0AD7        PL4ZPOSLO
01790 ;
01791 ;              Low byte (B7..0) of position vector z-component (z-coordinate) of
01792 ;              PLAYER4. Compare ZPOSLO ($0AD3). See also "ON POSITION VECTORS".
01793 ;
01794 ; $0B04..$0B34 XPOSLO
01795 ;
01796 ;              Table containing the low byte (B7..0) of position vector
01797 ;              x-components (x-coordinate) (49 bytes). Bytes 0..4 belong to
01798 ;              position vectors of PLAYER space objects (Zylon ships, photon
01799 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01800 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01801 ;              "ON POSITION VECTORS".
01802 ;
01803 ; $0B04        PL0XPOSLO
01804 ;
01805 ;              Low byte (B7..0) of position vector x-component (x-coordinate) of
01806 ;              PLAYER0. Compare XPOSLO ($0B04). See also "ON POSITION VECTORS".
01807 ;
01808 ; $0B05        PL1XPOSLO
01809 ;
01810 ;              Low byte (B7..0) of position vector x-component (x-coordinate) of
01811 ;              PLAYER1. Compare XPOSLO ($0B04). See also "ON POSITION VECTORS".
01812 ;
01813 ; $0B06        PL2XPOSLO
01814 ;
01815 ;              Low byte (B7..0) of position vector x-component (x-coordinate) of
01816 ;              PLAYER2. Compare XPOSLO ($0B04). See also "ON POSITION VECTORS".
01817 ;
01818 ; $0B07        PL3XPOSLO
01819 ;
01820 ;              Low byte (B7..0) of position vector x-component (x-coordinate) of
01821 ;              PLAYER3. Compare XPOSLO ($0B04). See also "ON POSITION VECTORS".
01822 ;
01823 ; $0B08        PL4XPOSLO
01824 ;
01825 ;              Low byte (B7..0) of position vector x-component (x-coordinate) of
01826 ;              PLAYER4. Compare XPOSLO ($0B04). See also "ON POSITION VECTORS".
01827 ;
01828 ; $0B35..$0B65 YPOSLO
01829 ;
01830 ;              Table containing the low byte (B7..0) of position vector
01831 ;              y-components (y-coordinate) (49 bytes). Bytes 0..4 belong to
01832 ;              position vectors of PLAYER space objects (Zylon ships, photon
01833 ;              torpedoes, etc.). Bytes 5..48 belong to position vectors of
01834 ;              PLAYFIELD space objects (stars, explosion fragments). See also
01835 ;              "ON POSITION VECTORS".
01836 ;
01837 ; $0B35        PL0YPOSLO
01838 ;
01839 ;              Low byte (B7..0) of position vector y-component (y-coordinate) of
01840 ;              PLAYER0. Compare YPOSLO ($0B35). See also "ON POSITION VECTORS". 
01841 ;
01842 ; $0B36        PL1YPOSLO
01843 ;
01844 ;              Low byte (B7..0) of position vector y-component (y-coordinate) of
01845 ;              PLAYER1. Compare YPOSLO ($0B35). See also "ON POSITION VECTORS".
01846 ;
01847 ; $0B37        PL2YPOSLO
01848 ;
01849 ;              Low byte (B7..0) of position vector y-component (y-coordinate) of
01850 ;              PLAYER2. Compare YPOSLO ($0B35). See also "ON POSITION VECTORS".
01851 ;
01852 ; $0B38        PL3YPOSLO
01853 ;
01854 ;              Low byte (B7..0) of position vector y-component (y-coordinate) of
01855 ;              PLAYER3. Compare YPOSLO ($0B35). See also "ON POSITION VECTORS".
01856 ;
01857 ; $0B39        PL4YPOSLO
01858 ;
01859 ;              Low byte (B7..0) of position vector y-component (y-coordinate) of
01860 ;              PLAYER4. Compare YPOSLO ($0B35). See also "ON POSITION VECTORS".
01861 ;
01862 ; $0B66..$0B96 ZVEL
01863 ;
01864 ;              Table containing velocity vector z-components (z-velocities) (49
01865 ;              bytes). Bytes 0..4 belong to velocity vectors of PLAYER space
01866 ;              objects (Zylon ships, photon torpedoes, etc.). Bytes 5..48 belong
01867 ;              to velocity vectors of PLAYFIELD space objects (stars, explosion
01868 ;              fragments). Each z-velocity is stored in the binary format
01869 ;              %sxxxxxxx where
01870 ;                %s = 0   -> Positive sign (moving in flight direction)
01871 ;                %s = 1   -> Negative sign (moving in reverse flight direction)
01872 ;                %xxxxxxx -> Unsigned 7-bit velocity value in <KM/H>
01873 ;
01874 ;              See also "ON VELOCITY VECTORS".
01875 ;
01876 ; $0B66        PL0ZVEL
01877 ;
01878 ;              Velocity vector z-component (z-velocity) of PLAYER0. Compare ZVEL
01879 ;              ($0B66). See also "ON VELOCITY VECTORS".
01880 ;
01881 ; $0B67        PL1ZVEL
01882 ;
01883 ;              Velocity vector z-component (z-velocity) of PLAYER1. Compare ZVEL
01884 ;              ($0B66). See also "ON VELOCITY VECTORS".
01885 ;
01886 ; $0B68        PL2ZVEL
01887 ;
01888 ;              Velocity vector z-component (z-velocity) of PLAYER2. Compare ZVEL
01889 ;              ($0B66). See also "ON VELOCITY VECTORS".
01890 ;
01891 ; $0B69        PL3ZVEL
01892 ;
01893 ;              Velocity vector z-component (z-velocity) of PLAYER3. Compare ZVEL
01894 ;              ($0B66). See also "ON VELOCITY VECTORS".
01895 ;
01896 ; $0B6A        PL4ZVEL
01897 ;
01898 ;              Velocity vector z-component (z-velocity) of PLAYER4. Compare ZVEL
01899 ;              ($0B66). See also "ON VELOCITY VECTORS".
01900 ;
01901 ; $0B97..$0BC7 XVEL
01902 ;
01903 ;              Table containing velocity vector x-components (x-velocities) (49
01904 ;              bytes). Bytes 0..4 belong to velocity vectors of PLAYER space
01905 ;              objects (Zylon ships, photon torpedoes, etc.). Bytes 5..48 belong
01906 ;              to velocity vectors of PLAYFIELD space objects (stars, explosion
01907 ;              fragments). Each x-velocity is stored in the binary format
01908 ;              %sxxxxxxx where
01909 ;                %s = 0   -> Positive sign (moving to the right)
01910 ;                %s = 1   -> Negative sign (moving to the left)
01911 ;                %xxxxxxx -> Unsigned 7-bit velocity value in <KM/H>
01912 ;
01913 ;              See also "ON VELOCITY VECTORS".
01914 ;
01915 ; $0B97        PL0XVEL
01916 ;
01917 ;              Velocity vector x-component (x-velocity) of PLAYER0. Compare XVEL
01918 ;              ($0B97). See also "ON VELOCITY VECTORS". 
01919 ;
01920 ; $0B98        PL1XVEL
01921 ;
01922 ;              Velocity vector x-component (x-velocity) of PLAYER1. Compare XVEL
01923 ;              ($0B97). See also "ON VELOCITY VECTORS".
01924 ;
01925 ; $0B99        PL2XVEL
01926 ;
01927 ;              Velocity vector x-component (x-velocity) of PLAYER2. Compare XVEL
01928 ;              ($0B97). See also "ON VELOCITY VECTORS".
01929 ;
01930 ; $0B9A        PL3XVEL
01931 ;
01932 ;              Velocity vector x-component (x-velocity) of PLAYER3. Compare XVEL
01933 ;              ($0B97). See also "ON VELOCITY VECTORS".
01934 ;
01935 ; $0B9B        PL4XVEL
01936 ;
01937 ;              Velocity vector x-component (x-velocity) of PLAYER4. Compare XVEL
01938 ;              ($0B97). See also "ON VELOCITY VECTORS".
01939 ;
01940 ; $0BC8..$0BF8 YVEL
01941 ;
01942 ;              Table containing velocity vector y-components (y-velocities) (49
01943 ;              bytes). Bytes 0..4 belong to velocity vectors of PLAYER space
01944 ;              objects (Zylon ships, photon torpedoes, etc.). Bytes 5..48 belong
01945 ;              to velocity vectors of PLAYFIELD space objects (stars, explosion
01946 ;              fragments). Each y-velocity is stored in the binary format
01947 ;              %sxxxxxxx where
01948 ;                %s = 0   -> Positive sign (moving up)
01949 ;                %s = 1   -> Negative sign (moving down)
01950 ;                %xxxxxxx -> Unsigned 7-bit velocity value in <KM/H>
01951 ;
01952 ;              See also "ON VELOCITY VECTORS".
01953 ;
01954 ; $0BC8        PL0YVEL
01955 ;
01956 ;              Velocity vector y-component (y-velocity) of PLAYER0. Compare YVEL
01957 ;              ($0BC8). See also "ON VELOCITY VECTORS". 
01958 ;
01959 ; $0BC9        PL1YVEL
01960 ;
01961 ;              Velocity vector y-component (y-velocity) of PLAYER1. Compare YVEL
01962 ;              ($0BC8). See also "ON VELOCITY VECTORS".
01963 ;
01964 ; $0BCA        PL2YVEL
01965 ;
01966 ;              Velocity vector y-component (y-velocity) of PLAYER2. Compare YVEL
01967 ;              ($0BC8). See also "ON VELOCITY VECTORS".
01968 ;
01969 ; $0BCB        PL3YVEL
01970 ;
01971 ;              Velocity vector y-component (y-velocity) of PLAYER3. Compare YVEL
01972 ;              ($0BC8). See also "ON VELOCITY VECTORS".
01973 ;
01974 ; $0BCC        PL4YVEL
01975 ;
01976 ;              Velocity vector y-component (y-velocity) of PLAYER4. Compare YVEL
01977 ;              ($0BC8). See also "ON VELOCITY VECTORS".
01978 ;
01979 ; $0BF9..$0C29 PIXELROWNEW
01980 ;
01981 ;              Table containing the new pixel row number of space objects (49
01982 ;              bytes). Bytes 0..4 belong to PLAYER space objects and contain
01983 ;              Player/Missile (PM) pixel row numbers. They are counted from
01984 ;              vertical PM position 0, which is offscreen. Bytes 5..48 belong to
01985 ;              PLAYFIELD space objects (stars, explosion fragments) and contain
01986 ;              PLAYFIELD pixel row numbers. They are counted from the top border
01987 ;              of the PLAYFIELD and have values of 0..99. See also PIXELROW
01988 ;              ($0C5B).
01989 ;
01990 ; $0BF9        PL0ROWNEW
01991 ;
01992 ;              New pixel row number of PLAYER0 in Player/Missile pixels. See
01993 ;              also PIXELROWNEW ($0BF9).
01994 ;
01995 ; $0BFA        PL1ROWNEW
01996 ;
01997 ;              New pixel row number of PLAYER1 in Player/Missile pixels. See
01998 ;              also PIXELROWNEW ($0BF9).
01999 ;
02000 ; $0BFB        PL2ROWNEW
02001 ;
02002 ;              New pixel row number of PLAYER2 in Player/Missile pixels. See
02003 ;              also PIXELROWNEW ($0BF9).
02004 ;
02005 ; $0BFC        PL3ROWNEW
02006 ;
02007 ;              New pixel row number of PLAYER3 in Player/Missile pixels. See
02008 ;              also PIXELROWNEW ($0BF9).
02009 ;
02010 ; $0BFD        PL4ROWNEW
02011 ;
02012 ;              New pixel row number of PLAYER4 in Player/Missile pixels. See
02013 ;              also PIXELROWNEW ($0BF9).
02014 ;
02015 ; $0C2A..$0C5A PIXELCOLUMN
02016 ;
02017 ;              Table containing the pixel column number of space objects (49
02018 ;              bytes). Bytes 0..4 belong to PLAYER space objects and contain
02019 ;              Player/Missile (PM) pixel column numbers. They are counted from
02020 ;              horizontal PM position 0, which is offscreen. Bytes 5..48 belong
02021 ;              to PLAYFIELD space objects (stars, explosion fragments) and
02022 ;              contain PLAYFIELD pixel column numbers. They are counted from the
02023 ;              left border of the PLAYFIELD and have values of 0..159.
02024 ;
02025 ; $0C2A        PL0COLUMN
02026 ;
02027 ;              Pixel column number of PLAYER0 in Player/Missile pixels. See also
02028 ;              PIXELCOLUMN ($0C2A).
02029 ;
02030 ; $0C2B        PL1COLUMN
02031 ;
02032 ;              Pixel column number of PLAYER1 in Player/Missile pixels. See also
02033 ;              PIXELCOLUMN ($0C2A).
02034 ;
02035 ; $0C2C        PL2COLUMN
02036 ;
02037 ;              Pixel column number of PLAYER2 in Player/Missile pixels. See also
02038 ;              PIXELCOLUMN ($0C2A).
02039 ;
02040 ; $0C2D        PL3COLUMN
02041 ;
02042 ;              Pixel column number of PLAYER3 in Player/Missile pixels. See also
02043 ;              PIXELCOLUMN ($0C2A).
02044 ;
02045 ; $0C2E        PL4COLUMN
02046 ;
02047 ;              Pixel column number of PLAYER4 in Player/Missile pixels. See also
02048 ;              PIXELCOLUMN ($0C2A).
02049 ;
02050 ; $0C5B..$0C8B PIXELROW
02051 ;
02052 ;              Table containing the pixel row number of space objects (49
02053 ;              bytes). Bytes 0..4 belong to PLAYER space objects and contain
02054 ;              Player/Missile (PM) pixel row numbers. They are counted from
02055 ;              vertical PM position 0, which is offscreen. Bytes 5..48 belong to
02056 ;              PLAYFIELD space objects (stars, explosion fragments) and contain
02057 ;              PLAYFIELD pixel row numbers. They are counted from the top border
02058 ;              of the PLAYFIELD and have values of 0..99. See also PIXELROWNEW
02059 ;              ($0BF9).
02060 ;
02061 ; $0C5B        PL0ROW
02062 ;
02063 ;              Pixel row number of PLAYER0 in Player/Missile pixels. See also
02064 ;              PIXELROW ($0C5B).
02065 ;
02066 ; $0C5C        PL1ROW
02067 ;
02068 ;              Pixel row number of PLAYER1 in Player/Missile pixels. See also
02069 ;              PIXELROW ($0C5B).
02070 ;
02071 ; $0C5D        PL2ROW
02072 ;
02073 ;              Pixel row number of PLAYER2 in Player/Missile pixels. See also
02074 ;              PIXELROW ($0C5B).
02075 ;
02076 ; $0C5E        PL3ROW
02077 ;
02078 ;              Pixel row number of PLAYER3 in Player/Missile pixels. See also
02079 ;              PIXELROW ($0C5B).
02080 ;
02081 ; $0C5F        PL4ROW
02082 ;
02083 ;              Pixel row number of PLAYER4 in Player/Missile pixels. See also
02084 ;              PIXELROW ($0C5B).
02085 ;
02086 ; $0C8C..$0CBC PIXELBYTEOFF
02087 ;
02088 ;              Table containing a byte offset into PLAYFIELD memory for each
02089 ;              PLAYFIELD space object (stars, explosion fragments) (49 bytes):
02090 ;              the number of bytes from the start of the PLAYFIELD row to the
02091 ;              byte containing the space object pixel in the same PLAYFIELD row.
02092 ;              In other words, the pixel column modulo 4 (1 byte = 4 GRAPHICS7
02093 ;              pixels).
02094 ;
02095 ;              NOTE: Only bytes 5..48 are used for PLAYFIELD space objects in
02096 ;              this way. Bytes 0..4 are used differently. See PL0SHAPTYPE
02097 ;              ($0C8C)..PL4SHAPTYPE ($0C90).
02098 ;
02099 ; $0C8C        PL0SHAPTYPE
02100 ;
02101 ;              Shape type of PLAYER0. Used to index the PLAYER's set of shape
02102 ;              cells in tables PLSHAPOFFTAB ($BE2F) and PLSHPHEIGHTTAB ($BE7F).
02103 ;              Used values are:
02104 ;                $00 -> PHOTON TORPEDO
02105 ;                $10 -> ZYLON FIGHTER
02106 ;                $20 -> STARBASE RIGHT
02107 ;                $30 -> STARBASE CENTER
02108 ;                $40 -> STARBASE LEFT
02109 ;                $50 -> TRANSFER VESSEL
02110 ;                $60 -> METEOR
02111 ;                $70 -> ZYLON CRUISER
02112 ;                $80 -> ZYLON BASESTAR
02113 ;                $90 -> HYPERWARP TARGET MARKER
02114 ;
02115 ; $0C8D        PL1SHAPTYPE
02116 ;
02117 ;              Shape type of PLAYER1. Compare PL0SHAPTYPE ($0C8C).
02118 ;
02119 ; $0C8E        PL2SHAPTYPE
02120 ;
02121 ;              Shape type of PLAYER2. Compare PL0SHAPTYPE ($0C8C).
02122 ;
02123 ; $0C8F        PL3SHAPTYPE
02124 ;
02125 ;              Shape type of PLAYER3. Compare PL0SHAPTYPE ($0C8C).
02126 ;
02127 ; $0C90        PL4SHAPTYPE
02128 ;
02129 ;              Shape type of PLAYER4. Compare PL0SHAPTYPE ($0C8C).
02130 ;
02131 ; $0CBD..$0CED PIXELSAVE
02132 ;
02133 ;              Table containing the byte of PLAYFIELD memory before drawing the
02134 ;              PLAYFIELD space object pixel into it (star, explosion fragments),
02135 ;              for each PLAYFIELD space object (49 bytes). 
02136 ;
02137 ;              NOTE: Only bytes 5..48 are used for PLAYFIELD space objects in
02138 ;              this way. Bytes 0..4 are used differently. See PL0HEIGHT
02139 ;              ($0CBD)..PL4HEIGHT ($0CC1).
02140 ;
02141 ; $0CBD        PL0HEIGHT
02142 ;
02143 ;              Shape height of PLAYER0
02144 ;
02145 ; $0CBE        PL1HEIGHT
02146 ;
02147 ;              Shape height of PLAYER1
02148 ;
02149 ; $0CBF        PL2HEIGHT
02150 ;
02151 ;              Shape height of PLAYER2
02152 ;
02153 ; $0CC0        PL3HEIGHT
02154 ;
02155 ;              Shape height of PLAYER3
02156 ;
02157 ; $0CC1        PL4HEIGHT
02158 ;
02159 ;              Shape height of PLAYER4
02160 ;
02161 ; $0CEE..$0D1E PIXELBYTE
02162 ;
02163 ;              Table containing a 1-byte bit pattern for 4 pixels in the color
02164 ;              of the space object's pixel, for each PLAYFIELD space object (49
02165 ;              bytes). 
02166 ;
02167 ;              NOTE: Only bytes 5..48 are used for PLAYFIELD space objects in
02168 ;              this way. Bytes 0..4 are used differently. See PL0HEIGHTNEW
02169 ;              ($0CEE)..PL4HEIGHTNEW ($0CF2).
02170 ;
02171 ; $0CEE        PL0HEIGHTNEW
02172 ;
02173 ;              New shape height of PLAYER0
02174 ;
02175 ; $0CEF        PL1HEIGHTNEW
02176 ;
02177 ;              New shape height of PLAYER1
02178 ;
02179 ; $0CF0        PL2HEIGHTNEW
02180 ;
02181 ;              New shape height of PLAYER2
02182 ;
02183 ; $0CF1        PL3HEIGHTNEW
02184 ;
02185 ;              New shape height of PLAYER3
02186 ;
02187 ; $0CF2        PL4HEIGHTNEW
02188 ;
02189 ;              New shape height of PLAYER4
02190 ;
02191 ; $0D1F..$0D32 TITLETXT
02192 ;
02193 ;              Title text line, contains ATASCII-coded characters (20 bytes)
02194 ;
02195 ; $0D35..$0DE8 GCPFMEM
02196 ;
02197 ;              Galactic Chart PLAYFIELD memory (20 characters x 9 rows = 180
02198 ;              bytes)
02199 ;
02200 ; $0DE9..$0EE8 MAPTO80
02201 ;
02202 ;              Lookup table to convert values in $00..$FF to values of 0..80
02203 ;              (255 bytes). Used to map position vector components (coordinates)
02204 ;              to pixel row or column numbers relative to the PLAYFIELD center. 
02205 ;
02206 ; $0EE9..$0FE8 MAPTOBCD99
02207 ;
02208 ;              Lookup table to convert values in $00..$FF to BCD-values of
02209 ;              00..99 (255 bytes). Used in subroutines UPDPANEL ($B804) and
02210 ;              SHOWDIGITS ($B8CD) to convert values to a 2-digit decimal readout
02211 ;              value of the Control Panel Display.
02212 ;
02213 ; $1000..$1F77 PFMEM
02214 ;
02215 ;              PLAYFIELD graphics memory (40 bytes x 100 rows = 4000 bytes, 1
02216 ;              byte stores 4 pixels, 40 bytes = 160 pixels in GRAPHICS7 mode = 1
02217 ;              PLAYFIELD row of pixels).
02218 ;
02219 ;              NOTE: The Display List displays only PLAYFIELD rows 0..98.
02220
02221 ;*******************************************************************************
02222 ;*                                                                             *
02223 ;*                         S Y S T E M   S Y M B O L S                         *
02224 ;*                                                                             *
02225 ;*******************************************************************************
02226
02227 VDSLST          = $0200                               ; Display List Interrupt (DLI) vector
02228 VIMIRQ          = $0216                               ; Interrupt request (IRQ) immediate vector
02229 VVBLKI          = $0222                               ; Vertical blank immediate vector
02230 HPOSP0          = $D000                               ; Horizontal position of PLAYER0
02231 HPOSP1          = $D001                               ; Horizontal position of PLAYER1
02232 HPOSP2          = $D002                               ; Horizontal position of PLAYER2
02233 HPOSP3          = $D003                               ; Horizontal position of PLAYER3
02234 HPOSM0          = $D004                               ; Horizontal position of MISSILE0
02235 HPOSM1          = $D005                               ; Horizontal position of MISSILE1
02236 HPOSM2          = $D006                               ; Horizontal position of MISSILE2
02237 HPOSM3          = $D007                               ; Horizontal position of MISSILE3
02238 M0PL            = $D008                               ; MISSILE0 to PLAYER collisions
02239 M1PL            = $D009                               ; MISSILE1 to PLAYER collisions
02240 M2PL            = $D00A                               ; MISSILE2 to PLAYER collisions
02241 M3PL            = $D00B                               ; MISSILE3 to PLAYER collisions
02242 P3PL            = $D00F                               ; PLAYER3 to PLAYER collisions
02243 TRIG0           = $D010                               ; Joystick 0 trigger
02244 COLPM0          = $D012                               ; Color and brightness of PLAYER0
02245 COLPF0          = $D016                               ; Color and brightness of PLAYFIELD0
02246 PRIOR           = $D01B                               ; Priority selection register
02247 GRACTL          = $D01D                               ; Graphics control register
02248 HITCLR          = $D01E                               ; Clear collision register
02249 CONSOL          = $D01F                               ; Function keys register
02250 AUDF1           = $D200                               ; Audio channel 1 frequency
02251 AUDF2           = $D202                               ; Audio channel 2 frequency
02252 AUDC2           = $D203                               ; Audio channel 2 control
02253 AUDF3           = $D204                               ; Audio channel 3 frequency
02254 AUDC3           = $D205                               ; Audio channel 3 control
02255 AUDF4           = $D206                               ; Audio channel 4 frequency
02256 AUDC4           = $D207                               ; Audio channel 4 control
02257 AUDCTL          = $D208                               ; Audio control
02258 KBCODE          = $D209                               ; Keyboard code
02259 STIMER          = $D209                               ; Start POKEY timers
02260 RANDOM          = $D20A                               ; Random number generator
02261 IRQEN           = $D20E                               ; Interrupt request (IRQ) enable
02262 SKCTL           = $D20F                               ; Serial port control
02263 PORTA           = $D300                               ; Port A
02264 PACTL           = $D302                               ; Port A control
02265 DMACTL          = $D400                               ; Direct Memory Access (DMA) control
02266 DLIST           = $D402                               ; Display List pointer
02267 PMBASE          = $D407                               ; Player/Missile base address (high byte)
02268 CHBASE          = $D409                               ; Character set base address (high byte)
02269 WSYNC           = $D40A                               ; Wait for horizontal synchronization
02270 VCOUNT          = $D40B                               ; Vertical line counter
02271 NMIEN           = $D40E                               ; Non-maskable interrupt (NMI) enable
02272 ROMCHARSET      = $E000                               ; ROM character set
02273
02274 ;*******************************************************************************
02275 ;*                                                                             *
02276 ;*                           G A M E   S Y M B O L S                           *
02277 ;*                                                                             *
02278 ;*******************************************************************************
02279
02280 MISSIONLEVEL    = $62
02281 FKEYCODE        = $63
02282 ISDEMOMODE      = $64
02283 NEWTITLEPHR     = $65
02284 IDLECNTHI       = $66
02285 ISVBISYNC       = $67
02286 MEMPTR          = $68
02287
02288 DIVIDEND        = $6A
02289 JOYSTICKDELTA   = $6D
02290
02291
02292 VELOCITYLO      = $70
02293 NEWVELOCITY     = $71
02294 COUNT8          = $72
02295 EXPLLIFE        = $73
02296 CLOCKTIM        = $74
02297 DOCKSTATE       = $75
02298 COUNT256        = $76
02299 IDLECNTLO       = $77
02300 ZYLONUNITTIM    = $78
02301 MAXSPCOBJIND    = $79
02302 OLDMAXSPCOBJIND = $7A
02303 ISSTARBASESECT  = $7B
02304 ISTRACKCOMPON   = $7C
02305 DRAINSHIELDS    = $7D
02306 DRAINATTCOMP    = $7E
02307 ENERGYCNT       = $7F
02308 DRAINENGINES    = $80
02309 SHIELDSCOLOR    = $81
02310 PL3HIT          = $82
02311 PL4HIT          = $83
02312 OLDTRIG0        = $84
02313
02314 ISTRACKING      = $86
02315 BARRELNR        = $87
02316 LOCKONLIFE      = $88
02317 PLTRACKED       = $89
02318 HITBADNESS      = $8A
02319 REDALERTLIFE    = $8B
02320 WARPDEPRROW     = $8C
02321 WARPDEPRCOLUMN  = $8D
02322 WARPARRVROW     = $8E
02323 WARPARRVCOLUMN  = $8F
02324 CURRSECTOR      = $90
02325 WARPENERGY      = $91
02326 ARRVSECTOR      = $92
02327 HUNTSECTOR      = $93
02328 HUNTSECTCOLUMN  = $94
02329 HUNTSECTROW     = $95
02330 NEWZYLONDIST    = $96
02331 OLDZYLONDIST    = $9E
02332 HUNTTIM         = $9F
02333 BLIPCOLUMN      = $A0
02334 BLIPROW         = $A1
02335 BLIPCYCLECNT    = $A2
02336 ISINLOCKON      = $A3
02337 DIRLEN          = $A4
02338 PENROW          = $A5
02339 PENCOLUMN       = $A6
02340 CTRLDZYLON      = $A7
02341 ZYLONFLPAT0     = $A8
02342 ZYLONFLPAT1     = $A9
02343 MILESTTIM0      = $AA
02344 MILESTTIM1      = $AB
02345 MILESTVELINDZ0  = $AC
02346 MILESTVELINDZ1  = $AD
02347 MILESTVELINDX0  = $AE
02348 MILESTVELINDX1  = $AF
02349 MILESTVELINDY0  = $B0
02350 MILESTVELINDY1  = $B1
02351 ZYLONVELINDZ0   = $B2
02352 ZYLONVELINDZ1   = $B3
02353 ZYLONVELINDX0   = $B4
02354 ZYLONVELINDX1   = $B5
02355 ZYLONVELINDY0   = $B6
02356 ZYLONVELINDY1   = $B7
02357 ISBACKATTACK0   = $B8
02358 ISBACKATTACK1   = $B9
02359 ZYLONTIMX0      = $BA
02360 ZYLONTIMX1      = $BB
02361 ZYLONTIMY0      = $BC
02362 ZYLONTIMY1      = $BD
02363 TORPEDODELAY    = $BE
02364 ZYLONATTACKER   = $BF
02365 WARPSTATE       = $C0
02366 VELOCITYHI      = $C1
02367 TRAILDELAY      = $C2
02368 TRAILIND        = $C3
02369 WARPTEMPCOLUMN  = $C4
02370 WARPTEMPROW     = $C5
02371 VEERMASK        = $C6
02372 VICINITYMASK    = $C7
02373 JOYSTICKX       = $C8
02374 JOYSTICKY       = $C9
02375 KEYCODE         = $CA
02376 SCORE           = $CB
02377 SCOREDRANKIND   = $CD
02378 SCOREDCLASSIND  = $CE
02379 TITLELIFE       = $CF
02380 SHIPVIEW        = $D0
02381 TITLEPHR        = $D1
02382 BEEPFRQIND      = $D2
02383 BEEPREPEAT      = $D3
02384 BEEPTONELIFE    = $D4
02385 BEEPPAUSELIFE   = $D5
02386 BEEPPRIORITY    = $D6
02387 BEEPFRQSTART    = $D7
02388 BEEPLIFE        = $D8
02389 BEEPTOGGLE      = $D9
02390 NOISETORPTIM    = $DA
02391 NOISEEXPLTIM    = $DB
02392 NOISEAUDC2      = $DC
02393 NOISEAUDC3      = $DD
02394 NOISEAUDF1      = $DE
02395 NOISEAUDF2      = $DF
02396 NOISEFRQINC     = $E0
02397 NOISELIFE       = $E1
02398 NOISEZYLONTIM   = $E2
02399 NOISEHITLIFE    = $E3
02400 PL0SHAPOFF      = $E4
02401 PL1SHAPOFF      = $E5
02402 PL2SHAPOFF      = $E6
02403 PL3SHAPOFF      = $E7
02404 PL4SHAPOFF      = $E8
02405 PL0LIFE         = $E9
02406 PL1LIFE         = $EA
02407 PL2LIFE         = $EB
02408 PL3LIFE         = $EC
02409 PL4LIFE         = $ED
02410 PL0COLOR        = $EE
02411 PL1COLOR        = $EF
02412 PL2COLOR        = $F0
02413 PL3COLOR        = $F1
02414 PF0COLOR        = $F2
02415 PF1COLOR        = $F3
02416 PF2COLOR        = $F4
02417 PF3COLOR        = $F5
02418 BGRCOLOR        = $F6
02419 PF0COLORDLI     = $F7
02420 PF1COLORDLI     = $F8
02421 PF2COLORDLI     = $F9
02422 PF3COLORDLI     = $FA
02423 BGRCOLORDLI     = $FB
02424 DSPLST          = $0280
02425 PL4DATA         = $0300
02426 PL0DATA         = $0400
02427 PL1DATA         = $0500
02428 PL2DATA         = $0600
02429 PL3DATA         = $0700
02430 PFMEMROWLO      = $0800
02431 PFMEMROWHI      = $0864
02432 GCMEMMAP        = $08C9
02433 PANELTXT        = $0949
02434 VELOCD1         = $094B
02435 KILLCNTD1       = $0950
02436 ENERGYD1        = $0955
02437 TRACKC1         = $095A
02438 TRACKDIGIT      = $095C
02439 THETAC1         = $0960
02440 PHIC1           = $0966
02441 RANGEC1         = $096C
02442 GCTXT           = $0971
02443 GCWARPD1        = $097D
02444 GCTRGCNT        = $098D
02445 GCSTATPHO       = $0992
02446 GCSTATENG       = $0993
02447 GCSTATSHL       = $0994
02448 GCSTATCOM       = $0995
02449 GCSTATLRS       = $0996
02450 GCSTATRAD       = $0997
02451 GCSTARDAT       = $09A3
02452 ZPOSSIGN        = $09AD
02453 PL2ZPOSSIGN     = $09AF
02454 PL3ZPOSSIGN     = $09B0
02455 PL4ZPOSSIGN     = $09B1
02456 XPOSSIGN        = $09DE
02457 PL2XPOSSIGN     = $09E0
02458 PL3XPOSSIGN     = $09E1
02459 PL4XPOSSIGN     = $09E2
02460 YPOSSIGN        = $0A0F
02461 PL2YPOSSIGN     = $0A11
02462 PL3YPOSSIGN     = $0A12
02463 PL4YPOSSIGN     = $0A13
02464 ZPOSHI          = $0A40
02465 PL0ZPOSHI       = $0A40
02466 PL2ZPOSHI       = $0A42
02467 PL3ZPOSHI       = $0A43
02468 PL4ZPOSHI       = $0A44
02469 XPOSHI          = $0A71
02470 PL2XPOSHI       = $0A73
02471 PL3XPOSHI       = $0A74
02472 PL4XPOSHI       = $0A75
02473 YPOSHI          = $0AA2
02474 PL2YPOSHI       = $0AA4
02475 PL3YPOSHI       = $0AA5
02476 PL4YPOSHI       = $0AA6
02477 ZPOSLO          = $0AD3
02478 PL2ZPOSLO       = $0AD5
02479 PL3ZPOSLO       = $0AD6
02480 PL4ZPOSLO       = $0AD7
02481 XPOSLO          = $0B04
02482 PL2XPOSLO       = $0B06
02483 PL3XPOSLO       = $0B07
02484 PL4XPOSLO       = $0B08
02485 YPOSLO          = $0B35
02486 PL2YPOSLO       = $0B37
02487 PL3YPOSLO       = $0B38
02488 PL4YPOSLO       = $0B39
02489 ZVEL            = $0B66
02490 PL0ZVEL         = $0B66
02491 PL1ZVEL         = $0B67
02492 PL2ZVEL         = $0B68
02493 PL3ZVEL         = $0B69
02494 PL4ZVEL         = $0B6A
02495 XVEL            = $0B97
02496 PL0XVEL         = $0B97
02497 PL1XVEL         = $0B98
02498 PL2XVEL         = $0B99
02499 PL3XVEL         = $0B9A
02500 PL4XVEL         = $0B9B
02501 YVEL            = $0BC8
02502 PL0YVEL         = $0BC8
02503 PL1YVEL         = $0BC9
02504 PL2YVEL         = $0BCA
02505 PL3YVEL         = $0BCB
02506 PL4YVEL         = $0BCC
02507 PIXELROWNEW     = $0BF9
02508 PL0ROWNEW       = $0BF9
02509 PL1ROWNEW       = $0BFA
02510 PL2ROWNEW       = $0BFB
02511 PL3ROWNEW       = $0BFC
02512 PL4ROWNEW       = $0BFD
02513 PIXELCOLUMN     = $0C2A
02514 PL0COLUMN       = $0C2A
02515 PL1COLUMN       = $0C2B
02516 PL2COLUMN       = $0C2C
02517 PL3COLUMN       = $0C2D
02518 PL4COLUMN       = $0C2E
02519 PIXELROW        = $0C5B
02520 PL0ROW          = $0C5B
02521 PL1ROW          = $0C5C
02522 PL2ROW          = $0C5D
02523 PL3ROW          = $0C5E
02524 PL4ROW          = $0C5F
02525 PIXELBYTEOFF    = $0C8C
02526 PL0SHAPTYPE     = $0C8C
02527 PL1SHAPTYPE     = $0C8D
02528 PL2SHAPTYPE     = $0C8E
02529 PL3SHAPTYPE     = $0C8F
02530 PL4SHAPTYPE     = $0C90
02531 PIXELSAVE       = $0CBD
02532 PL0HEIGHT       = $0CBD
02533 PL1HEIGHT       = $0CBE
02534 PL2HEIGHT       = $0CBF
02535 PL3HEIGHT       = $0CC0
02536 PL4HEIGHT       = $0CC1
02537 PIXELBYTE       = $0CEE
02538 PL0HEIGHTNEW    = $0CEE
02539 PL1HEIGHTNEW    = $0CEF
02540 PL2HEIGHTNEW    = $0CF0
02541 PL3HEIGHTNEW    = $0CF1
02542 PL4HEIGHTNEW    = $0CF2
02543 TITLETXT        = $0D1F
02544 GCPFMEM         = $0D35
02545 MAPTO80         = $0DE9
02546 MAPTOBCD99      = $0EE9
02547 PFMEM           = $1000
02548
02549                 *= $A000
02550
02551 ;*******************************************************************************
02552 ;*                                                                             *
02553 ;*                G A M E   D A T A   ( P A R T   1   O F   2 )                *
02554 ;*                                                                             *
02555 ;*******************************************************************************
02556
02557 ;*** Number of space objects ***************************************************
02558
02559 NUMSPCOBJ.PL    = 5                                   ; Number of PLAYER space objects
02560 NUMSPCOBJ.STARS = 12                                  ; Number of PLAYFIELD space objects (stars only)
02561 NUMSPCOBJ.NORM  = NUMSPCOBJ.PL+NUMSPCOBJ.STARS        ; Normal number of space objects
02562 NUMSPCOBJ.ALL   = 49                                  ; Maximum number of space objects
02563
02564 ;*** PLAYER shape data offsets *************************************************
02565
02566 SHAP.TORPEDO    = $00                                 ; Photon torpedo
02567 SHAP.ZFIGHTER   = $10                                 ; Zylon fighter
02568 SHAP.STARBASEL  = $20                                 ; Starbase (left part)
02569 SHAP.STARBASEC  = $30                                 ; Starbase (center part)
02570 SHAP.STARBASER  = $40                                 ; Starbase (right part)
02571 SHAP.TRANSVSSL  = $50                                 ; Transfer vessel
02572 SHAP.METEOR     = $60                                 ; Meteor
02573 SHAP.ZCRUISER   = $70                                 ; Zylon cruiser
02574 SHAP.ZBASESTAR  = $80                                 ; Zylon basestar
02575 SHAP.HYPERWARP  = $90                                 ; Hyperwarp Target Marker
02576
02577 ;*** ROM character set constants ***********************************************
02578 ROM.SPC         = $00                                 ; ROM character ' '
02579 ROM.DOT         = $0E                                 ; ROM character '.'
02580 ROM.0           = $10                                 ; ROM character '0'
02581 ROM.1           = $11                                 ; ROM character '1'
02582 ROM.2           = $12                                 ; ROM character '2'
02583 ROM.3           = $13                                 ; ROM character '3'
02584 ROM.4           = $14                                 ; ROM character '4'
02585 ROM.5           = $15                                 ; ROM character '5'
02586 ROM.9           = $19                                 ; ROM character '9'
02587 ROM.COLON       = $1A                                 ; ROM character ':'
02588 ROM.A           = $21                                 ; ROM character 'A'
02589 ROM.C           = $23                                 ; ROM character 'C'
02590 ROM.D           = $24                                 ; ROM character 'D'
02591 ROM.E           = $25                                 ; ROM character 'E'
02592 ROM.G           = $27                                 ; ROM character 'G'
02593 ROM.L           = $2C                                 ; ROM character 'L'
02594 ROM.N           = $2E                                 ; ROM character 'N'
02595 ROM.P           = $30                                 ; ROM character 'P'
02596 ROM.R           = $32                                 ; ROM character 'R'
02597 ROM.S           = $33                                 ; ROM character 'S'
02598 ROM.T           = $34                                 ; ROM character 'T'
02599 ROM.W           = $37                                 ; ROM character 'W'
02600 ROM.Y           = $39                                 ; ROM character 'Y'
02601
02602 ;*** Custom character set constants ********************************************
02603 CCS.COL1        = $40                                 ; COLOR1 bits for text in GR1/2 text mode
02604 CCS.COL2        = $80                                 ; COLOR2 bits for text in GR1/2 text mode
02605 CCS.COL3        = $C0                                 ; COLOR3 bits for text in GR1/2 text mode
02606
02607 CCS.0           = 0                                   ; Custom character '0'
02608 CCS.1           = 1                                   ; Custom character '1'
02609 CCS.2           = 2                                   ; Custom character '2'
02610 CCS.3           = 3                                   ; Custom character '3'
02611 CCS.4           = 4                                   ; Custom character '4'
02612 CCS.5           = 5                                   ; Custom character '5'
02613 CCS.6           = 6                                   ; Custom character '6'
02614 CCS.7           = 7                                   ; Custom character '7'
02615 CCS.8           = 8                                   ; Custom character '8'
02616 CCS.9           = 9                                   ; Custom character '9'
02617 CCS.SPC         = 10                                  ; Custom character ' '
02618 CCS.COLON       = 11                                  ; Custom character ':'
02619 CCS.BORDERSW    = 12                                  ; Custom character 'BORDER SOUTHWEST'
02620 CCS.E           = 13                                  ; Custom character 'E'
02621 CCS.INF         = 14                                  ; Custom character 'INFINITY'
02622 CCS.MINUS       = 15                                  ; Custom character '-'
02623 CCS.PLUS        = 16                                  ; Custom character '+'
02624 CCS.PHI         = 17                                  ; Custom character 'PHI'
02625 CCS.V           = 18                                  ; Custom character 'V'
02626 CCS.R           = 19                                  ; Custom character 'R'
02627 CCS.THETA       = 20                                  ; Custom character 'THETA'
02628 CCS.K           = 21                                  ; Custom character 'K'
02629 CCS.T           = 22                                  ; Custom character 'T'
02630 CCS.C           = 23                                  ; Custom character 'C'
02631 CCS.BORDERS     = 24                                  ; Custom character 'BORDER SOUTH'
02632 CCS.BORDERW     = 25                                  ; Custom character 'BORDER WEST'
02633 CCS.CORNERSW    = 26                                  ; Custom character 'CORNER SOUTHWEST'
02634 CCS.STARBASE    = 27                                  ; Custom character 'STARBASE SECTOR'
02635 CCS.4ZYLONS     = 28                                  ; Custom character '4-ZYLON SECTOR'
02636 CCS.3ZYLONS     = 29                                  ; Custom character '3-ZYLON SECTOR'
02637 CCS.2ZYLONS     = 30                                  ; Custom character '2-ZYLON SECTOR'
02638
02639 ;*** Custom character set ******************************************************
02640 ;
02641 ; 0        1        2        3        4        5        6        7
02642 ; ........ ........ ........ ........ ........ ........ ........ ........
02643 ; .####### ..##.... .####... .####... .##..... .####... .####... .#####..
02644 ; .#...### ...#.... ....#... ....#... .##..... .#...... .#..#... .#...#..
02645 ; .#...### ...#.... ....#... ....#... .##..... .#...... .#...... .....#..
02646 ; .#...### ...#.... .####... .#####.. .##.##.. .####... .#...... ...###..
02647 ; .#...### ..###... .#...... ....##.. .#####.. ....#... .######. ...#....
02648 ; .#...### ..###... .#...... ....##.. ....##.. ....#... .#....#. ...#....
02649 ; .####### ..###... .####... .#####.. ....##.. .####... .######. ...#....
02650 ;
02651 ; 8        9        10       11       12       13       14       15
02652 ; ........ ........ ........ ..###... #....... ........ ........ ........
02653 ; ..###... .#####.. ........ ..###... #....... ..####.. .##..##. ........
02654 ; ..#.#... .#...#.. ........ ..###... #....... ..#..... #..##..# ........
02655 ; ..#.#... .#...#.. ........ ........ #....... ..#..... #..##..# .######.
02656 ; .#####.. .#####.. ........ ........ #....... .####... #..##..# ........
02657 ; .##.##.. ....##.. ........ ..###... #....... .##..... .##..##. ........
02658 ; .##.##.. ....##.. ........ ..###... #....... .##..... ........ ........
02659 ; .#####.. ....##.. ........ ..###... ######## .#####.. ........ ........
02660 ;
02661 ; 16       17       18       19       20       21       22       23
02662 ; ........ ........ .##..##. ........ ........ ........ #######. ######..
02663 ; ...##... ...##... .##..##. .#####.. ...###.. .#...##. #..#..#. #...##..
02664 ; ...##... .######. .##..##. .#...#.. ..#####. .#...##. ...#.... #...##..
02665 ; ...##... ##.##.## .##..##. .#...#.. .##...## .#...#.. ...##... #.......
02666 ; .######. #..##..# .##..##. .#####.. .#.###.# .#####.. ...##... #.......
02667 ; ...##... ##.##.## ..#.##.. .##.#... .##...## .##..#.. ...##... #.......
02668 ; ...##... .######. ..###... .##.##.. ..#####. .##..##. ...##... #....#..
02669 ; ...##... ...##... ..##.... .##.##.. ...###.. .##..##. ...##... ######..
02670 ;
02671 ; 24       25       26       27       28       29       30
02672 ; ........ #....... ........ #....... #....... #....... #.......
02673 ; ........ #....... ........ #.#.#.#. #..##... #...###. #.##....
02674 ; ........ #....... ........ #..###.. #....... #....... #..##...
02675 ; ........ #....... ........ #.#####. #.##.##. #.###... #.#####.
02676 ; ........ #....... ........ #..###.. #....... #....... #..##...
02677 ; ........ #....... ........ #.#.#.#. #...##.. #..###.. #.##....
02678 ; ........ #....... ........ #....... #....... #....... #.......
02679 ; ######## #....... #....... ######## ######## ######## ########
02680
02681 CHARSET         .BYTE $00,$7F,$47,$47,$47,$47,$47,$7F ; Custom character '0'
02682                 .BYTE $00,$30,$10,$10,$10,$38,$38,$38 ; Custom character '1'
02683                 .BYTE $00,$78,$08,$08,$78,$40,$40,$78 ; Custom character '2'
02684                 .BYTE $00,$78,$08,$08,$7C,$0C,$0C,$7C ; Custom character '3'
02685                 .BYTE $00,$60,$60,$60,$6C,$7C,$0C,$0C ; Custom character '4'
02686                 .BYTE $00,$78,$40,$40,$78,$08,$08,$78 ; Custom character '5'
02687                 .BYTE $00,$78,$48,$40,$40,$7E,$42,$7E ; Custom character '6'
02688                 .BYTE $00,$7C,$44,$04,$1C,$10,$10,$10 ; Custom character '7'
02689                 .BYTE $00,$38,$28,$28,$7C,$6C,$6C,$7C ; Custom character '8'
02690                 .BYTE $00,$7C,$44,$44,$7C,$0C,$0C,$0C ; Custom character '9'
02691                 .BYTE $00,$00,$00,$00,$00,$00,$00,$00 ; Custom character ' '
02692                 .BYTE $38,$38,$38,$00,$00,$38,$38,$38 ; Custom character ':'
02693                 .BYTE $80,$80,$80,$80,$80,$80,$80,$FF ; Custom character 'BORDER SOUTHWEST'
02694                 .BYTE $00,$3C,$20,$20,$78,$60,$60,$7C ; Custom character 'E'
02695                 .BYTE $00,$66,$99,$99,$99,$66,$00,$00 ; Custom character 'INFINITY'
02696                 .BYTE $00,$00,$00,$7E,$00,$00,$00,$00 ; Custom character '-'
02697                 .BYTE $00,$18,$18,$18,$7E,$18,$18,$18 ; Custom character '+'
02698                 .BYTE $00,$18,$7E,$DB,$99,$DB,$7E,$18 ; Custom character 'PHI'
02699                 .BYTE $66,$66,$66,$66,$66,$2C,$38,$30 ; Custom character 'V'
02700                 .BYTE $00,$7C,$44,$44,$7C,$68,$6C,$6C ; Custom character 'R'
02701                 .BYTE $00,$1C,$3E,$63,$5D,$63,$3E,$1C ; Custom character 'THETA'
02702                 .BYTE $00,$46,$46,$44,$7C,$64,$66,$66 ; Custom character 'K'
02703                 .BYTE $FE,$92,$10,$18,$18,$18,$18,$18 ; Custom character 'T'
02704                 .BYTE $FC,$8C,$8C,$80,$80,$80,$84,$FC ; Custom character 'C'
02705                 .BYTE $00,$00,$00,$00,$00,$00,$00,$FF ; Custom character 'BORDER SOUTH'
02706                 .BYTE $80,$80,$80,$80,$80,$80,$80,$80 ; Custom character 'BORDER WEST'
02707                 .BYTE $00,$00,$00,$00,$00,$00,$00,$80 ; Custom character 'CORNER SOUTHWEST'
02708                 .BYTE $80,$AA,$9C,$BE,$9C,$AA,$80,$FF ; Custom character 'STARBASE SECTOR'
02709                 .BYTE $80,$98,$80,$B6,$80,$8C,$80,$FF ; Custom character '4-ZYLON SECTOR'
02710                 .BYTE $80,$8E,$80,$B8,$80,$9C,$80,$FF ; Custom character '3-CYCLON SECTOR'
02711                 .BYTE $80,$B0,$98,$BE,$98,$B0,$80,$FF ; Custom character '2-ZYLON SECTOR'
02712
02713 ;*** Header text of Long-Range Scan view (shares spaces with following header) *
02714 LRSHEADER       .BYTE $00,$00,$6C,$6F,$6E,$67,$00,$72 ; "  LONG RANGE SCAN"
02715                 .BYTE $61,$6E,$67,$65,$00,$73,$63,$61
02716                 .BYTE $6E
02717
02718 ;*** Header text of Aft view (shares spaces with following header) *************
02719 AFTHEADER       .BYTE $00,$00,$00,$00,$00,$00,$61,$66 ; "      AFT VIEW   "
02720                 .BYTE $74,$00,$76,$69,$65,$77,$00,$00
02721                 .BYTE $00
02722
02723 ;*** Header text of Galactic Chart view ****************************************
02724 GCHEADER        .BYTE $00,$00,$00,$67,$61,$6C,$61,$63 ; "   GALACTIC CHART   "
02725                 .BYTE $74,$69,$63,$00,$63,$68,$61,$72
02726                 .BYTE $74,$00,$00,$00
02727
02728 ;*** Display List of Galactic Chart view ***************************************
02729 DLSTGC          .BYTE $60                             ; BLK7
02730                 .BYTE $46,<GCHEADER,>GCHEADER         ; GR2 @ GCHEADER
02731                 .BYTE $F0                             ; BLK8 + DLI
02732                 .BYTE $47,<GCPFMEM,>GCPFMEM           ; GR1 @ GCPFMEM
02733                 .BYTE $07                             ; GR1
02734                 .BYTE $07                             ; GR1
02735                 .BYTE $07                             ; GR1
02736                 .BYTE $07                             ; GR1
02737                 .BYTE $07                             ; GR1
02738                 .BYTE $07                             ; GR1
02739                 .BYTE $07                             ; GR1
02740                 .BYTE $07                             ; GR1
02741                 .BYTE $80                             ; BLK1 + DLI
02742                 .BYTE $46,<TITLETXT,>TITLETXT         ; GR2 @ TITLETXT
02743                 .BYTE $46,<GCTXT,>GCTXT               ; GR2 @ GCTXT
02744                 .BYTE $06                             ; GR2
02745                 .BYTE $06                             ; GR2
02746                 .BYTE $41,<DSPLST,>DSPLST             ; JMP @ DSPLST
02747
02748 ;*******************************************************************************
02749 ;*                                                                             *
02750 ;*                              G A M E   C O D E                              *
02751 ;*                                                                             *
02752 ;*******************************************************************************
02753
02754 ;*******************************************************************************
02755 ;*                                                                             *
02756 ;*                                  INITCOLD                                   *
02757 ;*                                                                             *
02758 ;*                       Initialize program (Cold start)                       *
02759 ;*                                                                             *
02760 ;*******************************************************************************
02761
02762 ; DESCRIPTION
02763 ;
02764 ; Initializes the program, then continues into the game loop at GAMELOOP
02765 ; ($A1F3).
02766 ;
02767 ; There are four entry points to initialization:
02768 ;
02769 ; (1)  INITCOLD ($A14A) is entered at initial cartridge startup (cold start).
02770 ;      This initializes POKEY, resets the idle counter, sets the mission level
02771 ;      to NOVICE mission, and clears the function key code. POKEY is enabled to
02772 ;      receive keyboard input. Code execution continues into INITSELECT ($A15A)
02773 ;      below.
02774 ;
02775 ; (2)  INITSELECT ($A15A) is entered from GAMELOOP ($A1F3) after the SELECT
02776 ;      function key has been pressed. This loads the title phrase offset for the
02777 ;      copyright notice. Code execution continues into INITDEMO ($A15C) below. 
02778 ;
02779 ; (3)  INITDEMO ($A15C) is entered when the program switches into demo mode.
02780 ;      This loads the demo mode flag. Code execution continues into INITSTART
02781 ;      ($A15E) below.
02782 ;
02783 ; (4)  INITSTART ($A15E) is entered from GAMELOOP ($A1F3) after the START
02784 ;      function key has been pressed. This enqueues the new title phrase and
02785 ;      enables or disables demo mode, depending on the preloaded value.
02786 ;
02787 ; Initialization continues with the following steps: 
02788 ;
02789 ; (1)  Clear the custom chip registers and zero-page program variables from
02790 ;      ISVBISYNC ($0067) on.
02791 ;
02792 ;      NOTE: Because of loop jamming there is a loop index overshoot. Instead of
02793 ;      clearing memory at addresses $0067..$00FB, the memory at addresses
02794 ;      $0067..$0166 is cleared. This does no harm because $0100..$0166 is a yet
02795 ;      unused part of the 6502 CPU stack.
02796 ;
02797 ;      NOTE: At address $A175 a hack is necessary in the source code to fake a
02798 ;      STA ISVBISYNC,X instruction with a 16-bit address. ISVBISYNC ($0067) is a
02799 ;      zero-page address and regular assemblers would translate STA ISVBISYNC,X
02800 ;      into the byte sequence $95 $67, not $9D $67 $00. This indicates that the
02801 ;      original ROM was maybe created using a special assembler, perhaps a
02802 ;      cross-assembler.  
02803 ;
02804 ; (2)  Initialize the 6502 CPU (reset the stack pointer, disable decimal mode).
02805 ;
02806 ; (3)  Clear program memory from $0200..$1FFF in subroutine CLRMEM ($AE0F).
02807 ;
02808 ; (4)  Set the address vectors of the IRQ, VBI, and DLI handlers.
02809 ;
02810 ; (5)  Enable input from Joystick 0.
02811 ;
02812 ; (6)  Enable Player/Missile graphics, providing a fifth PLAYER.
02813 ;
02814 ;      BUG (at $A1A6): The set PLAYER-PLAYFIELD priority arranges PLAYERs in
02815 ;      front of the PLAYFIELD. This makes sense as space objects represented by
02816 ;      PLAYERs (for example, Zylon ships, photon torpedoes, and meteors) move in
02817 ;      front of the stars, which are part of the PLAYFIELD. However, PLAYERs
02818 ;      also move in front of the cross hairs, which are also part of the
02819 ;      PLAYFIELD. Suggested fix: None, technically not possible.
02820 ;
02821 ; (7)  Do more initialization in subroutine INITIALIZE ($B3BA).
02822 ;
02823 ; (8)  Set display to Front view.
02824 ;
02825 ; (9)  Show or hide the Control Panel Display (bottom text window) in subroutine
02826 ;      MODDLST ($ADF1), depending on the demo mode flag.
02827 ;
02828 ; (10) Initialize our starship's velocity equivalent to speed key '6'.
02829 ;
02830 ; (11) Enable the Display List.
02831 ;
02832 ; (12) Initialize the number of space objects to 16 (5 PLAYER space objects + 12
02833 ;      PLAYFIELD space objects (stars)).
02834 ;
02835 ; (13) Set the title phrase to the selected mission level in subroutine SETTITLE
02836 ;      ($B223).
02837 ;
02838 ; (14) Enable the IRQ, DLI, and VBI interrupts.
02839 ;
02840 ; Code execution continues into the game loop at GAMELOOP ($A1F3).
02841
02842 INITCOLD        LDA #0                  ;
02843                 STA SKCTL               ; POKEY: Initialization
02844                 STA IDLECNTHI           ; Reset idle counter
02845                 STA MISSIONLEVEL        ; Mission level := NOVICE mission
02846                 STA FKEYCODE            ; Clear function key code
02847                 LDA #$03                ; POKEY: Enable keyboard scan and debounce
02848                 STA SKCTL               ;
02849
02850 ;*** Entry point when SELECT function key was pressed **************************
02851 INITSELECT      LDY #$2F                ; Prep title phrase "COPYRIGHT ATARI 1979"
02852
02853 ;*** Entry point when program switches into demo mode **************************
02854 INITDEMO        LDA #$FF                ; Prep demo mode flag
02855
02856 ;*** Entry point when START function key was pressed ***************************
02857 INITSTART       STY NEWTITLEPHR         ; Enqueue new title phrase
02858                 STA ISDEMOMODE          ; Store demo mode flag
02859
02860 ;*** More initialization *******************************************************
02861                 LDA #0                  ; Clear custom chip registers, zero-page variables
02862                 TAX                     ;
02863 LOOP001         STA HPOSP0,X            ; Clear $D000..$D0FF (GTIA registers)
02864                 STA DMACTL,X            ; Clear $D400..$D4FF (ANTIC registers)
02865                 CPX #$0F                ;
02866                 BCS SKIP001             ;
02867                 STA AUDF1,X             ; Clear $D200..$D20E (POKEY registers)
02868
02869 SKIP001         STA PORTA,X             ; Clear $D300..$D3FF (PIA registers)
02870                                         ; Clear $0067..$0166 (zero-page program variables)
02871                 .BYTE $9D               ; HACK: Fake STA ISVBISYNC,X with 16-bit address
02872                 .WORD ISVBISYNC         ;
02873                 INX                     ;
02874                 BNE LOOP001             ;
02875
02876                 DEX                     ; Reset 6502 CPU stack pointer
02877                 TXS                     ;
02878
02879                 CLD                     ; Clear 6502 CPU decimal mode
02880
02881                 LDA #$02                ; Clear $0200..$1FFF (program memory)
02882                 JSR CLRMEM              ;
02883
02884                 LDA #<IRQHNDLR          ; Set IRQ handler (VIMIRQ)
02885                 STA VIMIRQ              ;
02886                 LDA #>IRQHNDLR          ;
02887                 STA VIMIRQ+1            ;
02888
02889                 LDA #<VBIHNDLR          ; Set VBI and DLI handler (VVBLKI and VDSLST)
02890                 STA VVBLKI              ;
02891                 LDA #<DLSTHNDLR         ;
02892                 STA VDSLST              ;
02893                 LDA #>VBIHNDLR          ;
02894                 STA VVBLKI+1            ;
02895                 LDA #>DLSTHNDLR         ;
02896                 STA VDSLST+1            ;
02897
02898                 LDA #$04                ; PIA: Enable PORTA (Joystick 0)
02899                 STA PACTL               ;
02900                 LDA #$11                ; GTIA: Enable PLAYER4, prio: PLs > PFs > BGR (!)
02901                 STA PRIOR               ; (PLAYERs appear behind cross hairs)
02902                 LDA #$03                ; GTIA: Enable DMA for PLAYERs and MISSILEs
02903                 STA GRACTL              ;
02904
02905                 JSR INITIALIZE          ; Init Display List, tables, Galactic Chart, etc.
02906
02907                 LDX #$0A                ; Set Front view
02908                 JSR SETVIEW             ;
02909
02910                 LDA ISDEMOMODE          ; If in/not in demo mode hide/show...
02911                 AND #$80                ; ...Control Panel Display (bottom text window)
02912                 TAY                     ;
02913                 LDX #$5F                ;
02914                 LDA #$08                ;
02915                 JSR MODDLST             ;
02916
02917                 LDA #32                 ; Init our starship's velocity (= speed key '6')
02918                 STA NEWVELOCITY         ;
02919
02920                 LDA #<DSPLST            ; ANTIC: Set Display List
02921                 STA DLIST               ;
02922                 LDA #>DSPLST            ;
02923                 STA DLIST+1             ;
02924
02925                 LDA #$3E                ; ANTIC: Enable Display List DMA, single-line PM
02926                 STA DMACTL              ; resolution, PM DMA, normal-width PLAYFIELD
02927
02928                 LDA #0                  ; ANTIC: Set PM memory base address
02929                 STA PMBASE              ;
02930
02931                 LDA #NUMSPCOBJ.NORM-1   ; Set normal number of space objects
02932                 STA MAXSPCOBJIND        ; (5 PLAYER spc objs + 12 PLAYFIELD spc objs (stars))
02933
02934                 LDX MISSIONLEVEL        ; Set title phrase
02935                 LDY MISSIONPHRTAB,X     ; NOVICE, PILOT, WARRIOR, or COMMANDER MISSION
02936                 JSR SETTITLE            ;
02937
02938                 LDA #$40                ; POKEY: Enable keyboard interrupt (IRQ)
02939                 STA IRQEN               ;
02940
02941                 CLI                     ; Enable all IRQs
02942
02943                 LDA #$C0                ; ANTIC: Enable DLI and VBI
02944                 STA NMIEN               ;
02945
02946 ;*******************************************************************************
02947 ;*                                                                             *
02948 ;*                                  GAMELOOP                                   *
02949 ;*                                                                             *
02950 ;*******************************************************************************
02951
02952 ; DESCRIPTION
02953 ;
02954 ; The game loop is the main part of the program. It is basically an infinite
02955 ; loop that collects input, computes the game state, and updates the display. It
02956 ; executes the following steps:
02957 ;
02958 ; (1)  Synchronize the start of the game loop with the vertical blank phase of
02959 ;      the TV beam, which flagged by the Vertical Blank Interrupt handler
02960 ;      VBIHNDLR ($A6D1). This prevents screen flicker while the PLAYFIELD is
02961 ;      redrawn at the begin of the game loop, because during the vertical blank
02962 ;      phase the TV beam is turned off and nothing is rendered on the TV
02963 ;      display. 
02964 ;
02965 ; (2)  Erase all PLAYFIELD space objects (stars, explosion fragments) from the
02966 ;      PLAYFIELD that were drawn in the previous game loop iteration.
02967 ;
02968 ; (3)  Draw the updated PLAYFIELD space objects (stars, explosion fragments)
02969 ;      into the PLAYFIELD (skip this if in hyperspace).
02970 ;
02971 ; (4)  If the idle counter has reached its trigger value then clear the center
02972 ;      of the PLAYFIELD, an 8 x 2 pixel rectangle with a top-left position at
02973 ;      pixel column number 76 and pixel row number 49 (?).
02974 ;
02975 ; (5)  Clear all PLAYER shapes.
02976 ;
02977 ; (6)  Update the vertical position of all PLAYERs and update all PLAYER shapes.
02978 ;
02979 ; (7)  Update the horizontal position of all PLAYERs.
02980 ;
02981 ; (8)  Rotate the position vector of all space objects horizontally and
02982 ;      vertically, according to the saved joystick position (skip this if in
02983 ;      Galactic Chart view) using subroutine ROTATE ($B69B).
02984 ;
02985 ; (9)  Move our starship forward in space. Our starship is always located at the
02986 ;      center of the program's 3D coordinate system, so all space objects are
02987 ;      moved along the z-axis toward our starship by subtracting a displacement
02988 ;      from their z-coordinate. The amount of the displacement depends on our
02989 ;      starship's velocity.
02990 ;
02991 ;      BUG (at $A3C1): This operation is not applied to Photon torpedoes (?).
02992 ;      Suggested fix: Remove LDA PL0SHAPTYPE,X and BEQ SKIP011. 
02993 ;
02994 ; (10) Add the proper velocity vector of all space objects to their position
02995 ;      vector (except for stars, which do not have any proper motion).
02996 ;
02997 ;      BUG (at $A419): The correct maximum loop index is NUMSPCOBJ.ALL*3 = 147
02998 ;      instead of 144. Suggested fix: Replace CMP #144 with CMP #147.
02999 ;
03000 ; (11) Correct the position vector components (coordinates) of all PLAYER space
03001 ;      objects if they have over- or underflowed during the calculations of the
03002 ;      previous steps.
03003 ;
03004 ; (12) Calculate the perspective projection of the position vectors of all space
03005 ;      objects and from that their pixel row and column number (applies to Front
03006 ;      and Aft view) using subroutines PROJECTION ($AA21), SCREENCOLUMN ($B6FB),
03007 ;      and SCREENROW ($B71E). If a space object (star, explosion fragment) moved
03008 ;      offscreen then a new space object is automatically created in subroutine
03009 ;      SCREENCOLUMN ($B6FB).
03010 ;
03011 ; (13) Handle hyperwarp marker selection in the Galactic Chart view in
03012 ;      subroutine SELECTWARP ($B162).
03013 ;
03014 ; (14) If in Long-Range Scan view, compute the pixel column number and the pixel
03015 ;      row number of all PLAYFIELD space objects (stars, explosion fragments) on
03016 ;      the plane established by the z and x axis of the 3D coordinate system
03017 ;      using subroutines SCREENCOLUMN ($B6FB) and SCREENROW ($B71E). Our
03018 ;      starship's shape is drawn using subroutine DRAWLINES ($A76F). If the
03019 ;      Long-Range Scan is OK then PLAYFIELD space object pixel numbers are
03020 ;      computed and drawn. This is skipped if the Long-Range Scan is destroyed. 
03021 ;
03022 ; (15) Update all PLAYER shapes, heights, and colors (see detailed description
03023 ;      below).
03024 ;
03025 ; (16) Flash a red alert when leaving hyperspace into a sector containing Zylon
03026 ;      ships by setting appropriate colors to PLAYFIELD2 and BACKGROUND.
03027 ;
03028 ; (17) Update the color of all PLAYFIELD space objects (stars, explosion
03029 ;      fragments). The color calculation is similar to that of the PLAYER color
03030 ;      calculation in (15). It also computes a range index and uses the same
03031 ;      color lookup table FOURCOLORPIXEL ($BA90). If a star in the Aft view
03032 ;      became too distant (z-coordinate < -$F000 (-4096) <KM>) its position is
03033 ;      re-initialized in subroutine INITPOSVEC ($B764).
03034 ;
03035 ; (18) If in demo mode skip input handling and jump directly to function key
03036 ;      handling (28).
03037 ;
03038 ; (19) Handle keyboard input in subroutine KEYBOARD ($AFFE).
03039 ;
03040 ; (20) Handle joystick input. Store the current joystick directions in JOYSTICKX
03041 ;      ($C8) and JOYSTICKY ($C9).
03042 ;
03043 ; (21) Check if our starship's photon torpedoes have hit a target in subroutine
03044 ;      COLLISION ($AF3D). This subroutine triggers a game over if all Zylon
03045 ;      ships have been destroyed.
03046 ;
03047 ; (22) Handle the joystick trigger in subroutine TRIGGER ($AE29).
03048 ;
03049 ; (23) Handle the Attack Computer and Tracking Computer. If the Attack Computer
03050 ;      is neither destroyed nor switched off then execute the following steps:
03051 ;
03052 ;      o   Update the Attack Computer Display's blip and lock-on markers in
03053 ;          subroutine UPDATTCOMP ($A7BF) (if in Front view).
03054 ;
03055 ;      o   Update the tracking index of the currently tracked PLAYER space
03056 ;          object. If a Zylon ship is tracked, then make sure to always track
03057 ;          the Zylon ship that launched the last Zylon photon torpedo. If this
03058 ;          Zylon ship is not alive then track the other Zylon ship - if alive.
03059 ;
03060 ;      o   If the Tracking Computer is on then switch to the view that shows the
03061 ;          tracked PLAYER space object by emulating pressing the 'F' (Front
03062 ;          view) or 'A' (Aft view) key (only if in Front or Aft view).
03063 ;
03064 ; (24) Handle docking at a starbase in subroutine DOCKING ($ACE6).
03065 ;
03066 ; (25) Handle maneuvering both of our starship's photon torpedoes, the single
03067 ;      Zylon photon torpedo, and the attacking Zylon ships in subroutine
03068 ;      MANEUVER ($AA79). This subroutine also automatically creates meteors and
03069 ;      new Zylon ships.
03070 ;
03071 ; (26) Check if our starship was hit by a Zylon photon torpedo (skip this if in
03072 ;      a starbase sector): Its x, y, and z coordinates must be within a range of
03073 ;      -($0100)..+$00FF (-256..+255) <KM> of our starship.
03074 ;
03075 ; (27) If our starship was hit then execute the following steps:
03076 ;
03077 ;      o   Damage or destroy one of our starship's subsystems in subroutine
03078 ;          DAMAGE ($AEE1).
03079 ;
03080 ;      o   Trigger an explosion in subroutine INITEXPL ($AC6B), 
03081 ;
03082 ;      o   Store the severity of the hit.
03083 ;
03084 ;      o   End the lifetime of the Zylon photon torpedo.
03085 ;
03086 ;      o   Subtract 100 energy units for being hit by the Zylon photon torpedo
03087 ;          in subroutine DECENERGY ($B86F). 
03088 ;
03089 ;      o   Trigger the noise sound pattern SHIELD EXPLOSION in subroutine NOISE
03090 ;          ($AEA8). 
03091 ;
03092 ;      If the Shields were down during the hit, our starship is destroyed.
03093 ;      Execute the following steps:
03094 ;
03095 ;      o   Switch to Front view.
03096 ;
03097 ;      o   Flash the title phrase "SHIP DESTROYED BY ZYLON FIRE".
03098 ;
03099 ;      o   Add the mission bonus to the internal game score in subroutine
03100 ;          GAMEOVER ($B10A).
03101 ;
03102 ;      o   Hide the Control Panel Display (bottom text window) in subroutine
03103 ;          MODDLST ($ADF1).
03104 ;
03105 ;      o   Clear the PLAYFIELD in subroutine CLRPLAYFIELD ($AE0D).
03106 ;
03107 ;      o   Enable the STARSHIP EXPLOSION noise. 
03108 ;
03109 ; (28) Handle the function keys START and SELECT. If SELECT has been pressed
03110 ;      cycle through the next of the 4 mission levels. If either START or SELECT
03111 ;      have been pressed, reset the idle counter, then jump to the corresponding
03112 ;      program initialization subroutines INITSTART ($A15E) or INITSELECT
03113 ;      ($A15A), respectively. 
03114 ;
03115 ; (29) Update the Control Panel Display in subroutine UPDPANEL ($B804).
03116 ;
03117 ; (30) Handle hyperwarp in subroutine HYPERWARP ($A89B).
03118 ;
03119 ; (31) Update the text in the title line in subroutine UPDTITLE ($B216).
03120 ;
03121 ; (32) Move Zylon units, decrease lifetime of photon torpedoes, elapse game
03122 ;      time, etc. in subroutine FLUSHGAMELOOP ($B4E4). This subroutine also
03123 ;      triggers a game over if our starship's energy is zero.
03124 ;
03125 ; (33) Jump back to the start of the game loop for the next game loop iteration.
03126
03127 L.HEIGHTCNT     = $6A                   ; Height counter during copying a PLAYER shape
03128 L.ZPOSOFF       = $6E                   ; Offset to z-coordinate
03129 L.VELOCITYHI    = $6B                   ; Velocity vector component (high byte)
03130 L.VECCOMPIND    = $6A                   ; Position vector component index. Used values are:
03131                                         ;   0 -> z-component
03132                                         ;   1 -> x-component
03133                                         ;   2 -> y-component
03134 L.RANGEINDEX    = $6A                   ; Range index for space object, computed from the
03135                                         ; distance to our starship. Used to pick the shape
03136                                         ; cell index of the PLAYERs shape data and shape
03137                                         ; height. Used values are: 0..15.
03138 L.FOURCOLORPIX  = $6A                   ; 1-byte bit pattern for 4 pixels of same color
03139 L.COLORMASK     = $6B                   ; Color/brightness to modify PLAYER color
03140
03141 ;*** (1) Synchronize game loop with execution of VBI ***************************
03142 GAMELOOP        LDA ISVBISYNC           ; Wait for execution of VBI
03143                 BEQ GAMELOOP            ;
03144
03145                 LDA #0                  ; VBI is executed, clear VBI sync flag
03146                 STA ISVBISYNC           ;
03147
03148 ;*** (2) Erase PLAYFIELD space objects (stars, explosion fragments) ************
03149                 LDA OLDMAXSPCOBJIND     ; Skip if no space objects in use
03150                 BEQ SKIP002             ;
03151
03152                 LDX #NUMSPCOBJ.PL-1     ; Loop over all PLAYFIELD space objs (X index > 4)
03153 LOOP002         INX                     ;
03154                 LDY PIXELROW,X          ; Load pixel row number of PLAYFIELD space object
03155
03156                 LDA PFMEMROWLO,Y        ; Point MEMPTR to start of pixel's row...
03157                 STA MEMPTR              ; ...in PLAYFIELD memory
03158                 LDA PFMEMROWHI,Y        ;
03159                 STA MEMPTR+1            ;
03160
03161                 LDY PIXELBYTEOFF,X      ; Get within-row-offset to byte with space obj pixel
03162                 LDA PIXELSAVE,X         ; Load saved byte
03163                 STA (MEMPTR),Y          ; Restore byte of PLAYFIELD memory
03164
03165                 CPX OLDMAXSPCOBJIND     ;
03166                 BCC LOOP002             ; Next PLAYFIELD space object
03167
03168                 LDA #0                  ; Clear number of space objects
03169                 STA OLDMAXSPCOBJIND     ;
03170
03171 ;*** (3) Draw PLAYFIELD space objects (stars, explosion fragments) *************
03172 SKIP002         LDA WARPSTATE           ; Skip during hyperspace
03173                 BMI SKIP003             ;
03174
03175                 LDX MAXSPCOBJIND        ; Update number of space objects
03176                 STX OLDMAXSPCOBJIND     ;
03177
03178 LOOP003         LDA PIXELROWNEW,X       ; Loop over all PLAYFIELD space objs (X index > 4)
03179                 STA PIXELROW,X          ; Update pixel row number of PLAYFIELD space object
03180
03181                 TAY                     ;
03182                 LDA PFMEMROWLO,Y        ; Point MEMPTR to start of pixel's row...
03183                 STA MEMPTR              ; ...in PLAYFIELD memory
03184                 LDA PFMEMROWHI,Y        ;
03185                 STA MEMPTR+1            ;
03186
03187                 LDA PIXELCOLUMN,X       ; Convert pixel column number to within-row-offset
03188                 LSR A                   ; ...of byte with space obj pixel (4 pixels = 1 byte)
03189                 LSR A                   ;
03190                 STA PIXELBYTEOFF,X      ; Store within-row-offset
03191
03192                 TAY                     ;
03193                 LDA (MEMPTR),Y          ; Load pixel's byte from PLAYFIELD memory
03194                 STA PIXELSAVE,X         ; Save it (for restoring it in next game loop)
03195                 ORA PIXELBYTE,X         ; Blend with pixel's color bit-pattern
03196                 STA (MEMPTR),Y          ; Store byte in PLAYFIELD memory
03197
03198                 DEX                     ;
03199                 CPX #NUMSPCOBJ.PL-1     ;
03200                 BNE LOOP003             ; Next PLAYFIELD space object
03201
03202 ;*** (4) Clear PLAYFIELD center if idle counter is up (?) **********************
03203                                         ; PLAYFIELD addresses of...
03204 PFMEM.C76R49    = PFMEM+49*40+76/4      ; ...pixel column number 76, row number 49
03205 PFMEM.C80R49    = PFMEM+49*40+80/4      ; ...pixel column number 80, row number 49
03206 PFMEM.C76R50    = PFMEM+50*40+76/4      ; ...pixel column number 76, row number 50
03207 PFMEM.C80R50    = PFMEM+50*40+80/4      ; ...pixel column number 80, row number 50
03208
03209 SKIP003         LDA IDLECNTHI           ; Skip if idle counter not negative
03210                 BPL SKIP004             ;
03211
03212                 LDA #0                  ; Clear pixels of 8 x 2 pixel rectangle...
03213                 STA PFMEM.C76R50        ; ...@ column number 76, row number 49 (?)
03214                 STA PFMEM.C80R50        ;
03215                 STA PFMEM.C80R49        ;
03216                 STA PFMEM.C76R49        ;
03217
03218 ;*** (5) Clear all PLAYER shapes ***********************************************
03219 SKIP004         LDA #0                  ; Clear shape of PLAYER4
03220                 LDY PL4ROW              ;
03221                 LDX PL4HEIGHT           ;
03222 LOOP004         STA PL4DATA,Y           ;
03223                 INY                     ;
03224                 DEX                     ;
03225                 BPL LOOP004             ;
03226
03227                 LDY PL3ROW              ; Clear shape of PLAYER3
03228                 LDX PL3HEIGHT           ;
03229 LOOP005         STA PL3DATA,Y           ;
03230                 INY                     ;
03231                 DEX                     ;
03232                 BPL LOOP005             ;
03233
03234                 LDY PL2ROW              ; Clear shape of PLAYER2
03235                 LDX PL2HEIGHT           ;
03236 LOOP006         STA PL2DATA,Y           ;
03237                 INY                     ;
03238                 DEX                     ;
03239                 BPL LOOP006             ;
03240
03241                 LDY PL1ROW              ; Clear shape of PLAYER1
03242                 LDX PL1HEIGHT           ;
03243 LOOP007         STA PL1DATA,Y           ;
03244                 INY                     ;
03245                 DEX                     ;
03246                 BPL LOOP007             ;
03247
03248                 LDY PL0ROW              ; Clear shape of PLAYER0
03249                 LDX PL0HEIGHT           ;
03250 LOOP008         STA PL0DATA,Y           ;
03251                 INY                     ;
03252                 DEX                     ;
03253                 BPL LOOP008             ;
03254
03255 ;*** (6) Update PLAYER vertical positions and update PLAYER shapes *************
03256                 LDA PL4SHAPTYPE         ; CARRY := PLAYER4 a PHOTON TORPEDO (shape type 0)?
03257                 CMP #1                  ;
03258                 LDY PL4SHAPOFF          ; Load PLAYER4 shape data offset
03259
03260                 LDX PL4ROWNEW           ; Update vertical position of PLAYER4
03261                 STX PL4ROW              ;
03262
03263                 LDA PL4HEIGHTNEW        ; Update PLAYER4 shape height
03264                 STA L.HEIGHTCNT         ;
03265                 STA PL4HEIGHT           ;
03266
03267 LOOP009         LDA PLSHAP1TAB,Y        ; Load PLAYER4 shape byte from shape data table
03268                 BCS SKIP005             ; Skip if PLAYER4 not PHOTON TORPEDO (shape type 0)
03269                 AND RANDOM              ; AND random bits to shape byte
03270 SKIP005         STA PL4DATA,X           ; Store shape byte in PLAYER4 data area
03271                 INY                     ;
03272                 INX                     ;
03273                 DEC L.HEIGHTCNT         ;
03274                 BPL LOOP009             ; Next row of PLAYER4 shape
03275
03276                 LDA PL3SHAPTYPE         ; Repeat above with PLAYER3
03277                 CMP #1                  ;
03278                 LDY PL3SHAPOFF          ;
03279                 LDX PL3ROWNEW           ;
03280                 STX PL3ROW              ;
03281                 LDA PL3HEIGHTNEW        ;
03282                 STA L.HEIGHTCNT         ;
03283                 STA PL3HEIGHT           ;
03284 LOOP010         LDA PLSHAP1TAB,Y        ;
03285                 BCS SKIP006             ;
03286                 AND RANDOM              ;
03287 SKIP006         STA PL3DATA,X           ;
03288                 INX                     ;
03289                 INY                     ;
03290                 DEC L.HEIGHTCNT         ;
03291                 BPL LOOP010             ;
03292
03293                 LDA PL2SHAPTYPE         ; Repeat above with PLAYER2
03294                 CMP #1                  ;
03295                 LDY PL2SHAPOFF          ;
03296                 LDX PL2ROWNEW           ;
03297                 STX PL2ROW              ;
03298                 LDA PL2HEIGHTNEW        ;
03299                 STA L.HEIGHTCNT         ;
03300                 STA PL2HEIGHT           ;
03301 LOOP011         LDA PLSHAP1TAB,Y        ;
03302                 BCS SKIP007             ;
03303                 AND RANDOM              ;
03304 SKIP007         STA PL2DATA,X           ;
03305                 INX                     ;
03306                 INY                     ;
03307                 DEC L.HEIGHTCNT         ;
03308                 BPL LOOP011             ;
03309
03310                 LDY PL1SHAPOFF          ; Repeat above with PLAYER1 (without torpedo part)
03311                 LDX PL1ROWNEW           ;
03312                 STX PL1ROW              ;
03313                 LDA PL1HEIGHTNEW        ;
03314                 STA L.HEIGHTCNT         ;
03315                 STA PL1HEIGHT           ;
03316 LOOP012         LDA PLSHAP2TAB,Y        ;
03317                 STA PL1DATA,X           ;
03318                 INX                     ;
03319                 INY                     ;
03320                 DEC L.HEIGHTCNT         ;
03321                 BPL LOOP012             ;
03322
03323                 LDY PL0SHAPOFF          ; Repeat above with PLAYER0 (without torpedo part)
03324                 LDX PL0ROWNEW           ;
03325                 STX PL0ROW              ;
03326                 LDA PL0HEIGHTNEW        ;
03327                 STA L.HEIGHTCNT         ;
03328                 STA PL0HEIGHT           ;
03329 LOOP013         LDA PLSHAP2TAB,Y        ;
03330                 STA PL0DATA,X           ;
03331                 INX                     ;
03332                 INY                     ;
03333                 DEC L.HEIGHTCNT         ;
03334                 BPL LOOP013             ;
03335
03336 ;*** (7) Update PLAYER horizontal positions ************************************
03337                 LDA PL0COLUMN           ; Update horizontal position of PLAYER0
03338                 STA HPOSP0              ;
03339                 LDA PL1COLUMN           ; Update horizontal position of PLAYER1
03340                 STA HPOSP1              ;
03341                 LDA PL2COLUMN           ; Update horizontal position of PLAYER2
03342                 STA HPOSP2              ;
03343                 LDA PL3COLUMN           ; Update horizontal position of PLAYER3
03344                 STA HPOSP3              ;
03345                 LDA PL4COLUMN           ; Update horizontal position of PLAYER4
03346                 STA HPOSM3              ;
03347                 CLC                     ;
03348                 ADC #2                  ;
03349                 STA HPOSM2              ;
03350                 ADC #2                  ;
03351                 STA HPOSM1              ;
03352                 ADC #2                  ;
03353                 STA HPOSM0              ;
03354
03355 ;*** (8) Rotate space objects horizontally and vertically **********************
03356                 BIT SHIPVIEW            ; Skip if in Galactic Chart view
03357                 BMI SKIP009             ;
03358
03359 ;*** Rotate horizontally *******************************************************
03360                 LDA JOYSTICKX           ; Skip if joystick centered horizontally
03361                 BEQ SKIP008             ;
03362
03363                 STA JOYSTICKDELTA       ; Save JOYSTICKX (used in subroutine ROTATE)
03364                 LDY MAXSPCOBJIND        ; Loop over all space objects in use
03365 LOOP014         STY L.ZPOSOFF           ; Save offset to z-coordinate
03366                 CLC                     ;
03367
03368                 TYA                     ;
03369                 TAX                     ; X := offset to z-coordinate
03370                 ADC #NUMSPCOBJ.ALL      ;
03371                 TAY                     ; Y := offset to x-coordinate
03372                 JSR ROTATE              ; Calc new x-coordinate (horizontal rot @ y-axis)
03373
03374                 TYA                     ;
03375                 TAX                     ; X := offset to x-coordinate
03376                 LDY L.ZPOSOFF           ; Y := offset to z-coordinate
03377                 JSR ROTATE              ; Calc new z-coordinate (horizontal rot @ y-axis)
03378                 DEY                     ;
03379                 BPL LOOP014             ; Next space object
03380
03381 ;*** Rotate vertically *********************************************************
03382 SKIP008         LDA JOYSTICKY           ; Skip if joystick centered vertically
03383                 BEQ SKIP009             ;
03384
03385                 STA JOYSTICKDELTA       ; Save JOYSTICKY (used in subroutine ROTATE)
03386                 LDY MAXSPCOBJIND        ; Loop over all space objects in use
03387 LOOP015         STY L.ZPOSOFF           ; Save offset to z-coordinate
03388                 CLC                     ;
03389
03390                 TYA                     ;
03391                 TAX                     ; X := offset to z-coordinate
03392                 ADC #NUMSPCOBJ.ALL*2    ;
03393                 TAY                     ; Y := offset to y-coordinate
03394                 JSR ROTATE              ; Calc new y-coordinate (vertical rot @ x-axis)
03395
03396                 TYA                     ;
03397                 TAX                     ; X := offset to y-coordinate
03398                 LDY L.ZPOSOFF           ; Y := offset to z-coordinate
03399                 JSR ROTATE              ; Calc new z-coordinate (vertical rot @ x-axis)
03400                 DEY                     ;
03401                 BPL LOOP015             ; Next space object
03402
03403 ;*** (9) Move all space objects along z-axis (toward our starship) *************
03404 SKIP009         LDX MAXSPCOBJIND        ; Loop over all space objects in use
03405 LOOP016         CPX #NUMSPCOBJ.PL       ; Skip if PLAYFIELD space object (X index > 4)
03406                 BCS SKIP010             ;
03407
03408                 LDA PL0SHAPTYPE,X       ; Skip if next PLAYER space obj is PHOTON TORPEDO (!)
03409                 BEQ SKIP011             ;
03410
03411 SKIP010         SEC                     ; New z-coordinate := old z-coordinate -
03412                 LDA ZPOSLO,X            ; ...our starship's velocity
03413                 SBC VELOCITYLO          ; (signed 24-bit subtraction)
03414                 STA ZPOSLO,X            ;
03415                 LDA ZPOSHI,X            ;
03416                 SBC VELOCITYHI          ;
03417                 STA ZPOSHI,X            ;
03418                 LDA ZPOSSIGN,X          ;
03419                 SBC #0                  ;
03420                 STA ZPOSSIGN,X          ;
03421
03422 SKIP011         DEX                     ;
03423                 BPL LOOP016             ; Next space object
03424
03425 ;*** (10) Add space object's velocity vector to space object's position vector *
03426                 LDX MAXSPCOBJIND        ; Loop over all space objects in use
03427 LOOP017         CPX #NUMSPCOBJ.NORM-1   ; Skip if space object is star (X index 5..16)...
03428                 BNE SKIP012             ; ...because stars don't move by themselves
03429                 LDX #4                  ;
03430
03431 SKIP012         TXA                     ;
03432 LOOP018         TAY                     ; Loop over all 3 coordinates
03433
03434                 LDA #0                  ; Expand 8-bit velocity vector component to 16-bit:
03435                 STA L.VELOCITYHI        ; ...16-bit velocity (high byte) = L.VELOCITYHI := 0
03436                 LDA ZVEL,Y              ; ...16-bit velocity (low byte)  = A := ZVEL,Y
03437                 BPL SKIP013             ; Skip if 16-bit velocity >= 0 (positive)
03438
03439                 EOR #$7F                ; 16-bit velocity < 0 (negative)...
03440                 CLC                     ; ...calculate two's-complement of 16-bit velocity
03441                 ADC #1                  ;
03442                 BCS SKIP013             ;
03443                 DEC L.VELOCITYHI        ;
03444
03445 SKIP013         CLC                     ; New coordinate := old coordinate + 16-bit velocity
03446                 ADC ZPOSLO,Y            ; (signed 24-bit addition)
03447                 STA ZPOSLO,Y            ;
03448                 LDA ZPOSHI,Y            ;
03449                 ADC L.VELOCITYHI        ;
03450                 STA ZPOSHI,Y            ;
03451                 LDA ZPOSSIGN,Y          ;
03452                 ADC L.VELOCITYHI        ;
03453                 STA ZPOSSIGN,Y          ;
03454
03455                 TYA                     ;
03456                 CLC                     ;
03457                 ADC #NUMSPCOBJ.ALL      ;
03458                 CMP #144                ; (!)
03459                 BCC LOOP018             ; Next coordinate
03460
03461                 DEX                     ;
03462                 BPL LOOP017             ; Next space object
03463
03464 ;*** (11) Correct over/underflow of PLAYER space objects' position vector ******
03465                 LDY #NUMSPCOBJ.PL-1     ;
03466 LOOP019         TYA                     ; Loop over all PLAYER space objects (X index < 5)
03467                 TAX                     ;
03468
03469                 LDA #2                  ; Loop over all 3 coordinates
03470                 STA L.VECCOMPIND        ;
03471
03472 LOOP020         LDA ZPOSSIGN,X          ; Load sign of coordinate
03473                 CMP #2                  ;
03474                 BCC SKIP015             ; Skip if sign = 0 (negative) or 1 (positive)
03475
03476                 ASL A                   ; SUMMARY: Space object out-of-bounds correction
03477                 LDA #0                  ; If new coordinate > +65535 <KM> subtract 256 <KM>
03478                 STA ZPOSSIGN,X          ; ...until new coordinate <= +65535 <KM>
03479                 BCS SKIP014             ; If new coordinate < -65536 <KM> add 256 <KM>
03480                 INC ZPOSSIGN,X          ; ...until new coordinate >= -65536 <KM>
03481                 EOR #$FF                ;
03482 SKIP014         STA ZPOSHI,X            ;
03483
03484 SKIP015         TXA                     ;
03485                 CLC                     ;
03486                 ADC #NUMSPCOBJ.ALL      ;
03487                 TAX                     ;
03488                 DEC L.VECCOMPIND        ;
03489                 BPL LOOP020             ; Next coordinate
03490
03491                 DEY                     ;
03492                 BPL LOOP019             ; Next space object
03493
03494 ;*** (12) Calc perspective projection of space objects *************************
03495                 LDA SHIPVIEW            ; Skip if in Long-Range Scan or Galactic Chart view
03496                 CMP #$02                ;
03497                 BCS SKIP019             ;
03498
03499                 LDX MAXSPCOBJIND        ; Loop over all space objects in use
03500 LOOP021         LDA #255                ; Prep magic offscreen pixel number value
03501                 LDY ZPOSSIGN,X          ; Compare sign of z-coordinate with view mode
03502                 CPY SHIPVIEW            ;
03503                 BEQ SKIP018             ; Equal? Space object is offscreen -> New space obj!
03504
03505                 LDA YPOSSIGN,X          ; Prepare projection division...
03506                 BNE SKIP016             ; DIVIDEND (16-bit value) := ABS(y-coordinate)
03507                 SEC                     ; (used in subroutine PROJECTION)
03508                 LDA #0                  ;
03509                 SBC YPOSLO,X            ;
03510                 STA DIVIDEND            ;
03511                 LDA #0                  ;
03512                 SBC YPOSHI,X            ;
03513                 STA DIVIDEND+1          ;
03514                 JMP JUMP001             ;
03515 SKIP016         LDA YPOSLO,X            ;
03516                 STA DIVIDEND            ;
03517                 LDA YPOSHI,X            ;
03518                 STA DIVIDEND+1          ;
03519
03520 JUMP001         JSR PROJECTION          ; Calc pixel row number rel. to screen center
03521                 JSR SCREENROW           ; Calc pixel row number rel. to top-left of screen
03522
03523                 LDA XPOSSIGN,X          ; Prepare projection division...
03524                 BNE SKIP017             ; DIVIDEND (16-bit value) := ABS(x-coordinate)
03525                 SEC                     ; (used in subroutine PROJECTION)
03526                 LDA #0                  ;
03527                 SBC XPOSLO,X            ;
03528                 STA DIVIDEND            ;
03529                 LDA #0                  ;
03530                 SBC XPOSHI,X            ;
03531                 STA DIVIDEND+1          ;
03532                 JMP JUMP002             ;
03533 SKIP017         LDA XPOSLO,X            ;
03534                 STA DIVIDEND            ;
03535                 LDA XPOSHI,X            ;
03536                 STA DIVIDEND+1          ;
03537
03538 JUMP002         JSR PROJECTION          ; Calc pixel column number rel. to screen center
03539 SKIP018         JSR SCREENCOLUMN        ; Calc pixel column number rel. to top-left of screen
03540                 DEX                     ;
03541                 BPL LOOP021             ; Next space object
03542
03543 ;*** (13) Handle hyperwarp marker selection in Galactic Chart view *************
03544 SKIP019         JSR SELECTWARP          ; Handle hyperwarp marker in Galactic Chart view
03545
03546 ;*** (14) Compute and draw Long-Range Scan view star field on z-x plane ********
03547                 BIT SHIPVIEW            ; Skip if not in Long-Range Scan view
03548                 BVC SKIP022             ;
03549
03550                 LDX #$31                ; Draw our starship's shape
03551                 JSR DRAWLINES           ;
03552
03553                 BIT GCSTATLRS           ; Skip if Long-Range Scan destroyed
03554                 BVS SKIP022             ;
03555
03556                 LDX MAXSPCOBJIND        ; Loop over all space objects in use
03557 LOOP022         LDA ZPOSHI,X            ; Load z-coordinate (high byte)
03558                 LDY ZPOSSIGN,X          ; Load sign of z-coordinate
03559                 BNE SKIP020             ;
03560                 EOR #$FF                ; A := ABS(z-coordinate (high byte))
03561 SKIP020         TAY                     ;
03562                 LDA MAPTO80,Y           ; Calc pixel row number rel. to screen center
03563                 JSR SCREENROW           ; Calc pixel row number rel. to top-left of screen
03564
03565                 LDA XPOSHI,X            ; Load x-coordinate (high byte)
03566                 LDY XPOSSIGN,X          ; Load sign of x-coordinate
03567                 BNE SKIP021             ;
03568                 EOR #$FF                ; A := ABS(x-coordinate (high byte))
03569 SKIP021         TAY                     ;
03570                 LDA MAPTO80,Y           ; Calc pixel column number rel. to screen center
03571                 JSR SCREENCOLUMN        ; Calc pixel column number rel. to top-left of screen
03572
03573                 DEX                     ;
03574                 BPL LOOP022             ; Next space object
03575
03576 ;*** (15) Update PLAYER shapes, heights, and colors ****************************
03577
03578 ; DESCRIPTION
03579 ;
03580 ; In a loop over all PLAYERs, the following steps are executed:
03581 ;
03582 ; o   Clear the PLAYER shape offset and height.
03583 ;
03584 ; o   If in Galactic Chart view or in Long-Range Scan view, preload a random
03585 ;     color and a magic z-coordinate (distance value) for PLAYER3..4
03586 ;     (representing hyperwarp markers in Galactic Chart view and blips in the
03587 ;     Long-Range Scan view, like, for example, Zylon ships, meteors - or even
03588 ;     the Hyperwarp Target Marker during hyperwarp!).
03589 ;
03590 ; o   If in Front or Aft view, execute the following steps:
03591 ;
03592 ;      o   Skip dead PLAYERs.
03593 ;
03594 ;      o   Preload the distance value for the remaining live PLAYERs.
03595 ;
03596 ;      o   If we are in a starbase sector, combine PLAYER0..2 into a three-part
03597 ;          starbase shape. Compute the pixel column numbers and pixel row
03598 ;          numbers of PLAYER0..1 such that they are arranged left (PLAYER0) and
03599 ;          right (PLAYER1) of PLAYER2. In addition, preload a color mask, a
03600 ;          counter actually, that will make the starbase pulsate in brightness.
03601 ;
03602 ;     BUG (at $A512): The code at $A512 that skips the combination operation for
03603 ;     PLAYER2..4 jumps for PLAYER3..4 to SKIP025 at $A52A instead of SKIP026 at
03604 ;     $A52E. Thus it stores a color mask which does not only make the starbase
03605 ;     PLAYER0..2 pulsate in brightness but also PLAYER3..4 in a starbase sector,
03606 ;     for example the transfer vessel, photon torpedoes, etc. - or even the
03607 ;     Hyperwarp Target Marker when hyperwarping out of such a sector! Suggested
03608 ;     fix: None, code hard to untwist.
03609 ;
03610 ; o   After storing the color mask, check if the PLAYER shape is still above the
03611 ;     bottom edge of the PLAYFIELD.
03612 ;
03613 ;     BUG (at $A534): The test checks the vertical position of the top edge of
03614 ;     the PLAYER against the bottom edge of the PLAYFIELD above the Console
03615 ;     Panel Display (= Player/Missile pixel row number 204). This is not
03616 ;     completely accurate as the Console Panel Display starts at PM pixel row
03617 ;     number 208. For example, if you carefully navigate a starbase to the
03618 ;     bottom edge of the PLAYFIELD, at a certain point the center of the
03619 ;     starbase shape bleeds over the bottom edge of the PLAYFIELD (while
03620 ;     sometimes even losing its left and right wings!). Suggested fix: None, as
03621 ;     a more elaborate test may consume too many bytes of the cartridge ROM
03622 ;     memory in order to fix a rarely noticed visual glitch.
03623 ;
03624 ; o   Convert the preloaded distance value of a PLAYER space object closer than
03625 ;     $2000 (8192) <KM> into a range index of 0..15. PLAYER space objects more
03626 ;     distant than $2000 (8192) <KM> are skipped and not displayed.
03627 ;
03628 ;     Later, this range index will pick not only the correct brightness for the
03629 ;     PLAYER (the closer the space object the brighter its PLAYER) but also the
03630 ;     correct PLAYER shape cell and height (the closer the space object the
03631 ;     larger the PLAYER shape and height). 
03632 ;
03633 ; o   Update the PLAYER's shape offset and height. On the way to the shape
03634 ;     offset and height add the PLAYER's shape type to the range index and
03635 ;     divide it by 2 to arrive at the shape offset index and height index (the
03636 ;     same value). Use this index to pick the correct shape data and shape
03637 ;     heights from a set of shape cells and their corresponding heights, stored
03638 ;     in tables PLSHAPOFFTAB ($BE2F) and PLSHPHEIGHTTAB ($BE7F), respectively.
03639 ;
03640 ;     Remember that magic distance value used in the Galactic Chart and
03641 ;     Long-Range Scan view? Its value of $F2 is actually part of a negative
03642 ;     z-coordinate which is inverted to $0D00, leading to a range index of 13,
03643 ;     which, after the division by 2, picks shape cell 6. Shape cell 6 (the
03644 ;     seventh shape cell) of all space objects (except the starbase) is the
03645 ;     Long-Range Scan blip's dot (see PLSHAPOFFTAB ($BE2F) and PLSHPHEIGHTTAB
03646 ;     ($BE7F)).
03647 ;
03648 ; o   Update the PLAYER's color/brightness by picking the appropriate values
03649 ;     with the range index from lookup tables PLSHAPCOLORTAB ($BFD1) and
03650 ;     PLSHAPBRITTAB ($BFDB). Apply some special effects to the color/brightness
03651 ;     of certain PLAYERs, such as using random colors for Zylon basestars, or
03652 ;     using the precomputed pulsating brightness value for a starbase.
03653
03654 SKIP022         LDX #NUMSPCOBJ.PL       ; Loop over all PLAYER space objects (X index < 5)
03655 LOOP023         DEX                     ;
03656                 BPL SKIP023             ; Jump into loop body below
03657                 JMP JUMP003             ; Loop is finished, skip loop body
03658
03659 ;*** Clear PLAYER shape offsets and heights ************************************
03660 SKIP023         LDA #0                  ;
03661                 STA PL0SHAPOFF,X        ; Clear PLAYER shape offset
03662                 STA PL0HEIGHTNEW,X      ; Clear new PLAYER shape height
03663
03664 ;*** Preload stuff for hyperwarp markers and Long-Range Scan blips *************
03665                 BIT SHIPVIEW            ; Skip if not in Galactic Chart view
03666                 BPL SKIP024             ;
03667
03668                 CPX #3                  ; Next PLAYER space object if PLAYER0..2
03669                 BCC LOOP023             ;
03670
03671 LOOP024         LDA RANDOM              ; Prep random color mask for warp markers/LRS blips
03672                 LDY #$F2                ; Prep magic z-coordinate for warp markers/LRS blips
03673                 BMI SKIP026             ; Unconditional jump
03674
03675 SKIP024         CMP PL0LIFE,X           ; Next PLAYER space object if this PLAYER not alive
03676                 BEQ LOOP023             ;
03677
03678                 BVS LOOP024             ; Skip back if in Long-Range Scan view
03679
03680 ;*** Preload stuff for other views *********************************************
03681
03682                 LDY PL0ZPOSHI,X         ; Prep z-coordinate (high byte)
03683
03684 ;*** Combine PLAYER0..2 to starbase shape **************************************
03685                 BIT ISSTARBASESECT      ; Skip if no starbase in this sector
03686                 BVC SKIP026             ;
03687
03688                 CPX #2                  ; Skip if PLAYER2..4
03689                 BCS SKIP025             ; (!)
03690
03691                 LDA PL2COLUMN           ; Calc new PM pixel column number for PLAYER0..1:
03692                 CLC                     ; Load PLAYER2 (starbase center) pixel column number
03693                 ADC PLSTARBAOFFTAB,X    ; ...add PLAYER left/right offset (starbase wings)
03694                 STA PL0COLUMN,X         ; Store new PM pixel column number of starbase wing
03695
03696                 LDA PL2ROWNEW           ; Calc new PM pixel row number for PLAYER0..1:
03697                 CLC                     ; Add vertical offset (= 4 PM pixels) to PLAYER2's
03698                 ADC #4                  ;
03699                 STA PL0ROWNEW,X         ; Store new PM pixel row number of starbase wing
03700
03701                 LDY PL2ZPOSHI           ; Prep Y with z-coordinate (high byte) of starbase
03702
03703 SKIP025         LDA COUNT256            ; Prep color mask with B3..0 of counter
03704                 AND #$0F                ; ...(= brightness bits cause pulsating brightness)
03705
03706 SKIP026         STA L.COLORMASK         ; Store color mask
03707
03708 ;*** Check if PLAYER is below PLAYFIELD bottom edge ****************************
03709                 TYA                     ; A := z-coordinate (high byte)
03710
03711                 LDY PL0ROWNEW,X         ; Next PLAYER space object if top of PM shape...
03712                 CPY #204                ; ...is below PLAYFIELD bottom... (!)
03713                 BCS LOOP023             ; ...(PM pixel row number >= 204)
03714
03715 ;*** Convert PLAYER z-coordinate to range index in 0..15 ***********************
03716                 LDY SHIPVIEW            ; Skip if in Front view...
03717                 BEQ SKIP027             ;
03718                 EOR #$FF                ; ...else invert z-coordinate (high byte)
03719
03720 SKIP027         CMP #$20                ; Next PLAYER space object if this one too far away
03721                 BCS LOOP023             ; ...(z-coordinate >= $20** (8192) <KM>)
03722
03723                 CMP #16                 ; Load z-coordinate (high byte) and...
03724                 BCC SKIP028             ;
03725                 LDA #15                 ;
03726 SKIP028         STA L.RANGEINDEX        ; ...trim to range index in 0..15
03727
03728 ;*** Update PLAYER shape offset and height *************************************
03729                 ORA PL0SHAPTYPE,X       ; Calc offset to shape table (shape type+range index)
03730                 LSR A                   ;
03731                 TAY                     ; Divide by 2 to get offset in 0..7 into shape data
03732                 LDA PLSHAPOFFTAB,Y      ; Update new PLAYER shape offset
03733                 STA PL0SHAPOFF,X        ;
03734                 LDA PLSHPHEIGHTTAB,Y    ; Update new PLAYER shape height
03735                 STA PL0HEIGHTNEW,X      ;
03736
03737 ;*** Calculate PLAYER color/brightness value ***********************************
03738                 TYA                     ; Pick color (B7..4) using PLAYER shape type
03739                 LSR A                   ;
03740                 LSR A                   ;
03741                 LSR A                   ;
03742                 TAY                     ;
03743                 LDA PLSHAPCOLORTAB,Y    ;
03744                 CPY #8                  ; Pick random color if ZYLON BASESTAR (shape type 8)
03745                 BNE SKIP029             ;
03746                 EOR RANDOM              ;
03747 SKIP029         LDY L.RANGEINDEX        ;
03748                 EOR PLSHAPBRITTAB,Y     ; Pick brightness (B3..0) using range index and merge
03749
03750                 EOR L.COLORMASK         ; Modify color/brightness of PLAYER
03751
03752                 LDY PLCOLOROFFTAB,X     ; Get PLAYER color offset
03753                 STA PL0COLOR,Y          ; Store color in PLAYER color register
03754                 JMP LOOP023             ; Next PLAYER space object
03755
03756 ;*** (16) Flash red alert ******************************************************
03757 JUMP003         LDY #$AF                ; Prep PLAYFIELD2 color {BRIGHT BLUE-GREEN}
03758                 LDX SHIELDSCOLOR        ; Prep Shields color {DARK GREEN} or {BLACK}
03759
03760                 LDA REDALERTLIFE        ; Skip if red alert is over
03761                 BEQ SKIP030             ;
03762
03763                 DEC REDALERTLIFE        ; Decrement lifetime of red alert
03764                 LDY #$4F                ; Prep PLAYFIELD2 color {BRIGHT ORANGE}
03765
03766                 AND #$20                ; Switch colors every 64 game loops
03767                 BEQ SKIP030             ;
03768
03769                 LDX #$42                ; Load BACKGROUND color {DARK ORANGE}
03770                 LDY #$60                ; Load PLAYFIELD2 color {DARK PURPLE BLUE}
03771
03772 SKIP030         STY PF2COLOR            ; Store PLAYFIELD2 color
03773                 STX BGRCOLOR            ; Store BACKGROUND color
03774
03775 ;*** (17) Update color of PLAYFIELD space objects (stars, explosion fragments) *
03776                 LDX MAXSPCOBJIND        ; Loop over all PLAYFIELD space objs (X index > 4)
03777 LOOP025         LDA ZPOSHI,X            ; Prep z-coordinate (high byte)
03778                 LDY SHIPVIEW            ;
03779                 CPY #1                  ; Skip if not in Aft view
03780                 BNE SKIP032             ;
03781
03782                 CMP #$F0                ; Skip if star not too far (z < $F0** (-4096) <KM>)
03783                 BCS SKIP031             ;
03784                 JSR INITPOSVEC          ; Re-init position vector
03785 SKIP031         EOR #$FF                ; Invert z-coordinate (high byte)
03786
03787 SKIP032         CMP #16                 ; Convert z-coordinate (high byte)
03788                 BCC SKIP033             ; ...into range index 0..15
03789                 LDA #15                 ;
03790
03791 SKIP033         ASL A                   ; Compute index to pixel color table:
03792                 AND #$1C                ; Use bits B3..1 from range index as B4..2.
03793                 ORA COUNT8              ; Combine with random bits B3..0 from counter
03794
03795                 TAY                     ;
03796                 LDA FOURCOLORPIXEL,Y    ; Load 1-byte bit pattern for 4 pixels of same color
03797                 STA L.FOURCOLORPIX      ; ...and temporarily save it
03798
03799                 LDA PIXELCOLUMN,X       ; Load pixel mask to mask 1 pixel out of 4 pixels:
03800                 AND #$03                ; Use B1..0 from pixel column number...
03801                 TAY                     ;
03802                 LDA PIXELMASKTAB,Y      ; ...to pick mask to filter pixel in byte
03803                 AND L.FOURCOLORPIX      ; ...AND with 1-byte bit pattern for 4 pixels
03804                 STA PIXELBYTE,X         ; ...store byte (used in repaint step of game loop)
03805
03806                 DEX                     ;
03807                 CPX #NUMSPCOBJ.PL       ;
03808                 BCS LOOP025             ; Next PLAYFIELD space object
03809
03810 ;*** (18) Skip input handling if in demo mode **********************************
03811                 BIT ISDEMOMODE          ; If in demo mode skip to function keys
03812                 BVC SKIP034             ;
03813                 JMP SKIP040             ;
03814
03815 ;*** (19) Handle keyboard input ************************************************
03816 SKIP034         JSR KEYBOARD            ; Handle keyboard input
03817
03818 ;*** (20) Handle joystick input ************************************************
03819                 LDA PORTA               ; Load Joystick 0 directions
03820                 TAY                     ; ...Bits B0..3 -> Right, left, down, up.
03821                 AND #$03                ; ...Bit = 0/1 -> Stick pressed/not pressed
03822                 TAX                     ; JOYSTICKY := +1 -> Up
03823                 LDA STICKINCTAB,X       ; JOYSTICKY :=  0 -> Centered
03824                 STA JOYSTICKY           ; JOYSTICKY := -1 -> Down
03825                 TYA                     ;
03826                 LSR A                   ;
03827                 LSR A                   ;
03828                 AND #$03                ;
03829                 TAX                     ; JOYSTICKX := -1 -> Left
03830                 LDA STICKINCTAB,X       ; JOYSTICKX :=  0 -> Centered
03831                 STA JOYSTICKX           ; JOYSTICKX := +1 -> Right
03832
03833 ;*** (21) Check if our starship's photon torpedoes have hit a target ***********
03834                 JSR COLLISION           ; Check if our starship's photon torpedoes have hit
03835
03836 ;*** (22) Handle joystick trigger **********************************************
03837                 JSR TRIGGER             ; Handle joystick trigger
03838
03839 ;*** (23) Handle Attack Computer and Tracking Computer *************************
03840                 BIT GCSTATCOM           ; Skip if Attack Computer destroyed
03841                 BVS SKIP038             ;
03842
03843                 LDA DRAINATTCOMP        ; Skip if Attack Computer off
03844                 BEQ SKIP038             ;
03845
03846                 LDA SHIPVIEW            ; Skip if not in Front view
03847                 BNE SKIP035             ;
03848
03849                 JSR UPDATTCOMP          ; Update Attack Computer Display
03850
03851 SKIP035         LDX TRACKDIGIT          ; Load index of tracked space object
03852
03853                 LDA ZYLONATTACKER       ; Skip if ship of current Zylon torpedo is tracked
03854                 BMI SKIP036             ;
03855                 TAX                     ; ...else override Tracking Computer...
03856                 ORA #$80                ;
03857                 STA ZYLONATTACKER       ; ...and mark Zylon torpedo's ship as being tracked
03858
03859 SKIP036         LDA PL0LIFE,X           ; Skip if tracked space object still alive
03860                 BNE SKIP037             ;
03861
03862                 TXA                     ;
03863                 EOR #$01                ;
03864                 TAX                     ;
03865                 LDA PL0LIFE,X           ; Check if other Zylon ship still alive
03866                 BNE SKIP037             ; ...yes -> Keep new index
03867                 LDX TRACKDIGIT          ; ...no  -> Revert to old index of tracked space obj
03868
03869 SKIP037         STX TRACKDIGIT          ; Store index of tracked space object
03870
03871                 LDA ISTRACKCOMPON       ; Skip if tracking computer is turned off
03872                 BEQ SKIP038             ;
03873
03874                 LDA SHIPVIEW            ; Skip if in Long-Range Scan or Galactic Chart view
03875                 CMP #2                  ;
03876                 BCS SKIP038             ;
03877
03878                 EOR #$01                ;
03879                 CMP ZPOSSIGN,X          ; Skip if tracked space object in our starship's...
03880                 BEQ SKIP038             ; ...view direction
03881
03882                 TAX                     ;
03883                 LDA TRACKKEYSTAB,X      ; Pick 'F' or 'A' (Front or Aft view) keyboard code
03884                 STA KEYCODE             ; ...and store it (= emulate pressing 'F' or 'A' key)
03885
03886 ;*** (24) Handle docking to starbase *******************************************
03887 SKIP038         JSR DOCKING             ; Handle docking to starbase
03888
03889 ;*** (25) Handle maneuvering ***************************************************
03890                 JSR MANEUVER            ; Handle maneuvering photon torpedoes and Zylon ships
03891
03892 ;*** (26) Was our starship hit by Zylon photon torpedo? ************************
03893                 LDA ISSTARBASESECT      ; Skip hit check if in starbase sector
03894                 BNE SKIP040             ;
03895
03896                 LDA PL2LIFE             ; Skip hit check if PLAYER2 (Zylon photon torpedo)...
03897                 BEQ SKIP040             ; ...not alive
03898
03899                 LDY PL2ZPOSHI           ; Our starship was not hit if Zylon photon torpedo's
03900                 INY                     ; ...z-coordinate is not in -256..255 <KM> or...
03901                 CPY #$02                ;
03902                 BCS SKIP040             ;
03903
03904                 LDY PL2XPOSHI           ; ...x-coordinate is not in -256..255 <KM> or...
03905                 INY                     ;
03906                 CPY #$02                ;
03907                 BCS SKIP040             ;
03908
03909                 LDY PL2YPOSHI           ; ...y-coordinate is not in -256..255 <KM>.
03910                 INY                     ;
03911                 CPY #$02                ;
03912                 BCS SKIP040             ;
03913
03914 ;*** (27) Our starship was hit! ************************************************
03915                 JSR DAMAGE              ; Damage or destroy some subsystem
03916
03917                 LDY #2                  ; Trigger explosion at PLAYER2 (Zylon photon torpedo)
03918                 JSR INITEXPL            ;
03919
03920                 LDX #$7F                ; Prep HITBADNESS := SHIELDS HIT
03921                 LDA SHIELDSCOLOR        ; Skip if Shields are up (SHIELDSCOLOR not {BLACK}).
03922                 BNE SKIP039             ;
03923
03924                 LDX #$0A                ; Set Front view
03925                 JSR SETVIEW             ;
03926
03927                 LDY #$23                ; Set title phrase "SHIP DESTROYED BY ZYLON FIRE"
03928                 LDX #8                  ; Set mission bonus offset
03929                 JSR GAMEOVER            ; Game over
03930
03931                 LDX #$5F                ; Hide Control Panel Display (bottom text window)
03932                 LDY #$80                ;
03933                 LDA #$08                ;
03934                 JSR MODDLST             ;
03935
03936                 JSR CLRPLAYFIELD        ; Clear PLAYFIELD
03937
03938                 LDX #64                 ; Enable STARSHIP EXPLOSION noise (see SOUND)
03939                 STX NOISEHITLIFE        ;
03940
03941                 LDX #$FF                ; Prep HITBADNESS := STARSHIP DESTROYED
03942
03943 SKIP039         STX HITBADNESS          ; Store HITBADNESS
03944                 LDA #0                  ; Zylon photon torpedo lifetime := 0 game loops
03945                 STA PL2LIFE             ;
03946                 LDA #2                  ; Init Zylon photon torpedo trigger
03947                 STA TORPEDODELAY        ;
03948
03949                 LDX #1                  ; ENERGY := ENERGY - 100 after photon torpedo hit
03950                 JSR DECENERGY           ;
03951
03952                 LDX #$0A                ; Play noise sound pattern SHIELD EXPLOSION
03953                 JSR NOISE               ;
03954
03955 ;*** (28) Handle function keys *************************************************
03956 SKIP040         LDY FKEYCODE            ; Prep old function key code
03957                 LDA CONSOL              ; POKEY: Load function key code
03958
03959                 EOR #$FF                ; Store inverted and masked function key code
03960                 AND #$03                ;
03961                 STA FKEYCODE            ;
03962                 BEQ SKIP042             ; Skip if no function key pressed
03963
03964                 DEY                     ;
03965                 BPL SKIP042             ; Skip if SELECT or START still pressed
03966                 STA IDLECNTHI           ; Reset idle counter to a value in 1..3 (?)
03967                 CMP #2                  ; Skip if SELECT function key pressed
03968                 BCS SKIP041             ;
03969
03970                 LDA #0                  ; START function key pressed:
03971                 TAY                     ; Prep empty title phrase offset
03972                 JMP INITSTART           ; Reenter game loop via INITSTART
03973
03974 SKIP041         INC MISSIONLEVEL        ; SELECT function key pressed:
03975                 LDA MISSIONLEVEL        ; Cycle through next of 4 mission levels
03976                 AND #$03                ;
03977                 STA MISSIONLEVEL        ;
03978                 JMP INITSELECT          ; Reenter game loop via INITSELECT
03979
03980 ;*** (29) Update Control Panel Display *****************************************
03981 SKIP042         JSR UPDPANEL            ; Update Control Panel Display
03982
03983 ;*** (30) Handle hyperwarp *****************************************************
03984                 JSR HYPERWARP           ; Handle hyperwarp
03985
03986 ;*** (31) Update title line ****************************************************
03987                 JSR UPDTITLE            ; Update title line
03988
03989 ;*** (32) Flush game loop iteration ********************************************
03990                 JSR FLUSHGAMELOOP       ; Move Zylon units, age torpedoes, elapse time
03991
03992 ;*** (33) Jump back to begin of game loop **************************************
03993                 JMP GAMELOOP            ; Next game loop iteration
03994
03995 ;*******************************************************************************
03996 ;*                                                                             *
03997 ;*                                  VBIHNDLR                                   *
03998 ;*                                                                             *
03999 ;*                      Vertical Blank Interrupt Handler                       *
04000 ;*                                                                             *
04001 ;*******************************************************************************
04002
04003 ; DESCRIPTION
04004 ;
04005 ; This subroutine is executed during the Vertical Blank Interrupt (VBI) when the
04006 ; TV beam has reached the bottom-right corner of the TV screen and is switched
04007 ; off to return to the top-left position. This situation is called the "vertical
04008 ; blank phase".
04009 ;
04010 ; This subroutine signals its execution with flag ISVBISYNC ($67) (which is
04011 ; examined by GAMELOOP ($A1F3) to synchronize the execution of the game loop
04012 ; with the start of this subroutine). Then it switches the character set to the
04013 ; ROM character set, sets the BACKGROUND color depending on the severity of a
04014 ; Zylon photon torpedo hit and view mode, copies PLAYER and PLAYFIELD color
04015 ; registers to their corresponding hardware registers, clears the Player/Missile
04016 ; collision registers, calls the sound effects code in subroutine SOUND ($B2AB),
04017 ; and increments the idle counter. If the idle counter reaches the value $8000
04018 ; the title phrase is cleared and the program is switched to demo mode.
04019 ;
04020 ; BUG (at $A6EC): Because the values of SHIPVIEW ($D0) are $00, $01, $40, and
04021 ; $80, a value of 3 overspecifies the comparison. Suggested fix: Replace CMP #3
04022 ; with CMP #2, which may make the code clearer.
04023 ;
04024 ; BUG (at $A712): Demo mode is entered via a JMP instruction, which proceeds
04025 ; directly into GAMELOOP ($A1F3). Thus code execution never returns to pop the
04026 ; registers pushed on the stack during entry of this subroutine. Suggested fix:
04027 ; None.
04028
04029 VBIHNDLR        LDA #$FF                ; Signals entering Vertical Blank Interrupt
04030                 STA ISVBISYNC           ;
04031
04032                 LDA #>ROMCHARSET        ; Switch character set to ROM character set
04033                 STA CHBASE              ;
04034
04035                 LDX BGRCOLOR            ; Preload BACKGROUND color
04036                 LDA RANDOM              ; Preload random number
04037                 BIT HITBADNESS          ; Check if our starship was hit
04038                 BVC SKIP044             ; If HITBADNESS has a value of...
04039                 BMI SKIP043             ; $00 -> NO HIT             (BGR color := unchanged)
04040                 AND #$72                ; $7F -> SHIELDS HIT        (BGR color := %01rr00r0)
04041                 ORA #$40                ; $FF -> STARSHIP DESTROYED (BGR color := %01rr00r0)
04042 SKIP043         TAX                     ;
04043 SKIP044         LDA SHIPVIEW            ; Skip if in Front or Aft view
04044                 CMP #3                  ; (!)
04045                 BCC SKIP045             ;
04046                 LDX #$A0                ; Preload BACKGROUND color {DARK BLUE GREEN}...
04047 SKIP045         STX BGRCOLOR            ; Store BACKGROUND color
04048
04049                 LDX #8                  ; Copy all color registers to hardware registers
04050 LOOP026         LDA PL0COLOR,X          ;
04051                 STA COLPM0,X            ;
04052                 DEX                     ;
04053                 BPL LOOP026             ;
04054
04055                 STA HITCLR              ; Clear Player/Missile collision registers
04056
04057                 JSR SOUND               ; Call sound effects
04058
04059                 INC IDLECNTLO           ; Increment 16-bit idle counter
04060                 BNE SKIP046             ;
04061                 LDA IDLECNTHI           ;
04062                 BMI SKIP046             ;
04063                 INC IDLECNTHI           ;
04064                 BPL SKIP046             ; Skip if idle counter value of $8000 not reached yet
04065
04066                 LDY #$00                ; Prep empty title phrase offset
04067                 JMP INITDEMO            ; Enter demo mode (!)
04068
04069 SKIP046         JMP JUMP004             ; Return via DLI return code
04070
04071 ;*******************************************************************************
04072 ;*                                                                             *
04073 ;*                                  DLSTHNDLR                                  *
04074 ;*                                                                             *
04075 ;*                       Display List Interrupt Handler                        *
04076 ;*                                                                             *
04077 ;*******************************************************************************
04078
04079 ; DESCRIPTION
04080 ;
04081 ; This subroutine is executed during the Display List Interrupt (DLI). It
04082 ; switches the character set to the ROM character set if the DLI occurs at ANTIC
04083 ; line 96 (video line 192), otherwise to the custom character set. The former
04084 ; happens in the Galactic Chart view where the ROM character set is used in the
04085 ; Galactic Chart Panel Display.
04086 ;
04087 ; Then, the DLI PLAYFIELD colors are copied to the corresponding hardware
04088 ; registers and the values of the collision hardware registers for PLAYER3..4
04089 ; (our starship's photon torpedoes) are copied to the corresponding zero-page
04090 ; variables PL3HIT ($82) and PL4HIT ($83).
04091
04092 DLSTHNDLR       PHA                     ; Push A
04093                 TXA                     ;
04094                 PHA                     ; Push X
04095                 TYA                     ;
04096                 PHA                     ; Push Y
04097
04098                 LDA #>ROMCHARSET        ; Switch to ROM charset if ANTIC line counter = 96
04099                 LDY VCOUNT              ; ...else switch to custom character set
04100                 CPY #96                 ;
04101                 BEQ SKIP047             ;
04102                 LDA #>CHARSET           ;
04103 SKIP047         STA CHBASE              ;
04104
04105                 LDX #4                  ; Loop over all PLAYFIELD colors
04106                 STA WSYNC               ; Stop and wait for horizontal TV beam sync
04107 LOOP027         LDA PF0COLORDLI,X       ; Copy DLI PLAYFIELD colors to hardware registers
04108                 STA COLPF0,X            ;
04109                 DEX                     ;
04110                 BPL LOOP027             ; Next PLAYFIELD color
04111
04112                 LDA M0PL                ; Merge MISSILE-to-PLAYER collision registers...
04113                 ORA M1PL                ;
04114                 ORA M2PL                ;
04115                 ORA M3PL                ;
04116                 STA PL4HIT              ; ...and store them in PL4HIT
04117                 LDA P3PL                ; Copy PLAYER3-to-PLAYER coll. register to PL3HIT
04118                 STA PL3HIT              ;
04119
04120 JUMP004         PLA                     ; Pop Y
04121                 TAY                     ;
04122                 PLA                     ; Pop X
04123                 TAX                     ;
04124                 PLA                     ; Pop A
04125                 RTI                     ; Return from interrupt
04126
04127 ;*******************************************************************************
04128 ;*                                                                             *
04129 ;*                                  IRQHNDLR                                   *
04130 ;*                                                                             *
04131 ;*                       Interrupt Request (IRQ) Handler                       *
04132 ;*                                                                             *
04133 ;*******************************************************************************
04134
04135 ; DESCRIPTION
04136 ;
04137 ; This subroutine is executed during immediate interrupt requests (IRQs), such
04138 ; as after pressing a key on the keyboard. It clears and disables all IRQs
04139 ; except the interrupt raised by a pressed key. If a key has been pressed, its
04140 ; hardware code is collected and the bits of the SHIFT and CONTROL keys are
04141 ; added. The resulting keyboard code is stored in KEYCODE ($CA).
04142
04143 IRQHNDLR        PHA                     ; Push A
04144                 LDA #0                  ; POKEY: Disable all IRQs
04145                 STA IRQEN               ;
04146                 LDA #$40                ; POKEY: Enable keyboard interrupt (IRQ)
04147                 STA IRQEN               ;
04148                 LDA KBCODE              ; POKEY: Load keyboard key code
04149                 ORA #$C0                ; Combine with SHIFT and CONTROL key bits
04150                 STA KEYCODE             ; Store keyboard code
04151                 PLA                     ; Pop A
04152                 RTI                     ; Return from interrupt
04153
04154 ;*******************************************************************************
04155 ;*                                                                             *
04156 ;*                                  DRAWLINES                                  *
04157 ;*                                                                             *
04158 ;*                     Draw horizontal and vertical lines                      *
04159 ;*                                                                             *
04160 ;*******************************************************************************
04161
04162 ; DESCRIPTION
04163 ;
04164 ; Draws the Attack Computer Display (in Front view), cross hairs (in Front and
04165 ; Aft view), and our starship's shape (in Long-Range Scan view) on the PLAYFIELD
04166 ; (if the Attack Computer is not destroyed) by being passed an offset to table
04167 ; DRAWLINESTAB ($BAF9). This table consists of a list of 3-byte elements,
04168 ; terminated by an end marker byte ($FE). Each such element defines a single
04169 ; horizontal or vertical line, and is passed via memory addresses DIRLEN ($A4),
04170 ; PENROW ($A5), and PENCOLUMN ($A6) to subroutine DRAWLINE ($A782), which
04171 ; executes the actual drawing. See subroutine DRAWLINE ($A782) and table
04172 ; DRAWLINESTAB ($BAF9) for a description of the 3-byte elements. 
04173 ;
04174 ; With every call of this subroutine the blip cycle counter is initialized to
04175 ; the start of the DELAY phase (see subroutine UPDATTCOMP ($A7BF)).
04176 ;
04177 ; NOTE: The entry to this subroutine is in mid-code, not at the beginning.
04178 ;
04179 ; INPUT
04180 ;
04181 ;   X = Offset into DRAWLINESTAB ($BAF9). Used values are:
04182 ;     $00 -> Draw Attack Computer Display and cross hairs (Front view)
04183 ;     $2A -> Draw Aft view cross hairs (Aft view)
04184 ;     $31 -> Draw our starship's shape (Long-Range Scan view)
04185
04186 LOOP028         STA DIRLEN,Y            ; Store byte of 3-byte element
04187                 INX                     ;
04188                 DEY                     ;
04189                 BPL SKIP048             ; Next byte of 3-byte element until 3 bytes copied
04190                 JSR DRAWLINE            ; Draw line on PLAYFIELD
04191
04192 DRAWLINES       LDA #5                  ; Init blip cycle to DELAY phase...
04193                 STA BLIPCYCLECNT        ; ...delays drawing each row
04194
04195                 BIT GCSTATCOM           ; Return if Attack Computer destroyed
04196                 BVS SKIP049             ;
04197
04198                 LDY #2                  ;
04199 SKIP048         LDA DRAWLINESTAB,X      ; Load byte of 3-byte element
04200                 CMP #$FE                ; Loop until end marker byte ($FE) encountered
04201                 BNE LOOP028             ;
04202 SKIP049         RTS                     ; Return
04203
04204 ;*******************************************************************************
04205 ;*                                                                             *
04206 ;*                                  DRAWLINE                                   *
04207 ;*                                                                             *
04208 ;*                  Draw a single horizontal or vertical line                  *
04209 ;*                                                                             *
04210 ;*******************************************************************************
04211
04212 ; DESCRIPTION
04213 ;
04214 ; Draws a single horizontal or vertical transparent line.
04215 ;
04216 ; There are two entries to this subroutine:
04217 ;
04218 ; (1)  DRAWLINE ($A782) is entered from subroutine DRAWLINES ($A76F) to draw a
04219 ;      line in COLOR1.
04220 ;
04221 ; (2)  DRAWLINE2 ($A784) is entered from subroutine UPDATTCOMP ($A7BF) to draw
04222 ;      the blip in COLOR2 in the Attack Computer Display.
04223 ;
04224 ; The position, direction, and length of the line is defined by three bytes
04225 ; passed in memory addresses DIRLEN ($A4), PENROW ($A5), and PENCOLUMN ($A6). 
04226 ;
04227 ; A drawing operation draws one transparent line. It uses both the color
04228 ; register number of the overwritten (old) and the overwriting (new) pixel to
04229 ; decide on the new pixel color register number. This results in a transparent
04230 ; drawing effect. See the table below for all resulting combinations of color
04231 ; registers.
04232 ;
04233 ; +-----------+---------------+
04234 ; |           |   Old Color   |
04235 ; |           |   Register    |
04236 ; | New Color +---------------+
04237 ; | Register  | 0 | 1 | 2 | 3 |
04238 ; +-----------+---+---+---+---+
04239 ; |         0 | 0 | 1 | 2 | 3 |
04240 ; +-----------+---+---+---+---+
04241 ; |         1 | 1 | 1 | 3 | 3 |
04242 ; +-----------+---+---+---+---+
04243 ; |         2 | 2 | 3 | 2 | 3 |
04244 ; +-----------+---+---+---+---+
04245 ; |         3 | 3 | 3 | 3 | 3 |
04246 ; +-----------+---+---+---+---+
04247 ;
04248 ; For example, COLOR1 overwritten by COLOR2 yields COLOR3. If you look closely
04249 ; at the blip (in COLOR2) on the Attack Computer Display (in COLOR1) the lines
04250 ; of the Attack Computer Display shine through (in COLOR3) where they overlap.
04251 ;
04252 ; INPUT
04253 ;
04254 ;   DIRLEN    ($A4) = B7 = 0 -> Draw line to the right
04255 ;                     B7 = 1 -> Draw line downward
04256 ;                     B6..0  -> Length of line in pixels
04257 ;   PENROW    ($A5) = Start pixel row number of line
04258 ;   PENCOLUMN ($A6) = Start pixel column number of line
04259
04260 L.PIXELBYTEOFF  = $6A                   ; Within-row-offset to byte with pixel in PLAYFIELD
04261 L.BITPAT        = $6B                   ; 1-byte bit pattern for 4 pixels of same color
04262 L.DIRSAV        = $6E                   ; Saves DIRLEN
04263
04264 DRAWLINE        LDA #$55                ; Copy 1-byte bit pattern for 4 pixels of COLOR1
04265 DRAWLINE2       STA L.BITPAT            ;
04266                 LDA DIRLEN              ; Copy direction (and length) of line
04267                 STA L.DIRSAV            ;
04268                 AND #$7F                ; Strip direction bit
04269                 STA DIRLEN              ; Store length of line
04270
04271 LOOP029         LDY PENROW              ; Loop over length of line to be drawn
04272                 LDA PFMEMROWLO,Y        ; Point MEMPTR to start of pen's pixel row...
04273                 STA MEMPTR              ; ...in PLAYFIELD memory
04274                 LDA PFMEMROWHI,Y        ;
04275                 STA MEMPTR+1            ;
04276
04277                 LDA PENCOLUMN           ; Calc and store pen's byte-within-row offset
04278                 LSR A                   ;
04279                 LSR A                   ;
04280                 STA L.PIXELBYTEOFF      ;
04281
04282                 LDA PENCOLUMN           ; Calc pixel-within-byte index
04283                 AND #$03                ;
04284                 TAY                     ;
04285
04286                 LDA PIXELMASKTAB,Y      ; Pick mask to filter pixel in byte
04287                 AND L.BITPAT            ; ...AND with bit pattern for 4 pixels of same color
04288                 LDY L.PIXELBYTEOFF      ;
04289                 ORA (MEMPTR),Y          ; Blend byte with new pixel and PLAYFIELD byte
04290                 STA (MEMPTR),Y          ; ...and store it back in PLAYFIELD memory
04291
04292                 BIT L.DIRSAV            ; Check direction bit B7
04293                 BPL SKIP050             ;
04294                 INC PENROW              ; If B7 = 1 -> Increment pen's pixel row number
04295                 BNE SKIP051             ;
04296 SKIP050         INC PENCOLUMN           ; If B7 = 0 -> Increment pen's pixel column number
04297
04298 SKIP051         DEC DIRLEN              ;
04299                 BNE LOOP029             ; Next pixel of line
04300                 RTS                     ; Return
04301
04302 ;*******************************************************************************
04303 ;*                                                                             *
04304 ;*                                 UPDATTCOMP                                  *
04305 ;*                                                                             *
04306 ;*                       Update Attack Computer Display                        *
04307 ;*                                                                             *
04308 ;*******************************************************************************
04309
04310 ; DESCRIPTION
04311 ;
04312 ; Draws the blip of the tracked space object and the lock-on markers into the
04313 ; Attack Computer Display. The actual drawing follows a cycle of 11 game loop
04314 ; iterations (numbered by this subroutine as "blip cycles" 0..10), which can be
04315 ; divided into three phases:
04316 ;
04317 ; (1)  Blip cycle 0..4: Draw blip shape row-by-row
04318 ;
04319 ;      Draw the blip's shape into the Attack Computer Display, one row each blip
04320 ;      cycle. After 5 blip cycles the blip shape is complete and completely
04321 ;      visible because between blip cycles, that is, game loop iterations, the
04322 ;      PLAYFIELD is not erased (only the PLAYFIELD space objects are). Drawing
04323 ;      is executed by branching to entry DRAWLINE2 ($A784) of subroutine
04324 ;      DRAWLINE ($A782). The blip shape is retrieved from table BLIPSHAPTAB
04325 ;      ($BF6E).
04326 ;
04327 ; (2)  Blip cycle 5..9: Delay
04328 ;
04329 ;      Delay the execution of blip cycle 10.
04330 ;
04331 ; (3)  Blip cycle 10: Update Attack Computer Display
04332 ;
04333 ;      After verifying that the tracked space object is alive, calculate the
04334 ;      blip's relative top-left pixel column and row number. Resulting values
04335 ;      are in -11..11 and -6..4, relative to the blip's top-left reference
04336 ;      position at pixel column number 131 and pixel row number 77,
04337 ;      respectively. 
04338 ;
04339 ;      Filter the Attack Computer Display area: Only pixels of COLOR1 within the
04340 ;      inner frame area (a 28 pixel wide x 15 pixel high rectangle with its
04341 ;      top-left corner at pixel column number 120 and pixel row number 71) pass
04342 ;      the filter operation. This effectively erases the blip.
04343 ;
04344 ;      If the blip is within -2..+2 pixels off its horizontal reference position
04345 ;      (pixel column numbers 129..132) then the tracked space object is in x
04346 ;      lock-on. Draw the x lock-on marker. 
04347 ;
04348 ;      If the tracked space object is in x lock-on and the blip is within -2..+1
04349 ;      pixels off its vertical reference position (pixel column numbers 75..78)
04350 ;      then the tracked space object is in x and y lock-on. Draw also the y
04351 ;      lock-on marker. 
04352 ;
04353 ;      If the tracked space object is in x and y lock-on and the tracked space
04354 ;      object's z-coordinate < +3072 (+$0C**) <KM> then the tracked space object
04355 ;      is in x, y and z lock-on. Draw also the z lock-on marker. 
04356 ;
04357 ;      If the tracked space object is in x, y, and z lock-on (and thus in
04358 ;      optimal firing range) set the ISINLOCKON ($A3) flag.
04359 ;
04360 ;      The following sketches show the Attack Computer Display area overlaid
04361 ;      with the Attack Computer Display frame:
04362 ;
04363 ;          119                                 119
04364 ;      70 ##############################    70 ##############################
04365 ;         #         ....#....          #       #             #              #
04366 ;         #         ....#....          #       #             #              #
04367 ;         #         ....#....          #       #             #              #
04368 ;         #         ....#....          #       #             #              #
04369 ;         #      ###############       #       #......###############.......#
04370 ;         #XXXX  #  .........  #   XXXX#       #......#.............#.......#
04371 ;         #      #  ..$......  #       #       #......#....$........#.......#
04372 ;         ########  .........  #########       ########.............#########
04373 ;         #      #  .........  #       #       #......#.............#.......#
04374 ;         #      #  .........  #       #       #YYYY..#.............#...YYYY#
04375 ;         #      ###############       #       #......###############.......#
04376 ;         #         ....#....          #       #.............#..............#
04377 ;         #         ....#....          #       #             #              #
04378 ;         #         ....#....          #       #             #              #
04379 ;         #         ....#....          #       #             #              #
04380 ;         ##############################       ##############################
04381 ;
04382 ;         X = x lock-on marker                 Y = y lock-on marker
04383 ;         . = x lock-on blip zone              . = y lock-on blip zone
04384 ;         $ = Blip's top-left reference        $ = Blip's top-left reference
04385 ;             position                             position
04386 ;
04387 ;         119
04388 ;      70 ##############################
04389 ;         #             #              #
04390 ;         #             #              #
04391 ;         #             #              #
04392 ;         #             #              #
04393 ;         #      ###############       #
04394 ;         #      #             #       #
04395 ;         #      #    $        #       #
04396 ;         ########             #########
04397 ;         #      #             #       #
04398 ;         #      #             #       #
04399 ;         #      ###############       #
04400 ;         #             #              #
04401 ;         #             #              #
04402 ;         #        ZZ   #  ZZ          #
04403 ;         #        ZZ   #  ZZ          #
04404 ;         ##############################
04405 ;
04406 ;         Z = z lock-on marker
04407 ;         $ = Blip's top-left reference
04408 ;             position
04409
04410 L.SHIFTSHAPE    = $6C                   ; Saves shifted byte of blip shape bit pattern
04411
04412 UPDATTCOMP      LDX TRACKDIGIT          ; Load index of tracked space object
04413                 LDY BLIPCYCLECNT        ; Load blip cycle counter
04414                 CPY #5                  ;
04415                 BCS SKIP054             ; Skip drawing blip if blip cycle > 5
04416
04417 ;*** Blip cycle 0..4: Draw blip shape one row each cycle ***********************
04418                 LDA BLIPCOLUMN          ; Init pen's pixel column number...
04419                 STA PENCOLUMN           ; ...with top position of blip shape
04420                 LDA BLIPSHAPTAB,Y       ; Load bit pattern of one row of blip shape
04421 LOOP030         ASL A                   ; Shift bit pattern one position to the left
04422                 STA L.SHIFTSHAPE        ; Temporarily save shifted shape byte
04423                 BCC SKIP052             ; Skip if shifted-out bit = 0
04424
04425                 LDA #$81                ; Store "draw a line of 1 pixel length downward"
04426                 STA DIRLEN              ; ...for call to DRAWLINE2
04427
04428                 LDA BLIPROW             ; Init pen's pixel row number...
04429                 STA PENROW              ; ...with leftmost position of blip shape
04430                 LDA #$AA                ; Load 1-byte bit pattern for 4 pixels of COLOR2
04431                 JSR DRAWLINE2           ; Draw pixel on PLAYFIELD
04432
04433 SKIP052         INC PENCOLUMN           ; Move pen one pixel to the right
04434                 LDA L.SHIFTSHAPE        ; Reload shifted shape byte
04435                 BNE LOOP030             ; Next horizontal pixel of blip shape
04436
04437                 INC BLIPROW             ; Move pen one pixel downward
04438 SKIP053         INC BLIPCYCLECNT        ; Increment blip cycle counter
04439                 RTS                     ; Return
04440
04441 ;*** Blip cycle 5..9: Delay ****************************************************
04442 SKIP054         CPY #10                 ; Return if blip cycle < 10
04443                 BCC SKIP053             ;
04444
04445 ;*** Blip cycle 10: Calculate new blip pixel row and column numbers ************
04446                 LDA PL0LIFE,X           ; Skip if tracked object not alive
04447                 BEQ SKIP059             ;
04448
04449                 LDA XPOSHI,X            ; Map x-coordinate of tracked space obj to -11..11:
04450                 LDY XPOSSIGN,X          ; Skip if tracked object on left screen half (x >= 0)
04451                 BEQ SKIP055             ;
04452
04453                 CMP #12                 ; Skip if x of tracked obj < +$0C** (< 3327) <KM>
04454                 BCC SKIP056             ;
04455                 LDA #11                 ; Prep relative pixel column number of 11, skip
04456                 BPL SKIP056             ;
04457
04458 SKIP055         CMP #-11                ; Skip if x of tracked obj >= -($0B**) (>=-2816) <KM>
04459                 BCS SKIP056             ;
04460                 LDA #-11                ; Prep relative pixel column number of -11
04461
04462 SKIP056         CLC                     ; Add 131 (= blip's top-left reference pixel column)
04463                 ADC #131                ;
04464                 STA BLIPCOLUMN          ; BLIPCOLUMN := 131 + -11..11
04465
04466                 LDA YPOSHI,X            ; Map y-coordinate of tracked space obj to -6..4:
04467                 EOR #$FF                ; Mirror y-coordinate on y-axis (displacement of +1)
04468                 LDY YPOSSIGN,X          ; Skip if tracked obj on lower screen half (y < 0)
04469                 BNE SKIP057             ;
04470
04471                 CMP #5                  ; Skip if mirrored y of tracked obj < +$05** <KM>
04472                 BCC SKIP058             ;
04473                 LDA #4                  ; Prep relative pixel row number of 4, skip
04474                 BPL SKIP058             ;
04475
04476 SKIP057         CMP #-6                 ; Skip if mirrored y of tracked obj >= -($06**) <KM>
04477                 BCS SKIP058             ;
04478                 LDA #-6                 ; Prep relative pixel row number of -6
04479
04480 SKIP058         CLC                     ; Add 77 (= blip's top-left ref. pixel row number)
04481                 ADC #77                 ;
04482                 STA BLIPROW             ; BLIPROW := 77 + -6..4
04483
04484                 LDA #0                  ; Reset blip cycle
04485                 STA BLIPCYCLECNT        ;
04486
04487 ;*** Filter Attack Computer Display frame area *********************************
04488                                         ; PLAYFIELD address of top-left of Attack Computer
04489 PFMEM.C120R71   = PFMEM+71*40+120/4     ; Display's inner frame @ pixel column 120, row 71
04490
04491 SKIP059         LDA #<PFMEM.C120R71     ; Point MEMPTR to start of frame's...
04492                 STA MEMPTR              ; ...inner top-left corner at column 120, row 71...
04493                 LDA #>PFMEM.C120R71     ; ...in PLAYFIELD memory
04494                 STA MEMPTR+1            ;
04495
04496                 LDX #14                 ; Traverse a 28 x 15 pixel rect of PLAYFIELD memory
04497 LOOP031         LDY #6                  ;
04498 LOOP032         LDA (MEMPTR),Y          ; Load byte (4 pixels) from PLAYFIELD memory
04499                 AND #$55                ; Filter COLOR1 pixels
04500                 STA (MEMPTR),Y          ; Store byte (4 pixels) back to PLAYFIELD memory
04501                 DEY                     ;
04502                 BPL LOOP032             ; Next 4 pixels in x-direction
04503
04504                 CLC                     ; Add 40 to MEMPTR
04505                 LDA MEMPTR              ; (40 bytes = 160 pixels = 1 PLAYFIELD row of pixels)
04506                 ADC #40                 ;
04507                 STA MEMPTR              ;
04508                 BCC SKIP060             ;
04509                 INC MEMPTR+1            ;
04510
04511 SKIP060         DEX                     ;
04512                 BPL LOOP031             ; Next row of pixels in y-direction
04513
04514 ;*** Prepare lock-on marker checks *********************************************
04515                 LDX TRACKDIGIT          ; Preload index of tracked space obj to check z-range
04516                 INY                     ; Y := 0, preloaded value of ISINLOCKON
04517
04518 ;*** Draw lock-on markers ******************************************************
04519                                         ; PLAYFIELD addresses of
04520 PFMEM.C120R76   = PFMEM+76*40+120/4     ; ...x lock-on marker @ pixel column 120, row 76
04521 PFMEM.C144R76   = PFMEM+76*40+144/4     ; ...x lock-on marker @ pixel column 144, row 76
04522 PFMEM.C120R80   = PFMEM+80*40+120/4     ; ...y lock-on marker @ pixel column 120, row 80
04523 PFMEM.C144R80   = PFMEM+80*40+144/4     ; ...y lock-on marker @ pixel column 144, row 80
04524 PFMEM.C128R84   = PFMEM+84*40+128/4     ; ...z lock-on marker @ pixel column 128, row 84
04525 PFMEM.C128R85   = PFMEM+85*40+128/4     ; ...z lock-on marker @ pixel column 128, row 85
04526 PFMEM.C136R84   = PFMEM+84*40+136/4     ; ...z lock-on marker @ pixel column 136, row 84
04527 PFMEM.C136R85   = PFMEM+85*40+136/4     ; ...z lock-on marker @ pixel column 136, row 85
04528
04529                 LDA LOCKONLIFE          ; If lock-on lifetime expired redraw lock-on markers
04530                 BEQ SKIP061             ;
04531
04532                 DEC LOCKONLIFE          ; else decr lock-on lifetime, skip drawing markers
04533                 BNE SKIP062             ;
04534
04535 SKIP061         LDA BLIPCOLUMN          ; Skip x, y, and z lock-on marker if blip's...
04536                 CMP #129                ; ...top-left pixel column number not in 129..132
04537                 BCC SKIP062             ;
04538                 CMP #133                ;
04539                 BCS SKIP062             ;
04540
04541                 LDA #$AA                ; Draw x lock-on marker (4 horiz. pixels of COLOR2)
04542                 STA PFMEM.C120R76       ; ...at pixel column 120, row 76
04543                 STA PFMEM.C144R76       ; ...at pixel column 144, row 76
04544
04545                 LDA BLIPROW             ; Skip y and z lock-on marker if blip's...
04546                 CMP #75                 ; ...top-left pixel row number not in 75...78
04547                 BCC SKIP062             ;
04548                 CMP #79                 ;
04549                 BCS SKIP062             ;
04550
04551                 LDA #$AA                ; Draw y lock-on marker (4 horiz. pixels of COLOR2)
04552                 STA PFMEM.C120R80       ; ...at pixel column 120, row 80
04553                 STA PFMEM.C144R80       ; ...at pixel column 144, row 80
04554
04555                 LDA ZPOSHI,X            ; Skip z lock-on marker if z >= +$0C** (>= 3072) <KM>
04556                 CMP #12                 ;
04557                 BCS SKIP062             ;
04558
04559                 LDY #$A0                ; Draw z lock-on marker (2 horiz. pixels of COLOR2)
04560                 STY PFMEM.C128R84       ; ...at pixel column 128, row 84 (prep lock-on flag)
04561                 STY PFMEM.C128R85       ; ...at pixel column 128, row 85
04562                 STY PFMEM.C136R84       ; ...at pixel column 136, row 84
04563                 STY PFMEM.C136R85       ; ...at pixel column 136, row 85
04564
04565 SKIP062         STY ISINLOCKON          ; Store lock-on flag (> 0 -> Tracked obj locked on)
04566                 RTS                     ; Return
04567
04568 ;*******************************************************************************
04569 ;*                                                                             *
04570 ;*                                  HYPERWARP                                  *
04571 ;*                                                                             *
04572 ;*                              Handle hyperwarp                               *
04573 ;*                                                                             *
04574 ;*******************************************************************************
04575
04576 ; DESCRIPTION
04577 ;
04578 ; Handles the hyperwarp sequence, which transports our starship from one sector
04579 ; to another. It can be divided into four phases:
04580 ;
04581 ; (1)  ACCELERATION PHASE
04582 ;
04583 ;      The ACCELERATION PHASE is entered after the hyperwarp sequence has been
04584 ;      engaged in subroutine KEYBOARD ($AFFE) by pressing the 'H' key. The
04585 ;      Hyperwarp Target Marker appears and our starship begins to accelerate.
04586 ;      When our starship's velocity reaches 128 <KM/H> (the VELOCITY readout of
04587 ;      the Control Panel Display displays "50"), the STAR TRAIL phase is
04588 ;      entered. 
04589 ;
04590 ;      The Hyperwarp Target Marker is represented by a space object some fixed
04591 ;      distance away in front of our starship as PLAYER3. It has a lifetime of
04592 ;      144 game loop iterations and is tracked. Thus, tracking handling in
04593 ;      subroutine UPDATTCOMP ($A7BF) provides drawing the x and y lock-on
04594 ;      markers in the Attack Computer Display when the Hyperwarp Target Marker
04595 ;      is centered. 
04596 ;
04597 ;      A temporary arrival location on the Galactic Chart was saved when the
04598 ;      hyperwarp was engaged in subroutine KEYBOARD ($AFFE). During the
04599 ;      ACCELERATION PHASE (and the subsequent STAR TRAIL PHASE) this location is
04600 ;      constantly updated depending on how much the Hyperwarp Target Marker
04601 ;      veers off its center position.
04602 ;
04603 ;      The actual arrival hyperwarp marker row and column numbers on the
04604 ;      Galactic Chart are the sum of the temporary arrival hyperwarp marker row
04605 ;      and column numbers stored when engaging the hyperwarp in subroutine
04606 ;      KEYBOARD ($AFFE) and the number of Player/Missile (PM) pixels which the
04607 ;      Hyperwarp Target Marker is off-center vertically and horizontally,
04608 ;      respectively, at the end of the STAR TRAIL PHASE.
04609 ;
04610 ;      NOTE: The used vertical center value of 119 PM pixels is the PM pixel row
04611 ;      number of the top edge of the centered Hyperwarp Target Marker (from top
04612 ;      to bottom: 8 PM pixels to the start of Display List + 16 PM pixels blank
04613 ;      lines + 100 PM pixels to the vertical PLAYFIELD center - 5 PM pixels
04614 ;      relative offset of the Hyperwarp Target Marker's shape center to the
04615 ;      shape's top edge = 119 PM pixels). Recall also that PLAYERs at
04616 ;      single-line resolution have PM pixels that are half as high as they are
04617 ;      wide.
04618 ;
04619 ;      NOTE: The used horizontal center value of 125 PM pixels is the PM pixel
04620 ;      row number of the left edge of the centered Hyperwarp Target Marker (from
04621 ;      left to right: 127 PM pixels to the PLAYFIELD center - 3 PM pixels
04622 ;      relative offset of the Hyperwarp Target Marker's shape center to the
04623 ;      shape's left edge = 125 PM pixels).
04624 ;
04625 ;      If during the ACCELERATION PHASE (and the subsequent STAR TRAIL PHASE)
04626 ;      you switch the Front view to another view, the Hyperwarp Target Marker
04627 ;      changes to a random position which results in arriving at a random
04628 ;      destination sector.
04629 ;
04630 ;      During the ACCELERATION PHASE (and the subsequent STAR TRAIL PHASE) in
04631 ;      all but NOVICE missions, the Hyperwarp Target Marker veers off with
04632 ;      random velocity in x and y direction, which is changed during 6% of game
04633 ;      loop iterations. Table VEERMASKTAB ($BED7) limits the maximum veer-off
04634 ;      velocity depending on the mission level:
04635 ;
04636 ;      +-----------+-----------------------------+
04637 ;      |  Mission  |      Veer-Off Velocity      |
04638 ;      +-----------+-----------------------------+
04639 ;      | NOVICE    |                   0  <KM/H> |
04640 ;      | PILOT     |  -63..-16, +16..+63  <KM/H> |
04641 ;      | WARRIOR   |  -95..-16, +16..+95  <KM/H> |
04642 ;      | COMMANDER | -127..-16, +16..+127 <KM/H> |
04643 ;      +-----------+-----------------------------+
04644 ;
04645 ; (2)  STAR TRAIL PHASE
04646 ;
04647 ;      When our starship's velocity reaches a velocity of 128 <KM/H> (the
04648 ;      VELOCITY readout of the Control Panel Display displays "50"), in addition
04649 ;      to all effects of the ACCELERATION PHASE, multiple star trails begin to
04650 ;      appear while our starship continues to accelerate. Each star trail is
04651 ;      initialized in subroutine INITTRAIL ($A9B4).
04652 ;
04653 ; (3)  HYPERSPACE PHASE
04654 ;
04655 ;      When our starship's velocity reaches a velocity of 254 <KM/H> (the
04656 ;      VELOCITY readout of the Control Panel Display displays "99") our starship
04657 ;      enters the HYPERSPACE PHASE (the VELOCITY readout of the Control Panel
04658 ;      Display displays the infinity symbol).
04659 ;
04660 ;      During the first pass of the HYPERSPACE PHASE the hyperwarp state is set
04661 ;      to HYPERSPACE. This makes the stars and the Hyperwarp Target Marker
04662 ;      disappear in GAMELOOP ($A1F3). Then, the beeper sound pattern HYPERWARP
04663 ;      TRANSIT is played in subroutine BEEP ($B3A6), the hyperwarp distance and
04664 ;      required hyperwarp energy is calculated in subroutine CALCWARP ($B1A7),
04665 ;      and the title line is preloaded with "HYPERSPACE". Code execution returns
04666 ;      via calling subroutine CLEANUPWARP ($A98D) where program variables are
04667 ;      already initialized to their post-hyperwarp values.
04668 ;
04669 ;      During subsequent passes of the HYPERSPACE PHASE, the calculated
04670 ;      hyperwarp energy is decremented in chunks of 10 energy units. Code
04671 ;      execution returns via calling subroutine DECENERGY ($B86F), which
04672 ;      decrements our starship's energy. After the calculated hyperwarp energy
04673 ;      is spent the DECELERATION PHASE is entered.
04674 ;
04675 ; (4)  DECELERATION PHASE
04676 ;
04677 ;      The title line flashes "HYPERWARP COMPLETE", the star field reappears and
04678 ;      our starship decelerates to a stop. The Engines and the hyperwarp are
04679 ;      disengaged and stopped in subroutine ENDWARP ($A987), the arrival
04680 ;      coordinates on the Galactic Chart are initialized, as well as the
04681 ;      vicinity mask.
04682 ;
04683 ;      The vicinity mask limits the position vector components (coordinates) of
04684 ;      space objects in the arrival sector relative to our starship. The
04685 ;      vicinity mask is picked from table VICINITYMASKTAB ($BFB3) by an index
04686 ;      calculated by the arrival y-coordinate modulo 8: The more you have placed
04687 ;      the arrival hyperwarp marker in the vertical center of a sector on the
04688 ;      Galactic Chart, the closer space objects in this sector will be to our
04689 ;      starship. For example, if you placed the arrival hyperwarp marker exactly
04690 ;      in the vertical middle of the sector the index will be 3, thus the space
04691 ;      objects inside the arrival sector will be in the vicinity of <= 4095 <KM>
04692 ;      of our starship. The following table lists the possible coordinates
04693 ;      depending on the calculated index:
04694 ;
04695 ;      +-------+-----------------------+
04696 ;      | Index |    ABS(Coordinate)    |
04697 ;      +-------+-----------------------+
04698 ;      |   0   | <= 65535 ($FF**) <KM> |
04699 ;      |   1   | <= 65535 ($FF**) <KM> |
04700 ;      |   2   | <= 16383 ($3F**) <KM> |
04701 ;      |   3   | <=  4095 ($0F**) <KM> |
04702 ;      |   4   | <= 16383 ($3F**) <KM> |
04703 ;      |   5   | <= 32767 ($7F**) <KM> |
04704 ;      |   6   | <= 65535 ($FF**) <KM> |
04705 ;      |   7   | <= 65535 ($FF**) <KM> |
04706 ;      +-------+-----------------------+
04707 ;
04708 ;      If there is a starbase in the arrival sector, its x and y coordinates are
04709 ;      initialized to random values within the interval defined by the vicinity
04710 ;      mask by using subroutine RNDINVXY ($B7BE). Its z-coordinate is forced to
04711 ;      a value >= +$71** (+28928) <KM>. Its velocity vector components are set
04712 ;      to 0 <KM/H>. 
04713 ;
04714 ;      If there are Zylon ships in the arrival sector then a red alert is
04715 ;      initialized by setting the red alert lifetime to 255 game loop
04716 ;      iterations, playing the beeper sound pattern RED ALERT in subroutine BEEP
04717 ;      ($B3A6) and setting the title phrase to "RED ALERT".
04718
04719 HYPERWARP       LDY WARPSTATE           ; Return if hyperwarp not engaged
04720                 BEQ SKIP066             ;
04721
04722                 LDA VELOCITYLO          ; If velocity >= 254 <KM/H> skip to HYPERSPACE PHASE
04723                 CMP #254                ;
04724                 BCS SKIP067             ;
04725
04726                 CMP #128                ; If velocity < 128 <KM/H> skip to ACCELERATION PHASE
04727                 BCC SKIP063             ;
04728
04729 ;*** STAR TRAIL PHASE **********************************************************
04730                 JSR INITTRAIL           ; Init star trail
04731
04732 ;*** ACCELERATION PHASE ********************************************************
04733 SKIP063         LDA #3                  ; Track Hyperwarp Target Marker (PLAYER3)
04734                 STA TRACKDIGIT          ;
04735
04736                 LDA #SHAP.HYPERWARP     ; PLAYER3 is HYPERWARP TARGET MARKER (shape type 9)
04737                 STA PL3SHAPTYPE         ;
04738                 STA PL3LIFE             ; PLAYER3 lifetime := 144 game loops
04739
04740                 LDA #$1F                ; PLAYER3 z-coordinate := $1F** (7936..8191) <KM>
04741                 STA PL3ZPOSHI           ;
04742
04743                 SEC                     ; New arrival hyperwarp marker row number is...
04744                 LDA PL3ROWNEW           ; WARPARRVROW := WARPTEMPROW + PL3ROWNEW...
04745                 SBC #119                ; ... - 119 PM pixels (top edge of centered...
04746                 CLC                     ; ...Hyperwarp Target Marker)
04747                 ADC WARPTEMPROW         ;
04748                 AND #$7F                ; Limit WARPARRVROW to 0..127
04749                 STA WARPARRVROW         ;
04750
04751                 SEC                     ; New arrival hyperwarp marker column number is...
04752                 LDA PL3COLUMN           ; WARPARRVCOLUMN := WARPTEMPCOLUMN + PL3COLUMN...
04753                 SBC #125                ; ... - 125 PM pixels (left edge of centered...
04754                 CLC                     ; ...Hyperwarp Target Marker)
04755                 ADC WARPTEMPCOLUMN      ;
04756                 AND #$7F                ; Limit WARPARRVCOLUMN to 0..127
04757                 STA WARPARRVCOLUMN      ;
04758
04759                 LDA MISSIONLEVEL        ; Skip if NOVICE mission
04760                 BEQ SKIP065             ;
04761
04762                 LDA RANDOM              ; Prep random number
04763                 LDY SHIPVIEW            ; Skip if in Front view
04764                 BEQ SKIP064             ;
04765
04766                 STA PL3COLUMN           ; Randomize PM pixel row and column number...
04767                 STA PL3ROWNEW           ; ...of Hyperwarp Target Marker
04768
04769 SKIP064         CMP #16                 ; Return in 94% (240:256) of game loops
04770                 BCS SKIP066             ;
04771
04772 ;*** Veer off Hyperwarp Target Marker and return *******************************
04773 SKIP065         LDA RANDOM              ; Prep random x-velocity of Hyperwarp Target Marker
04774                 ORA #$10                ; Velocity value >= 16 <KM/H>
04775                 AND VEERMASK            ; Limit velocity value by mission level
04776                 STA PL3XVEL             ; PLAYER3 x-velocity := velocity value
04777
04778                 LDA RANDOM              ; Prep random y-velocity of Hyperwarp Target Marker
04779                 ORA #$10                ; Velocity value >= 16 <KM/H>
04780                 AND VEERMASK            ; Limit velocity value by mission level
04781                 STA PL3YVEL             ; PLAYER3 y-velocity := velocity value
04782 SKIP066         RTS                     ; Return
04783
04784 ;*** HYPERSPACE PHASE **********************************************************
04785 SKIP067         TYA                     ; Skip if already in HYPERSPACE PHASE
04786                 BMI SKIP068             ;
04787
04788 ;*** HYPERSPACE PHASE (First pass) *********************************************
04789                 LDA #$FF                ; Set hyperwarp state to HYPERSPACE PHASE
04790                 STA WARPSTATE           ;
04791
04792                 LDX #$00                ; Play beeper sound pattern HYPERWARP TRANSIT
04793                 JSR BEEP                ;
04794
04795                 JSR CALCWARP            ; Calc hyperwarp energy
04796
04797                 LDY #$1B                ; Prep title phrase "HYPERSPACE"
04798                 JMP CLEANUPWARP         ; Return via CLEANUPWARP
04799
04800 ;*** HYPERSPACE PHASE (Second and later passes) ********************************
04801 SKIP068         DEC WARPENERGY          ; Decrement energy in chunks of 10 energy units
04802                 BEQ SKIP069             ; Skip to DECELERATION PHASE if hyperwarp energy zero
04803
04804                 LDX #2                  ; ENERGY := ENERGY - 10 and return
04805                 JMP DECENERGY           ;
04806
04807 ;*** DECELERATION PHASE ********************************************************
04808 SKIP069         LDY #$19                ; Prep title phrase "HYPERWARP COMPLETE"
04809                 JSR ENDWARP             ; Stop our starship
04810
04811                 LDA WARPARRVCOLUMN      ; Make the arrival hyperwarp marker column number...
04812                 STA WARPDEPRCOLUMN      ; ...the departure hyperwarp marker column number
04813                 LDA WARPARRVROW         ; Make the arrival hyperwarp marker row number...
04814                 STA WARPDEPRROW         ; ...the departure hyperwarp marker row number
04815
04816                 LSR A                   ; B3..1 of arrival hyperwarp marker row number...
04817                 AND #$07                ; ...pick vicinity mask
04818                 TAX                     ;
04819                 LDA VICINITYMASKTAB,X   ;
04820                 STA VICINITYMASK        ; Store vicinity mask (limits space obj coordinates)
04821
04822                 LDY ARRVSECTOR          ; Make the arrival sector the current sector
04823                 STY CURRSECTOR          ;
04824
04825 ;*** Init starbase in arrival sector *******************************************
04826                 LDA #0                  ; Clear starbase-in-sector flag
04827                 STA ISSTARBASESECT      ;
04828
04829                 LDX GCMEMMAP,Y          ; Skip if no starbase in arrival sector
04830                 BPL SKIP070             ;
04831
04832                 LDA #$FF                ; Set starbase-in-sector flag
04833                 STA ISSTARBASESECT      ;
04834
04835 ;*** Set position vector and velocity vector of starbase ***********************
04836                 LDY #0                  ;
04837 LOOP033         LDA #0                  ; Loop over all coordinates of starbase
04838                 STA PL2ZVEL,Y           ; Starbase velocity vector component := 0 <KM/H>
04839                 LDA #1                  ;
04840                 STA PL2ZPOSSIGN,Y       ; Starbase coordinate sign := + (positive)
04841                 LDA RANDOM              ; Prep random number...
04842                 AND VICINITYMASK        ; ...limit number range by vicinity mask, then...
04843                 STA PL2ZPOSHI,Y         ; ...store in starbase coordinate (high byte)
04844
04845                 TYA                     ;
04846                 CLC                     ;
04847                 ADC #NUMSPCOBJ.ALL      ;
04848                 TAY                     ;
04849                 CMP #NUMSPCOBJ.ALL*3    ;
04850                 BCC LOOP033             ; Next starbase coordinate
04851
04852                 LDA PL2ZPOSHI           ; Force starbase z-coordinate >= +$71** <KM>
04853                 ORA #$71                ;
04854                 STA PL2ZPOSHI           ;
04855                 LDX #2                  ; Randomly invert starbase x and y coordinates...
04856                 JMP RNDINVXY            ; ...and return
04857
04858 ;*** Flash red alert if Zylon sector entered ***********************************
04859 SKIP070         BEQ SKIP071             ; Skip if no Zylon ships in sector
04860
04861                 LDA #255                ; Red alert lifetime := 255 game loops
04862                 STA REDALERTLIFE        ;
04863
04864                 LDX #$06                ; Play beeper sound pattern RED ALERT
04865                 JSR BEEP                ;
04866
04867                 LDY #$75                ; Set title phrase "RED ALERT"
04868                 JSR SETTITLE            ;
04869
04870 SKIP071         RTS                     ; Return
04871
04872 ;*******************************************************************************
04873 ;*                                                                             *
04874 ;*                                  ABORTWARP                                  *
04875 ;*                                                                             *
04876 ;*                               Abort hyperwarp                               *
04877 ;*                                                                             *
04878 ;*******************************************************************************
04879
04880 ; DESCRIPTION
04881 ;
04882 ; Aborts hyperwarp.
04883 ;
04884 ; This subroutine is entered from subroutine KEYBOARD ($AFFE). It subtracts 100
04885 ; energy units for aborting the hyperwarp and preloads the title phrase with
04886 ; "HYPERWARP ABORTED". Code execution continues into subroutine ENDWARP
04887 ; ($A987). 
04888
04889 ABORTWARP       LDX #1                  ; ENERGY := ENERGY - 100 after hyperwarp abort
04890                 JSR DECENERGY           ;
04891
04892                 LDY #$17                ; Prep title phrase "HYPERWARP ABORTED"
04893
04894 ;*******************************************************************************
04895 ;*                                                                             *
04896 ;*                                   ENDWARP                                   *
04897 ;*                                                                             *
04898 ;*                                End hyperwarp                                *
04899 ;*                                                                             *
04900 ;*******************************************************************************
04901
04902 ; DESCRIPTION
04903 ;
04904 ; Ends hyperwarp.
04905 ;
04906 ; This subroutine stops our starship's Engines and resets the hyperwarp state.
04907 ; Code execution continues into subroutine CLEANUPWARP ($A98D).
04908
04909 ENDWARP         LDA #0                  ; Stop Engines
04910                 STA NEWVELOCITY         ;
04911                 STA WARPSTATE           ; Disengage hyperwarp
04912
04913 ;*******************************************************************************
04914 ;*                                                                             *
04915 ;*                                 CLEANUPWARP                                 *
04916 ;*                                                                             *
04917 ;*                        Clean up hyperwarp variables                         *
04918 ;*                                                                             *
04919 ;*******************************************************************************
04920
04921 ; DESCRIPTION
04922 ;
04923 ; Cleans up after a hyperwarp.
04924 ;
04925 ; This subroutine restores many hyperwarp related variables to their
04926 ; post-hyperwarp values: The number of used space objects is set to the regular
04927 ; value of 16 (5 PLAYER space objects + 12 PLAYFIELD space objects (stars)), our
04928 ; starship's velocity (high byte) is cleared as well as the explosion lifetime,
04929 ; the hit badness, the PLAYER3 shape type (Hyperwarp Target Marker), the Engines
04930 ; energy drain rate, and the lifetimes of the PLAYERs. The docking state is
04931 ; reset as well as the tracking digit. The title phrase is updated with either
04932 ; "HYPERSPACE" or "HYPERWARP ABORTED".
04933 ;
04934 ; INPUT
04935 ;
04936 ;   Y = Title phrase offset. Used values are: 
04937 ;     $17 -> "HYPERWARP ABORTED"
04938 ;     $1B -> "HYPERSPACE"
04939
04940 CLEANUPWARP     LDA #NUMSPCOBJ.NORM-1   ; Set normal number of space objects
04941                 STA MAXSPCOBJIND        ; (5 PLAYER spc objs + 12 PLAYFIELD spc objs (stars))
04942
04943                 LDA #0                  ;
04944                 STA VELOCITYHI          ; Turn off hyperwarp velocity
04945                 STA EXPLLIFE            ; Explosion lifetime := 0 game loops
04946                 STA HITBADNESS          ; HITBADNESS := NO HIT
04947                 STA PL3SHAPTYPE         ; Clear PLAYER3 shape type
04948                 STA DRAINENGINES        ; Clear Engines energy drain rate
04949                 CPY #$17                ; Skip if hyperwarp was aborted
04950                 BEQ SKIP072             ;
04951
04952                 STA PL0LIFE             ; Zylon ship 0 lifetime := 0 game loops
04953                 STA PL1LIFE             ; Zylon ship 1 lifetime := 0 game loops
04954
04955 SKIP072         STA PL2LIFE             ; Zylon photon torpedo lifetime := 0 game loops
04956                 STA PL3LIFE             ; Hyperwarp Target Marker lifetime := 0 game loops
04957                 STA PL4LIFE             ; Photon torpedo 1 lifetime := 0  game loops
04958                 STA DOCKSTATE           ; DOCKSTATE := NO DOCKING
04959                 STA TRACKDIGIT          ; Clear index of tracked space object
04960                 JMP SETTITLE            ; Set title phrase and return
04961
04962 ;*******************************************************************************
04963 ;*                                                                             *
04964 ;*                                  INITTRAIL                                  *
04965 ;*                                                                             *
04966 ;*         Initialize star trail during STAR TRAIL PHASE of hyperwarp          *
04967 ;*                                                                             *
04968 ;*******************************************************************************
04969
04970 ; DESCRIPTION
04971 ;
04972 ; BACKGROUND
04973 ;
04974 ; Star trails are displayed during the STAR TRAIL PHASE, that is, after the
04975 ; ACCELERATION PHASE and before the HYPERSPACE PHASE of the hyperwarp. 
04976 ;
04977 ; A star trail is formed by 6 stars represented by 6 PLAYFIELD space objects
04978 ; with continuous position vector indices in 17..48 (indices are wrapped around
04979 ; when greater than 48). Between the creation of two star trails there is delay
04980 ; of 4 game loop iterations.
04981 ;
04982 ; DETAILS
04983 ;
04984 ; This subroutine first decrements this star trail creation delay, returning if
04985 ; the delay is still counting down. If the delay falls below 0 then it continues
04986 ; accelerating our starship's velocity toward hyperwarp speed and then creates a
04987 ; new star trail:
04988 ;
04989 ; First, it raises the maximum index of used space objects to 48 (increasing the
04990 ; number of displayed space objects to 49), resets the star trail creation delay
04991 ; to 4 game loop iterations, then forms a new star trail of 6 stars represented
04992 ; by 6 PLAYFIELD space objects. The x and y coordinates for all 6 stars are the
04993 ; same, picked randomly from tables WARPSTARXTAB ($BB3A) and WARPSTARYTAB
04994 ; ($BB3E), respectively, with their signs changed randomly. Their z-coordinates
04995 ; are computed in increasing depth from at least +4608 (+$12**) <KM> in
04996 ; intervals of +80 (+$0050) <KM>. Their velocity vector components are set to 0
04997 ; <KM/H>.
04998
04999 L.RANGE         = $68                   ; z-coordinate of star in star trail (16-bit value)
05000 L.TRAILCNT      = $6E                   ; Star's index in star trail. Used values are: 0..5.
05001
05002 INITTRAIL       DEC TRAILDELAY          ; Decrement star trail delay
05003                 BPL SKIP074             ; Return if delay still counting
05004
05005                 LDA #1                  ; Turn on hyperwarp velocity
05006                 STA VELOCITYHI          ;
05007
05008                 LDA #NUMSPCOBJ.ALL-1    ; Max index of space objects (for star trail stars)
05009                 STA MAXSPCOBJIND        ;
05010
05011                 LDA #3                  ; Star trail delay := 3(+1) game loops
05012                 STA TRAILDELAY          ;
05013
05014                 LDX TRAILIND            ; Next avail. space obj index for star of star trail
05015
05016                 LDA #$12                ; Star z-coordinate := >= +$12** (+4608) <KM>
05017                 STA L.RANGE+1           ;
05018
05019                 LDA RANDOM              ; Calc random index to pick initial star coordinates
05020                 AND #$03                ;
05021                 TAY                     ;
05022                 LDA WARPSTARXTAB,Y      ; Pick x-coordinate (high byte) of star from table
05023                 STA XPOSHI,X            ;
05024                 LDA WARPSTARYTAB,Y      ;
05025                 STA YPOSHI,X            ; Pick y-coordinate (high byte) of star from table
05026                 JSR RNDINVXY            ; Randomize signs of x and y coordinates of star
05027
05028                 TXA                     ; Save space object index
05029                 TAY                     ;
05030                 LDA #5                  ; Loop over 5(+1) stars that form the star trail
05031                 STA L.TRAILCNT          ; Store star counter of star trail
05032
05033 LOOP034         CLC                     ; Place stars in z-coordinate intervals of +80 <KM>
05034                 LDA L.RANGE             ;
05035                 ADC #80                 ;
05036                 STA L.RANGE             ;
05037                 STA ZPOSLO,X            ;
05038                 LDA L.RANGE+1           ;
05039                 ADC #0                  ;
05040                 STA L.RANGE+1           ;
05041                 STA ZPOSHI,X            ;
05042
05043                 LDA #0                  ; Star's velocity vector components := 0 <KM/H>
05044                 STA ZVEL,X              ;
05045                 STA XVEL,X              ;
05046                 STA YVEL,X              ;
05047                 LDA #1                  ; Star's z-coordinate sign := + (= ahead of starship)
05048                 STA ZPOSSIGN,X          ;
05049
05050                 LDA #99                 ; Init pixel row and column numbers to magic...
05051                 STA PIXELROWNEW,X       ; ...offscreen value (triggers automatic recalc in...
05052                 STA PIXELCOLUMN,X       ; ...GAMELOOP's calls to SCREENCOLUMN and SCREENROW)
05053
05054                 JSR COPYPOSXY           ; Copy x and y coordinate from previous star in trail
05055
05056                 DEX                     ; Decrement space object index to next star
05057                 CPX #NUMSPCOBJ.NORM     ; If index reaches minimum value...
05058                 BCS SKIP073             ;
05059                 LDX #NUMSPCOBJ.ALL-1    ; ...wrap-around to maximum space object index
05060 SKIP073         DEC L.TRAILCNT          ;
05061                 BPL LOOP034             ; Next star of star trail
05062
05063                 STX TRAILIND            ; Save space object index of star trail's last star
05064 SKIP074         RTS                     ; Return
05065
05066 ;*******************************************************************************
05067 ;*                                                                             *
05068 ;*                                 PROJECTION                                  *
05069 ;*                                                                             *
05070 ;*         Calculate pixel column (or row) number from position vector         *
05071 ;*                                                                             *
05072 ;*******************************************************************************
05073
05074 ; Calculates the pixel column (or row) number of a position vector x (or y)
05075 ; component relative to the PLAYFIELD center by computing the perspective
05076 ; projection quotient
05077 ;
05078 ;     QUOTIENT := DIVIDEND / DIVISOR * 128
05079 ;
05080 ; with
05081 ;
05082 ;     DIVIDEND := ABS(x-coordinate (or y-coordinate)) / 2
05083 ;     DIVISOR  := ABS(z-coordinate) / 2  
05084 ;
05085 ; If the QUOTIENT is in 0..255, it is used as an index to pick the pixel column
05086 ; (or row) number from table MAPTO80 ($0DE9), returning values in 0..80.
05087 ;
05088 ; If the QUOTIENT is larger than 255 ("dividend overflow") or if the
05089 ; z-coordinate = 0 ("division by zero") then the error value 255 is returned.
05090 ;
05091 ; INPUT
05092 ;
05093 ;   X                   = Position vector index. Used values are: 0..48.
05094 ;   DIVIDEND ($6A..$6B) = Dividend (positive 16-bit value), contains the
05095 ;                         absolute value of the x (or y) coordinate.
05096 ;
05097 ; OUTPUT
05098 ;
05099 ;   A = Pixel column (or row) number relative to PLAYFIELD center. Used values
05100 ;       are: 
05101 ;     0..80 -> Pixel number
05102 ;     255   -> Error value indicating "dividend overflow" or "division by zero"
05103
05104 L.DIVISOR       = $68                   ; Divisor (16-bit value)
05105 L.QUOTIENT      = $6D                   ; Division result (unsigned 8-bit value)
05106 L.LOOPCNT       = $6E                   ; Division loop counter. Used values are: 7..0.
05107
05108 PROJECTION      LDA #0                  ; Init quotient result
05109                 STA L.QUOTIENT          ;
05110
05111                 LDA #7                  ; Init division loop counter
05112                 STA L.LOOPCNT           ;
05113
05114                 LSR DIVIDEND+1          ; DIVIDEND := x-coordinate (or y-coordinate) / 2
05115                 ROR DIVIDEND            ; (division by 2 to make B15 = 0?) (?)
05116
05117                 LDA SHIPVIEW            ; Skip if in Aft view
05118                 BNE SKIP075             ;
05119
05120                 LDA ZPOSHI,X            ; If in Front view -> DIVISOR := z-coordinate / 2
05121                 LSR A                   ; (division by 2 to make B15 = 0?) (?)
05122                 STA L.DIVISOR+1         ;
05123                 LDA ZPOSLO,X            ;
05124                 ROR A                   ;
05125                 STA L.DIVISOR           ;
05126                 JMP LOOP035             ;
05127
05128 SKIP075         SEC                     ; If in Aft view -> DIVISOR := - z-coordinate / 2
05129                 LDA #0                  ; (division by 2 to make B15 = 0?) (?)
05130                 SBC ZPOSLO,X            ;
05131                 STA L.DIVISOR           ;
05132                 LDA #0                  ;
05133                 SBC ZPOSHI,X            ;
05134                 LSR A                   ;
05135                 STA L.DIVISOR+1         ;
05136                 ROR L.DIVISOR           ;
05137
05138 LOOP035         ASL L.QUOTIENT          ; QUOTIENT := DIVIDEND / DIVISOR * 128
05139                 SEC                     ;
05140                 LDA DIVIDEND            ;
05141                 SBC L.DIVISOR           ;
05142                 TAY                     ;
05143                 LDA DIVIDEND+1          ;
05144                 SBC L.DIVISOR+1         ;
05145                 BCC SKIP076             ;
05146
05147                 STA DIVIDEND+1          ;
05148                 STY DIVIDEND            ;
05149                 INC L.QUOTIENT          ;
05150
05151 SKIP076         ASL DIVIDEND            ;
05152                 ROL DIVIDEND+1          ;
05153                 BCC SKIP077             ;
05154
05155                 LDA #255                ; Return 255 if division by zero or dividend overflow
05156                 RTS                     ;
05157
05158 SKIP077         DEC L.LOOPCNT           ;
05159                 BPL LOOP035             ; Next division loop iteration
05160
05161                 LDY L.QUOTIENT          ; Prep with quotient
05162                 LDA MAPTO80,Y           ; Pick and return pixel column (or row) number...
05163 SKIP078         RTS                     ; ...relative to PLAYFIELD center
05164
05165 ;*******************************************************************************
05166 ;*                                                                             *
05167 ;*                                  MANEUVER                                   *
05168 ;*                                                                             *
05169 ;*     Maneuver our starship's and Zylon photon torpedoes and Zylon ships      *
05170 ;*                                                                             *
05171 ;*******************************************************************************
05172
05173 ; DESCRIPTION
05174 ;
05175 ; This subroutine maneuvers both of our starship's photon torpedoes, the single
05176 ; Zylon photon torpedo, and the one or two Zylon ships that are simultaneously
05177 ; displayed on the screen. It also creates meteors and new Zylon ships. This
05178 ; subroutine is executed only if our starship is not in a starbase sector and
05179 ; hyperwarp is not engaged.
05180 ;
05181 ; BACKGROUND
05182 ;
05183 ; When a Zylon ship is initialized, a "flight pattern" is assigned to it. There
05184 ; are 3 flight patterns (0, 1, and 4) which are picked from table ZYLONFLPATTAB
05185 ; ($BF91).
05186 ;
05187 ; The flight pattern determines the maximum velocity with which a Zylon ship can
05188 ; move along each axis of the 3D coordinate system, that is the maximum value of
05189 ; a velocity vector component. Velocity vector components for Zylon ships are
05190 ; picked from the Zylon velocity table ZYLONVELTAB ($BF99):
05191 ;
05192 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05193 ; | Velocity Index  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
05194 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05195 ; | Velocity <KM/H> | +62 | +30 | +16 |  +8 |  +4 |  +2 |  +1 |  0  |
05196 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05197 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05198 ; | Velocity Index  |  8  |  9  |  10 |  11 |  12 |  13 |  14 |  15 |
05199 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05200 ; | Velocity <KM/H> |  0  |  -1 |  -2 |  -4 |  -8 | -16 | -30 | -62 |
05201 ; +-----------------+-----+-----+-----+-----+-----+-----+-----+-----+
05202 ;
05203 ; The index into the Zylon velocity table ZYLONVELTAB ($BF99) corresponding to
05204 ; the maximum velocity is called the "maximum velocity index". The following
05205 ; table shows the flight patterns, their maximum velocity indices, and their
05206 ; corresponding velocities:
05207 ;
05208 ; +----------------+------------------+------------------+
05209 ; | Flight Pattern | Maximum Velocity | Maximum Velocity |
05210 ; |                |      Index       |                  |
05211 ; +----------------+------------------+------------------+
05212 ; |       0        |         0        |    +62 <KM/H>    |
05213 ; |       0        |        15        |    -62 <KM/H>    |
05214 ; |       1        |         1        |    +30 <KM/H>    |
05215 ; |       1        |        14        |    -30 <KM/H>    |
05216 ; |       4        |         4        |     +4 <KM/H>    |
05217 ; |       4        |        11        |     -4 <KM/H>    |
05218 ; +----------------+------------------+------------------+
05219 ;
05220 ; Because flight pattern 0 produces the fastest-moving Zylon ships, which
05221 ; maneuver aggressively, it is called the "attack flight pattern".
05222 ;
05223 ; Each Zylon ship has a set of 3 maximum velocity indices, one for each of its
05224 ; velocity vector components.
05225 ;
05226 ; Each Zylon ship has also one more set of 3 velocity indices, called "Zylon
05227 ; velocity indices", one for each of its velocity vector components. They are
05228 ; used to pick the current values of the velocity vector components from the
05229 ; Zylon velocity table ZYLONVELTAB ($BF99).
05230 ;
05231 ; In order to maneuver Zylon ships this subroutine uses the concept of
05232 ; "milestone velocity indices". By using delay timers, called "Zylon timers",
05233 ; this subroutine gradually increases or decreases the Zylon velocity indices
05234 ; with every game loop iteration to eventually match the corresponding milestone
05235 ; velocity indices. By incrementing a Zylon velocity index a Zylon ship
05236 ; accelerates toward the negative direction of a coordinate axis. By
05237 ; decrementing a Zylon velocity index a Zylon ship accelerates toward the
05238 ; positive direction of a coordinate axis. If one milestone velocity index is
05239 ; matched or a "milestone timer" has counted down to 0, a new milestone velocity
05240 ; index is calculated and the matching of the current Zylon velocity indices
05241 ; with the new milestone velocity indices repeats.
05242 ;
05243 ; DETAILS
05244 ;
05245 ; For quick lookup, the following table lists the PLAYERs and what space objects
05246 ; they represent in this subroutine:
05247 ;
05248 ; +--------+---------------------------------+
05249 ; | PLAYER |           Represents            |
05250 ; +--------+---------------------------------+
05251 ; |    0   | Zylon Ship 0                    |
05252 ; |    1   | Zylon Ship 1                    |
05253 ; |    2   | Zylon Photon Torpedo, Meteor    |
05254 ; |    3   | Our starship's Photon Torpedo 0 |
05255 ; |    4   | Our starship's Photon Torpedo 1 |
05256 ; +--------+---------------------------------+
05257 ;
05258 ; This subroutine executes the following steps:
05259 ;
05260 ; (1)  Update the x and y velocity vector components of both of our starship's
05261 ;      photon torpedoes 0 and 1.
05262 ;
05263 ;      The x and y velocity vector components of both of our starship's photon
05264 ;      torpedoes 0 and 1 are only updated if they are tracking (homing in on) a
05265 ;      target.
05266 ;
05267 ;      To update the y-velocity vector components of both of our starship's
05268 ;      photon torpedoes 0 and 1 the PLAYER row number difference between the
05269 ;      PLAYER of tracked target space object and the current location of the
05270 ;      PLAYER of our starship's photon torpedo 0 is passed to subroutine
05271 ;      HOMINGVEL ($AECA). It returns the new y-velocity vector component value
05272 ;      for both of our starship's photon torpedoes in <KM/H>. If the target is
05273 ;      located below our starship's photon torpedo 0 a value of 0 <KM/H> is
05274 ;      used.
05275 ;
05276 ;      NOTE: The new y-velocity vector components depend only on the PLAYER row
05277 ;      number of our starship's photon torpedo 0.
05278 ;
05279 ;      To update the x-velocity vector components of both of our starship's
05280 ;      photon torpedoes, the above calculation is repeated for the PLAYER column
05281 ;      numbers of each of our starship's photon torpedoes 0 and 1.
05282 ;
05283 ; (2)  Make the Zylon ships follow the rotation of our starship.
05284 ;
05285 ;      If you rotate our starship away from Zylon ships they adjust their course
05286 ;      such that they reappear in our starship's view.
05287 ;
05288 ;      This is achieved by 4 Zylon timers, one for each of both Zylon ships'
05289 ;      current x and y Zylon velocity indices. The Zylon timers are decremented
05290 ;      every game loop iteration. If any of them reach a value of 0, the
05291 ;      corresponding Zylon velocity index is incremented or decremented
05292 ;      depending on the current joystick position.
05293 ;
05294 ;      For example, if the Zylon timer for the x-velocity of Zylon ship 0
05295 ;      reaches 0 and at the same time the joystick is pushed left then the
05296 ;      x-Zylon velocity index of this Zylon ship is incremented. This
05297 ;      accelerates the Zylon ship toward negative x-direction ("left"): The
05298 ;      Zylon ship follows our starship's rotation. This works in Aft view, too,
05299 ;      where the direction of change of the Zylon velocity index is reversed.
05300 ;      After setting the new Zylon velocity index, it is used to pick a new
05301 ;      Zylon timer value for this Zylon velocity index: 
05302 ;
05303 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05304 ;      | Velocity Index                 |  0 |  1 |  2 |  3 |  4 |  5 |  6 |  7 |
05305 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05306 ;      | Zylon Timer Value (Game Loops) |  0 |  2 |  4 |  6 |  8 | 10 | 12 | 14 |
05307 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05308 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05309 ;      | Velocity Index                 |  8 |  9 | 10 | 11 | 12 | 13 | 14 | 15 |
05310 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05311 ;      | Zylon Timer Value (Game Loops) | 14 | 12 | 10 |  8 |  6 |  4 |  2 |  0 |
05312 ;      +--------------------------------+----+----+----+----+----+----+----+----+
05313 ;
05314 ; (3)  Update the x and y velocity vector components of the single Zylon photon
05315 ;      torpedo.
05316 ;
05317 ;      If a Zylon photon torpedo is moving toward our starship then update its x
05318 ;      and y velocity vector components. They are picked from table
05319 ;      ZYLONHOMVELTAB ($BF85) and depend on the mission level. The signs of the
05320 ;      velocity vector components are always set such that the Zylon photon
05321 ;      torpedo is guided toward our starship. 
05322 ;
05323 ; (4)  Create a meteor?
05324 ;
05325 ;      If PLAYER2, the PLAYER to represent a meteor, is either initial or not
05326 ;      alive, then attempt in 7 out of 8 game loop iterations to create a new
05327 ;      meteor. 
05328 ;
05329 ;      With a probability of 2% (4:256) a new meteor is created: Its shape type
05330 ;      is set to METEOR, its position vector components to random coordinates in
05331 ;      subroutine INITPOSVEC ($B764), its lifetime to 60 game loop iterations,
05332 ;      and its velocity vector components (velocities) to x-velocity: 0 <KM/H>,
05333 ;      y-velocity: 0 <KM/H>, z-velocity: -8 <KM/H>. Then code execution returns.
05334 ;
05335 ; (5)  Toggle Zylon ship control.
05336 ;
05337 ;      Every other game loop iteration, the program takes control of and
05338 ;      maneuvers the other Zylon ship.
05339 ;
05340 ; (6)  Create new Zylon ship?
05341 ;
05342 ;      If the program-controlled Zylon ship is not alive, check if both Zylon
05343 ;      ships are not alive and this is an empty sector. If so, then attempt to
05344 ;      create a meteor. Otherwise create a new Zylon ship with infinite
05345 ;      lifetime. Randomly pick its shape type from table ZYLONSHAPTAB ($BF89)
05346 ;      (BASESTAR, ZYLON CRUISER, or ZYLON FIGHTER) and its flight pattern from
05347 ;      table ZYLONFLPATTAB ($BF91) (attack flight pattern 0 is always picked in
05348 ;      a NOVICE mission). Then set the milestone timer to 1 game loop iteration
05349 ;      and the position vector of the Zylon ship to a position of at least
05350 ;      +28928 (+$71**) <KM> in front of our starship. The y-coordinate depends
05351 ;      on the value of VICINITYMASK ($C7). The x-coordinate is the sum of the
05352 ;      y-coordinate plus at least 4864..5119 ($13**) <KM>. Randomly choose the
05353 ;      signs of the x and y coordinates.
05354 ;
05355 ; (7)  Set the current flight pattern to attack flight pattern?
05356 ;
05357 ;      The current flight pattern of the Zylon ship will change to attack flight
05358 ;      pattern if it is close enough (z-coordinate < +8192 (+$20**) <KM>) and
05359 ;      one of the following conditions is met:
05360 ;
05361 ;      o   The Zylon ship is located behind our starship.
05362 ;
05363 ;      o   The shape of the Zylon ship is not initial and does not currently
05364 ;          appear as a blip in the Long-Range Scan view.
05365 ;
05366 ; (8)  Update the back-attack flag and the milestone velocity indices.
05367 ;
05368 ;      The milestone timer is decremented for the program-controlled Zylon ship.
05369 ;      If this timer reaches a value of 0 the following steps are executed:
05370 ;
05371 ;      o   The milestone timer is reset to a value of 120 game loop iterations.
05372 ;
05373 ;      o   The back-attack flag is updated. It determines if the
05374 ;          program-controlled Zylon ship not only attacks from the front of our
05375 ;          starship but also from the back. A back-attack takes place with a
05376 ;          probability of 19% (48:256) in WARRIOR or COMMANDER missions.
05377 ;
05378 ;      o   Course corrections are prepared for the program-controlled Zylon ship
05379 ;          by computing the new milestone vector indices, resulting in new
05380 ;          velocity vector components for this Zylon ship. The new milestone
05381 ;          velocity indices for each velocity vector component are randomly
05382 ;          chosen depending of the flight pattern. Recall that the Zylon
05383 ;          velocity index is changed gradually to match the milestone velocity
05384 ;          index. It corresponds to a maximum velocity vector component when
05385 ;          using this index to pick a velocity vector component from Zylon
05386 ;          velocity table ZYLONVELTAB ($BF99):
05387 ;
05388 ;          +----------------+----------------+------------------+
05389 ;          | Flight Pattern | New Milestone  | Maximum Velocity |
05390 ;          |                | Velocity Index | Vector Component |
05391 ;          +----------------+----------------+------------------+
05392 ;          |       0        |        0       |    +62 <KM/H>    |
05393 ;          |       0        |       15       |    -62 <KM/H>    |
05394 ;          |       1        |        1       |    +30 <KM/H>    |
05395 ;          |       1        |       14       |    -30 <KM/H>    |
05396 ;          |       4        |        4       |     +4 <KM/H>    |
05397 ;          |       4        |       11       |     -4 <KM/H>    |
05398 ;          +----------------+----------------+------------------+
05399 ;
05400 ; (9)  Update milestone velocity indices in attack flight pattern.
05401 ;
05402 ;      If a Zylon ship executes the attack flight pattern, its milestone
05403 ;      velocity indices are changed depending on the current location of the
05404 ;      Zylon ship as follows:
05405 ;
05406 ;      +--------------+-------------+----------------+------------+----------------+
05407 ;      | x-Coordinate |  Where on   |   Milestone    |  Velocity  | Zylon Ship     |
05408 ;      |              |   Screen    | Velocity Index |            | Accelerates... |
05409 ;      +--------------+-------------+----------------+------------+----------------+
05410 ;      | x <  0 <KM>  | left half   |       0        | +62 <KM/H> | to the right   |
05411 ;      | x >= 0 <KM>  | right half  |      15        | -62 <KM/H> | to the left    |
05412 ;      +--------------+-------------+----------------+------------+----------------+
05413 ;      +--------------+-------------+----------------+------------+----------------+
05414 ;      | y-Coordinate |  Where on   |   Milestone    |  Velocity  | Zylon Ship     |
05415 ;      |              |   Screen    | Velocity Index |            | Accelerates... |
05416 ;      +--------------+-------------+----------------+------------+----------------+
05417 ;      | y <  0 <KM>  | bottom half |       0        | +62 <KM/H> | up             |
05418 ;      | y >= 0 <KM>  | top half    |      15        | -62 <KM/H> | down           |
05419 ;      +--------------+-------------+----------------+------------+----------------+
05420 ;
05421 ;      Thus, with respect to its x and y coordinates, the Zylon ship oscillates
05422 ;      around the center of the Front or Aft view.
05423 ;
05424 ;      This is the behavior of the Zylon ship along the z-axis:
05425 ;
05426 ;      If the Zylon ship attacks from the front:
05427 ;
05428 ;      +--------------------------+----------------+------------+----------------+
05429 ;      |       z-Coordinate       |   Milestone    |  Velocity  | Zylon Ship     |
05430 ;      |                          | Velocity Index |            | Accelerates... |
05431 ;      +--------------------------+----------------+------------+----------------+
05432 ;      | z <  +2560 (+$0A00) <KM> |       0        | +62 <KM/H> | outbound       |
05433 ;      | z >= +2560 (+$0A00) <KM> |      15        | -62 <KM/H> | inbound        |
05434 ;      +--------------------------+----------------+------------+----------------+
05435 ;
05436 ;      In other words, the Zylon ship accelerates into positive z-direction
05437 ;      (outbound) up to a distance of +2560 (+$0A00) <KM>, then reverses its
05438 ;      course and returns back to our starship (inbound).
05439 ;
05440 ;      If the Zylon ship attacks from the back:
05441 ;
05442 ;      +--------------------------+----------------+------------+----------------+
05443 ;      |       z-Coordinate       |   Milestone    |  Velocity  | Zylon Ship     |
05444 ;      |                          | Velocity Index |            | Accelerates... |
05445 ;      +--------------------------+----------------+------------+----------------+
05446 ;      | z <  -2816 (-$F500) <KM> |       0        | +62 <KM/H> | inbound        |
05447 ;      | z >= -2816 (-$F500) <KM> |      15        | -62 <KM/H> | outbound       |
05448 ;      +--------------------------+----------------+------------+----------------+
05449 ;
05450 ;      In other words, the Zylon ship accelerates into negative z-direction
05451 ;      (outbound) up to a distance of -2816 (-$(0B00)) <KM>, then reverses its
05452 ;      course and returns back to our starship (inbound).
05453 ;
05454 ; (10) Change Zylon velocity index toward milestone velocity index.
05455 ;
05456 ;      Compare all 3 Zylon velocity indices of the program-controlled Zylon ship
05457 ;      with their corresponding milestone velocity indices. Increment or
05458 ;      decrement the former to better match the latter. Use the new Zylon
05459 ;      velocity indices to pick the current velocity values from Zylon velocity
05460 ;      table ZYLONVELTAB ($BF99). 
05461 ;
05462 ; (11) Launch a Zylon photon torpedo?
05463 ;
05464 ;      Prepare launching a Zylon photon torpedo if either of the following
05465 ;      conditions are met:
05466 ;
05467 ;      o   PLAYER2 is not used as a photon torpedo
05468 ;
05469 ;      o   The y-coordinate of the Zylon ship is in the range of -768..+767
05470 ;          (-$0300..+$2FF) <KM>. 
05471 ;
05472 ;      or if
05473 ;
05474 ;      o   The Zylon photon torpedo is not alive
05475 ;
05476 ;      o   The corresponding Zylon photon torpedo delay timer has reached a
05477 ;          value of 0
05478 ;
05479 ;      o   The y-coordinate of the Zylon ship is in the range of -768..+767
05480 ;          (-$0300..+$2FF) <KM>. 
05481 ;
05482 ;      At this point the z-velocity vector component of the Zylon photon torpedo
05483 ;      is preloaded with a value of -80 or +80 <KM/H> depending on the Zylon
05484 ;      ship being in front or behind of our starship, respectively. 
05485 ;
05486 ;      Launch a Zylon photon torpedo if both of the following conditions are
05487 ;      met:
05488 ;
05489 ;      o   The Zylon ship is in front or behind of our starship, with the
05490 ;          exception of a Zylon ship behind our starship in a NOVICE mission
05491 ;          (our starship will never be shot in the back in a NOVICE mission).
05492 ;
05493 ;      o   The z-coordinate of the Zylon ship (no matter if in front or behind
05494 ;          our starship) is closer than 8192 ($20**) <KM>.
05495 ;
05496 ;      Finally, the Zylon photon torpedo is launched with a lifetime of 62 game
05497 ;      loop iterations. Its position vector is copied from the launching Zylon
05498 ;      ship in subroutine COPYPOSVEC ($ACAF). In addition, the Zylon ship is
05499 ;      earmarked for the tracking computer.
05500
05501 L.CTRLDZYLON    = $6A                   ; Index of currently program-controlled Zylon ship.
05502                                         ; Used values are:
05503                                         ;   0 -> Control Zylon ship 0
05504                                         ;   1 -> Control Zylon ship 1
05505 NEG             = $80                   ; Negative sign bit for velocity vector component
05506
05507 MANEUVER        LDA WARPSTATE           ; Return if in starbase sector or hyperwarp engaged
05508                 ORA ISSTARBASESECT      ;
05509                 BNE SKIP078             ;
05510
05511 ;*** Update x and y velocity of both our starship's photon torpedoes 0 and 1 ***
05512                 LDA ISTRACKING          ; Skip this if ship's torpedoes not tracking a target
05513                 BEQ SKIP080             ;
05514
05515                 LDX PLTRACKED           ; Load PLAYER index of tracked target space object
05516
05517                 SEC                     ; Prep A := PLAYER row number of target...
05518                 LDA PL0ROWNEW,X         ; ...- PLAYER row number photon torpedo 0
05519                 SBC PL3ROWNEW           ;
05520                 BCC SKIP079             ; Skip if target above our starship's photon torpedo
05521                 LDA #0                  ; Prep A := 0
05522 SKIP079         JSR HOMINGVEL           ; Get y-velocity for homing photon torpedo 0 and 1
05523                 STA PL3YVEL             ; Store y-velocity photon torpedo 0
05524                 STA PL4YVEL             ; Store y-velocity photon torpedo 1
05525
05526                 SEC                     ; Prep A := PLAYER column number of target...
05527                 LDA PL3COLUMN           ; ...- PLAYER column number of photon torpedo 0
05528                 SBC PL0COLUMN,X         ;
05529                 JSR HOMINGVEL           ; Get x-velocity for homing photon torpedo 0
05530                 STA PL3XVEL             ; Store x-velocity of photon torpedo 0
05531
05532                 SEC                     ; Prep A := PLAYER column number of target...
05533                 LDA PL4COLUMN           ; ...- PLAYER column number of photon torpedo 1
05534                 SBC PL0COLUMN,X         ;
05535                 JSR HOMINGVEL           ; Get x-velocity for homing photon torpedo 1
05536                 STA PL4XVEL             ; Store x-velocity of photon torpedo 1
05537
05538 ;*** Make Zylon ships follow rotation of our starship **************************
05539 SKIP080         LDX #3                  ; Loop over x and y velocity indices of both Zylons
05540 LOOP036         DEC ZYLONTIMX0,X        ; Decrement Zylon timer
05541                 BPL SKIP085             ; Next timer if this one still counting down
05542
05543                 TXA                     ; Prep joystick (x or y) value in -1, 0, +1
05544                 LSR A                   ;
05545                 TAY                     ;
05546                 LDA JOYSTICKX,Y         ;
05547
05548                 LDY SHIPVIEW            ; Skip if in Front view
05549                 BEQ SKIP081             ;
05550
05551                 EOR #$FF                ; Invert joystick value (when in Aft view)
05552                 CLC                     ; (two's-complement)
05553                 ADC #1                  ;
05554
05555 SKIP081         CLC                     ; Add joystick value to Zylon velocity index
05556                 ADC ZYLONVELINDX0,X     ;
05557                 BPL SKIP082             ;
05558                 LDA #0                  ;
05559 SKIP082         CMP #16                 ; Limit new Zylon velocity index to 0..15 ...
05560                 BCC SKIP083             ;
05561                 LDA #15                 ;
05562 SKIP083         STA ZYLONVELINDX0,X     ; ...and store new Zylon velocity index
05563
05564                 CMP #8                  ; Calc new Zylon timer value in 0, 2, ..., 14
05565                 BCC SKIP084             ;
05566                 EOR #$0F                ;
05567 SKIP084         ASL A                   ;
05568                 STA ZYLONTIMX0,X        ; ...and store new Zylon timer value
05569
05570 SKIP085         DEX                     ;
05571                 BPL LOOP036             ; Next Zylon timer
05572
05573 ;*** Update x and y velocity of single Zylon photon torpedo ********************
05574                 LDA PL2SHAPTYPE         ; Skip if PLAYER2 not PHOTON TORPEDO (shape type 0)
05575                 BNE SKIP088             ;
05576
05577                 LDY MISSIONLEVEL        ; Depending on mission level...
05578                 LDA ZYLONHOMVELTAB,Y    ; ...pick (initially negative) Zylon torpedo velocity
05579
05580                 LDX PL2YPOSHI           ; If photon torpedo in upper screen half (y >= 0)...
05581                 BPL SKIP086             ; ...don't toggle velocity sign -> torpedo goes down
05582                 AND #$7F                ; ...toggle velocity sign       -> torpedo goes up
05583 SKIP086         STA PL2YVEL             ; Store new y-velocity of Zylon photon torpedo
05584
05585                 ORA #NEG                ; Restore negative sign bit of velocity
05586
05587                 LDX PL2XPOSHI           ; If photon torpedo in right screen half (x >= 0)...
05588                 BPL SKIP087             ; ...don't toggle velocity sign -> torpedo goes left
05589                 AND #$7F                ; ...toggle velocity sign       -> torpedo goes right
05590 SKIP087         STA PL2XVEL             ; Store new x-velocity of Zylon photon torpedo
05591
05592 ;*** Create new meteor? ********************************************************
05593 SKIP088         LDA COUNT256            ; Attempt meteor creation in 7 out of 8 game loops
05594                 AND #$03                ;
05595                 BEQ SKIP092             ;
05596
05597 SKIP089         LDA PL2SHAPOFF          ; If PLAYER2 shape is initial try to create a meteor
05598                 BEQ SKIP090             ;
05599
05600                 LDA PL2LIFE             ; Return if PLAYER2 alive
05601                 BNE SKIP091             ;
05602
05603 SKIP090         LDA RANDOM              ; Return in 98% (252:256) (do not create meteor)
05604                 CMP #4                  ;
05605                 BCS SKIP091             ;
05606
05607 ;*** Create new meteor! ********************************************************
05608                 LDA #SHAP.METEOR        ; PLAYER2 is METEOR (shape type 6)
05609                 STA PL2SHAPTYPE         ;
05610                 LDX #2                  ; Randomize position vector of meteor
05611                 JSR INITPOSVEC          ;
05612                 LDA #60                 ; Meteor lifetime := 60 game loops
05613                 STA PL2LIFE             ;
05614                 LDA #NEG!8              ; SUMMARY:
05615                 STA PL2ZVEL             ; x-velocity :=  0 <KM/H>
05616                 LDA #0                  ; y-velocity :=  0 <KM/H>
05617                 STA PL2COLUMN           ; z-velocity := -8 <KM/H>
05618                 STA PL2XVEL             ;
05619                 STA PL2YVEL             ; PLAYER2 column number := 0 (offscreen)
05620 SKIP091         RTS                     ; Return
05621
05622 ;*** Toggle Zylon ship control *************************************************
05623 SKIP092         LDA CTRLDZYLON          ; Toggle control to the other Zylon ship
05624                 EOR #$01                ;
05625                 STA CTRLDZYLON          ;
05626
05627 ;*** Create a new Zylon ship? **************************************************
05628                 TAX                     ; Save index of controlled Zylon ship
05629                 LDA PL0LIFE,X           ; Skip creating Zylon ship if its PLAYER still alive
05630                 BNE SKIP094             ;
05631
05632                 LDA PL0LIFE             ; If both Zylon ships are not alive...
05633                 ORA PL1LIFE             ;
05634                 AND #$01                ;
05635                 LDY CURRSECTOR          ; ...and this an empty sector...
05636                 CMP GCMEMMAP,Y          ;
05637                 BCS SKIP089             ; ...attempt to create meteor and return
05638
05639 ;*** Create a new Zylon ship! **************************************************
05640                 LDA #255                ; Zylon ship lifetime := 255 game loops (infinite)
05641                 STA PL0LIFE,X           ;
05642
05643                 LDA RANDOM              ; Pick a Zylon ship shape type (1 out of 8)
05644                 AND #$07                ;
05645                 TAY                     ;
05646                 LDA ZYLONSHAPTAB,Y      ;
05647                 STA PL0SHAPTYPE,X       ;
05648
05649                 LDA MISSIONLEVEL        ; Init Zylon's flight pattern (0 if NOVICE mission)
05650                 BEQ SKIP093             ;
05651                 LDA ZYLONFLPATTAB,Y     ;
05652 SKIP093         STA ZYLONFLPAT0,X       ;
05653
05654                 LDA #1                  ; Zylon ship's milestone timer := 1 game loop
05655                 STA MILESTTIM0,X        ;
05656
05657                 STA ZPOSSIGN,X          ; Put Zylon ship in front of our starship
05658                 LDA RANDOM              ;
05659                 AND VICINITYMASK        ; y-coordinate (high byte) := RND(0..VICINITYMASK)
05660                 STA YPOSHI,X            ;
05661                 ADC #19                 ; x-coordinate (high byte) := y (high byte) + 19
05662                 STA XPOSHI,X            ;
05663                 ORA #$71                ; z-coordinate (high byte) := >= +28928 (+$71**) <KM>
05664                 STA ZPOSHI,X            ;
05665                 JSR RNDINVXY            ; Randomly invert x and y coordinate of pos vector
05666
05667 ;*** Set current flight pattern to attack flight pattern? **********************
05668 SKIP094         LDA ZPOSHI,X            ; Skip if Zylon too distant (z >= +$20** <KM>)
05669                 CMP #$20                ;
05670                 BCS SKIP096             ;
05671
05672                 LDA ZPOSSIGN,X          ; Set attack flight pattern if Zylon is behind
05673                 BEQ SKIP095             ;
05674
05675                 LDA PL0SHAPOFF,X        ; Skip if Zylon shape initial
05676                 BEQ SKIP096             ;
05677
05678                 CMP #$29                ; Skip if Zylon shape is Long-Range Scan blip
05679                 BEQ SKIP096             ;
05680
05681 SKIP095         LDA #0                  ; Set attack flight pattern
05682                 STA ZYLONFLPAT0,X       ;
05683
05684 ;*** Update back-attack flag and milestone velocity indices ********************
05685 SKIP096         DEC MILESTTIM0,X        ; Skip if milestone timer still counting down
05686                 BPL SKIP099             ;
05687
05688                 LDA #120                ; Milestone timer := 120 game loops
05689                 STA MILESTTIM0,X        ;
05690
05691                 LDA MISSIONLEVEL        ; Back-attack flag := 1 in 19% (48:256) of...
05692                 LDY RANDOM              ; ...WARRIOR or COMMANDER missions
05693                 CPY #48                 ; ...              := 0 otherwise
05694                 BCC SKIP097             ;
05695                 LSR A                   ;
05696 SKIP097         LSR A                   ;
05697                 STA ISBACKATTACK0,X     ;
05698
05699                                         ; Loop over all 3 milestone velocity indices
05700                 LDA ZYLONFLPAT0,X       ; Set new milestone velocity index:
05701 LOOP037         BIT RANDOM              ; If Zylon flight pattern is...
05702                 BPL SKIP098             ; ...0 -> milestone velocity index := either 0 or 15
05703                 EOR #$0F                ; ...1 -> milestone velocity index := either 1 or 14
05704 SKIP098         STA MILESTVELINDZ0,X    ; ...4 -> milestone velocity index := either 4 or 11
05705                 INX                     ;
05706                 INX                     ;
05707                 CPX #6                  ;
05708                 BCC LOOP037             ; Next Zylon milestone velocity index
05709
05710 ;*** Update milestone velocity indices in attack flight pattern ****************
05711                 LDX CTRLDZYLON          ; Reload index of controlled Zylon ship
05712
05713 SKIP099         LDA ZYLONFLPAT0,X       ; Skip if not in attack flight pattern
05714                 BNE SKIP105             ;
05715
05716                 LDY CTRLDZYLON          ; Reload index of controlled Zylon ship
05717
05718                                         ; Loop over all 3 milestone velocity indices
05719 LOOP038         CPY #$31                ; Skip to handle x and y velocity index
05720                 BCS SKIP101             ;
05721                                         ; SUMMARY:
05722                 LDA ISBACKATTACK0,Y     ; Handle z-velocity index:
05723                 LSR A                   ;
05724                 LDA ZPOSHI,Y            ; If Zylon attacks from front...
05725                 BCS SKIP100             ; z <  $0A00 <KM> -> mil vel index := 0  (+62 <KM/H>)
05726                 CMP #$0A                ; z >= $0A00 <KM> -> mil vel index := 15 (-62 <KM/H>)
05727                 BCC SKIP103             ;
05728                 BCS SKIP101             ; If Zylon attacks from back...
05729 SKIP100         CMP #$F5                ; z >= $F500 <KM> -> mil vel index := 15 (-62 <KM/H>)
05730                 BCS SKIP102             ; z <  $F500 <KM> -> mil vel index := 0  (+62 <KM/H>)
05731
05732 SKIP101         LDA ZPOSSIGN,Y          ; Handle x and y velocity index:
05733                 LSR A                   ;
05734 SKIP102         LDA #15                 ; x >= 0 <KM> -> mil vel index := 15 (-62 <KM/H>)
05735                 BCS SKIP104             ; x <  0 <KM> -> mil vel index := 0  (+62 <KM/H>)
05736 SKIP103         LDA #0                  ; y >= 0 <KM> -> mil vel index := 15 (-62 <KM/H>)
05737 SKIP104         STA MILESTVELINDZ0,X    ; y <  0 <KM> -> mil vel index := 0  (+62 <KM/H>)
05738
05739                 CLC                     ; Adjust position vector component index
05740                 TYA                     ;
05741                 ADC #NUMSPCOBJ.ALL      ;
05742                 TAY                     ;
05743
05744                 INX                     ;
05745                 INX                     ;
05746                 CPX #6                  ;
05747                 BCC LOOP038             ; Next milestone velocity index
05748
05749 ;*** Acceleration: Change Zylon velocity index toward milestone velocity index *
05750                 LDX CTRLDZYLON          ; Reload index of controlled Zylon ship
05751 SKIP105         LDY CTRLDZYLON          ; Reload index of controlled Zylon ship
05752
05753                                         ; Loop over all 3 milestone velocity indices
05754 LOOP039         LDA ZYLONVELINDZ0,X     ; Compare Zylon velocity index with milestone index
05755                 CMP MILESTVELINDZ0,X    ;
05756                 BEQ SKIP107             ; Skip if equal
05757                 BCS SKIP106             ;
05758                 INC ZYLONVELINDZ0,X     ; Increm. Zylon velocity index if < milestone index
05759                 BCC SKIP107             ;
05760 SKIP106         DEC ZYLONVELINDZ0,X     ; Decrem. Zylon velocity index if >= milestone index
05761
05762 SKIP107         STX L.CTRLDZYLON        ; Save index of controlled Zylon ship
05763                 TAX                     ;
05764                 LDA ZYLONVELTAB,X       ; Pick new velocity value by Zylon velocity index
05765                 LDX L.CTRLDZYLON        ; Reload index of controlled Zylon ship
05766                 STA ZVEL,Y              ; Store new velocity vector component of Zylon ship
05767
05768                 TYA                     ; Next velocity vector component
05769                 CLC                     ;
05770                 ADC #NUMSPCOBJ.ALL      ;
05771                 TAY                     ;
05772
05773                 INX                     ;
05774                 INX                     ;
05775                 CPX #6                  ;
05776                 BCC LOOP039             ; Next milestone velocity index
05777
05778 ;*** Launch Zylon photon torpedo? **********************************************
05779
05780 ;*** Check PLAYER2 shape and lifetime ******************************************
05781                 LDX CTRLDZYLON          ; Reload index of controlled Zylon ship
05782
05783                 LDA PL2SHAPTYPE         ; Skip if PLAYER2 not PHOTON TORPEDO (shape type 0)
05784                 BNE SKIP109             ;
05785
05786                 LDA PL2LIFE             ; Return if Zylon photon torpedo still alive
05787                 BNE SKIP108             ;
05788
05789                 LDA TORPEDODELAY        ; Count down Zylon photon torpedo delay timer...
05790                 BEQ SKIP109             ; ...before launching next Zylon photon torpedo
05791                 DEC TORPEDODELAY        ;
05792 SKIP108         RTS                     ; Return
05793
05794 ;*** Check y-coordinate of Zylon ship ******************************************
05795 SKIP109         CLC                     ; Return if Zylon ship's y-coordinate not...
05796                 LDA YPOSHI,X            ; ...in -768..+767 (-$(0300)..+$2FF) <KM>.
05797                 ADC #2                  ;
05798                 CMP #5                  ;
05799                 BCS SKIP108             ;
05800
05801 ;*** Set Zylon photon torpedo's z-velocity *************************************
05802                 LDY #NEG!80             ; Prep Zylon torpedo's z-velocity := -80 <KM/H>
05803
05804                 LDA ZPOSSIGN,X          ; Prep Zylon ship's sign of z-coordinate
05805                 LSR A                   ;
05806                 LDA ZPOSHI,X            ; Prep Zylon ship's z-coordinate
05807                 BCS SKIP110             ; Skip if Zylon ship in front...
05808                 EOR #$FF                ; ...else invert loaded Zylon ship's z-coordinate
05809
05810                 LDY MISSIONLEVEL        ; Return (no torpedo from back) if NOVICE mission
05811                 BEQ SKIP108             ;
05812
05813                 LDY #80                 ; Preload Zylon torpedo's z-velocity := +80 <KM/H>
05814
05815 ;*** Is Zylon ship in range? ***************************************************
05816 SKIP110         CMP #$20                ; Return if Zylon ship too far...
05817                 BCS SKIP108             ; ... (ABS(z-coordinate) > 8192 ($20**) <KM>)
05818
05819                 STY PL2ZVEL             ; Store Zylon photon torpedo's z-velocity
05820
05821 ;*** Launch Zylon photon torpedo! **********************************************
05822
05823                 LDA #0                  ; PLAYER2 is PHOTON TORPEDO (shape type 0)
05824                 STA PL2SHAPTYPE         ;
05825                 STA PL2COLUMN           ; Zylon torpedo PLAYER column number := 0 (offscreen)
05826                 LDA #62                 ;
05827                 STA PL2LIFE             ; Zylon torpedo lifetime := 62 game loops
05828
05829                 LDX #2                  ; Prep source index for position vector copy
05830                 LDY CTRLDZYLON          ; Prep destination index for position vector copy
05831                 STY ZYLONATTACKER       ; Save Zylon ship index for tracking computer
05832                 JMP COPYPOSVEC          ; Copy position vector from Zylon ship to its torpedo
05833
05834 ;*******************************************************************************
05835 ;*                                                                             *
05836 ;*                                  INITEXPL                                   *
05837 ;*                                                                             *
05838 ;*                            Initialize explosion                             *
05839 ;*                                                                             *
05840 ;*******************************************************************************
05841
05842 ; DESCRIPTION
05843 ;
05844 ; Initializes the explosion's lifetime, the explosion fragments' position and
05845 ; velocity vectors as well as their pixel row and column numbers.
05846 ;
05847 ; An explosion has a lifetime of 128 game loop iterations. It consists of 32
05848 ; explosion fragment space objects with indices 17..48. The position vector of
05849 ; each explosion fragment is copied from the exploding PLAYER space object.
05850 ;
05851 ; The pixel column number of each explosion fragment is initialized to
05852 ;
05853 ;     PIXEL COLUMN NUMBER := PLAYER column number - 48 + RND(0..15)
05854 ;
05855 ; To convert PLAYER column numbers (in Player/Missile (PM) pixels) into pixel
05856 ; column numbers, the PLAYER column number of the left PLAYFIELD border (= 48)
05857 ; is subtracted and a random number is added.
05858 ;
05859 ; BUG (at $AC76): The added random number should not be in 0..15 but in 0..7
05860 ; because the exploding PLAYER is 8 pixels wide. The PLAYER column number
05861 ; represents the left edge of the PLAYER shape. When using a random number in
05862 ; 0..15, half of the pixels are located off to the right of the PLAYER, outside
05863 ; the PLAYER area. Suggested fix: Replace instruction AND #$0F with AND #$07. 
05864 ;
05865 ; The pixel row number of each explosion fragment is initialized to
05866 ;
05867 ;     PIXEL ROW NUMBER := (PLAYER row number - RND(0..15)) / 2 - 16
05868 ;
05869 ; BUG (at $AC88): To convert PLAYER row numbers (in PM pixels) into pixel row
05870 ; numbers, the PLAYER row number to the top PLAYFIELD border (= 16) should be
05871 ; subtracted first, then the division by 2 (instruction LRS A) should be applied
05872 ; to reduce the double-line PM resolution to the single-line PLAYFIELD
05873 ; resolution. Suggested fix: Swap instruction LRS A with SBC #16 which leads to
05874 ; the following formula for the pixel row number:
05875 ;
05876 ;     PIXEL ROW NUMBER := (PLAYER row number - 16 + RND(0..15)) / 2
05877 ;
05878 ; Incidentally, adding a random number in 0..15 is correct. PLAYER row number
05879 ; represents the top edge of the PLAYER shape, which is typically 16 PM pixels
05880 ; tall when representing a close space object.
05881 ;
05882 ; The velocity vector of explosion fragments is set to random x, y, and z
05883 ; velocity vector components in -7..+7 <KM/H>.
05884 ;
05885 ; INPUT
05886 ;
05887 ;   Y = PLAYER index from which the explosion originates. Used values are:
05888 ;     0 -> Explosion of PLAYER0 (Zylon ship 0)
05889 ;     1 -> Explosion of PLAYER1 (Zylon ship 1)
05890 ;     2 -> Explosion of PLAYER2 (Zylon photon torpedo, starbase, or meteor)
05891
05892 INITEXPL        LDA #128                ; Explosion lifetime := 128 game loops
05893                 STA EXPLLIFE            ;
05894
05895                 LDX #NUMSPCOBJ.ALL-1    ; Max index of space objects (for explosion frags)
05896                 STX MAXSPCOBJIND        ;
05897
05898                                         ; Loop over all explosion fragment position vectors
05899                                         ; (index 48..17)
05900 LOOP040         LDA RANDOM              ; PIXEL COLUMN NUM := PLAYER column - 48 + RND(0..15)
05901                 AND #$0F                ; (!)
05902                 ADC PL0COLUMN,Y         ;
05903                 SBC #48                 ;
05904                 STA PIXELCOLUMN,X       ;
05905
05906                 LDA RANDOM              ; PIXEL ROW NUM := (PLAYER row + RND(0..15)) / 2 - 16
05907                 AND #$0F                ;
05908                 ADC PL0ROWNEW,Y         ;
05909                 LSR A                   ; (!)
05910                 SBC #16                 ;
05911                 STA PIXELROWNEW,X       ;
05912
05913                 JSR COPYPOSVEC          ; Copy position vector of PLAYER to explosion frag
05914
05915                 LDA RANDOM              ; z-velocity := RND(-7..+7) <KM/H>
05916                 AND #NEG!7              ;
05917                 STA ZVEL,X              ;
05918                 LDA RANDOM              ; x-velocity := RND(-7..+7) <KM/H>
05919                 AND #NEG!7              ;
05920                 STA XVEL,X              ;
05921                 LDA RANDOM              ; y-velocity := RND(-7..+7) <KM/H>
05922                 AND #NEG!7              ;
05923                 STA YVEL,X              ;
05924
05925                 DEX                     ; Next explosion fragment position vector
05926                 CPX #16                 ;
05927                 BNE LOOP040             ;
05928                 RTS                     ; Return
05929
05930 ;*******************************************************************************
05931 ;*                                                                             *
05932 ;*                                 COPYPOSVEC                                  *
05933 ;*                                                                             *
05934 ;*                           Copy a position vector                            *
05935 ;*                                                                             *
05936 ;*******************************************************************************
05937
05938 ; DESCRIPTION
05939 ;
05940 ; Copies a position vector.
05941 ;
05942 ; Actually, this subroutine copies the z-coordinate only, then code execution
05943 ; continues into subroutine COPYPOSXY ($ACC1) to copy the x and y coordinate.
05944 ;
05945 ; INPUT
05946 ;
05947 ;   X = Destination position vector index. Used values are: 0..48.
05948 ;   Y = Source position vector index. Used values are: 0..48.
05949
05950 COPYPOSVEC      LDA ZPOSSIGN,Y          ;
05951                 STA ZPOSSIGN,X          ;
05952                 LDA ZPOSHI,Y            ;
05953                 STA ZPOSHI,X            ;
05954                 LDA ZPOSLO,Y            ;
05955                 STA ZPOSLO,X            ;
05956
05957 ;*******************************************************************************
05958 ;*                                                                             *
05959 ;*                                  COPYPOSXY                                  *
05960 ;*                                                                             *
05961 ;*          Copy x and y components (coordinates) of position vector           *
05962 ;*                                                                             *
05963 ;*******************************************************************************
05964
05965 ; DESCRIPTION
05966 ;
05967 ; Copies the x and y components (coordinates) of a position vector.
05968 ;
05969 ; INPUT
05970 ;
05971 ;   X = Destination position vector index. Used values are: 0..48.
05972 ;   Y = Source position vector index. Used values are: 0..48.
05973
05974 COPYPOSXY       LDA XPOSSIGN,Y          ;
05975                 STA XPOSSIGN,X          ;
05976                 LDA XPOSHI,Y            ;
05977                 STA XPOSHI,X            ;
05978                 LDA YPOSSIGN,Y          ;
05979                 STA YPOSSIGN,X          ;
05980                 LDA YPOSHI,Y            ;
05981                 STA YPOSHI,X            ;
05982                 LDA XPOSLO,Y            ;
05983                 STA XPOSLO,X            ;
05984                 LDA YPOSLO,Y            ;
05985                 STA YPOSLO,X            ;
05986 SKIP111         RTS                     ; Return
05987
05988 ;*******************************************************************************
05989 ;*                                                                             *
05990 ;*                                   DOCKING                                   *
05991 ;*                                                                             *
05992 ;*      Handle docking at starbase, launch and return of transfer vessel       *
05993 ;*                                                                             *
05994 ;*******************************************************************************
05995
05996 ; DESCRIPTION
05997 ;
05998 ; Handles docking at a starbase, launching and returning the transfer vessel,
05999 ; and repairing our starship's subsystems. 
06000 ;
06001 ; This subroutine changes, if in Front view, the PLAYER-PLAYFIELD priority such
06002 ; that PLAYERs like the starbase appear behind the cross hairs, which are part
06003 ; of the PLAYFIELD.
06004 ;
06005 ; BUG (at $ACEE): The starbase also appears behind the stars, which are also
06006 ; part of the PLAYFIELD - a rarely noticed glitch. In Aft view, the arrangement
06007 ; is reversed: PLAYERs are arranged in front of the PLAYFIELD. Then the starbase
06008 ; (and the transfer vessel) appear in front of the cross hairs! Suggested fix:
06009 ; None, technically not possible.
06010 ;
06011 ; The starbase is tracked and the PLAYER0..2 shape types are set to STARBASE
06012 ; RIGHT, STARBASE LEFT, and STARBASE CENTER, respectively, combining them into a
06013 ; 3-part starbase shape. 
06014 ;
06015 ; If this sector is still marked as a starbase sector but no more so on the
06016 ; Galactic Chart (if in the meantime either Zylon units have surrounded this
06017 ; sector and destroyed the starbase or you have destroyed the starbase with a
06018 ; photon torpedo) then the noise sound pattern SHIELD EXPLOSION is played in
06019 ; subroutine NOISE ($AEA8) and code execution returns.
06020 ;
06021 ; Otherwise a minimum distance to the starbase of +32 (+$0020) <KM> is enforced
06022 ; and the conditions for a successful docking are checked:
06023 ;
06024 ; DOCKING CONDITIONS
06025 ;
06026 ; A docking is successful if all of the following conditions are met:
06027 ;
06028 ; (1)  The PLAYER2 (STARBASE CENTER) column number is in 120..135. 
06029 ;
06030 ;      BUG (at $AD39): At first glance, the PLAYER column interval of 120..135
06031 ;      corresponds to an almost symmetric interval of -8..+7 PM pixels relative
06032 ;      to the horizontal center of the PLAYFIELD, at PLAYER column number 128
06033 ;      (48 PM pixels offset to left PLAYFIELD border + 80 PM pixels to the
06034 ;      PLAYFIELD center). This is correct only if the PLAYER column number were
06035 ;      to designate the horizontal center of the PLAYER. However it designates
06036 ;      its left edge! Thus the used pixel column number range 120..135 creates
06037 ;      an asymmetric horizontal docking position: A docking is successful if the
06038 ;      horizontal position of the starbase shape's center is roughly -5..+10 PM
06039 ;      pixels relative to the horizontal center of the PLAYFIELD. Suggested fix:
06040 ;      Replace SBC #120 with SBC #117. This leads to an interval of -8..+7
06041 ;      pixels relative to the horizontal center of the PLAYFIELD and better
06042 ;      symmetry in the horizontal docking position.
06043 ;
06044 ; (2)  The PLAYER2 (STARBASE CENTER) row number is in 104..119.
06045 ;
06046 ;      BUG (at $AD43): The PLAYER row interval of 104..119 corresponds to an
06047 ;      asymmetric interval of -20..-5 PM pixels relative to the vertical center
06048 ;      of the PLAYFIELD, at pixel row number 80 or PLAYER row number 124. It
06049 ;      lets you dock at a starbase that "sits" on top of the horizontal cross
06050 ;      hairs but not at one that "hangs" from them. Suggested fix: Replace SBC
06051 ;      #104 with SBC #108. This leads to an interval of -8..+7 pixels relative
06052 ;      to the vertical center of the PLAYFIELD (assuming a PLAYER2 shape of 16
06053 ;      pixel height, which is typical during docking) and better symmetry in the
06054 ;      vertical docking position. 
06055 ;
06056 ; (3)  The starbase is in correct distance in front of our starship: The
06057 ;      starbase's z-coordinate must be < +512 (+$02**) <KM>.
06058 ;
06059 ; (4)  Our starship is horizontally level with the starbase: The starbase's
06060 ;      y-coordinate must be < +256 (+$01**) <KM>.
06061 ;
06062 ; (5)  Our starship is at a complete halt.
06063 ;
06064 ; DOCKING SUCCESSFUL
06065 ;
06066 ; If the conditions for a successful docking are met, the subsequent docking and
06067 ; transfer operation can be divided in the following states, starting with state
06068 ; NOT DOCKED:
06069 ;
06070 ; (1)  NOT DOCKED 
06071 ;
06072 ;      The docking state is set to ORBIT ESTABLISHED and the title line is
06073 ;      updated with "ORBIT ESTABLISHED".
06074 ;
06075 ; (2)  ORBIT ESTABLISHED 
06076 ;
06077 ;      After waiting until the title line "ORBIT ESTABLISHED" has disappeared,
06078 ;      the transfer vessel is initialized and launched: The PLAYER4 shape type
06079 ;      is set to TRANSFER VESSEL. Its position vector is set to a position above
06080 ;      and in front of our starship, but behind the starbase:
06081 ;
06082 ;          x-coordinate :=     +0..+255 (+$00**) <KM>
06083 ;          y-coordinate :=   +256..+511 (+$01**) <KM> 
06084 ;          z-coordinate := +4096..+4351 (+$10**) <KM>
06085 ;
06086 ;      Its velocity vector is set to
06087 ;
06088 ;          x-velocity   := +1 <KM/H> 
06089 ;          y-velocity   := -1 <KM/H> 
06090 ;          z-velocity   := -7 <KM/H>
06091 ;
06092 ;      This will move the transfer vessel from behind the starbase into a
06093 ;      direction toward and a little to the lower right of our starship. The
06094 ;      lifetime of the transfer vessel (and its return journey) is set to 129
06095 ;      game loop iterations. Finally, the docking state is set to RETURN
06096 ;      TRANSFER VESSEL.
06097 ;
06098 ; (3)  RETURN TRANSFER VESSEL 
06099 ;
06100 ;      After checking if the transfer vessel has passed behind our starship, the
06101 ;      beeper sound pattern ACKNOWLEDGE is played in subroutine BEEP ($B3A6),
06102 ;      the title line is updated with "TRANSFER COMPLETE", our starship's
06103 ;      subsystems are repaired, and our starship's ENERGY readout is restored to
06104 ;      9999 energy units. by inverting the z-velocity the velocity vector of the
06105 ;      transfer vessel is changed to
06106 ;
06107 ;          x-velocity   := +1 <KM/H> 
06108 ;          y-velocity   := -1 <KM/H> 
06109 ;          z-velocity   := +7 <KM/H>
06110 ;
06111 ;      thus launching the transfer vessel on its return journey to the starbase.
06112 ;      The docking state is set to TRANSFER COMPLETE. Finally, the screen is
06113 ;      updated in subroutine UPDSCREEN ($B07B).
06114 ;
06115 ; (4)  TRANSFER COMPLETE 
06116 ;
06117 ;      This docking state marks the end of a successful docking and transfer
06118 ;      operation.
06119 ;
06120 ; DOCKING ABORTED
06121 ;
06122 ; If the docking conditions above are not met and the docking state is already
06123 ; ORBIT ESTABLISHED or RETURN TRANSFER VESSEL then the message "DOCKING ABORTED"
06124 ; is displayed and the docking state is set to NOT DOCKED.
06125
06126 DOCKING         LDA ISSTARBASESECT      ; Return if not in starbase sector
06127                 BEQ SKIP111             ;
06128
06129                 LDA SHIPVIEW            ; Skip if not in Front view
06130                 BNE SKIP112             ;
06131                 LDA #$14                ; GTIA: enable PLAYER4, prio: PFs > PLs > BGR (!)
06132                 STA PRIOR               ; (Cross hairs appear behind PLAYERs)
06133
06134 SKIP112         LDA #2                  ; Track starbase (PLAYER2)
06135                 STA TRACKDIGIT          ;
06136
06137 ;** Initialize starbase shape **************************************************
06138                 LDA #SHAP.STARBASEC     ; PLAYER2 is STARBASE CENTER (shape type 3)
06139                 STA PL2SHAPTYPE         ;
06140                 LDA #SHAP.STARBASEL     ; PLAYER1 is STARBASE LEFT (shape type 2)
06141                 STA PL1SHAPTYPE         ;
06142                 LDA #SHAP.STARBASER     ; PLAYER0 is STARBASE RIGHT (shape type 4)
06143                 STA PL0SHAPTYPE         ;
06144
06145                 LDA #255                ; Prep starbase lifetime := 255 game loops (infinite)
06146
06147                 LDX CURRSECTOR          ; Skip if starbase in current sector
06148                 LDY GCMEMMAP,X          ;
06149                 BMI SKIP113             ;
06150
06151                 LDA #0                  ; Prep starbase lifetime := 0 game loops (fast death)
06152
06153 SKIP113         STA PL0LIFE             ; PLAYER0 lifetime := either 0 or 255 game loops
06154                 STA PL1LIFE             ; PLAYER1 lifetime := either 0 or 255 game loops
06155                 STA PL2LIFE             ; PLAYER2 lifetime := either 0 or 255 game loops
06156                 STA ISSTARBASESECT      ; Store starbase-in-sector flag
06157                 BMI SKIP114             ; Skip if starbase in current sector
06158
06159                 LDY #2                  ; Init explosion at PLAYER2 (STARBASE CENTER)
06160                 JSR INITEXPL            ;
06161
06162                 LDX #$0A                ; Play noise sound pattern SHIELD EXPLOSION and return
06163                 JMP NOISE               ;
06164
06165 ;*** Keep minimum distance to starbase *****************************************
06166 SKIP114         LDA PL2ZPOSHI           ; Skip if starbase z-coordinate > +255 (+$00**) <KM>
06167                 BNE SKIP115             ;
06168
06169                 LDA PL2ZPOSLO           ; Approach starbase not closer than +32 (+$0020) <KM>
06170                 CMP #32                 ;
06171                 BCS SKIP115             ;
06172                 INC PL2ZPOSLO           ; ...else push starbase back
06173
06174 ;*** Check if in docking range *************************************************
06175 SKIP115         LDA PL2COLUMN           ; Abort docking if PLAYER column number of...
06176                 SEC                     ; ...PLAYER2 (STARBASE CENTER) not in 120..135.
06177                 SBC #120                ; (!)
06178                 CMP #16                 ;
06179                 BCS SKIP116             ;
06180
06181                 LDA PL2ROWNEW           ; Abort docking if PLAYER row number of...
06182                 SEC                     ; ...PLAYER2 (STARBASE CENTER) not in 104..119.
06183                 SBC #104                ; (!)
06184                 CMP #16                 ;
06185                 BCS SKIP116             ;
06186
06187                 LDA PL2ZPOSHI           ; Abort docking if...
06188                 CMP #2                  ; ... z-coordinate of starbase >= +512 (+$02**) <KM>
06189                 BCS SKIP116             ;
06190
06191                 LDA PL2ZPOSSIGN         ; Abort docking...
06192                 AND PL2YPOSSIGN         ; ...if starbase not in front and upper screen half
06193                 EOR #$01                ;
06194                 ORA VELOCITYLO          ; ...if our starship's velocity not zero
06195                 ORA PL2YPOSHI           ; ...if starbase not roughly vertically centered
06196                 ORA NEWVELOCITY         ; ...if our starship's new velocity not zero
06197                 BEQ SKIP119             ; Else skip and handle docking
06198
06199 ;*** Docking aborted ***********************************************************
06200 SKIP116         LDA DOCKSTATE           ; Skip if DOCKSTATE is NOT DOCKED, TRANSFER COMPLETE
06201                 CMP #2                  ;
06202                 BCC SKIP117             ;
06203
06204                 LDY #$1F                ; Set title phrase "DOCKING ABORTED"
06205                 JSR SETTITLE            ;
06206
06207 SKIP117         LDA #0                  ; DOCKSTATE := NOT DOCKED
06208                 STA DOCKSTATE           ;
06209 SKIP118         RTS                     ; Return
06210
06211 ;*** Docking successful, check docking state ***********************************
06212 SKIP119         BIT DOCKSTATE           ; Check DOCKSTATE
06213                 BVS SKIP120             ; If DOCKSTATE = ORBIT ESTABLISHED hide title line
06214                 BMI SKIP122             ; If DOCKSTATE = RETURN TRANSFER VESSEL return it
06215                 LDA DOCKSTATE           ;
06216                 BNE SKIP118             ; Return if DOCKSTATE not NOT DOCKED
06217                 DEC DOCKSTATE           ; DOCKSTATE := ORBIT ESTABLISHED
06218
06219                 LDY #$1C                ; Set title phrase "ORBIT ESTABLISHED" and return
06220                 JMP SETTITLE            ;
06221
06222 ;*** Orbit established *********************************************************
06223 SKIP120         LDX #0                  ; Enqueue new, empty title phrase
06224                 STX NEWTITLEPHR         ;
06225
06226                 LDY TITLEPHR            ; Return if "ORBIT ESTABLISHED" still displayed
06227                 BNE SKIP118             ;
06228
06229 ;*** Launch transfer vessel ****************************************************
06230                 LDA #SHAP.TRANSVSSL     ; PLAYER4 is TRANSFER VESSEL (shape 5)
06231                 STA PL4SHAPTYPE         ;
06232
06233                 LDA #1                  ; Place transfer vessel behind starbase:
06234                 STA PL4ZPOSSIGN         ; x-coordinate :=    +0..+255  (+$00**) <KM>
06235                 STA PL4XPOSSIGN         ; y-coordinate :=  +256..+511  (+$01**) <KM>
06236                 STA PL4YPOSSIGN         ; z-coordinate := +4096..+4351 (+$10**) <KM>
06237                 STA PL4YPOSHI           ;
06238                 STA PL4XVEL             ; Move transfer vessel toward our starship:
06239                 LDA #$10                ; x-velocity := +1 <KM/H>
06240                 STA PL4ZPOSHI           ; y-velocity := -1 <KM/H>
06241                 LDA #$00                ; z-velocity := -7 <KM/H>
06242                 STA PL4XPOSHI           ;
06243                 LDA #NEG!7              ;
06244                 STA PL4ZVEL             ;
06245                 LDA #NEG!1              ; DOCKSTATE := RETURN TRANSFER VESSEL
06246                 STA DOCKSTATE           ;
06247                 STA PL4YVEL             ;
06248                 STA PL4LIFE             ; Transfer vessel lifetime := 129 game loops
06249 SKIP121         RTS                     ; Return
06250
06251 ;*** Return transfer vessel ****************************************************
06252 SKIP122         LDA PL4ZPOSSIGN         ; Return if transfer vessel in front of our starship
06253                 BNE SKIP121             ;
06254
06255                 LDX #$0C                ; Play beeper sound pattern ACKNOWLEGDE
06256                 JSR BEEP                ;
06257
06258                 LDY #$21                ; Set title phrase "TRANSFER COMPLETE"
06259                 JSR SETTITLE            ;
06260
06261                 LDX #5                  ; Repair all 6 subsystems
06262 LOOP041         LDA PANELTXTTAB+73,X    ;
06263                 STA GCSTATPHO,X         ;
06264                 DEX                     ;
06265                 BPL LOOP041             ;
06266
06267                 LDA #CCS.COL2!CCS.9     ; Set starship's ENERGY readout to "9999" in COLOR2
06268                 LDX #3                  ;
06269 LOOP042         STA ENERGYD1,X          ;
06270                 DEX                     ;
06271                 BPL LOOP042             ;
06272
06273                 LDA #7                  ; Move transfer vessel back toward starbase:
06274                 STA PL4ZVEL             ; x-velocity := -1 <KM/H>
06275                 LDA #NEG!1              ; y-velocity := +1 <KM/H>
06276                 STA PL4XVEL             ; z-velocity := +7 <KM/H>
06277                 LDA #1                  ;
06278                 STA PL4YVEL             ;
06279
06280                 STA DOCKSTATE           ; DOCKSTATE := TRANSFER COMPLETE
06281                 JMP UPDSCREEN           ; Update screen and return
06282
06283 ;*******************************************************************************
06284 ;*                                                                             *
06285 ;*                                   MODDLST                                   *
06286 ;*                                                                             *
06287 ;*                             Modify Display List                             *
06288 ;*                                                                             *
06289 ;*******************************************************************************
06290
06291 ; DESCRIPTION
06292 ;
06293 ; Modifies the Display List to show and hide title, headers, and the Control
06294 ; Panel Display.
06295 ;
06296 ; INPUT
06297 ;
06298 ;   A = Number of bytes to copy into the Display List
06299 ;   X = Offset into Display List DSPLST ($0280)
06300 ;   Y = Offset into Display List fragment table DLSTFRAG ($BA62). If Y = $80
06301 ;       then no bytes are copied but the specified locations of the Display List
06302 ;       are overwritten with Display List instruction $0D (one row of
06303 ;       GRAPHICS7).
06304 ;
06305 ;   Used values are:
06306 ;
06307 ;    A    X    Y
06308 ;   $08  $5F  $00 -> Show Control Panel Display (bottom text window)
06309 ;   $08  $5F  $80 -> Hide Control Panel Display (bottom text window)
06310 ;   $07  $0F  $23 -> Show title line
06311 ;   $07  $0F  $80 -> Hide title line
06312 ;   $08  $02  $1B -> Show Display List header line of Front view
06313 ;   $08  $02  $13 -> Show Display List header line of Aft view
06314 ;   $08  $02  $0B -> Show Display List header line of Long-Range Scan view
06315 ;   $08  $02  $08 -> Show Display List header line of Galactic Chart view
06316
06317 L.NUMBYTES      = $6A                   ; Number of bytes to copy
06318
06319 MODDLST         SEI                     ; Disable IRQ
06320                 STA L.NUMBYTES          ; Save number of bytes to copy
06321
06322 LOOP043         LDA VCOUNT              ; Wait for ANTIC line counter >= 124 (PLAYFIELD...
06323                 CMP #124                ; ...bottom) before changing the Display List
06324                 BCC LOOP043             ;
06325
06326 LOOP044         LDA DLSTFRAG,Y          ; Load byte from Display List fragment table
06327                 INY                     ;
06328                 BPL SKIP123             ; Skip if fragment table index < $80
06329                 LDA #$0D                ; Prep Display List instruction $0D (GRAPHICS7)
06330 SKIP123         STA DSPLST,X            ; Store byte in Display List
06331                 INX                     ;
06332                 DEC L.NUMBYTES          ;
06333                 BNE LOOP044             ; Copy next byte
06334
06335                 CLI                     ; Enable IRQ
06336                 RTS                     ; Return
06337
06338 ;*******************************************************************************
06339 ;*                                                                             *
06340 ;*                                CLRPLAYFIELD                                 *
06341 ;*                                                                             *
06342 ;*                           Clear PLAYFIELD memory                            *
06343 ;*                                                                             *
06344 ;*******************************************************************************
06345
06346 ; DESCRIPTION
06347 ;
06348 ; Clears PLAYFIELD memory from $1000 to $1FFF.
06349 ;
06350 ; This subroutine sets the start address of the memory to be cleared then code
06351 ; execution continues into subroutine CLRMEM ($AE0F) where the memory is
06352 ; actually cleared.
06353
06354 CLRPLAYFIELD    LDA #$10
06355
06356 ;*******************************************************************************
06357 ;*                                                                             *
06358 ;*                                   CLRMEM                                    *
06359 ;*                                                                             *
06360 ;*                                Clear memory                                 *
06361 ;*                                                                             *
06362 ;*******************************************************************************
06363
06364 ; DESCRIPTION
06365 ;
06366 ; Clears memory from a given start address to memory address $1FFF. This
06367 ; subroutine is called in the following situations:
06368 ;
06369 ; (1)  In routine INITCOLD ($A14A) at the beginning of the program to initialize
06370 ;      the program's variables 
06371 ;
06372 ; (2)  In subroutine CLRPLAYFIELD ($AE0D) to clear PLAYFIELD memory.
06373 ;
06374 ; As a side effect this subroutine also clears the saved number of space objects
06375 ; and the lock-on flag.
06376 ;
06377 ; INPUT
06378 ;
06379 ;   A = Start address (high byte) of memory to be cleared. Used values are:
06380 ;     $02 -> Clear memory $0200..$1FFF during program initialization
06381 ;     $10 -> Clear PLAYFIELD memory $1000..$1FFF
06382
06383 CLRMEM          STA MEMPTR+1            ; Store start address (high byte) to be cleared
06384                 LDA #0                  ; Store start address (low byte) to be cleared
06385                 TAY                     ;
06386                 STA MEMPTR              ;
06387
06388                 STA ISINLOCKON          ; Clear lock-on flag
06389                 STA OLDMAXSPCOBJIND     ; Clear saved number of space objects
06390
06391 LOOP045         STA (MEMPTR),Y          ; Clear memory location
06392                 INY                     ;
06393                 BNE LOOP045             ;
06394
06395                 INC MEMPTR+1            ; Next page (= 256-byte block)
06396                 LDY MEMPTR+1            ;
06397                 CPY #$20                ;
06398                 TAY                     ;
06399                 BCC LOOP045             ; Loop until memory address $2000 reached
06400                 RTS                     ; Return
06401
06402 ;*******************************************************************************
06403 ;*                                                                             *
06404 ;*                                   TRIGGER                                   *
06405 ;*                                                                             *
06406 ;*                           Handle joystick trigger                           *
06407 ;*                                                                             *
06408 ;*******************************************************************************
06409
06410 ; DESCRIPTION
06411 ;
06412 ; This subroutine handles the joystick trigger and launches one of our
06413 ; starship's photon torpedo. If a target is in full lock-on then a second photon
06414 ; torpedo is prepared for automatic launch in the next game loop iteration.
06415 ;
06416 ; DETAILS
06417 ;
06418 ; If the trigger is pressed then reset the idle counter and, if not in
06419 ; hyperwarp, launch a photon torpedo with the following steps:
06420 ;
06421 ; (1)  If the trigger was pressed in this game loop iteration, a photon torpedo
06422 ;      will be launched if a previously launched photon torpedo is already under
06423 ;      way for at least 255 - 232 = 23 game loop iterations. This avoids firing
06424 ;      photon torpedoes too rapidly. 
06425 ;
06426 ; (2)  Start tracking a space object. If it is in full lock-on, set up the
06427 ;      lock-on timer, activate photon torpedo tracking, and tweak the last saved
06428 ;      trigger state such that our other photon torpedo (if available) is
06429 ;      launched automatically in the next game loop iteration.
06430 ;
06431 ; (3)  If the Photon Torpedoes are destroyed, do nothing.
06432 ;
06433 ; (4)  If the Photon Torpedoes are damaged, launch a photon torpedo from the
06434 ;      same barrel than the previous one. 
06435 ;
06436 ; (5)  If the Photon Torpedoes are not damaged, launch a photon torpedo from the
06437 ;      other barrel. 
06438 ;
06439 ; (6)  Set the lifetime of our starship's photon torpedo to infinite, set the
06440 ;      PLAYER shape to PHOTON TORPEDO. 
06441 ;
06442 ; (7)  Initialize the position vector of our starship's photon torpedo to:
06443 ;
06444 ;          x-coordinate := +256 (+$0100) <KM> (Right barrel)
06445 ;                          -256 (-$FF00) <KM> (Left barrel)
06446 ;          y-coordinate := -256 (-$FF00) <KM>
06447 ;          z-coordinate :=   +1 (+$0001) <KM>
06448 ;
06449 ; (8)  Initialize the velocity vector of our starship's photon torpedo to:
06450 ;
06451 ;          x-velocity   :=   +0 <KM/H>
06452 ;          y-velocity   :=   +0 <KM/H>
06453 ;          z-velocity   := +102 <KM/H> (All views but Aft view)
06454 ;                          -102 <KM/H> (Aft view)
06455 ;
06456 ; (9)  Subtract 10 energy units for launching our starship's photon torpedo.
06457 ;
06458 ; (10) Play the noise sound pattern PHOTON TORPEDO LAUNCHED by continuing code
06459 ;      execution into subroutine NOISE ($AEA8).
06460
06461 TRIGGER         LDA OLDTRIG0            ; Prep last trigger state
06462
06463                 LDY TRIG0               ; Copy current trigger state
06464                 STY OLDTRIG0            ;
06465                 BNE SKIP124             ; Return if trigger currently not pressed
06466
06467                 STY IDLECNTHI           ; Reset idle counter
06468
06469                 LDX WARPSTATE           ; Return if hyperwarp engaged
06470                 BNE SKIP124             ;
06471
06472                 LDX BARRELNR            ; Prep barrel number (0 -> left, 1 -> right)
06473
06474                 CMP #1                  ; If trigger is newly pressed -> handle tracking...
06475                 BEQ SKIP125             ; ...and launch our starship's photon torpedo...
06476                 BCS SKIP127             ; ...else launch our starship's photon torpedo only
06477 SKIP124         RTS                     ; Return
06478
06479 ;*** Set up our starship's photon torpedo tracking *****************************
06480 SKIP125         LDA PL3LIFE,X           ; Return if torpedo's lifetime >= 232 game loops
06481                 CMP #232                ;
06482                 BCS SKIP124             ;
06483
06484                 LDY TRACKDIGIT          ; Store index of tracked space object
06485                 STY PLTRACKED           ;
06486
06487                 LDA #12                 ; Prep lock-on lifetime := 12 game loops
06488                 LDY ISINLOCKON          ; If target is in full lock-on...
06489                 STY ISTRACKING          ; ...activate photon torpedo tracking
06490
06491                 BEQ SKIP126             ; Skip if target not in full lock-on
06492                 LDA #0                  ; Prep lock-on lifetime := 0 game loops
06493 SKIP126         STA LOCKONLIFE          ; Store lock-on lifetime (either 0 or 12 game loops)
06494
06495 ;*** Launch our starship's photon torpedo **************************************
06496 SKIP127         STY OLDTRIG0            ; Update last trigger state
06497                 BIT GCSTATPHO           ; Return if Photon Torpedoes are destroyed
06498                 BVS SKIP124             ;
06499
06500                 BMI SKIP128             ; If Photon Torpedoes damaged launch from same barrel
06501                 TXA                     ; ...else switch barrel from which to launch torpedo
06502                 EOR #$01                ;
06503                 STA BARRELNR            ;
06504
06505 SKIP128         TXA                     ; SUMMARY: Our starship's photon torpedo's...
06506                 STA PL3XPOSSIGN,X       ; x-coordinate := +256 (+$0100) <KM> (right barrel)
06507                 LDA BARRELXTAB,X        ; x-coordinate := -256 (-$FF00) <KM> (left barrel)
06508                 STA PL3XPOSHI,X         ; y-coordinate := -256 (-$FF00) <KM>
06509                 LDA #255                ; z-coordinate :=   +1 (+$0001) <KM>
06510                 STA PL3LIFE,X           ; ...lifetime := 255 game loops
06511                 STA PL3YPOSHI,X         ;
06512                 LDA #0                  ;
06513                 STA PL3SHAPTYPE,X       ; PLAYER3 or PLAYER4 is PHOTON TORPEDO (shape type 0)
06514                 STA PL3ZPOSHI,X         ;
06515                 STA PL3XPOSLO,X         ;
06516                 STA PL3YPOSSIGN,X       ;
06517                 STA PL3YPOSLO,X         ;
06518                 LDA #1                  ;
06519                 STA PL3ZPOSSIGN,X       ;
06520                 STA PL3ZPOSLO,X         ;
06521
06522                 LDA SHIPVIEW            ; SUMMARY: Our starship's photon torpedo's...
06523                 LSR A                   ; x-velocity :=   +0 <KM/H>
06524                 ROR A                   ; y-velocity :=   +0 <KM/H>
06525                 ORA #102                ; z-velocity := +102 <KM/H> (Other views)
06526                 STA PL3ZVEL,X           ; z-velocity := -102 <KM/H> (Aft view)
06527                 LDA #0                  ;
06528                 STA PL3XVEL,X           ;
06529                 STA PL3YVEL,X           ;
06530
06531                 LDX #2                  ; ENERGY := ENERGY - 10 for launching photon torpedo
06532                 JSR DECENERGY           ;
06533
06534                 LDX #$00                ; Play noise sound pattern PHOTON TORPEDO LAUNCHED
06535
06536 ;*******************************************************************************
06537 ;*                                                                             *
06538 ;*                                    NOISE                                    *
06539 ;*                                                                             *
06540 ;*                          Copy noise sound pattern                           *
06541 ;*                                                                             *
06542 ;*******************************************************************************
06543
06544 ; DESCRIPTION
06545 ;
06546 ; Copies a 10-byte noise sound pattern from table NOISEPATTAB ($BF20). The first
06547 ; 8 bytes are copied to the noise sound pattern area NOISETORPTIM
06548 ; ($DA)..NOISELIFE ($E1), the remaining 2 bytes are copied to audio registers
06549 ; AUDCTL ($D208) and AUDF3 ($D204). The noise sound pattern is automatically
06550 ; played in subroutine SOUND ($B2AB).
06551 ;
06552 ; NOTE: the first 8 bytes of each pattern in table NOISEPATTAB ($BF20) are
06553 ; copied in reverse order from memory. See subroutine SOUND ($B2AB) for details
06554 ; on the noise sound patterns stored in NOISEPATTAB ($BF20).
06555 ;
06556 ; Playing a SHIELD EXPLOSION or ZYLON EXPLOSION noise sound pattern overrides a
06557 ; currently playing PHOTON TORPEDO LAUNCHED noise sound pattern.
06558 ;
06559 ; Playing a PHOTON TORPEDO LAUNCHED noise sound pattern overrides a currently
06560 ; playing PHOTON TORPEDO LAUNCHED noise sound pattern if the latter has < 24
06561 ; TICKs to play.
06562 ;
06563 ; INPUT
06564 ;
06565 ;   X = Offset into table NOISEPATTAB ($BF20) to index noise sound patterns.
06566 ;       Used values are:
06567 ;     $00 -> PHOTON TORPEDO LAUNCHED
06568 ;     $0A -> SHIELD EXPLOSION (either our starship or a starbase explodes)
06569 ;     $14 -> ZYLON EXPLOSION
06570
06571 NOISE           TXA                     ; Skip if SHIELD EXPLOSION or ZYLON EXPLOSION playing
06572                 BNE SKIP129             ;
06573
06574                 LDA NOISELIFE           ; Return if PHOTON TORPEDO LAUNCHED noise sound pat.
06575                 CMP #24                 ; ...playing for yet more than 24 TICKs
06576                 BCS SKIP130             ;
06577
06578 SKIP129         LDY #7                  ; Copy noise sound pattern (in reverse order)
06579 LOOP046         LDA NOISEPATTAB,X       ;
06580                 STA NOISETORPTIM,Y      ;
06581                 INX                     ;
06582                 DEY                     ;
06583                 BPL LOOP046             ;
06584
06585                 LDA NOISEPATTAB,X       ; Copy AUDCTL from noise sound pattern table
06586                 STA AUDCTL              ;
06587                 LDA NOISEPATTAB+1,X     ; Copy AUDF3 from noise sound pattern table
06588                 STA AUDF3               ;
06589
06590 SKIP130         RTS                     ; Return
06591
06592 ;*******************************************************************************
06593 ;*                                                                             *
06594 ;*                                  HOMINGVEL                                  *
06595 ;*                                                                             *
06596 ;*      Calculate homing velocity of our starship's photon torpedo 0 or 1      *
06597 ;*                                                                             *
06598 ;*******************************************************************************
06599
06600 ; DESCRIPTION
06601 ;
06602 ; Calculates the x (or y) velocity vector component of our starship's photon
06603 ; torpedo 0 or 1 when it is tracking (homing in on) a target space object.
06604 ;
06605 ; Our starship's photon torpedo's x (or y) velocity vector component depends on
06606 ; the PLAYER column (or row) number difference between the target PLAYER and our
06607 ; starship's photon torpedo PLAYER in Player/Missile (PM) pixels. This
06608 ; difference is used as an index to pick the new x (or y) velocity vector
06609 ; component of out starship's photon torpedo from table HOMVELTAB ($BFC9):
06610 ;
06611 ; +---------------+--------------+
06612 ; | Difference in | New Velocity |
06613 ; |   PM Pixels   |  Component   |
06614 ; +---------------+--------------+
06615 ; |    >= +7      |   -64 <KM/H> |
06616 ; |       +6      |   -56 <KM/H> |
06617 ; |       +5      |   -48 <KM/H> |    
06618 ; |       +4      |   -40 <KM/H> |
06619 ; |       +3      |   -24 <KM/H> |
06620 ; |       +2      |   -16 <KM/H> |    
06621 ; |       +1      |    -8 <KM/H> |
06622 ; |        0      |     0 <KM/H> |
06623 ; |       -1      |    +8 <KM/H> |    
06624 ; |       -2      |   +16 <KM/H> |
06625 ; |       -3      |   +24 <KM/H> |
06626 ; |       -4      |   +40 <KM/H> |    
06627 ; |       -5      |   +48 <KM/H> |
06628 ; |       -6      |   +56 <KM/H> |    
06629 ; |    <= -7      |   +64 <KM/H> |
06630 ; +---------------+--------------+      
06631 ;
06632 ; INPUT
06633 ;
06634 ;   A     = PLAYER column (or row) number difference between the target PLAYER
06635 ;           and our starship's photon torpedo PLAYER in Player/Missile pixels
06636 ;
06637 ;   CARRY = Sign of the PLAYER column (or row) number difference. Used values
06638 ;           are:
06639 ;     0 -> Negative difference (target PLAYER column (or row) number < our
06640 ;          starship's photon torpedo PLAYER column (or row) number
06641 ;     1 -> Positive difference (target PLAYER column (or row) number >= our
06642 ;          starship's photon torpedo PLAYER column (or row) number
06643 ;
06644 ; OUTPUT
06645 ;
06646 ;   A = New velocity vector component of our starship's photon torpedo in <KM/H>
06647
06648 L.VELSIGN       = $6A                   ; Saves velocity sign
06649
06650 HOMINGVEL       LDY #NEG                ; Preload negative velocity sign
06651                 BCS SKIP131             ; Skip if difference is positive
06652
06653                 EOR #$FF                ; Invert to get absolute value of difference
06654                 LDY #0                  ; Preload positive velocity sign
06655
06656 SKIP131         STY L.VELSIGN           ; Save velocity sign
06657                 CMP #8                  ;
06658                 BCC SKIP132             ;
06659                 LDA #7                  ; Limit difference to 0..7
06660 SKIP132         TAY                     ;
06661                 LDA L.VELSIGN           ; Reload velocity sign
06662                 ORA HOMVELTAB,Y         ; Combine with homing velocity from table
06663                 RTS                     ; Return
06664
06665 ;*******************************************************************************
06666 ;*                                                                             *
06667 ;*                                   DAMAGE                                    *
06668 ;*                                                                             *
06669 ;*             Damage or destroy one of our starship's subsystems              *
06670 ;*                                                                             *
06671 ;*******************************************************************************
06672
06673 ; DESCRIPTION
06674 ;
06675 ; Damages or destroys one of our starship's subsystems. There are 6 subsystems:
06676 ;
06677 ; (1)  Photon Torpedoes
06678 ; (2)  Engines
06679 ; (3)  Shields
06680 ; (4)  Attack Computer
06681 ; (5)  Long-Range Scan
06682 ; (6)  Subspace Radio
06683 ;
06684 ; Their status is stored and displayed in the Galactic Chart Panel Display by
06685 ; the colored letters PESCLR. The color of each letter represents the
06686 ; subsystem's status:
06687 ;
06688 ; +---------------+------------------+
06689 ; | Letter Color  | Subsystem Status |
06690 ; +---------------+------------------+
06691 ; | {LIGHT GREEN} | OK               |
06692 ; | {CORN YELLOW} | Damaged          |
06693 ; | {PINK}        | Destroyed        |
06694 ; +---------------+------------------+
06695 ;
06696 ; This subroutine first makes sure that we are not in demo mode. Then it picks a
06697 ; random value in 0..255 and the damage probability value. The latter value
06698 ; depends on the mission level and is picked from table DAMAGEPROBTAB ($BF10):
06699 ;
06700 ; +-----------+-------------------+---------------+
06701 ; |  Mission  |       Damage      |    Damage     |
06702 ; |   Level   | Probability Value |  Probability  |
06703 ; +-----------+-------------------+---------------+
06704 ; | NOVICE    |          0        |  0% (  0:256) | 
06705 ; | PILOT     |         80        | 31% ( 80:256) |
06706 ; | WARRIOR   |        180        | 70% (180:256) |
06707 ; | COMMANDER |        254        | 99% (254:256) |
06708 ; +-----------+-------------------+---------------+
06709 ;
06710 ; If the random number is lower than the damage probability value, a randomly
06711 ; picked subsystem is about to get damaged (or destroyed). There is a built-in
06712 ; upfront probability of 25% (2:8) that no subsystem gets harmed.
06713 ;
06714 ; If the picked subsystem is already destroyed then another subsystem is picked.
06715 ;
06716 ; Then the title phrase offset is picked from table DAMAGEPHRTAB ($BF14) to
06717 ; display the damaged subsystem in the title line. Next, color bits are picked
06718 ; that indicate a damaged system.
06719 ;
06720 ; If the Zylon photon torpedo's lifetime >= 30 game loop iterations the
06721 ; subsystem will not only be damaged but destroyed.
06722 ;
06723 ; NOTE: The Zylon photon torpedo lifetime decreases from 62 to 0 game loop
06724 ; iterations. With a remaining lifetime >= 30 game loop iterations it is
06725 ; considered strong enough to destroy one of our starship's subsystems. There
06726 ; are two exceptions to this rule: If the Attack Computer was picked to be
06727 ; destroyed it will be damaged only - not destroyed - if the Long-Range Scan has
06728 ; been already destroyed, and vice versa.
06729 ;
06730 ; Then the title phrase offset from table DESTROYPHRTAB ($BF1A) is picked to
06731 ; display the destroyed subsystem in the title line. Next, color bits are picked
06732 ; that indicate a destroyed system.
06733 ;
06734 ; The color of the subsystem's status letter is adjusted in the Galactic Chart
06735 ; Panel Display. Next, the title phrase describing the subsystem's status is
06736 ; enqueued for display in the title line. If the Attack Computer has been
06737 ; destroyed it is switched off and the PLAYFIELD is cleared. The title line is
06738 ; updated with the "DAMAGE CONTROL" message. Finally, the beeper sound pattern
06739 ; DAMAGE REPORT is played in subroutine BEEP ($B3A6).
06740
06741 DAMAGE          BIT ISDEMOMODE          ; Return if in demo mode
06742                 BMI SKIP137             ;
06743
06744 ;*** Damage some subsystem *****************************************************
06745                 LDX MISSIONLEVEL        ; Prep mission level
06746 LOOP047         LDA RANDOM              ; Return if random number >= damage probability
06747                 CMP DAMAGEPROBTAB,X     ; ...(the latter depends on mission level)
06748                 BCS SKIP137             ;
06749
06750                 AND #$07                ; Randomly pick 1 of 6 subsystems
06751                 CMP #6                  ; Return if no subsystem picked
06752                 BCS SKIP137             ;
06753
06754                 TAX                     ;
06755                 LDA GCSTATPHO,X         ; Get picked subsystem status letter
06756                 ASL A                   ; Check bit B6 (= destroyed) of letter code
06757                 BMI LOOP047             ; Try again if subsystem already destroyed
06758
06759                 LDA PL2LIFE             ; Load Zylon photon torpedo lifetime...
06760                 CMP #30                 ; ...and compare it to 30 game loops
06761
06762                 LDA #CCS.COL2           ; Preload COLOR2 text color bits (= damaged status)
06763                 LDY DAMAGEPHRTAB,X      ; Preload title phrase offset of damaged subsystem
06764
06765                 BCC SKIP135             ; Skip if Zylon torpedo lifetime < 30 game loops
06766
06767                 CPX #3                  ; Skip if selected subsystem not Attack Computer
06768                 BNE SKIP133             ;
06769                 BIT GCSTATLRS           ; Skip if Long-Range Scan already destroyed
06770                 BVS SKIP135             ;
06771 SKIP133         CPX #4                  ; Skip if selected subsystem is not Long-Range Scan
06772                 BNE SKIP134             ;
06773                 BIT GCSTATCOM           ; Skip if Attack Computer already destroyed
06774                 BVS SKIP135             ;
06775
06776 SKIP134         LDA #CCS.COL3           ; Preload COLOR3 text color bits (= destroyed status)
06777                 LDY DESTROYPHRTAB,X     ; Preload title phrase offset of destroyed subsystem
06778
06779 SKIP135         ORA GCSTATPHO,X         ; Combine status letter with new color
06780                 STA GCSTATPHO,X         ;
06781                 STY NEWTITLEPHR         ; Enqueue damage status title phrase
06782                 BIT GCSTATCOM           ; Skip if Attack Computer OK or damaged
06783                 BVC SKIP136             ;
06784
06785                 LDA #0                  ; Switch Attack Computer off
06786                 STA DRAINATTCOMP        ;
06787                 JSR CLRPLAYFIELD        ; Clear PLAYFIELD
06788
06789 SKIP136         LDY #$52                ; Set title phrase "DAMAGE CONTROL..."
06790                 JSR SETTITLE            ;
06791
06792                 LDX #$12                ; Play beeper sound pattern DAMAGE REPORT
06793                 JSR BEEP                ;
06794
06795 SKIP137         RTS                     ; Return
06796
06797 ;*******************************************************************************
06798 ;*                                                                             *
06799 ;*                                  COLLISION                                  *
06800 ;*                                                                             *
06801 ;*            Detect a collision of our starship's photon torpedoes            *
06802 ;*                                                                             *
06803 ;*******************************************************************************
06804
06805 ; DESCRIPTION
06806 ;
06807 ; Both of our starship's photon torpedoes are checked if they have collided with
06808 ; a space object represented by PLAYER0..2, such as a Zylon ship, a Zylon photon
06809 ; torpedo, a starbase, or a meteor. 
06810 ;
06811 ; For quick lookup, the following table lists the PLAYERs and what space objects
06812 ; they represent:
06813 ;
06814 ; +--------+--------------------------------------------------+
06815 ; | PLAYER |                   Represents                     |
06816 ; +--------+--------------------------------------------------+
06817 ; |   0    | Zylon ship 0, Starbase Left                      |
06818 ; |   1    | Zylon ship 1, Starbase Right                     |
06819 ; |   2    | Zylon photon torpedo, Starbase Center, Meteor    | 
06820 ; |   3    | Our starship's photon torpedo 0                  |
06821 ; |   4    | Our starship's photon torpedo 1, Transfer Vessel |
06822 ; +--------+--------------------------------------------------+
06823 ;
06824 ; NOTE: Only space objects represented by PLAYER0..2 are checked for collisions.
06825 ; The transfer vessel of the starbase, represented by PLAYER4, is not checked
06826 ; and therefore cannot be destroyed by one of our starship's photon torpedoes.
06827 ;
06828 ; This subroutine first checks if our starship's photon torpedoes are
06829 ; represented by alive PLAYERs with PHOTON TORPEDO shape.
06830 ;
06831 ; In order to detect a collision with a space object, our starship's photon
06832 ; torpedo must compare its x, y, and z coordinates with the ones of the space
06833 ; object.
06834 ;
06835 ; Instead of comparing the x and y coordinates, however, this subroutines uses a
06836 ; much more efficient method by inspecting the Player/Missile collision
06837 ; registers, as the x and y axis of the 3D coordinate system establish the plane
06838 ; in which the TV screen lies. Each of our starship's photon torpedoes has its
06839 ; own Player/Missile collision register: PL3HIT ($82) for our starship's photon
06840 ; torpedo 0 and PL4HIT ($83) for our starship's photon torpedo 1. By inspecting
06841 ; these registers the hit space object is determined: 
06842 ;
06843 ; +---------------------------------------------------+-------------------------+
06844 ; |          Bits B2..0 of Collision Register         |        Hit PLAYER       |
06845 ; |              (0 -> Not Hit, 1 -> Hit)             |                         |
06846 ; +-----------------+----------------+----------------+                         |
06847 ; |     PLAYER2     |     PLAYER1    |    PLAYER0     |                         |
06848 ; | (Zylon torpedo) | (Zylon ship 1) | (Zylon ship 0) |                         |
06849 ; +-----------------+----------------+----------------+-------------------------+
06850 ; |        0        |        0       |        0       | None                    |
06851 ; |        0        |        0       |        1       | PLAYER0 (Zylon ship 0)  |
06852 ; |        0        |        1       |        0       | PLAYER1 (Zylon ship 1)  |
06853 ; |        0        |        1       |        1       | PLAYER1 (Zylon ship 1)  |
06854 ; |        1        |        0       |        0       | PLAYER2 (Zylon torpedo) |
06855 ; |        1        |        0       |        1       | PLAYER2 (Zylon torpedo) |
06856 ; |        1        |        1       |        0       | PLAYER1 (Zylon ship 1)  |
06857 ; |        1        |        1       |        1       | PLAYER1 (Zylon ship 1)  |
06858 ; +-----------------+----------------+----------------+-------------------------+
06859 ;
06860 ; If the lifetime of the hit space object has already expired, then the hit is
06861 ; ignored.
06862 ;
06863 ; A collision along the z-axis happens if the z-coordinate of our starship's
06864 ; photon torpedo is close enough to the z-coordinate of the space object:
06865 ;
06866 ; The absolute value of the z-coordinate of the space object is converted into a
06867 ; range index in 0..7. This index picks a minimum and a maximum z-coordinate
06868 ; from tables HITMINZTAB ($BF7D) and HITMAXZTAB ($BF75). If the absolute value
06869 ; of the z-coordinate of our starship's photon torpedo is inside this interval,
06870 ; then our starship's photon torpedo has hit the space object. The following
06871 ; table lists the relevant values: 
06872 ;
06873 ; +-----------------------+-------+--------------------------+--------------------------+
06874 ; | ABS(z-Coordinate)     | Range | Min ABS(z-Coordinate)    | Max ABS(z-Coordinate)    |
06875 ; | of Space Object       | Index | of Photon Torpedo to Hit | of Photon Torpedo to Hit |
06876 ; +-----------------------+-------+--------------------------+--------------------------+
06877 ; | <=   511 ($01**) <KM> |   0   |           0 ($00**) <KM> |      < 3328 ($0C**) <KM> |
06878 ; | <=  1023 ($03**) <KM> |   1   |           0 ($00**) <KM> |      < 3328 ($0C**) <KM> |
06879 ; | <=  1535 ($05**) <KM> |   2   |           0 ($00**) <KM> |      < 3328 ($0C**) <KM> |
06880 ; | <=  2047 ($07**) <KM> |   3   |         512 ($02**) <KM> |      < 3328 ($0C**) <KM> |
06881 ; | <=  2559 ($09**) <KM> |   4   |        1024 ($04**) <KM> |      < 3840 ($0E**) <KM> |
06882 ; | <=  3071 ($0B**) <KM> |   5   |        1536 ($06**) <KM> |      < 3840 ($0E**) <KM> |
06883 ; | <=  3583 ($0D**) <KM> |   6   |        2048 ($08**) <KM> |      < 3840 ($0E**) <KM> |
06884 ; | <= 65535 ($FF**) <KM> |   7   |        3072 ($0C**) <KM> |      < 8448 ($20**) <KM> |
06885 ; +-----------------------+-------+--------------------------+--------------------------+
06886 ;
06887 ; if a collision has been detected, the "age" (= initial lifetime - remaining
06888 ; lifetime) of our starship's photon torpedo is calculated. This age is used to
06889 ; delay playing the ZYLON EXPLOSION noise sound pattern but also to determine
06890 ; the strength of our starship's photon torpedo. Only photon torpedoes of an age
06891 ; < 15 game loop iterations can destroy a Zylon basestar.
06892 ;
06893 ; Some clean-up work is done before the actual explosion: The lock-on timer, our
06894 ; starship's photon torpedo lifetime, and the hit space object's PLAYER lifetime
06895 ; is set to 0. 
06896 ;
06897 ; If a meteor or a Zylon photon torpedo have been hit, then the score is not
06898 ; changed, skipping right to the explosion part. Otherwise, our starship's
06899 ; photon torpedo tracking flag is cleared and the Galactic Chart Map is updated.
06900 ; If a starbase was destroyed, then 3 points are added to the score. If a Zylon
06901 ; ship was destroyed, then 6 points are added to the score and the Zylon KILL
06902 ; COUNTER readout of the Control Panel Display is incremented. Next, the
06903 ; explosion is initialized in subroutine INITEXPL ($AC6B).
06904 ;
06905 ; NOTE: This subroutine lacks proper explosion initialization if the starbase
06906 ; was hit. The actual explosion initialization is done in subroutine DOCKING
06907 ; ($ACE6) when the code finds out that the starbase sector is no more marked as
06908 ; such in the Galactic Chart.
06909 ;
06910 ; Finally, the Galactic Chart Map is searched for a remaining Zylon unit. If
06911 ; none is found then the mission is complete and code execution continues into
06912 ; subroutine GAMEOVER2 ($B121), ending the game. 
06913
06914 L.PLHIT         = $6B                   ; Saves PLAYER (and space object) index of hit PLAYER
06915 L.VIEWDIR       = $6C                   ; Saves view direction. Used values are:
06916                                         ;   $00 -> Front view
06917                                         ;   $FF -> Aft view
06918
06919 COLLISION       LDX #2                  ; Loop over our starship's two photon torpedoes
06920 LOOP048         DEX                     ;
06921                 BPL SKIP138             ; Branch into loop body below
06922                 RTS                     ; Return
06923
06924 ;*** Photon torpedo sanity checks **********************************************
06925 SKIP138         LDA PL3SHAPTYPE,X       ; Next photon torpedo if PLAYER not a PHOTON TORPEDO
06926                 BNE LOOP048             ;
06927
06928                 LDA PL3LIFE,X           ; Next photon torpedo if PLAYER not alive
06929                 BEQ LOOP048             ;
06930
06931 ;*** Check if our starship's photon torpedo has hit in x-y plane ***************
06932                 LDA PL3HIT,X            ; Check Player/Missile collision register
06933                 AND #$07                ; Next torpedo if no torpedo-to-PLAYER collision
06934                 BEQ LOOP048             ;
06935
06936                 LSR A                   ; Find out which of PLAYER0..2 was hit in PLAYFIELD
06937                 CMP #3                  ;
06938                 BNE SKIP139             ;
06939                 LSR A                   ;
06940 SKIP139         TAY                     ; Save resulting index of hit PLAYER
06941
06942                 LDA PL0LIFE,Y           ; Next torpedo if PLAYER0..2 (= targets) not alive
06943                 BEQ LOOP048             ;
06944
06945 ;*** Has our starship's photon torpedo hit within valid z-coordinate interval? *
06946                 LDA SHIPVIEW            ; Skip if in Front view
06947                 BEQ SKIP140             ;
06948                 LDA #$FF                ; Calculate range index...
06949 SKIP140         STA L.VIEWDIR           ; Saves view direction
06950                 EOR ZPOSHI,Y            ; Calc ABS(z-coordinate (high byte)) of hit object
06951                 CMP #16                 ; Limit range index to 0..7
06952                 BCC SKIP141             ;
06953                 LDA #15                 ;
06954 SKIP141         LSR A                   ;
06955                 STY L.PLHIT             ; Save index of hit PLAYER
06956
06957                 TAY                     ;
06958                 LDA L.VIEWDIR           ; Reload view direction
06959                 EOR PL3ZPOSHI,X         ; Calc ABS(z-coordinate (high byte)) of torpedo
06960
06961                 CMP HITMAXZTAB,Y        ; Next torpedo if torpedo >= max hit z-coordinate
06962                 BCS LOOP048             ;
06963
06964                 CMP HITMINZTAB,Y        ; Next torpedo if torpedo < min hit z-coordinate
06965                 BCC LOOP048             ;
06966
06967 ;*** Our starship's photon torpedo has hit within valid z-coordinate interval! *
06968                 LDY L.PLHIT             ; Reload index of hit PLAYER
06969                 SEC                     ; Calc "age" of photon torpedo in game loops to...
06970                 LDA #255                ; delay playing ZYLON EXPLOSION noise sound pattern
06971                 SBC PL3LIFE,X           ;
06972                 STA NOISEZYLONTIM       ;
06973
06974                 CMP #15                 ; Skip if photon torpedo "age" < 15
06975                 BCC SKIP142             ;
06976                 LDA PL0SHAPTYPE,Y       ; CARRY := PLAYER is ZYLON BASESTAR (shape type 8)
06977                 CMP #SHAP.ZBASESTAR     ; (and torpedo "age" good to destroy ZYLON BASESTAR)
06978
06979 ;*** Clean up our starship's photon torpedo and hit PLAYER *********************
06980 SKIP142         LDA #0                  ; Lock-on lifetime := 0 game loops
06981                 STA LOCKONLIFE          ;
06982                 STA PL3LIFE,X           ; Photon torpedo's lifetime := 0 game loops
06983                 BCS SKIP144             ; If CARRY set do not score, just do explosion
06984
06985                 STA PL0LIFE,Y           ; Hit PLAYER lifetime := 0 game loops
06986
06987                 LDA PL0SHAPTYPE,Y       ; If hit PLAYER is...
06988                 BEQ SKIP144             ; ...a PHOTON TORPEDO (shape type 0)...
06989                 CMP #SHAP.METEOR        ; ...or a METEOR (shape type 6)...
06990                 BEQ SKIP144             ; ...do not score, just do explosion
06991
06992                 LDA #0                  ; Clear photon torpedo tracking flag
06993                 STA ISTRACKING          ;
06994
06995 ;*** Zylon ship (or starbase) destroyed! ***************************************
06996                 LDX CURRSECTOR          ; Decrement Zylon count on Galactic Chart
06997                 DEC GCMEMMAP,X          ;
06998                 BPL SKIP143             ; Skip if destroyed space object was Zylon ship
06999
07000 ;*** Starbase destroyed! *******************************************************
07001                 LDA #0                  ; Remove destroyed starbase from Galactic Chart
07002                 STA GCMEMMAP,X          ;
07003                 SEC                     ; SCORE := SCORE - 3 for destroying starbase
07004                 LDA SCORE               ;
07005                 SBC #3                  ;
07006                 STA SCORE               ;
07007                 LDA SCORE+1             ;
07008                 SBC #0                  ;
07009                 STA SCORE+1             ;
07010                 RTS                     ; Return
07011
07012 ;*** Zylon ship destroyed! *****************************************************
07013 SKIP143         CLC                     ; SCORE := SCORE + 6 for destroying Zylon ship
07014                 LDA SCORE               ;
07015                 ADC #6                  ;
07016                 STA SCORE               ;
07017                 LDA SCORE+1             ;
07018                 ADC #0                  ;
07019                 STA SCORE+1             ;
07020
07021                 LDX #1                  ; Increment Zylon KILL COUNTER readout...
07022 LOOP049         INC KILLCNTD1,X         ; ...of Control Panel Display
07023                 LDA KILLCNTD1,X         ;
07024                 CMP #[CCS.COL1!CCS.9]+1 ;
07025                 BCC SKIP144             ;
07026                 LDA #[CCS.COL1!CCS.0]   ;
07027                 STA KILLCNTD1,X         ;
07028                 DEX                     ;
07029                 BPL LOOP049             ;
07030
07031 SKIP144         JSR INITEXPL            ; Init explosion at hit PLAYER
07032
07033 ;*** Any Zylon ships left? *****************************************************
07034                 LDX #127                ; Scan all sectors of Galactic Chart
07035 LOOP050         LDA GCMEMMAP,X          ;
07036                 BMI SKIP145             ;
07037                 BNE SKIP146             ; Return if Zylon sector found
07038 SKIP145         DEX                     ;
07039                 BPL LOOP050             ;
07040
07041 ;*** Game over (Mission Complete) **********************************************
07042                 LDY #$3F                ; Set title phrase "MISSION COMPLETE"
07043                 LDX #0                  ; Set mission bonus offset
07044                 JSR GAMEOVER2           ; Game over
07045 SKIP146         RTS                     ; Return
07046
07047 ;*******************************************************************************
07048 ;*                                                                             *
07049 ;*                                  KEYBOARD                                   *
07050 ;*                                                                             *
07051 ;*                            Handle Keyboard Input                            *
07052 ;*                                                                             *
07053 ;*******************************************************************************
07054
07055 ; DESCRIPTION
07056 ;
07057 ; If a keyboard code has been collected during a keyboard IRQ in the Immediate
07058 ; Interrupt Request handler IRQHNDLR ($A751), the idle counter is reset and the
07059 ; PLAYER-PLAYFIELD priority arranges the PLAYERs in front of the PLAYFIELD.
07060 ; Then, the keyboard code is compared with keyboard codes of table KEYTAB
07061 ; ($BABE). If no match is found the "WHAT'S WRONG" message is displayed in the
07062 ; title line and code execution returns.
07063 ;
07064 ; If one of the speed keys '0'..'9' has been pressed, a pending hyperwarp is
07065 ; aborted in subroutine ABORTWARP ($A980) and code execution returns. Otherwise
07066 ; the Engines drain rate is adjusted as well as the new velocity of our
07067 ; starship. If the Engines are damaged, a maximum speed is possible equivalent
07068 ; to speed key '5'.
07069 ;
07070 ; If one of our starship's view keys 'F' (Front), 'A' (Aft), 'G' (Galactic
07071 ; Chart), or 'L' (Long-Range Scan) have been pressed, the Display List is
07072 ; modified accordingly in subroutine MODDLST ($ADF1) and a new star field of 12
07073 ; stars is created with the help of subroutine INITPOSVEC ($B764). Code
07074 ; execution returns via subroutine UPDSCREEN ($B07B).
07075 ;
07076 ; If one of the 'T' (Tracking Computer), 'S' (Shields) or 'C' (Attack Computer)
07077 ; keys have been pressed, the corresponding status bits are toggled and the
07078 ; title line is updated with the corresponding title phrase. The beeper sound
07079 ; pattern ACKNOWLEDGE is played in subroutine BEEP ($B3A6). The tracking letter
07080 ; of the Control Panel Display is updated and the PLAYFIELD is cleared in
07081 ; subroutine CLRPLAYFIELD ($AE0D). If the Attack Computer is on, the Front or
07082 ; Aft view cross hairs are drawn, depending on the current view of our starship,
07083 ; via subroutine DRAWLINES ($A76F).
07084 ;
07085 ; If the 'H' (Hyperwarp) key has been pressed then the hyperwarp is engaged. Our
07086 ; starship's velocity is set to the maximum value, the Engines drain rate is
07087 ; increased to the equivalent of speed key '7'. Star trails are prepared. The
07088 ; position vector of the Hyperwarp Target Marker (PLAYER3) is set to the
07089 ; following values:
07090 ;
07091 ;     x-coordinate :=   +0 (+$0000) <KM>
07092 ;     y-coordinate := +256 (+$0100) <KM>
07093 ;     z-coordinate :=    + (+$****) <KM> (sign only)
07094 ;
07095 ; The velocity vector is set to the following values:
07096 ;
07097 ;     x-velocity   :=  (not initialized)
07098 ;     y-velocity   :=  (not initialized)
07099 ;     z-velocity   :=          +0 <KM/H>
07100 ;
07101 ; The temporary arrival hyperwarp marker column and row numbers are saved. If
07102 ; not in a NOVICE mission, the maximum veer-off velocity of the Hyperwarp Target
07103 ; Marker during hyperwarp is picked from table VEERMASKTAB ($BED7). This value
07104 ; depends on the selected hyperwarp energy (and thus on the distance to
07105 ; hyperwarp). Finally, the title line displays the "HYPERWARP ENGAGED" message.
07106 ;
07107 ; If the 'M' (Manual target selector) key has been pressed, the tracked target
07108 ; space object is swapped and the corresponding digit of the Control Panel
07109 ; Display is toggled between 0 and 1.
07110 ;
07111 ; If the 'P' (Pause) key has been pressed, an endless loop waits until the
07112 ; joystick is pushed.
07113 ;
07114 ; BUG (at $B103): The endless loop branches back one instruction too far.
07115 ; Suggested fix: Branch to instruction LDA PORTA at $B0FE.
07116 ;
07117 ; If the 'INV' (Abort mission) key has been pressed, the mission is aborted by
07118 ; setting the mission bonus offset, then displaying the "MISSION ABORTED"
07119 ; message in the title line. Code execution continues into subroutine GAMEOVER
07120 ; ($B10A).
07121 ;
07122 ; NOTE: This subroutine has two additional entry points:
07123 ;
07124 ; (1)  SETVIEW ($B045), which is used to enforce the Front view. It is entered
07125 ;      from the game loop GAMELOOP ($A1F3) and subroutines INITSTART ($A15E) and
07126 ;      DECENERGY ($B86F).
07127 ;
07128 ; (2)  UPDSCREEN ($B07B), which draws the cross hairs, the Attack Computer
07129 ;      Display and sets the tracking letter of the Control Panel Display. It is
07130 ;      entered from subroutine DOCKING ($ACE6).
07131
07132 L.KEYCODE       = $6A                   ; Saves pressed keyboard code
07133
07134 KEYBOARD        LDA KEYCODE             ; Return if no keyboard code collected
07135                 BEQ SKIP150             ;
07136
07137                 LDX #20                 ; Prep keyboard code table loop index
07138                 STA L.KEYCODE           ; Save keyboard code
07139
07140                 LDA #0                  ; Reset idle counter
07141                 STA IDLECNTHI           ;
07142                 STA KEYCODE             ; Clear keyboard code
07143
07144                 LDA #$11                ; GTIA: enable PLAYER4, prio: PLs > PFs > BGR
07145                 STA PRIOR               ; (PLAYERs appear behind cross hairs)
07146
07147 ;*** Search keyboard code in lookup table **************************************
07148
07149 LOOP051         LDA KEYTAB,X            ; Loop over all valid keyboard codes
07150                 CMP L.KEYCODE           ;
07151                 BEQ SKIP147             ; Branch if matching entry found
07152                 DEX                     ;
07153                 BPL LOOP051             ; Next keyboard code
07154
07155                 LDY #$10                ; No match found...
07156                 JMP SETTITLE            ; ...set title phrase "WHATS WRONG?" and return
07157
07158 ;*** Handle '0'..'9' keyboard keys (speed) *************************************
07159 SKIP147         CPX #10                 ; Skip section if keyboard code does not match
07160                 BCS SKIP151             ;
07161
07162                 LDA WARPSTATE           ; Skip if hyperwarp disengaged...
07163                 BEQ SKIP148             ;
07164                 JMP ABORTWARP           ; ...else abort hyperwarp
07165
07166 SKIP148         BIT GCSTATENG           ; Skip if Engines are OK or destroyed
07167                 BVC SKIP149             ;
07168                 CPX #6                  ; Allow max velocity equivalent to speed key '5'
07169                 BCC SKIP149             ;
07170                 LDX #5                  ;
07171
07172 SKIP149         LDA DRAINRATETAB,X      ; Set Engines energy drain rate
07173                 STA DRAINENGINES        ;
07174                 LDA VELOCITYTAB,X       ; Set new velocity
07175                 STA NEWVELOCITY         ;
07176 SKIP150         RTS                     ; Return
07177
07178 ;*** Handle 'F', 'A', 'L', 'G' keyboard keys (our starship's views) ************
07179 SKIP151         CPX #14                 ; Skip section if keyboard code does not match
07180                 BCS SKIP152             ;
07181
07182 ;*** Entry to force Front view after program init and failed missions **********
07183 SETVIEW         LDA VIEWMODETAB-10,X    ; Store our starship's view type
07184                 STA SHIPVIEW            ;
07185
07186                 LDY DLSTFRAGOFFTAB-10,X ; Get DL fragment offset (Front, Aft, LRS, GC)
07187                 LDX #$02                ; Switch to corresponding view
07188                 LDA #$08                ;
07189                 JSR MODDLST             ;
07190
07191                 LDX #NUMSPCOBJ.NORM-1   ; Create new star field of 12 stars
07192 LOOP052         JSR INITPOSVEC          ;
07193                 DEX                     ;
07194                 CPX #NUMSPCOBJ.PL       ;
07195                 BCS LOOP052             ;
07196
07197                 BCC UPDSCREEN           ; Return via updating screen (below)
07198
07199 ;*** Handle 'T', 'S', 'C' keyboard keys (Tracking, Shields, Attack Computer) ***
07200 SKIP152         CPX #17                 ; Skip section if keyboard code does not match
07201                 BCS SKIP156             ;
07202
07203                 LDY MSGOFFTAB-14,X      ; Prep title phrase offset "... OFF"
07204                 LDA ISTRACKCOMPON-14,X  ; Toggle status bits (also energy consumption values)
07205                 EOR MSGBITTAB-14,X      ;
07206                 STA ISTRACKCOMPON-14,X  ;
07207                 BEQ SKIP153             ;
07208                 LDY MSGONTAB-14,X       ; Prep title phrase offset "... ON"
07209 SKIP153         JSR SETTITLE            ; Set title phrase to "... ON" or "... OFF" version
07210
07211                 LDX #$0C                ; Play beeper sound pattern ACKNOWLEDGE
07212                 JSR BEEP                ;
07213
07214 ;*** Update PLAYFIELD (Cross hairs, Attack Computer, set tracking letter) ******
07215 UPDSCREEN       LDX #CCS.T              ; Get custom char 'T' (entry point TRANSFER COMPLETE)
07216                 LDY ISTRACKCOMPON       ;
07217                 BEQ SKIP154             ; Skip if Tracking Computer is on
07218
07219                 INX                     ; Get custom char 'C'
07220
07221 SKIP154         STX TRACKC1             ; Store tracking character in Control Panel Display
07222                 JSR CLRPLAYFIELD        ; Clear PLAYFIELD
07223                 LDA DRAINATTCOMP        ; Return if Attack Computer off
07224                 BEQ SKIP150             ;
07225
07226                 LDX SHIPVIEW            ; If Aft view   -> Draw Aft cross hairs and return
07227                 BEQ SKIP155             ; If Front view -> Draw Front cross hairs and ...
07228                 CPX #$01                ;                  ...Attack Computer and return
07229                 BNE SKIP150             ;
07230                 LDX #$2A                ;
07231 SKIP155         JMP DRAWLINES           ;
07232
07233 ;*** Handle 'H' keyboard key (Hyperwarp) ***************************************
07234 SKIP156         CPX #17                 ; Skip if keyboard code does not match
07235                 BNE SKIP158             ;
07236
07237 ;*** Engage Hyperwarp **********************************************************
07238                 LDA WARPSTATE           ; Return if hyperwarp engaged
07239                 BNE SKIP159             ;
07240
07241                 LDA #$7F                ; Engage hyperwarp
07242                 STA WARPSTATE           ;
07243                 LDA #255                ; Set new velocity
07244                 STA NEWVELOCITY         ;
07245                 LDA #30                 ; Set Engines energy drain rate (= speed key '7')
07246                 STA DRAINENGINES        ;
07247
07248                 LDA #NUMSPCOBJ.ALL-1    ; Set space obj index of first star of star trail
07249                 STA TRAILIND            ;
07250                 LDA #0                  ; Clear star trail delay
07251                 STA TRAILDELAY          ;
07252
07253                 STA PL3XPOSHI           ; Init position vector and velocity vector of...
07254                 STA PL3XPOSLO           ; ... Hyperwarp Target Marker (PLAYER3):
07255                 STA PL3YPOSLO           ; x-coordinate :=   +0 (+$0000) <KM>
07256                 STA PL3ZVEL             ; y-coordinate := +256 (+$0100) <KM>
07257                 LDA #1                  ; z-coordinate :=    + (+$****) <KM> (sign only)
07258                 STA PL3ZPOSSIGN         ; z-velocity := +0 <KM/H>
07259                 STA PL3XPOSSIGN         ;
07260                 STA PL3YPOSSIGN         ;
07261                 STA PL3YPOSHI           ;
07262
07263                 LDA WARPARRVCOLUMN      ; Store temp arrival hyperwarp marker column number
07264                 STA WARPTEMPCOLUMN      ;
07265                 LDA WARPARRVROW         ; Store temp arrival hyperwarp marker row number
07266                 STA WARPTEMPROW         ;
07267
07268                 LDA MISSIONLEVEL        ; Skip if NOVICE mission
07269                 BEQ SKIP157             ;
07270
07271                 LDA WARPENERGY          ; Bits B0..1 of hyperwarp energy index a table...
07272                 ROL A                   ; ...containing the maximum value of how much the...
07273                 ROL A                   ; ...Hyperwarp Target Marker will veer off during...
07274                 ROL A                   ; ...hyperwarp
07275                 AND #$03                ;
07276                 TAY                     ;
07277                 LDA VEERMASKTAB,Y       ;
07278
07279 SKIP157         STA VEERMASK            ; Store veer-off velocity limitation mask
07280
07281                 LDY #$11                ; Set title phrase "HYPERWARP ENGAGED" and return
07282                 JMP SETTITLE            ;
07283
07284 ;*** Handle 'M' keyboard key (Manual Target Selector) key **********************
07285 SKIP158         CPX #19                 ; Skip if keyboard code does not match
07286                 BCS SKIP160             ;
07287
07288                 LDA TRACKDIGIT          ; Toggle digit of tracked space object of...
07289                 EOR #$01                ; ... Control Panel Display
07290                 AND #$01                ;
07291                 STA TRACKDIGIT          ;
07292 SKIP159         RTS                     ; Return
07293
07294 ;*** Handle 'P' keyboard key (Pause) *******************************************
07295 SKIP160         BNE SKIP161             ; Skip if keyboard code does not match
07296
07297                 LDA PORTA               ; Push joystick to resume action
07298                 CMP #$FF                ;
07299                 BEQ SKIP160             ; (!)
07300                 RTS                     ; Return
07301
07302 ;*** Handle 'INV' keyboard key (Abort Mission) *********************************
07303 SKIP161         LDY #$76                ; Preload title phrase "MISSION ABORTED..."
07304                 LDX #$04                ; Set mission bonus offset
07305
07306 ;*******************************************************************************
07307 ;*                                                                             *
07308 ;*                                  GAMEOVER                                   *
07309 ;*                                                                             *
07310 ;*                              Handle game over                               *
07311 ;*                                                                             *
07312 ;*******************************************************************************
07313
07314 ; DESCRIPTION
07315 ;
07316 ; Handles game over, including calculating the scored rank and class.
07317 ;
07318 ; This subroutine has two entry points: 
07319 ;
07320 ; (1)  GAMEOVER ($B10A) is entered at the end of a failed mission (mission
07321 ;      aborted, zero energy, or starship destroyed by Zylon fire). Essentially,
07322 ;      our starship is shut down. Code execution continues into GAMEOVER2
07323 ;      ($B121) below.
07324 ;
07325 ; (2)  GAMEOVER2 ($B121) is entered at the end of a successful mission (all
07326 ;      Zylon ships destroyed). It puts the program in demo mode, enqueues the
07327 ;      corresponding game over message, and calculates the scored rank and
07328 ;      class.
07329 ;
07330 ;      The scored rank and class are based on the total score: the score
07331 ;      accumulated during the game plus a mission bonus, which depends on the
07332 ;      mission level and how the mission ended (mission complete, mission
07333 ;      aborted, or starship destroyed by Zylon fire). The mission bonus is
07334 ;      picked from table BONUSTAB ($BEDD).
07335 ;
07336 ;      The scored rank index is taken from bits B8..4 of the total score and
07337 ;      limited to values of 0..18. It indexes table RANKTAB ($BEE9) for the rank
07338 ;      string. The rank string is displayed in subroutine SETTITLE ($B223).
07339 ;
07340 ;      The scored class index is taken from bits B3..0 (for rank indices 0,
07341 ;      11..14) and computed from bits B4..1 (for rank indices 1..10 and 15..18).
07342 ;      It takes values of 0..15. It indexes table CLASSTAB ($BEFC) for the class
07343 ;      digit. The class digit is displayed in subroutine SETTITLE ($B223).
07344 ;
07345 ;      For quick lookup, the following table lists rank and class from the total
07346 ;      score. Pick the cell with the closest value <= your score then read the
07347 ;      rank and class off the left and the top of the table, respectively.
07348 ;
07349 ;      For example, a score of 90 results in a ranking of "Novice Class 4", a
07350 ;      score of 161 results in a ranking of "Pilot Class 3".
07351 ;
07352 ; +------------------------------+---------------------------------------------------------------+
07353 ; |     Minimum Total Score      |                        Class Index                            |
07354 ; |                              |  0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15|
07355 ; +-------+----------------------+---------------------------------------------------------------+
07356 ; | Rank  |                      |                           Class                               |
07357 ; | Index |         Rank         |  5   5   5   4   4   4   4   3   3   3   2   2   2   1   1   1|
07358 ; +-------+----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
07359 ; |     0 | Galactic Cook        |  0|  1|  2|  3|  4|  5|  6|  7|  8|  9| 10| 11| 12| 13| 14| 15|
07360 ; |     1 | Garbage Scow Captain | 16| 18| 20| 22| 24| 26| 28| 30|   |   |   |   |   |   |   |   |
07361 ; |     2 | Garbage Scow Captain |   |   |   |   |   |   |   |   | 32| 34| 36| 38| 40| 42| 44| 46|
07362 ; |     3 | Rookie               | 48| 50| 52| 54| 56| 58| 60| 62|   |   |   |   |   |   |   |   |
07363 ; |     4 | Rookie               |   |   |   |   |   |   |   |   | 64| 66| 68| 70| 72| 74| 76| 78|
07364 ; |     5 | Novice               | 80| 82| 84| 86| 88| 90| 92| 94|   |   |   |   |   |   |   |   |
07365 ; |     6 | Novice               |   |   |   |   |   |   |   |   | 96| 98|100|102|104|106|108|110|
07366 ; |     7 | Ensign               |112|114|116|118|120|122|124|126|   |   |   |   |   |   |   |   |
07367 ; |     8 | Ensign               |   |   |   |   |   |   |   |   |128|130|132|134|136|138|140|142|
07368 ; |     9 | Pilot                |144|146|148|150|152|154|156|158|   |   |   |   |   |   |   |   |
07369 ; |    10 | Pilot                |   |   |   |   |   |   |   |   |160|162|164|166|168|170|172|174|
07370 ; |    11 | Ace                  |176|177|178|179|180|181|182|183|184|185|186|187|188|189|190|191|
07371 ; |    12 | Lieutenant           |192|193|194|195|196|197|198|199|200|201|202|203|204|205|206|207|
07372 ; |    13 | Warrior              |208|209|210|211|212|213|214|215|216|217|218|219|220|221|222|223|
07373 ; |    14 | Captain              |224|225|226|227|228|229|230|231|232|233|234|235|236|237|238|239|
07374 ; |    15 | Commander            |240|242|244|246|248|250|252|254|   |   |   |   |   |   |   |   |
07375 ; |    16 | Commander            |   |   |   |   |   |   |   |   |256|258|260|262|264|266|268|270|
07376 ; |    17 | Star Commander       |272|274|276|278|280|282|284|286|   |   |   |   |   |   |   |   |
07377 ; |    18 | Star Commander       |   |   |   |   |   |   |   |   |288|290|292|294|296|298|300|302|
07378 ; +-------+----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
07379 ;
07380 ;      NOTE: This subroutine also clears the vertical and horizontal joystick
07381 ;      directions.
07382 ;
07383 ; INPUT
07384 ;
07385 ;   X = Offset to index table BONUSTAB ($BEDD) of mission bonus values. Used
07386 ;       values are:
07387 ;     $00 -> Mission complete
07388 ;     $04 -> Mission was aborted due to zero energy
07389 ;     $08 -> Our starship was destroyed by Zylon fire
07390 ;
07391 ;   Y = Title phrase offset. Used values are:
07392 ;     $3F -> "MISSION COMPLETE"
07393 ;     $31 -> "MISSION ABORTED ZERO ENERGY"
07394 ;     $23 -> "SHIP DESTROYED BY ZYLON FIRE"
07395
07396 ;*** Game over (Mission failed) ************************************************
07397 GAMEOVER        LDA #0                  ;
07398                 STA PL3LIFE             ; PLAYER3 lifetime := 0 game loops
07399                 STA BEEPPRIORITY        ; Mute beeper
07400                 STA TITLEPHR            ; Clear title line
07401                 STA REDALERTLIFE        ; Red alert flash lifetime := 0 game loops
07402                 STA AUDC4               ; Mute audio channel 4
07403                 STA NEWVELOCITY         ; Shut down Engines
07404                 STA SHIELDSCOLOR        ; Set Shields color to {BLACK}
07405                 STA DRAINSHIELDS        ; Switch off Shields
07406                 STA WARPSTATE           ; Disengage hyperwarp
07407                 STA VELOCITYHI          ; Turn off hyperwarp velocity
07408
07409 ;*** Game over (Mission successful) ********************************************
07410 GAMEOVER2       LDA #$FF                ; Enter demo mode
07411                 STA ISDEMOMODE          ;
07412
07413                 STY NEWTITLEPHR         ; Enqueue title phrase
07414
07415 ;*** Calculate total score *****************************************************
07416                 TXA                     ;
07417                 ORA MISSIONLEVEL        ;
07418                 TAX                     ;
07419                 LDA BONUSTAB,X          ; Retrieve mission bonus
07420                 CLC                     ; Add mission bonus and game score
07421                 ADC SCORE               ;
07422                 TAX                     ;
07423                 LDA #0                  ;
07424
07425                 STA JOYSTICKY           ; Clear vertical joystick delta
07426                 STA JOYSTICKX           ; Clear horizontal joystick delta
07427
07428                 ADC SCORE+1             ;
07429                 BMI SKIP165             ; Return if total score < 0 (= total score of 0)
07430
07431 ;*** Calculate scored rank *****************************************************
07432                 LSR A                   ;
07433                 TXA                     ;
07434                 ROR A                   ;
07435                 LSR A                   ;
07436                 LSR A                   ;
07437                 LSR A                   ; Use bits B8..4 of total score as rank index
07438                 CMP #19                 ; Limit scored rank index to 0..18
07439                 BCC SKIP162             ;
07440                 LDA #18                 ;
07441                 LDX #15                 ; Prep class index of 15
07442 SKIP162         STA SCOREDRANKIND       ; Store scored rank index
07443
07444 ;*** Calculate scored class ****************************************************
07445                 TAY                     ;
07446                 TXA                     ;
07447                 CPY #0                  ;
07448                 BEQ SKIP164             ;
07449                 CPY #11                 ;
07450                 BCC SKIP163             ;
07451                 CPY #15                 ;
07452                 BCC SKIP164             ;
07453 SKIP163         LSR A                   ;
07454                 EOR #$08                ;
07455 SKIP164         AND #$0F                ;
07456                 STA SCOREDCLASSIND      ; Store scored class index, is 0..15
07457
07458 SKIP165         RTS                     ; Return
07459
07460 ;*******************************************************************************
07461 ;*                                                                             *
07462 ;*                                 SELECTWARP                                  *
07463 ;*                                                                             *
07464 ;*             Select hyperwarp arrival location on Galactic Chart             *
07465 ;*                                                                             *
07466 ;*******************************************************************************
07467
07468 ; DESCRIPTION
07469 ;
07470 ; This subroutine executes the following steps:
07471 ;
07472 ; (1)  Check if we are in Galactic Chart view and not in hyperwarp.
07473 ;
07474 ; (2)  Update the Galactic Chart in subroutine DRAWGC ($B4B9) if the Subspace
07475 ;      Radio is not damaged.
07476 ;
07477 ; (3)  Move the arrival hyperwarp marker (PLAYER4) across the Galactic Chart
07478 ;      every other game loop iteration. The current location of our starship is
07479 ;      indicated by the departure hyperwarp marker (PLAYER3).
07480 ;
07481 ; Code execution continues into subroutine CALCWARP ($B1A7) to calculate the
07482 ; required hyperwarp energy.
07483 ;
07484 ; NOTE: To calculate the horizontal position of PLAYER3..4 an offset of 61 is
07485 ; added (from left to right: 48 Player/Missile (PM) pixels to the left edge of
07486 ; the screen + 16 PM pixels to the left border of the Galactic Chart - 3 PM
07487 ; pixels relative offset of the PLAYER shape's horizontal center to its left
07488 ; edge = 61 PM pixels).
07489 ;
07490 ; NOTE: To calculate the vertical position of PLAYER3..4 an offset of 63 is
07491 ; added (from top to bottom: 8 Player/Missile (PM) pixels to the start of the
07492 ; Display List + 56 PM pixels to the first row of sectors - 1 PM pixel relative
07493 ; offset of the PLAYER shape's vertical center to its top edge (?) = 63 PM
07494 ; pixels).
07495
07496 SELECTWARP      LDA WARPSTATE           ; Return if hyperwarp engaged
07497                 BNE SKIP166             ;
07498
07499                 LDA SHIPVIEW            ; Return if not in Galactic Chart view
07500                 BMI SKIP167             ;
07501 SKIP166         RTS                     ; Return
07502
07503 SKIP167         BIT GCSTATRAD           ; Skip if Subspace Radio is damaged or destroyed
07504                 BMI SKIP168             ;
07505
07506                 JSR DRAWGC              ; Redraw Galactic Chart
07507
07508 SKIP168         LDA COUNT8              ; Move hyperwarp markers only every other game loop
07509                 AND #$01                ; (slowing down movement of hyperwarp markers)
07510                 BNE CALCWARP            ;
07511
07512 ;*** Calc arrival hyperwarp marker column and row numbers, update PLAYER4 pos **
07513                 CLC                     ;
07514                 LDA WARPARRVCOLUMN      ; Load arrival hyperwarp marker column number
07515                 ADC JOYSTICKX           ; Add joystick x-delta
07516                 AND #$7F                ; Limit value to 0..127
07517                 STA WARPARRVCOLUMN      ; Save new arrival hyperwarp marker column number
07518                 CLC                     ;
07519                 ADC #61                 ; Add offset of 61
07520                 STA PL4COLUMN           ; Store as PLAYER4 column number
07521
07522                 CLC                     ;
07523                 LDA WARPARRVROW         ; Load arrival hyperwarp marker row number
07524                 ADC JOYSTICKY           ; Add joystick y-delta
07525                 AND #$7F                ; Limit value to 0..127
07526                 STA WARPARRVROW         ; Save new arrival hyperwarp marker row number
07527                 CLC                     ;
07528                 ADC #63                 ; Add offset of 63
07529                 STA PL4ROWNEW           ; Store as PLAYER4 row number
07530
07531 ;*** Calc departure hyperwarp marker column and row numbers, update PLAYER3 pos 
07532                 LDA WARPDEPRROW         ; Load departure hyperwarp marker row number
07533                 CLC                     ;
07534                 ADC #63                 ; Add offset of 63
07535                 STA PL3ROWNEW           ; Store as PLAYER3 row number
07536
07537                 LDA WARPDEPRCOLUMN      ; Load departure hyperwarp marker column number
07538                 CLC                     ;
07539                 ADC #61                 ; Add offset of 61
07540                 STA PL3COLUMN           ; Store as PLAYER3 column number
07541
07542 ;*******************************************************************************
07543 ;*                                                                             *
07544 ;*                                  CALCWARP                                   *
07545 ;*                                                                             *
07546 ;*                   Calculate and display hyperwarp energy                    *
07547 ;*                                                                             *
07548 ;*******************************************************************************
07549
07550 ; DESCRIPTION
07551 ;
07552 ; Calculates and displays the hyperwarp energy in the Galactic Chart view.
07553 ;
07554 ; This subroutine executes the following steps:
07555 ;
07556 ; (1)  Determine the arrival sector from the arrival hyperwarp marker position.
07557 ;
07558 ; (2)  If the Subspace Radio is not destroyed, update the target number digit of
07559 ;      the Galactic Chart Panel Display.
07560 ;
07561 ; (3)  Calculate the hyperwarp energy that is required to hyperwarp from the
07562 ;      departure hyperwarp marker to the arrival hyperwarp marker based on the
07563 ;      "block-distance":
07564 ;
07565 ;          DISTANCE := DELTAC + DELTAR / 2
07566 ;
07567 ;          where
07568 ;
07569 ;          DELTAC := ABS(WARPARRVCOLUMN - WARPDEPRCOLUMN)
07570 ;          DELTAR := ABS(WARPARRVROW - WARPDEPRROW)
07571 ;
07572 ;      NOTE: Dividing DELTAR by 2 is because PLAYERs at single-line resolution
07573 ;      have Player/Missile pixels that are half as high as they are wide.
07574 ;
07575 ;      The hyperwarp energy, divided by 10, is the sum of a value picked from
07576 ;      the hyperwarp energy table WARPENERGYTAB ($BADD) indexed by DISTANCE / 8)
07577 ;      plus a remainder computed from Bits B1..0 of DISTANCE. 
07578 ;
07579 ; (4)  Store the hyperwarp energy value in WARPENERGY ($91).
07580 ;
07581 ; (5)  Update the HYPERWARP ENERGY readout of the Galactic Chart Panel Display.
07582
07583 L.WARPARRVCOL   = $6A                   ; Saves arrival sector column number
07584 L.DIFFC         = $6A                   ; Saves diff column value
07585
07586 ;*** Calculate arrival sector **************************************************
07587 CALCWARP        LDA WARPARRVCOLUMN      ;
07588                 LSR A                   ;
07589                 LSR A                   ;
07590                 LSR A                   ;
07591                 STA L.WARPARRVCOL       ; A := arrival sector column 0..15
07592                 LDA WARPARRVROW         ;
07593                 AND #$70                ; A := arrival sector row (0..7) * 16
07594                 ORA L.WARPARRVCOL       ;
07595                 STA ARRVSECTOR          ; Save arrival sector (format %0rrrcccc)
07596
07597 ;*** Update target number digit of Galactic Chart Panel Display ****************
07598                 TAX                     ;
07599                 LDA GCMEMMAP,X          ; Get number of Zylon ships in arrival sector
07600                 BPL SKIP169             ; Skip if no starbase in arrival sector
07601                 LDA #0                  ; Clear number of Zylon ships
07602 SKIP169         ORA #CCS.COL2!ROM.0     ; Merge COLOR2 bits with number of Zylon ships
07603                 BIT GCSTATRAD           ; Skip if Subspace Radio destroyed
07604                 BVS SKIP170             ;
07605
07606                 STA GCTRGCNT            ; Set target number digit of Galactic Chart Panel
07607
07608 ;*** Calculate energy to hyperwarp between hyperwarp markers *******************
07609 SKIP170         SEC                     ; A := DIFFC := ABS(WARPARRVCOLUMN - WARPDEPRCOLUMN)
07610                 LDA WARPARRVCOLUMN      ; (Column value difference)
07611                 SBC WARPDEPRCOLUMN      ;
07612                 BCS SKIP171             ;
07613                 EOR #$FF                ;
07614                 ADC #1                  ;
07615 SKIP171         STA L.DIFFC             ;
07616
07617                 SEC                     ; A := DIFFR := ABS(WARPARRVROW - WARPDEPRROW)
07618                 LDA WARPARRVROW         ; (Row value difference)
07619                 SBC WARPDEPRROW         ;
07620                 BCS SKIP172             ;
07621                 EOR #$FF                ;
07622                 ADC #1                  ;
07623
07624 SKIP172         LSR A                   ; A := DISTANCE := DIFFR / 2 + DIFFC
07625                 CLC                     ;
07626                 ADC L.DIFFC             ;
07627
07628                 TAY                     ; Save DISTANCE
07629                 LSR A                   ; Calc index into hyperwarp energy table
07630                 LSR A                   ;
07631                 LSR A                   ;
07632                 TAX                     ;
07633
07634                 TYA                     ; Load DISTANCE value
07635                 AND #$03                ; Get DISTANCE bits B1..0
07636                 CLC                     ;
07637                 ADC WARPENERGYTAB,X     ; Add hyperwarp energy from table
07638                 STA WARPENERGY          ; Save hyperwarp energy
07639
07640 ;*** Update HYPERWARP ENERGY readout of Galactic Chart Panel Display ***********
07641                 TAY                     ; Prep with hyperwarp energy value
07642
07643                 LDA #ROM.0              ; Set HYPERWARP ENERGY readout digit1..3 to '0'
07644                 STA GCWARPD1            ;
07645                 STA GCWARPD1+1          ;
07646                 STA GCWARPD1+2          ;
07647
07648 LOOP053         LDX #2                  ; Loop over HYPERWARP ENERGY readout digit3..1
07649 LOOP054         INC GCWARPD1,X          ; Increment digit value
07650                 LDA GCWARPD1,X          ;
07651                 CMP #ROM.9+1            ;
07652                 BCC SKIP173             ; Skip if energy digit <= '9'
07653
07654                 LDA #ROM.0              ; Replace energy digit with '0'
07655                 STA GCWARPD1,X          ;
07656                 DEX                     ;
07657                 BPL LOOP054             ; Next energy digit
07658
07659 SKIP173         DEY                     ; Decrement HYPERWARP ENERGY readout value
07660                 BNE LOOP053             ;
07661                 RTS                     ; Return
07662
07663 ;*******************************************************************************
07664 ;*                                                                             *
07665 ;*                                  UPDTITLE                                   *
07666 ;*                                                                             *
07667 ;*                              Update title line                              *
07668 ;*                                                                             *
07669 ;*******************************************************************************
07670
07671 ; DESCRIPTION
07672 ;
07673 ; Updates the title phrase displayed in the title line.
07674 ;
07675 ; If no title phrase has been set then fetch the offset of the next ("enqueued")
07676 ; title phrase to be displayed. If one has been set then code execution
07677 ; continues into subroutine SETTITLE ($B223), otherwise code execution returns.
07678 ;
07679 ; If a title phrase has been set then decrement the lifetime of the currently
07680 ; displayed title phrase segment. If its lifetime has reached a value of 0 then
07681 ; branch to subroutine SETTITLE ($B223) to display the next segment.
07682
07683 UPDTITLE        LDA TITLEPHR            ; Skip if no title phrase set
07684                 BEQ SKIP175             ;
07685
07686                 DEC TITLELIFE           ; Decrement title phrase segment lifetime
07687                 BEQ SKIP176             ; If lifetime expired show next title segment
07688
07689 SKIP174         RTS                     ; Return
07690
07691 SKIP175         LDY NEWTITLEPHR         ; Prep enqueued new title phrase
07692                 BEQ SKIP174             ; Return if not set
07693
07694 ;*******************************************************************************
07695 ;*                                                                             *
07696 ;*                                  SETTITLE                                   *
07697 ;*                                                                             *
07698 ;*                       Set title phrase in title line                        *
07699 ;*                                                                             *
07700 ;*******************************************************************************
07701
07702 ; DESCRIPTION
07703 ;
07704 ; Displays a title phrase in the title line. 
07705 ;
07706 ; INTRODUCTION
07707 ;
07708 ; Title phrases are picked from the title phrase table PHRASETAB ($BBAA). They
07709 ; consist of one or more phrase tokens. Each token is a byte representing a word
07710 ; in word table WORDTAB ($BC2B). Two special tokens are placeholders for the
07711 ; scored class ($FC) and scored rank ($FD) strings.
07712 ;
07713 ; A title phrase is split up into one or more title phrase segments, each
07714 ; fitting into the title line. One title phrase segment is displayed after the
07715 ; other after a delay called the "title segment lifetime".
07716 ;
07717 ; Phrase tokens, except the tokens for the scored class ($FC) and for the scored
07718 ; rank ($FD), contain the number of a word in word table WORDTAB ($BC2B) and may
07719 ; contain an end-of-segment or end-of-phrase marker bit.
07720 ;
07721 ; DETAILS
07722 ;
07723 ; The Display List is modified by subroutine MODDLST ($ADF1) to display the
07724 ; title line. Then, the title line is cleared and the words of the title phrase
07725 ; are copied into it using the passed offset into title phrase table PHRASETAB
07726 ; ($BBAA). If the offset has a value of $FF the title line is hidden in
07727 ; subroutine MODDLST ($ADF1). 
07728 ;
07729 ; INPUT
07730 ;
07731 ;   Y = Offset into title phrase table PHRASETAB ($BBAA). Used values are:
07732 ;     $FF  -> Hide title line
07733 ;     else -> Offset into title phrase table PHRASETAB ($BBAA), with explicitly
07734 ;             used values:
07735 ;
07736 ;     $01 -> "COMPUTER ON"
07737 ;     $04 -> "COMPUTER OFF"
07738 ;     $07 -> "SHIELDS ON"
07739 ;     $09 -> "SHIELDS OFF"
07740 ;     $0B -> "COMPUTER TRACKING ON"
07741 ;     $0E -> "TRACKING OFF"
07742 ;     $13 -> "STARBASE SURROUNDED"
07743 ;     $15 -> "STARBASE DESTROYED"
07744 ;     $1F -> "DOCKING ABORTED"
07745 ;     $21 -> "TRANSFER COMPLETE"
07746 ;     $4A -> "NOVICE MISSION"
07747 ;     $4C -> "PILOT MISSION"
07748 ;     $4E -> "WARRIOR MISSION"
07749 ;     $50 -> "COMMANDER MISSION"
07750 ;     $52 -> "DAMAGE CONTROL..."
07751 ;     $75 -> "RED ALERT"
07752
07753 L.WORD          = $6A                   ; Saves word number of WORDTAB ($BC2A). Used values
07754                                         ; are $00..$3F.
07755 L.COLUMNPOS     = $6B                   ; Saves cursor column position during copying text
07756                                         ; into title line
07757 L.TOKEN         = $6C                   ; Saves title phrase token from PHRASETAB ($BBAA),
07758                                         ; contains bit-encoded information about one word in
07759                                         ; the title phrase:
07760                                         ; B7..6 = %00 -> Copy next word to title line
07761                                         ; B7..6 = %01 -> End-of-phrase reached, apply short
07762                                         ;                delay, then hide title line. Title
07763                                         ;                segment lifetime = 60 game loops.
07764                                         ; B7..6 = %10 -> End-of-segment reached. Title
07765                                         ;                segment lifetime = 60 game loops
07766                                         ; B7..6 = %11 -> End-of-phrase reached, apply long
07767                                         ;                delay, then hide title line. Title
07768                                         ;                segment lifetime = 254 game loops.
07769                                         ;                Used with title phrases
07770                                         ;                  "STARBASE SURROUNDED"
07771                                         ;                  "STARBASE DESTROYED"
07772                                         ;                  "HYPERSPACE"
07773                                         ;                  "RED ALERT"
07774                                         ; B5..0       -> Word number of WORDTAB ($BC2A)
07775
07776 SETTITLE        STY TITLEPHR            ; Save title phrase offset
07777
07778                 LDY #$23                ; Show title line
07779                 LDX #$0F                ;
07780                 LDA #$07                ;
07781                 JSR MODDLST             ;
07782
07783 ;*** Init cursor column position and clear title line **************************
07784 SKIP176         LDX #19                 ; There are 19(+1) characters to clear
07785                 LDA #0                  ;
07786                 STA L.COLUMNPOS         ; Init cursor column position
07787
07788 LOOP055         STA TITLETXT,X          ; Clear character in title line
07789                 DEX                     ;
07790                 BPL LOOP055             ;
07791
07792 ;*** If title phrase offset = $FF then hide title line *************************
07793 SKIP177         LDX TITLEPHR            ; Load title phrase offset
07794                 INC TITLEPHR            ; Prepare title phrase offset for next word
07795                 BNE SKIP178             ; ...skip if it turned 0
07796
07797                 LDX #$0F                ; Remove title line and return
07798                 LDY #$80                ;
07799                 LDA #$07                ;
07800                 JMP MODDLST             ;
07801
07802 SKIP178         LDA PHRASETAB,X         ; Get phrase token
07803
07804 ;*** Display scored class? *****************************************************
07805                 CMP #$FC                ; Skip if not "scored class" token
07806                 BNE SKIP179             ;
07807
07808                 LDY SCOREDCLASSIND      ; Get scored class index, is in 0..15
07809                 LDA CLASSTAB,Y          ; Load scored class number digit
07810                 LDX L.COLUMNPOS         ; Load cursor position
07811                 STA TITLETXT,X          ; Store class in title line
07812                 LDA #60                 ; Title segment lifetime := 60 game loops
07813                 STA TITLELIFE           ;
07814                 RTS                     ; Return
07815
07816 ;*** Display scored rank? ******************************************************
07817 SKIP179         CMP #$FD                ; Skip if not "scored rank" token
07818                 BNE SKIP180             ;
07819
07820                 LDY SCOREDRANKIND       ; Get scored rank index, is in 0..18
07821                 LDA RANKTAB,Y           ; Load rank word number
07822
07823 ;*** Search word of token in word table ****************************************
07824 SKIP180         STA L.TOKEN             ; Save phrase token
07825                 AND #$3F                ; Strip bits B6..7 from phrase token
07826                 STA L.WORD              ; Store word number (bits B5..0)
07827
07828                 LDA #<[WORDTAB-1]       ; Point MEMPTR to WORDTAB-1
07829                 STA MEMPTR              ;
07830                 LDA #>[WORDTAB-1]       ;
07831                 STA MEMPTR+1            ;
07832
07833 LOOP056         INC MEMPTR              ; Increment MEMPTR
07834                 BNE SKIP181             ;
07835                 INC MEMPTR+1            ;
07836
07837 SKIP181         LDY #0                  ;
07838                 LDA (MEMPTR),Y          ; Load character of word
07839                 BPL LOOP056             ; Loop until end-of-word marker (bit B7) found
07840                 DEC L.WORD              ;
07841                 BNE LOOP056             ; Loop until word found
07842
07843 ;*** Copy word to title line, add space ****************************************
07844 LOOP057         AND #$3F                ; Strip color bits B6..7 from character
07845                 EOR #CCS.COL2!$20       ; Merge COLOR2 bits and convert to ATASCII
07846                 LDX L.COLUMNPOS         ; Copy character to title line
07847                 INC L.COLUMNPOS         ; Increment cursor column position
07848                 STA TITLETXT,X          ;
07849                 INY                     ;
07850                 LDA (MEMPTR),Y          ; Load next character of word
07851                 BPL LOOP057             ; Next character of word if no end-of-word marker
07852                 INC L.COLUMNPOS         ; Word was copied. Add space after word.
07853
07854 ;*** Decide to copy another word, etc. *****************************************
07855                 LDA #60                 ; SUMMARY:
07856                 BIT L.TOKEN             ; If bits B7..6 of phrase token...
07857                 BPL SKIP182             ; %00 -> Copy next word to title line
07858                 BVC SKIP183             ; %01 -> End-of-phrase, short delay, hide title line
07859                 LDA #254                ;        Title segment lifetime := 60 game loops
07860 SKIP182         BVC SKIP177             ; %10 -> End-of-segment.
07861                 LDY #$FF                ;        Title segment lifetime := 60 game loops
07862                 STY TITLEPHR            ; %11 -> End-of-phrase, long delay, hide title line
07863 SKIP183         STA TITLELIFE           ;        Title segment lifetime := 254 game loops
07864                 RTS                     ; Return
07865
07866 ;*******************************************************************************
07867 ;*                                                                             *
07868 ;*                                    SOUND                                    *
07869 ;*                                                                             *
07870 ;*                            Handles sound effects                            *
07871 ;*                                                                             *
07872 ;*******************************************************************************
07873
07874 ; DESCRIPTION
07875 ;
07876 ; This subroutine handles the sound effects. It is called every vertical blank
07877 ; phase, that is, every TICK (1/60 s on an NTSC ATARI Home Computer system, 1/50
07878 ; s on a PAL ATARI Home Computer system) from the Vertical Blank Interrupt
07879 ; handler VBIHNDLR ($A6D1).
07880 ;
07881 ; The program uses all of the available 4 audio channels: Audio channels 1, 2,
07882 ; and 3 are shared among the Engines sound effects and the "noise sound
07883 ; patterns" (explosion and photon torpedo sound effects), while audio channel 4
07884 ; is used for "beeper sound patterns" (status report sound effects). The
07885 ; following sections explain the beeper sound patterns and the noise sound
07886 ; patterns:
07887 ;
07888 ; o   BEEPER SOUND PATTERNS
07889 ;
07890 ;     There are the following beeper sound patterns:
07891 ;
07892 ;     (1)  HYPERWARP TRANSIT
07893 ;     (2)  RED ALERT
07894 ;     (3)  ACKNOWLEDGE
07895 ;     (4)  DAMAGE REPORT
07896 ;     (5)  MESSAGE FROM STARBASE
07897 ;
07898 ;     They are encoded in table BEEPPATTAB ($BF3E) in 6-byte long "beeper sound
07899 ;     patterns". 
07900 ;
07901 ;     Another table, BEEPFRQTAB ($BF5C), stores the frequencies for the tones
07902 ;     of each beeper sound pattern, terminated by a marker byte ($FF).
07903 ;
07904 ;     BUG (at $BF5C): The pattern frequencies in table BEEPFRQTAB ($BF5C) at
07905 ;     offset $00 are unused. Suggested Fix: Remove from code.
07906 ;
07907 ;     Whenever the program calls subroutine BEEP ($B3A6), that subroutine sets
07908 ;     up a beeper sound pattern for playing by copying 6 bytes from the pattern
07909 ;     table BEEPPATTAB ($BF3E) to BEEPFRQIND ($D2)..BEEPFRQSTART ($D7).
07910 ;     Subroutine SOUND ($B2AB) detects the copied beeper sound pattern and plays
07911 ;     the encoded tones and pauses.
07912 ;
07913 ;     The relevant variables for playing a beeper sound pattern are the
07914 ;     following (see also figures at BEEPPATTAB ($BF3E)):
07915 ;
07916 ;     BEEPFRQIND    ($D2)   = Running index into table BEEPFRQTAB ($BF5C)
07917 ;     BEEPREPEAT    ($D3)   = Number of times that the beeper sound pattern is
07918 ;                             repeated - 1
07919 ;     BEEPTONELIFE  ($D4)   = Lifetime of tone in TICKs - 1
07920 ;     BEEPPAUSELIFE ($D5)   = Lifetime of pause in TICKs - 1 ($FF -> No pause)
07921 ;     BEEPPRIORITY  ($D6)   = Beeper sound pattern priority. A playing beeper
07922 ;                             sound pattern is stopped if a beeper sound pattern
07923 ;                             of higher priority is about to be played. A value
07924 ;                             of 0 indicates that no beeper sound pattern is
07925 ;                             playing at the moment.
07926 ;     BEEPFRQSTART  ($D7)   = Index to first byte of the beeper sound pattern in
07927 ;                             table BEEPFRQTAB ($BF5C)
07928 ;
07929 ;     BEEPLIFE      ($D8)   = Lifetime of the current tone or pause in TICKs
07930 ;     BEEPTOGGLE    ($D9)   = Indicates that either a tone (0) or a pause (not
07931 ;                             0) is currently playing.
07932 ;
07933 ; o   NOISE SOUND PATTERNS
07934 ;
07935 ;     There are the following noise sound patterns:
07936 ;
07937 ;     (1)  PHOTON TORPEDO LAUNCHED
07938 ;     (2)  SHIELD EXPLOSION
07939 ;     (3)  ZYLON EXPLOSION
07940 ;
07941 ;     They are encoded in table NOISEPATTAB ($BF20) in 10-byte long "noise sound
07942 ;     patterns". 
07943 ;
07944 ;     Whenever the program calls subroutine NOISE ($AEA8), that subroutine  sets
07945 ;     up a noise sound pattern for being played by copying 10 bytes from the
07946 ;     pattern table NOISEPATTAB ($BF20) to NOISETORPTIM ($DA)..NOISELIFE ($E1)
07947 ;     and hardware sound registers AUDCTL ($D208) and AUDF3 ($D204).
07948 ;
07949 ;     The relevant variables for playing a noise sound pattern are the
07950 ;     following:
07951 ;
07952 ;     NOISETORPTIM  ($DA)   = Delay timer for PHOTON TORPEDO LAUNCHED noise
07953 ;                             sound pattern
07954 ;     NOISEEXPLTIM  ($DB)   = Delay timer for SHIELD EXPLOSION and ZYLON
07955 ;                             EXPLOSION noise sound patterns
07956 ;     NOISEAUDC2    ($DC)   = Audio channel 1/2 control shadow register
07957 ;     NOISEAUDC3    ($DD)   = Audio channel 3   control shadow register
07958 ;     NOISEAUDF1    ($DE)   = Audio channel 1 frequency shadow register
07959 ;     NOISEAUDF2    ($DF)   = Audio channel 2 frequency shadow register
07960 ;     NOISEFRQINC   ($E0)   = Audio channel 1/2 frequency increment
07961 ;     NOISELIFE     ($E1)   = Noise sound pattern lifetime
07962 ;
07963 ;     AUDCTL        ($D208) = POKEY: Audio control
07964 ;     AUDF3         ($D204) = POKEY: Audio channel 3 frequency audio register
07965 ;
07966 ;     There are two more variables that trigger noise effects. They are not part
07967 ;     of the noise sound pattern table:
07968 ;
07969 ;     NOISEZYLONTIM ($E2)  = Delay timer to trigger the ZYLON EXPLOSION noise
07970 ;                            sound pattern. It is set in subroutine COLLISION
07971 ;                            ($AF3D) when the impact of one of our starship's
07972 ;                            photon torpedoes with a target is imminent. The
07973 ;                            timer is decremented every TICK. When it reaches a
07974 ;                            value of 0 the ZYLON EXPLOSION noise sound pattern
07975 ;                            is played in subroutine SOUND ($B2AB). 
07976 ;     NOISEHITLIFE ($E3)   = Lifetime of the STARSHIP EXPLOSION noise when our
07977 ;                            starship was destroyed by a Zylon photon torpedo.
07978 ;                            It is set in GAMELOOP ($A1F3) to a value of 64
07979 ;                            TICKs. When it reaches a value of 0 the STARSHIP
07980 ;                            EXPLOSION noise is played in subroutine SOUND
07981 ;                            ($B2AB).
07982 ;
07983 ; SUBROUTINE DETAILS
07984 ;
07985 ; This subroutine executes the following steps:
07986 ;
07987 ; (1)  Play beeper sound pattern
07988 ;
07989 ;      The playing of a beeper sound pattern is started, continued, or stopped.
07990 ;
07991 ; (2)  Play ZYLON EXPLOSION noise sound pattern
07992 ;
07993 ;      If the explosion of a target space object is imminent (subroutine
07994 ;      COLLISION ($AF3D) has set NOISEZYLONTIM ($E2) to the number of game loop
07995 ;      iterations that will pass until our starship's photon torpedo will hit
07996 ;      the target), the timer NOISEZYLONTIM ($E2) is decremented every TICK. If
07997 ;      it reaches a value of 0, then the noise sound pattern ZYLON EXPLOSION is
07998 ;      played.
07999 ;
08000 ; (3)  Play starship's Engines sound
08001 ;
08002 ;      If the Engines are louder than the current noise sound pattern then the
08003 ;      noise sound pattern is terminated and the values for the audio channels
08004 ;      1..3 are updated: 
08005 ;
08006 ;      The velocity of our starship determines the pitch and the volume of the
08007 ;      Engines: the higher the velocity, the higher the pitch and the volume of
08008 ;      the Engines. The incremented value of VELOCITYLO ($70) is used as a "base
08009 ;      value" %abcdefgh.
08010 ;
08011 ;      Audio channels 1 and 2 are combined to a 16-bit audio channel 1/2,
08012 ;      clocked at 1.79 MHz. The inverted bits (represented by an overscore)
08013 ;      B7..0 of the base value form bits B12..5 of the 16-bit frequency value of
08014 ;      audio channel 1/2. Bits B7..4 of the base value form bits B3..0 of the
08015 ;      volume of audio channel 1/2, with noise distortion bit B7 set:
08016 ;                               ________
08017 ;      AUDF1/2 ($D202..3) := %000abcdefgh00000
08018 ;      AUDC2   ($D203)    := %1000abcd
08019 ;
08020 ;      Audio channel 3 is also clocked at 1.79 MHz. The inverted bits B7..0 of
08021 ;      the base value form bits B7..0 of the frequency value of audio channel 3.
08022 ;      Bits B6..4 of the base value form bits B3..0 of the volume of audio
08023 ;      channel 3, with noise distortion bit B7 set:
08024 ;                            ________
08025 ;      AUDF3   ($D204)    := %abcdefgh
08026 ;      AUDC3   ($D205)    := %10000bcd
08027 ;
08028 ;      Code execution returns at this point.
08029 ;
08030 ; (4)  Play ZYLON EXPLOSION or SHIELD EXPLOSION noise sound pattern
08031 ;
08032 ;      If the ZYLON EXPLOSION or SHIELD EXPLOSION noise sound pattern was set
08033 ;      up, the explosion noise timer NOISEEXPLTIM ($DB) is decremented every
08034 ;      TICK. It starts either with a value of 4 TICKs with a ZYLON EXPLOSION
08035 ;      noise sound pattern or with a value of 8 TICKs with a SHIELD EXPLOSION
08036 ;      noise sound pattern, set up in subroutine NOISE ($AEA8). If it reaches a
08037 ;      value of 0, then the shadow control register of audio channel 1/2
08038 ;      switches to "noise distortion" at maximum volume.
08039 ;
08040 ; (5)  Play PHOTON TORPEDO LAUNCHED noise sound pattern
08041 ;
08042 ;      If the PHOTON TORPEDO LAUNCHED noise sound pattern was set up, the photon
08043 ;      torpedo noise timer NOISETORPTIM ($DA) is decremented every TICK. It
08044 ;      starts with a value of 8 TICKs, set in subroutine TRIGGER ($AE29). The
08045 ;      noise distortion and volume for the shadow control register of audio
08046 ;      channel 3 is picked from table NOISETORPVOLTAB ($BFEB), the noise
08047 ;      frequency for audio channel 3 is picked from table NOISETORPFRQTAB
08048 ;      ($BFF3). If the photon torpedo noise timer reaches a value of 0, then the
08049 ;      shadow control registers of audio channel 1/2 switch to "tone distortion"
08050 ;      at maximum volume and a frequency of $0202.
08051 ;
08052 ;      NOTE: Using a real-time volume envelope stored in table NOISETORPVOLTAB
08053 ;      ($BFEB) for a launched photon torpedo results in the distinctive
08054 ;      "whooshing" photon torpedo sound.
08055 ;
08056 ; (6)  Play STARSHIP EXPLOSION noise
08057 ;
08058 ;      If our starship was hit by a Zylon photon torpedo then NOISEHITLIFE ($E3)
08059 ;      was set to 64 TICKs in routine GAMELOOP ($A1F3). While this value is
08060 ;      decremented every TICK, a random frequency value is stored to audio
08061 ;      channel 3 and the distortion bit of the shadow control register of audio
08062 ;      channel 3 is randomly toggled.
08063 ;
08064 ; (7)  Increase audio channels 1/2 frequency
08065 ;
08066 ;      The 16-bit frequency value of audio channels 1/2 (both shadow registers
08067 ;      and audio registers) is increased every TICK by an increment picked from
08068 ;      the currently playing noise sound pattern.
08069 ;
08070 ; (8)  Mute audio channels gradually
08071 ;
08072 ;      Toward the end of a noise sound pattern's lifetime all audio channels
08073 ;      gradually mute their volume every other TICK until completely silent. 
08074
08075 ;*** Play beeper sound pattern *************************************************
08076 SOUND           LDA BEEPPRIORITY        ; Skip if beeper sound pattern not in use
08077                 BEQ SKIP185             ;
08078
08079                 DEC BEEPLIFE            ; Decrement beeper lifetime
08080                 BPL SKIP185             ; Skip if beeper lifetime still counting down
08081
08082                 LDA BEEPTOGGLE          ; Load tone/pause toggle
08083                 BEQ LOOP058             ; Skip if a tone is playing or is to be played
08084
08085                 LDA BEEPPAUSELIFE       ; Load pause lifetime
08086                 BMI LOOP058             ; Skip if duration = $FF (no pause)
08087                 STA BEEPLIFE            ; Store pause lifetime as beeper lifetime
08088                 LDY #0                  ; Prep AUDC4 (zero volume)
08089                 BEQ SKIP184             ; Skip unconditionally
08090
08091 LOOP058         LDA BEEPTONELIFE        ; Load tone lifetime
08092                 STA BEEPLIFE            ; Store tone lifetime as beeper lifetime
08093                 LDX BEEPFRQIND          ; Load frequency index
08094                 INC BEEPFRQIND          ; Increment frequency index
08095                 LDA BEEPFRQTAB,X        ; Store tone frequency from frequency table in AUDF4
08096                 STA AUDF4               ;
08097                 LDY #$A8                ; Prep AUDC4 (tone distortion + medium volume)
08098                 CMP #$FF                ; Skip if frequency not $FF (there are more tones)
08099                 BNE SKIP184             ;
08100
08101                 LDA BEEPFRQSTART        ; Rewind pattern frequency pointer
08102                 STA BEEPFRQIND          ;
08103                 DEC BEEPREPEAT          ; Decrement sequence counter
08104                 BPL LOOP058             ; Keep playing until sequence counter < 0
08105
08106                 LDY #0                  ; Prep AUDC4 with zero volume
08107                 STY BEEPPRIORITY        ; Stop playing beeper sound pattern
08108
08109 SKIP184         STY AUDC4               ; Store in AUDC4
08110                 STY BEEPTOGGLE          ; Store in BEEPTOGGLE
08111
08112 ;*** Play ZYLON EXPLOSION noise sound pattern **********************************
08113 SKIP185         LDA NOISEZYLONTIM       ; Skip if ZYLON EXPLOSION timer not in use
08114                 BEQ SKIP186             ;
08115
08116                 DEC NOISEZYLONTIM       ; Decrement ZYLON EXPLOSION timer
08117                 BNE SKIP186             ; Skip if ZYLON EXPLOSION timer still counting down
08118
08119                 LDX #$14                ; Play noise sound pattern ZYLON EXPLOSION
08120                 JSR NOISE               ;
08121
08122 ;*** Play our starship's Engines sound *****************************************
08123 SKIP186         LDX VELOCITYLO          ; Skip if Engines softer than noise sound pattern
08124                 TXA                     ;
08125                 LSR A                   ;
08126                 LSR A                   ;
08127                 LSR A                   ;
08128                 LSR A                   ;
08129                 LSR A                   ;
08130                 CMP NOISELIFE           ;
08131                 BCC SKIP187             ;
08132
08133                 LDA #0                  ; Terminate noise sound pattern
08134                 STA NOISELIFE           ;
08135
08136                 INX                     ;
08137                 TXA                     ; A := %abcdefgh = VELOCITYLO + 1
08138                 EOR #$FF                ;           ________
08139                 STA AUDF3               ; AUDF3 := %abcdefgh
08140
08141                 TAX                     ;                ________
08142                 ASL A                   ; AUDF2/1 := %000abcdefgh00000
08143                 ASL A                   ;
08144                 ASL A                   ;
08145                 ASL A                   ;
08146                 ASL A                   ;
08147                 STA AUDF1               ;
08148                 TXA                     ;
08149                 LSR A                   ;
08150                 LSR A                   ;
08151                 LSR A                   ;
08152                 STA AUDF2               ;
08153
08154                 LSR A                   ; AUDC2 := %1000abcd
08155                 EOR #$8F                ; (noise distortion + B7..B4 bits for volume)
08156                 STA AUDC2               ;
08157
08158                 AND #$87                ; AUDC3 := %10000bcd
08159                 STA AUDC3               ; (noise distortion + B6..B4 bits for volume)
08160
08161                 LDA #$70                ; Clock audio channel 1 and 3 @ 1.79 MHz and...
08162                 STA AUDCTL              ; ...combine audio channel 1/2 to 16-bit channel
08163
08164                 RTS                     ; Return
08165
08166 ;*** Play ZYLON EXPLOSION or SHIELD EXPLOSION noise ****************************
08167 SKIP187         LDA NOISEEXPLTIM        ; Skip if explosion noise timer not in use
08168                 BEQ SKIP188             ;
08169
08170                 DEC NOISEEXPLTIM        ; Decrement explosion noise timer (4 or 8 TICKs long)
08171                 BNE SKIP188             ; Skip if explosion noise timer still counting down
08172
08173                 LDA #$8F                ; Shadow register AUDC2 := (noise dist. + max volume)
08174                 STA NOISEAUDC2          ;
08175
08176 ;*** Play PHOTON TORPEDO LAUNCHED noise sound **********************************
08177 SKIP188         LDX NOISETORPTIM        ; Skip if photon torpedo noise timer not in use
08178                 BEQ SKIP190             ;
08179
08180                 DEC NOISETORPTIM        ; Decrement photon torpedo noise timer (8 TICKs long)
08181                 BNE SKIP189             ; Skip if torpedo noise timer still counting down
08182
08183                 LDA #$AF                ; Shadow register AUDC2 := (tone dist. + max volume)
08184                 STA NOISEAUDC2          ;
08185                 LDA #$02                ; Set frequency $0202 to AUDF1/2's shadow...
08186                 STA NOISEAUDF1          ; ...registers
08187                 STA NOISEAUDF2          ;
08188
08189 SKIP189         LDA NOISETORPVOLTAB-1,X ; Pick torpedo noise + volume shape (X in 1..8)...
08190                 STA NOISEAUDC3          ; ...and store it in AUDC3's shadow register
08191                 LDA NOISETORPFRQTAB-1,X ; Pick photon torpedo noise frequency (X in 1..8)...
08192                 STA AUDF3               ; ...and store it in AUDF3
08193                 STA STIMER              ; Reset POKEY audio timers
08194
08195 ;*** Play STARSHIP EXPLOSION noise when our starship is hit ********************
08196 SKIP190         LDA NOISEHITLIFE        ; Skip if STARSHIP EXPLOSION noise not in use
08197                 BEQ SKIP191             ;
08198
08199                 DEC NOISEHITLIFE        ; Decrement STARSHIP EXPLOSION noise lifetime
08200                 LDA RANDOM              ; Set random frequency to AUDF3
08201                 STA AUDF3               ;
08202                 AND #$20                ; Toggle noise/tone dist. of AUDC3's shadow register
08203                 EOR NOISEAUDC3          ; ...randomly
08204                 STA NOISEAUDC3          ;
08205
08206 ;*** Increase 16-bit frequency of audio channels 1/2 (shadow registers also) ***
08207 SKIP191         CLC                     ; Increase 16-bit frequency value of AUDF1/2...
08208                 LDA NOISEAUDF1          ; ...and its shadow register by...
08209                 ADC NOISEFRQINC         ; ...noise sound pattern frequency increment
08210                 STA NOISEAUDF1          ; AUDF1/2 := NOISEAUDF1/2 := ...
08211                 STA AUDF1               ; ...NOISEAUDF1/2 + NOISEFRQINC
08212                 LDA NOISEAUDF2          ;
08213                 ADC #0                  ;
08214                 STA NOISEAUDF2          ;
08215                 STA AUDF2               ;
08216
08217 ;*** Gradually mute audio channels while noise sound pattern expires ***********
08218                 LDX NOISEAUDC2          ; Prep AUDC2's shadow register value
08219                 LDY NOISEAUDC3          ; Prep AUDC3's shadow register value
08220
08221                 LDA COUNT8              ; Decrement volumes every other TICK
08222                 LSR A                   ;
08223                 BCC SKIP193             ;
08224
08225                 LDA NOISELIFE           ; Skip if noise sound pattern not in use
08226                 BEQ SKIP193             ;
08227
08228                 DEC NOISELIFE           ; Decrement noise sound pattern lifetime
08229
08230                 CMP #17                 ; Mute noise sound pattern only in...
08231                 BCS SKIP193             ; ...the last 16 TICKs of its lifetime
08232
08233                 TXA                     ; Decrement volume of AUDC2's shadow register
08234                 AND #$0F                ;
08235                 BEQ SKIP192             ;
08236                 DEX                     ;
08237                 STX NOISEAUDC2          ;
08238
08239 SKIP192         TYA                     ; Decrement volume of AUDC3's shadow register
08240                 AND #$0F                ;
08241                 BEQ SKIP193             ;
08242                 DEY                     ;
08243                 STY NOISEAUDC3          ;
08244
08245 SKIP193         STX AUDC2               ; Store shadow register values to audio registers
08246                 STY AUDC3               ;
08247
08248                 RTS                     ; Return
08249
08250 ;*******************************************************************************
08251 ;*                                                                             *
08252 ;*                                    BEEP                                     *
08253 ;*                                                                             *
08254 ;*                          Copy beeper sound pattern                          *
08255 ;*                                                                             *
08256 ;*******************************************************************************
08257
08258 ; DESCRIPTION
08259 ;
08260 ; Copies a 6-byte beeper sound pattern from beeper sound pattern table
08261 ; BEEPPATTAB ($BF3E) to BEEPFRQIND ($D2)..BEEPFRQSTART ($D7), provided that no
08262 ; beeper sound pattern with higher priority is currently playing. The beeper
08263 ; sound pattern will then be automatically played in subroutine SOUND ($B2AB).
08264 ; See subroutine SOUND ($B2AB) for more information on beeper sound patterns. 
08265 ;
08266 ; NOTE: The bytes from table BEEPPATTAB ($BF3E) are copied in reverse order.
08267 ;
08268 ; INPUT
08269 ;
08270 ;   X = Offset to beeper sound pattern in table BEEPPATTAB ($BF3E). Used values
08271 ;       are:
08272 ;     $00 -> HYPERWARP TRANSIT
08273 ;     $06 -> RED ALERT
08274 ;     $0C -> ACKNOWLEDGE
08275 ;     $12 -> DAMAGE REPORT
08276 ;     $18 -> MESSAGE FROM STARBASE
08277
08278 BEEP            LDA BEEPPATTAB,X        ; Return if beeper sound pattern of...
08279                 CMP BEEPPRIORITY        ; ...higher priority is playing
08280                 BCC SKIP194             ;
08281
08282                 LDY #5                  ; Copy 6-byte beeper sound pattern (in reverse order)
08283 LOOP059         LDA BEEPPATTAB,X        ;
08284                 STA BEEPFRQIND,Y        ;
08285                 INX                     ;
08286                 DEY                     ;
08287                 BPL LOOP059             ;
08288
08289 SKIP194         RTS                     ; Return
08290
08291 ;*******************************************************************************
08292 ;*                                                                             *
08293 ;*                                 INITIALIZE                                  *
08294 ;*                                                                             *
08295 ;*                          More game initialization                           *
08296 ;*                                                                             *
08297 ;*******************************************************************************
08298
08299 ; DESCRIPTION
08300 ;
08301 ; This subroutine executes the following initialization steps:
08302 ;
08303 ; (1)  Set up Display List
08304 ;
08305 ;      A Display List is created at DSPLST ($0280). It starts with 2 x 8 = 16
08306 ;      blank video lines, followed by 90 GRAPHICS7 rows. After a deliberate gap
08307 ;      in Display List instructions, which will be filled dynamically during the
08308 ;      game by calls to subroutine MODDLST ($ADF1), it ends with a Display List
08309 ;      wait-and-jump-back instruction to the start of the Display List at DSPLST
08310 ;      ($0280).
08311 ;
08312 ;      NOTE: The PLAYFIELD color table PFCOLORTAB ($BFA9) is copied to zero-page
08313 ;      table PF0COLOR ($F2) by loop jamming.
08314 ;
08315 ; (2)  Create lookup tables
08316 ;
08317 ;      The first lookup table MAPTO80 ($0DE9) maps a byte value of 0..255 to
08318 ;      0..80. This table is used to map unsigned (absolute) position vector
08319 ;      components (coordinates) to pixel (or PLAYER) row and column numbers.
08320 ;
08321 ;      NOTE: The PLAYFIELD is 160 pixels wide. Pixel column numbers relative the
08322 ;      horizontal PLAYFIELD center are in -80..79, hence the range of this
08323 ;      lookup table. Pixel row numbers relative the vertical PLAYFIELD center
08324 ;      are in -50..49, thus they also fit in the range of this lookup table.
08325 ;
08326 ;      The second lookup table MAPTOBCD99 ($0EE9) maps a byte value of 0..255 to
08327 ;      a BCD-encoded value in 00..99. This table is used to convert byte values
08328 ;      into decimal 2-digit values displayed by the THETA (in "gradons"), PHI
08329 ;      (in "gradons"), RANGE (in "centrons"), and VELOCITY (in "metrons per
08330 ;      second") readouts of the Console Panel Display.
08331 ;
08332 ;      The third and fourth lookup tables accelerate drawing of PLAYFIELD space
08333 ;      objects: In combination they contain the 16-bit start addresses of each
08334 ;      of the 100 rows of PLAYFIELD memory. The low bytes of the 16-bit
08335 ;      addresses are stored in table PFMEMROWLO ($0800). The high bytes are
08336 ;      stored in table PFMEMROWHI ($0864).
08337 ;
08338 ;      NOTE: The address increment is 40 (40 bytes = 160 pixels in GRAPHICS7
08339 ;      mode = 1 PLAYFIELD row of pixels). 
08340 ;
08341 ;      NOTE: The PLAYFIELD consists of 90 GRAPHICS7 rows when the Control Panel
08342 ;      Display is displayed at the bottom. When the Control Panel Display is not
08343 ;      displayed, for example in demo mode, the PLAYFIELD contains additional
08344 ;      GRAPHICS7 rows.  
08345 ;
08346 ; (3)  Copy Control Panel Display and Galactic Chart Panel Display texts
08347 ;
08348 ;      The texts of the Control Panel Display and the Galactic Chart Panel
08349 ;      Display are copied to their respective locations in memory by loop
08350 ;      jamming.
08351 ;
08352 ; (4)  Initialize Zylon unit movement timer
08353 ;
08354 ;      The timer that triggers the movement of Zylon units in the Galactic Chart
08355 ;      is initialized to a value of 99. See subroutine FLUSHGAMELOOP ($B4E4) for
08356 ;      more information on Zylon unit movement.
08357 ;
08358 ; (5)  Create Galactic Chart
08359 ;
08360 ;      The Galactic Chart memory map GCMEMMAP ($08C9) is initialized. It
08361 ;      represents 16 columns x 8 rows of sectors. Each sector contains one of
08362 ;      the 4 sector types stored in table SECTORTYPETAB ($BBA6) (starbase, 4
08363 ;      Zylon ships, 3 Zylon ships, and 2 or 1 Zylon ships), and empty sectors.
08364 ;      Before distributing the sector types, the initial position of our
08365 ;      starship is blocked on the Galactic Chart at sector row 4, sector column
08366 ;      8, so that it will not be inadvertently occupied while other sector types
08367 ;      are distributed. The number of each of the sector types to be distributed
08368 ;      is the mission level plus 2. While Zylon units can be placed anywhere,
08369 ;      starbases are placed neither at the borders of the Galactic Chart nor in
08370 ;      a sector adjacent to an occupied sector. 
08371 ;
08372 ;      After having initialized the Galactic Chart memory map, the top border of
08373 ;      the Galactic Chart is drawn with characters from the custom character
08374 ;      set.
08375 ;
08376 ;      Finally, the sector in which our starship is located and the arrival and
08377 ;      departure hyperwarp marker column and row numbers are initialized.
08378 ;
08379 ; (6)  Apply a final tweak
08380 ;
08381 ;      The last entry of lookup table MAPTOBCD99 ($0EE9) is tweaked to a value
08382 ;      of CCS.INF * 16 + CCS.SPC. It is used to display an infinity symbol by
08383 ;      the RANGE readout of the Control Panel Display in subroutine SHOWCOORD
08384 ;      ($B8A7).
08385 ;
08386 ; Code execution continues into subroutine DRAWGC ($B4B9), which draws the
08387 ; content of the Galactic Chart with characters from the custom character set.
08388
08389 L.MEMPTR1       = $68                   ; 16-bit memory pointer
08390 L.MEMPTR2       = $6A                   ; 16-bit memory pointer
08391 L.SECTORTYPE    = $6A                   ; Saves sector type. Used values are:
08392                                         ;   $CF -> Sector contains starbase
08393                                         ;   $04 -> Sector contains 4 Zylon ships
08394                                         ;   $03 -> Sector contains 3 Zylon ships
08395                                         ;   $02 -> Sector contains 2 or 1 Zylon ships
08396 L.SECTORCNT     = $6B                   ; Saves number of sectors of the current sector type
08397
08398 ;*** Initialize Display List and copy color table ******************************
08399 INITIALIZE      LDX #89                 ; Set 89(+1) GRAPHICS7 rows from DSPLST+5 on
08400 LOOP060         LDA #$0D                ; Prep DL instruction $0D (one row of GRAPHICS7)
08401                 STA DSPLST+5,X          ; DSPLST+5,X := one row of GRAPHICS7
08402                 CPX #10                 ;
08403                 BCS SKIP195             ;
08404                 LDA PFCOLORTAB,X        ; Copy PLAYFIELD color table to zero-page table
08405                 STA PF0COLOR,X          ; (loop jamming)
08406 SKIP195         DEX                     ;
08407                 BPL LOOP060             ;
08408
08409                 LDA #$70                ; DSPLST     := BLK8
08410                 STA DSPLST              ; DSPLST+1   := BLK8
08411                 STA DSPLST+1            ;
08412                 LDA #$41                ; DSPLST+103 := WAITJMP @ DSPLST
08413                 STA DSPLST+103          ;
08414                 LDA #<DSPLST            ;
08415                 STA DSPLST+104          ;
08416                 LDA #>DSPLST            ;
08417                 STA DSPLST+105          ;
08418
08419 ;*** Calculate lookup tables ***************************************************
08420                 LDX #0                  ; Clear both 16-bit memory pointers
08421                 STX L.MEMPTR1           ;
08422                 STX L.MEMPTR1+1         ;
08423                 STX L.MEMPTR2           ;
08424                 STX L.MEMPTR2+1         ;
08425
08426 ;*** Calc MAPTO80 map (converts value of $00..$FF to value in 0..80) ***********
08427 LOOP061         CLC                     ;
08428                 LDA L.MEMPTR1           ;
08429                 ADC #81                 ;
08430                 STA L.MEMPTR1           ;
08431                 LDA L.MEMPTR1+1         ;
08432                 STA MAPTO80,X           ;
08433                 ADC #0                  ;
08434                 STA L.MEMPTR1+1         ;
08435
08436 ;*** Calc MAPTOBCD99 map (converts value of $00..$FF to BCD-value in 00..99) ***
08437                 CLC                     ;
08438                 LDA L.MEMPTR2           ;
08439                 ADC #100                ;
08440                 STA L.MEMPTR2           ;
08441                 LDA L.MEMPTR2+1         ;
08442                 STA MAPTOBCD99,X        ;
08443                 SED                     ;
08444                 ADC #0                  ;
08445                 CLD                     ;
08446                 STA L.MEMPTR2+1         ;
08447                 INX                     ;
08448                 BNE LOOP061             ;
08449
08450 ;*** Calculate PLAYFIELD memory row addresses, copy Panel Display texts ********
08451                 LDX #<PFMEM             ; Point L.MEMPTR1 to start of PLAYFIELD memory
08452                 STX L.MEMPTR1           ; (X = 0, because PFMEM is at $1000)
08453                 LDA #>PFMEM             ;
08454                 STA L.MEMPTR1+1         ;
08455
08456 LOOP062         CLC                     ;
08457                 LDA L.MEMPTR1           ;
08458                 STA PFMEMROWLO,X        ; Store 16-bit value of L.MEMPTR1 in PFMEMROWHI/LO
08459                 ADC #40                 ; Add 40 to L.MEMPTR
08460                 STA L.MEMPTR1           ; (40 bytes = 160 pixels = 1 PLAYFIELD row)
08461                 LDA L.MEMPTR1+1         ;
08462                 STA PFMEMROWHI,X        ;
08463                 ADC #0                  ;
08464                 STA L.MEMPTR1+1         ;
08465
08466                 LDA PANELTXTTAB,X       ; Copy Control and Galactic Chart Panel Display texts
08467                 STA PANELTXT,X          ; (loop jamming)
08468
08469                 INX                     ;
08470                 CPX #100                ;
08471                 BCC LOOP062             ; Loop 100 times
08472
08473 ;*** Set Zylon unit movement timer *********************************************
08474                 DEX                     ;
08475                 STX ZYLONUNITTIM        ; Init Zylon unit movement timer to 99 game loops
08476
08477 ;*** Create memory map of the Galactic Chart ***********************************
08478                 LDX #3                  ; Loop over all 3(+1) sector types
08479                 STX GCMEMMAP+4*16+8     ; Block our starship's initial position at center of
08480                                         ; ...Galactic Chart (sector row 4, sector column 8)
08481
08482 LOOP063         LDA SECTORTYPETAB,X     ; Prep sector type
08483                 STA L.SECTORTYPE        ;
08484
08485                 LDY MISSIONLEVEL        ; Number sectors of current type := mission level + 2
08486                 INY                     ;
08487                 INY                     ;
08488                 STY L.SECTORCNT         ;
08489
08490 LOOP064         LDA RANDOM              ; Load random sector 0..127 from GC memory map
08491                 AND #$7F                ;
08492                 TAY                     ;
08493                 LDA GCMEMMAP,Y          ;
08494                 BNE LOOP064             ; If sector already occupied, pick another
08495
08496                 LDA L.SECTORTYPE        ; Reload sector type
08497                 BPL SKIP196             ; Skip if sector not to be occupied by starbase
08498
08499                 CPY #$10                ; Place starbase...
08500                 BCC LOOP064             ; ...not in first sector row of Galactic Chart
08501                 CPY #$70                ;
08502                 BCS LOOP064             ; ...not in last sector row of Galactic Chart
08503                 TYA                     ;
08504                 AND #$0F                ;
08505                 BEQ LOOP064             ; ...not in first sector column of Galactic Chart
08506                 CMP #15                 ;
08507                 BEQ LOOP064             ; ...not in last sector column of Galactic Chart
08508                 LDA GCMEMMAP-1,Y        ; ...not east  of an occupied sector
08509                 ORA GCMEMMAP+1,Y        ; ...not west  of an occupied sector
08510                 ORA GCMEMMAP+16,Y       ; ...not south of an occupied sector
08511                 ORA GCMEMMAP-16,Y       ; ...not north of an occupied sector
08512                 BNE LOOP064             ;
08513
08514                 LDA L.SECTORTYPE        ; Reload sector type
08515
08516 SKIP196         STA GCMEMMAP,Y          ; Store sector type in Galactic Chart memory map
08517                 DEC L.SECTORCNT         ;
08518                 BPL LOOP064             ; Next sector
08519                 DEX                     ;
08520                 BPL LOOP063             ; Next sector type
08521
08522 ;*** Clear Galactic Chart and draw top border **********************************
08523                 LDX #180                ; Clear Galactic Chart PLAYFIELD
08524 LOOP065         LDA #CCS.SPC            ;
08525                 STA GCPFMEM-1,X         ;
08526                 DEX                     ;
08527                 BNE LOOP065             ;
08528
08529                 LDX #15                 ; Draw top border (15(+1) characters)
08530 LOOP066         LDA #CCS.BORDERS        ;
08531                 STA GCPFMEM+2,X         ;
08532                 DEX                     ;
08533                 BPL LOOP066             ;
08534
08535                 LDA #CCS.CORNERSW       ; Draw NORTHEAST corner (1 character)
08536                 STA GCPFMEM+18          ;
08537
08538                 LDA #0                  ; Release starship's position at center of Galactic
08539                 STA GCMEMMAP+4*16+8     ; ...Chart (sector row 4, sector column 8)
08540
08541 ;*** Initialize current sector and hyperwarp marker column and row numbers *****
08542                 LDA #$48                ; Place our starship's current sector at
08543                 STA CURRSECTOR          ; ...sector row 4, sector column 8
08544                 LDA #$43                ; Init departure & arrival hyperwarp marker column
08545                 STA WARPDEPRCOLUMN      ;
08546                 STA WARPARRVCOLUMN      ;
08547                 LDA #$47                ; Init departure & arrival hyperwarp marker row
08548                 STA WARPARRVROW         ;
08549                 STA WARPDEPRROW         ;
08550
08551 ;*** Tweak last entry of MAPTOBCD99 ********************************************
08552                 LDA #CCS.INF*16+CCS.SPC ; Last entry of MAPTOBCD99: 'INFINITY'+'SPACE' char
08553                 STA MAPTOBCD99+255      ;
08554
08555 ;*******************************************************************************
08556 ;*                                                                             *
08557 ;*                                   DRAWGC                                    *
08558 ;*                                                                             *
08559 ;*                             Draw Galactic Chart                             *
08560 ;*                                                                             *
08561 ;*******************************************************************************
08562
08563 ; DESCRIPTION
08564 ;
08565 ; Draws the content of the Galactic Chart memory map in GCMEMMAP ($08C9) to the
08566 ; Galactic Chart PLAYFIELD memory at GCPFMEM ($0D35). 
08567 ;
08568 ; NOTE: CPU register X indexes the Galactic Chart memory map GCMEMMAP ($08C9)
08569 ; (16 x 8 bytes). CPU register Y indexes the Galactic Chart PLAYFIELD memory
08570 ; GCPFMEM ($0D35) (20 x 9 bytes).
08571 ;
08572 ; NOTE: Sectors with 1 or 2 Zylon ships display the same symbol in the Galactic
08573 ; Chart.
08574
08575 L.GCMEMMAPIND   = $6A                   ; Saves Galactic Chart memory map index
08576
08577 DRAWGC          LDY #0                  ; Clear Galactic Chart PLAYFIELD memory index
08578                 STY L.GCMEMMAPIND       ; Clear Galactic Chart memory map index
08579
08580 LOOP067         LDX L.GCMEMMAPIND       ; Load sector of Galactic Chart memory map
08581                 LDA GCMEMMAP,X          ;
08582                 BPL SKIP197             ; Skip if not a starbase sector
08583                 LDA #5                  ; Prep sector character index for starbase
08584
08585 SKIP197         TAX                     ; Load sector character index
08586                 LDA SECTORCHARTAB,X     ; Load custom character set code from table...
08587                 STA GCPFMEM+22,Y        ; ...and store it in Galactic Chart PLAYFIELD memory
08588                 INY                     ; Increment Galactic Chart PLAYFIELD memory index
08589                 INC L.GCMEMMAPIND       ; Increment Galactic Chart memory map index
08590                 LDA L.GCMEMMAPIND       ;
08591                 AND #$0F                ;
08592                 BNE LOOP067             ; Next sector column until right border reached
08593
08594                 LDA #CCS.BORDERW        ; Draw right border
08595                 STA GCPFMEM+22,Y        ;
08596
08597                 INY                     ; Adjust Galactic Chart PLAYFIELD memory index
08598                 INY                     ;
08599                 INY                     ;
08600                 INY                     ;
08601                 CPY #$A0                ;
08602                 BCC LOOP067             ; Next sector until bottom-right sector reached
08603
08604                 RTS                     ; Return
08605
08606 ;*******************************************************************************
08607 ;*                                                                             *
08608 ;*                                FLUSHGAMELOOP                                *
08609 ;*                                                                             *
08610 ;*         Handle remaining tasks at the end of a game loop iteration          *
08611 ;*                                                                             *
08612 ;*******************************************************************************
08613
08614 ; DESCRIPTION
08615 ;
08616 ; This subroutine handles at the end of a game loop iteration the following
08617 ; tasks:
08618 ;
08619 ; (1)  Increment counters COUNT256 ($76) and COUNT8 ($72).
08620 ;
08621 ; (2)  If our starship's energy has dropped below 1000 units then flash a {PINK}
08622 ;      alert that changes to {DARK GREY BLUE} and back to {PINK} every 128 game
08623 ;      loop iterations.
08624 ;
08625 ; (3)  Set the Shields color and the Control Panel background color every 8 game
08626 ;      loop iterations:
08627 ;
08628 ;      o   If the Shields are up and OK then set the Shields color to {DARK
08629 ;          GREEN} and the Control Panel background color to {DARK BLUE}.
08630 ;
08631 ;      o   If the Shields are up and damaged there is a probability of 78%
08632 ;          (200:256) that the Shield color is not changed.
08633 ;
08634 ;      o   If the Shields are down, damaged, or destroyed then set the Shields
08635 ;          color to {BLACK}.
08636 ;
08637 ;      o   If the Shields are destroyed then set the Control Panel background
08638 ;          color to {ORANGE}.
08639 ;
08640 ; (4)  Decrement the lifetime of our starship's and Zylon photon torpedoes.
08641 ;
08642 ; (5)  Decrement the lifetime of an explosion. If the explosion lifetime is less
08643 ;      than 112 game loop iterations, clear HITBADNESS ($8A) (thus the explosion
08644 ;      cannot destroy our starship). If the explosion lifetime is less than 24
08645 ;      (?) game loops decrement the number of explosion fragments. This makes
08646 ;      explosion fragments disappear gradually toward the end of an explosion.
08647 ;
08648 ; (6)  Increment every 40 game loop iterations the stardate clock of the
08649 ;      Galactic Chart Panel Display.
08650 ;
08651 ; (7)  Move Zylon units in the Galactic Chart.
08652 ;
08653 ;      Every 50 game loop iterations (or 100 game loop iterations when a
08654 ;      starbase is surrounded by Zylon units) decrement the score.
08655 ;
08656 ; Code execution continues if the program is not in demo mode with the following
08657 ; steps:
08658 ;
08659 ; (1)  Search the Galactic Chart for starbases surrounded by Zylon units.
08660 ;      Destroy any such starbase: Replace it with a 2-Zylon sector and subtract
08661 ;      18 points from the score. If the Subspace Radio was not destroyed, then
08662 ;      flash the title phrase "STARBASE DESTROYED" and play the beeper sound
08663 ;      pattern MESSAGE FROM STARBASE in subroutine BEEP ($B3A6).
08664 ;
08665 ; (2)  Every 8 game loop iterations the Zylon units decide, which starbase to
08666 ;      hunt: First, 128 randomly picked sectors are searched for a starbase. If
08667 ;      no starbase was found in this way, the sectors of the Galactic Chart are
08668 ;      scanned systematically left-to-right, top-to-bottom. If a starbase was
08669 ;      found then its sector, sector column, and sector row are saved, otherwise
08670 ;      code execution returns.
08671 ;
08672 ; (3)  Now the Zylon units converge toward the sector of the hunted starbase:
08673 ;      All sectors of the Galactic Chart are scanned. For any sector with a
08674 ;      Zylon unit that was not moved yet (its sector does not have the temporary
08675 ;      "already-moved" bit B5 set) its movement probability value is picked from
08676 ;      table MOVEPROBTAB ($BFBB):
08677 ;
08678 ;      +---------------+-------------+----------------+
08679 ;      |  Sector Type  |  Movement   |   Movement     | 
08680 ;      |               | Probability |  Probability   |
08681 ;      |               |    Value    |                |
08682 ;      +---------------+-------------+----------------+
08683 ;      | Empty sector  |       0     |   0% (  0:256) | 
08684 ;      | 1 Zylon ship  |     255     | 100% (255:256) |
08685 ;      | 2 Zylon ships |     255     | 100% (255:256) | 
08686 ;      | 3 Zylon ships |     192     |  75% (192:256) | 
08687 ;      | 4 Zylon ships |      32     |  13% ( 32:256) |
08688 ;      +---------------+-------------+----------------+
08689 ;
08690 ;      If this value is less or equal than a random number in 0..255 then the
08691 ;      Zylon unit is moved to another sector. A Zylon unit that currently
08692 ;      occupies the sector of our starship is not moved.
08693 ;
08694 ;      BUG (at $B620): The instruction to check the marker bit B5 of the sector
08695 ;      is CPY #$0A. This works, as sectors containing Zylon units that need to
08696 ;      be moved have values of 2..4, see table SECTORTYPETAB ($BBA6). Suggested
08697 ;      fix: Replace CPY #$0A with CPY #$20, which may make the code clearer.
08698 ;
08699 ; (4)  For every Zylon unit that is about to be moved, 9 distances ("block
08700 ;      distances") between the Zylon unit and the starbase are calculated by
08701 ;      tentatively moving the Zylon unit into each of its 8 adjacent sectors -
08702 ;      and by moving it not at all. The sector offsets are taken from table
08703 ;      COMPASSOFFTAB ($BFC0) which stores direction offsets in the following
08704 ;      order: NORTH, NORTHWEST, WEST, SOUTHWEST, SOUTH, SOUTHEAST, EAST,
08705 ;      NORTHEAST, CENTER. All 9 distances are stored in 9 consecutive bytes at
08706 ;      NEWZYLONDIST ($96).
08707 ;
08708 ;      NOTE: The last calculated distance is the current distance between Zylon
08709 ;      unit and starbase.
08710 ;
08711 ;      The Zylon unit moves to the first of the 8 adjacent sectors that matches
08712 ;      the following conditions: 
08713 ;
08714 ;      (1)  It is closer to the starbase than the Zylon unit's current sector.
08715 ;
08716 ;      (2)  It is located inside the Galactic Chart.
08717 ;
08718 ;      (3)  It is empty.
08719 ;
08720 ;      (4)  It is not the sector containing our starship.
08721 ;
08722 ;      If a suitable new sector was found then the Zylon unit is moved to this
08723 ;      sector, which is marked with the "already-moved" marker bit B5 in the
08724 ;      Galactic Chart memory map. This marker bit prevents a Zylon unit that has
08725 ;      been already moved from being moved again. The old Zylon unit sector is
08726 ;      cleared. 
08727 ;
08728 ;      If no suitable new sector was found then the above distance calculations
08729 ;      are repeated once again by adding 1 to the current distance between the
08730 ;      Zylon unit and the starbase. This may provoke a Zylon unit to move that
08731 ;      would not have moved in the previous set of distance calculations.
08732 ;
08733 ;      After having moved all Zylon units the sectors are stripped of the
08734 ;      "already-moved" marker bit B5.
08735 ;
08736 ; (5)  If a starbase has been surrounded then the Zylon unit movement timer is
08737 ;      reset to 99, buying our starship some time to destroy one of the
08738 ;      surrounding Zylon units. If the Subspace Radio is not destroyed, then the
08739 ;      message "STARBASE SURROUNDED" is flashed in the title line and the beeper
08740 ;      sound pattern MESSAGE FROM STARBASE is played in subroutine BEEP ($B3A6).
08741
08742 L.ISDESTROYED   = $6A                   ; Flags the destruction of a starbase.
08743                                         ; Used values are:
08744                                         ;   $00 -> Starbase not destroyed
08745                                         ;   $02 -> Starbase has been destroyed
08746 L.NEWSECTOR     = $6A                   ; Sector to which the Zylon unit is tentatively moved
08747 L.ABSDIFFCOL    = $6B                   ; Absolute difference between new Zylon and starbase
08748                                         ;   column on Galactic Chart in PM pixels
08749 L.LOOPCNT2      = $6B                   ; Loop counter. Used values are: 0..1.
08750 L.DIRECTIONIND  = $6A                   ; Compass rose direction index.
08751                                         ; Used values are: 0..7.
08752
08753 ;*** Increment counters and flash low-energy alert *****************************
08754 FLUSHGAMELOOP   INC COUNT256            ; Increment COUNT256 counter
08755
08756                 LDX #$90                ; Prep DLI background color {DARK GREY BLUE}
08757                 LDA COUNT256            ;
08758                 BPL SKIP198             ; Skip if counter < 128.
08759
08760                 LDY ENERGYD1            ; When energy drops below 1000 units...
08761                 CPY #CCS.COL2!CCS.0     ;
08762                 BNE SKIP198             ;
08763                 LDX #$44                ; ...prep new DLI background color {PINK}
08764
08765 SKIP198         AND #$03                ; Increment COUNT8
08766                 STA COUNT8              ;
08767                 BNE SKIP202             ; Skip setting colors but every 8 game loops
08768
08769 ;*** Set Shields and Control Panel background color ****************************
08770                 LDY DRAINSHIELDS        ; Skip if Shields are off
08771                 BEQ SKIP201             ;
08772
08773                 LDY #$A0                ; Prep Shields color {DARK GREEN}
08774                 BIT GCSTATSHL           ; Skip if Shields are OK
08775                 BPL SKIP200             ;
08776                 BVS SKIP199             ; Skip if Shields are destroyed
08777                 LDA RANDOM              ; If Shields are damaged, Shields colors are...
08778                 CMP #200                ; ...unchanged with probability of 78% (200:256)
08779                 BCC SKIP201             ;
08780
08781 SKIP199         LDY #$00                ; Prep Shields color {BLACK}
08782 SKIP200         TYA                     ;
08783                 BNE SKIP201             ;
08784
08785                 LDX #$26                ; Prep Control Panel background color {ORANGE}
08786
08787 SKIP201         STY SHIELDSCOLOR        ; Store Shields color
08788                 STX BGRCOLORDLI         ; Store Control Panel background color
08789
08790 ;*** Decrement lifetime of our starship's and Zylon photon torpedoes ***********
08791 SKIP202         LDX #2                  ; Loop over PLAYER2..4
08792
08793 LOOP068         LDA PL2SHAPTYPE,X       ; Next PLAYER if not PHOTON TORPEDO (shape type 0)
08794                 BNE SKIP203             ;
08795
08796                 LDA PL2LIFE,X           ; Next PLAYER if this PLAYER not alive
08797                 BEQ SKIP203             ;
08798
08799                 DEC PL2LIFE,X           ; Decrement photon torpedo PLAYER lifetime
08800
08801 SKIP203         DEX                     ;
08802                 BPL LOOP068             ; Next PLAYER
08803
08804 ;*** Decrement lifetime of explosion *******************************************
08805                 LDA EXPLLIFE            ; Skip if explosion lifetime expired
08806                 BEQ SKIP206             ;
08807
08808                 DEC EXPLLIFE            ; Decrement explosion lifetime
08809                 BNE SKIP204             ; Skip if explosion lifetime still counting
08810
08811                 LDX #NUMSPCOBJ.NORM     ; Explosion finished,...
08812                 STX MAXSPCOBJIND        ; ...restore normal number of space objects
08813
08814 SKIP204         CMP #112                ; Skip if explosion lifetime >= 112 game loops
08815                 BCS SKIP205             ;
08816
08817                 LDX #0                  ; HITBADNESS := NO HIT
08818                 STX HITBADNESS          ;
08819
08820 SKIP205         CMP #24                 ; Skip if explosion lifetime >= 24 game loops (?)
08821                 BCS SKIP206             ;
08822
08823                 DEC MAXSPCOBJIND        ; Decrement number of explosion fragment space objs
08824
08825 ;*** Increment stardate clock **************************************************
08826 SKIP206         DEC CLOCKTIM            ; Decrement stardate clock timer
08827                 BPL SKIP209             ; Return if timer is still counting
08828
08829                 LDA #40                 ; Reset stardate clock timer to 40 game loops
08830                 STA CLOCKTIM            ;
08831
08832                 LDX #4                  ; Increment stardate clock of Galactic Chart Panel
08833 LOOP069         INC GCSTARDAT,X         ;
08834                 LDA GCSTARDAT,X         ;
08835                 CMP #[CCS.COL3!ROM.9]+1 ;
08836                 BCC SKIP208             ;
08837                 LDA #[CCS.COL3!ROM.0]   ;
08838                 STA GCSTARDAT,X         ;
08839                 CPX #3                  ;
08840                 BNE SKIP207             ;
08841                 DEX                     ;
08842 SKIP207         DEX                     ;
08843                 BPL LOOP069             ;
08844
08845 ;*** Decrement Zylon unit movement timer ***************************************
08846 SKIP208         DEC ZYLONUNITTIM        ; Decrement Zylon unit movement timer
08847                 BMI SKIP210             ; If timer < 0 move Zylon units
08848
08849 SKIP209         RTS                     ; Return
08850
08851 ;*** Restore Zylon unit movement timer and decrement score *********************
08852 SKIP210         LDA #49                 ; Reset Zylon unit movement timer to 49
08853                 STA ZYLONUNITTIM        ;
08854
08855                 LDA SCORE               ; SCORE := SCORE - 1
08856                 BNE SKIP211             ;
08857                 DEC SCORE+1             ;
08858 SKIP211         DEC SCORE               ;
08859
08860                 LDX ISDEMOMODE          ; Return if in demo mode
08861                 BNE SKIP209             ;
08862
08863 ;*** Is starbase surrounded? ***************************************************
08864                 STX L.ISDESTROYED       ; Init L.ISDESTROYED with 0 (starbase not destroyed)
08865 LOOP070         LDA GCMEMMAP,X          ; Loop over all sectors, load sector type
08866                 BPL SKIP212             ; Skip if not a starbase sector
08867
08868                 JSR ISSURROUNDED        ; Skip if starbase sector not completely surrounded
08869                 BEQ SKIP212             ;
08870
08871 ;*** Starbase is surrounded, destroy starbase **********************************
08872                 LDA #2                  ; Replace starbase sector with 2-Zylon sector
08873                 STA GCMEMMAP,X          ;
08874                 STA L.ISDESTROYED       ; Flag destruction of starbase
08875
08876                 SEC                     ; SCORE := SCORE - 18
08877                 LDA SCORE               ;
08878                 SBC #18                 ;
08879                 STA SCORE               ;
08880                 LDA SCORE+1             ;
08881                 SBC #0                  ;
08882                 STA SCORE+1             ;
08883
08884 SKIP212         INX                     ;
08885                 BPL LOOP070             ; Next sector
08886
08887 ;*** Report starbase destruction ***********************************************
08888                 LDA L.ISDESTROYED       ; Skip if no starbase has been destroyed
08889                 BEQ SKIP213             ;
08890
08891                 BIT GCSTATRAD           ; Skip notification if Subspace Radio destroyed
08892                 BVS SKIP213             ;
08893
08894                 LDY #$15                ; Set title phrase "STARBASE DESTROYED"
08895                 JSR SETTITLE            ;
08896
08897                 LDX #$18                ; Play beeper sound pattern MESSAGE FROM STARBASE
08898                 JSR BEEP                ;
08899
08900 ;*** Pick new starbase to be hunted by Zylon units *****************************
08901 SKIP213         DEC HUNTTIM             ; Decrement hunting timer
08902                 BMI SKIP214             ; If timer < 0 decide which starbase to hunt
08903
08904                 LDX HUNTSECTOR          ; Skip if Zylon units already picked starbase to hunt
08905                 LDA GCMEMMAP,X          ;
08906                 BMI SKIP215             ;
08907
08908 SKIP214         LDA #7                  ; Reset hunting timer
08909                 STA HUNTTIM             ;
08910
08911                 LDY #127                ; Loop over 127(+1) randomly picked sectors
08912 LOOP071         LDA RANDOM              ;
08913                 AND #$7F                ;
08914                 TAX                     ;
08915                 LDA GCMEMMAP,X          ; Skip if starbase sector found
08916                 BMI SKIP215             ;
08917                 DEY                     ;
08918                 BPL LOOP071             ; Next sector
08919
08920                 LDX #127                ; Loop over all sectors of the Galactic Chart
08921 LOOP072         LDA GCMEMMAP,X          ;
08922                 BMI SKIP215             ; Skip if starbase sector found
08923                 DEX                     ;
08924                 BPL LOOP072             ; Next sector
08925
08926                 RTS                     ; Return (no starbase sector found)
08927
08928 ;*** Store coordinates of starbase to be hunted ********************************
08929 SKIP215         STX HUNTSECTOR          ; Store hunted starbase sector column and row
08930                 TXA                     ;
08931                 AND #$0F                ;
08932                 STA HUNTSECTCOLUMN      ;
08933                 TXA                     ;
08934                 LSR A                   ;
08935                 LSR A                   ;
08936                 LSR A                   ;
08937                 LSR A                   ;
08938                 STA HUNTSECTROW         ;
08939
08940 ;*** Move all Zylon units toward hunted starbase *******************************
08941                 LDX #$FF                ;
08942 LOOP073         INX                     ; Loop over all sectors to move Zylon units
08943                 BPL SKIP218             ; Jump into loop body below
08944
08945 ;*** Strip marker bits from moved Zylon units **********************************
08946                 LDX #0                  ;
08947 LOOP074         LDA GCMEMMAP,X          ; Loop over all sectors
08948                 AND #$DF                ;
08949                 STA GCMEMMAP,X          ; Strip marker bit B5 from moved Zylon units
08950                 INX                     ;
08951                 BPL LOOP074             ; Next sector
08952
08953 ;*** Handle surrounded starbase ************************************************
08954                 BIT GCSTATRAD           ; Return if Subspace Radio is destroyed
08955                 BVS SKIP217             ;
08956
08957                 LDX #0                  ; Loop over all sectors
08958 LOOP075         LDA GCMEMMAP,X          ;
08959                 BPL SKIP216             ; Skip if not a starbase sector
08960                 JSR ISSURROUNDED        ; Skip if starbase not surrounded
08961                 BEQ SKIP216             ;
08962
08963                 LDA #99                 ; Yes, starbase surrounded...
08964                 STA ZYLONUNITTIM        ; ...set Zylon unit movement timer to 99
08965
08966                 LDY #$13                ; Set title phrase "STARBASE SURROUNDED"
08967                 JSR SETTITLE            ;
08968
08969                 LDX #$18                ; Play beeper sound pattern MESSAGE FROM STARBASE...
08970                 JMP BEEP                ; ...and return
08971
08972 SKIP216         INX                     ;
08973                 BPL LOOP075             ; Next sector
08974
08975 SKIP217         RTS                     ; Return
08976
08977 ;*** Move single Zylon unit ****************************************************
08978 SKIP218         LDY GCMEMMAP,X          ; X contains current sector
08979                 CPY #$0A                ; Next sector if it has marker bit B5 set (!)
08980                 BCS LOOP073             ;
08981
08982                 LDA RANDOM              ; Get random number
08983                 CMP MOVEPROBTAB,Y       ; Get movement probability
08984                 BCS LOOP073             ; Next sector if movement probability < random number
08985
08986                 CPX CURRSECTOR          ; Next sector if this is our starship's sector
08987                 BEQ LOOP073             ;
08988
08989 ;*** Compute distance to starbase by moving Zylon unit into 9 directions *******
08990                 LDY #8                  ; Loop over 8(+1) possible directions
08991 LOOP076         CLC                     ;
08992                 TXA                     ;
08993                 ADC COMPASSOFFTAB,Y     ; Add direction offset to current sector
08994                 STA L.NEWSECTOR         ; Store new sector
08995
08996                 AND #$0F                ; Calc distance ("block distance") between...
08997                 SEC                     ; ...starbase sector and tentative new Zylon sector
08998                 SBC HUNTSECTCOLUMN      ;
08999                 BCS SKIP219             ;
09000                 EOR #$FF                ;
09001                 ADC #1                  ;
09002 SKIP219         STA L.ABSDIFFCOL        ;
09003                 LDA L.NEWSECTOR         ;
09004                 LSR A                   ;
09005                 LSR A                   ;
09006                 LSR A                   ;
09007                 LSR A                   ;
09008                 SEC                     ;
09009                 SBC HUNTSECTROW         ;
09010                 BCS SKIP220             ;
09011                 EOR #$FF                ;
09012                 ADC #1                  ;
09013 SKIP220         CLC                     ;
09014                 ADC L.ABSDIFFCOL        ;
09015
09016                 STA NEWZYLONDIST,Y      ; Store distance in distance array
09017                 DEY                     ;
09018                 BPL LOOP076             ; Next direction
09019
09020 ;*** Pick the shortest distance to starbase ************************************
09021                 LDA #1                  ; Loop over compass rose directions twice to...
09022                 STA L.LOOPCNT2          ; ...provoke movement regardless of truncation errors
09023
09024 LOOP077         LDY #7                  ;
09025 LOOP078         LDA NEWZYLONDIST,Y      ; Loop over all 7(+1) compass rose directions
09026                 CMP OLDZYLONDIST        ;
09027                 BCS SKIP222             ; Next direction if new distance > current distance
09028
09029                 CLC                     ; Calc new Galactic Chart sector for Zylon unit
09030                 TXA                     ;
09031                 ADC COMPASSOFFTAB,Y     ;
09032                 BMI SKIP222             ; Next direction if new sector outside Galactic Chart
09033
09034                 STY L.DIRECTIONIND      ; Save compass rose direction index
09035                 TAY                     ;
09036                 LDA GCMEMMAP,Y          ;
09037                 BNE SKIP221             ; Next direction if new sector not empty
09038
09039                 LDA GCMEMMAP,X          ; Preload Zylon sector type to be moved
09040                 CPY CURRSECTOR          ;
09041                 BEQ SKIP221             ; Next direction if sector is our starship's sector
09042
09043                 ORA #$20                ; New sector for Zylon unit found!
09044                 STA GCMEMMAP,Y          ; Temporarily mark that sector with marker bit B5
09045                 LDA #0                  ;
09046                 STA GCMEMMAP,X          ; Clear old Zylon unit sector
09047                 BEQ SKIP223             ; Next sector (unconditional branch)
09048
09049 SKIP221         LDY L.DIRECTIONIND      ; Restore compass rose direction index
09050 SKIP222         DEY                     ; Next compass rose direction
09051                 BPL LOOP078             ;
09052
09053                 INC OLDZYLONDIST        ; Increment center distance
09054                 DEC L.LOOPCNT2          ;
09055                 BPL LOOP077             ; Loop over all compass rose directions one more time
09056
09057 SKIP223         JMP LOOP073             ; Next sector
09058
09059 ; *******************************************************************************
09060 ; *                                                                             *
09061 ; *                                   ROTATE                                    *
09062 ; *                                                                             *
09063 ; *        Rotate position vector component (coordinate) by fixed angle         *
09064 ; *                                                                             *
09065 ; *******************************************************************************
09066
09067 ; DESCRIPTION
09068 ;
09069 ; This subroutine rotates a position vector component (coordinate) of a space
09070 ; object by a fixed angle around the center of the 3D coordinate system, the
09071 ; location of our starship. This is used in the Front, Aft, and Long-Range Scan
09072 ; views to rotate space objects in and out of the view. Although the code is
09073 ; deceptively short, there is some interesting math involved, so a more detailed
09074 ; discussion is in order.
09075 ;
09076 ; ROTATION MATHEMATICS
09077 ;
09078 ; The program uses a left-handed 3D coordinate system with the positive x-axis
09079 ; pointing to the right, the positive y-axis pointing up, and the positive
09080 ; z-axis pointing into flight direction.
09081 ;
09082 ; A rotation in this coordinate system around the y-axis (horizontal rotation)
09083 ; can be expressed as 
09084 ;
09085 ;     x' :=   cos(ry) * x + sin(ry) * z    (1a)
09086 ;     z' := - sin(ry) * x + cos(ry) * z    (1b)
09087 ;
09088 ; where ry is the clockwise rotation angle around the y-axis, x and z are the
09089 ; coordinates before this rotation, and the primed coordinates x' and z' the
09090 ; coordinates after this rotation. The y-coordinate is not changed by this
09091 ; rotation.
09092 ;
09093 ; A rotation in this coordinate system around the x-axis (vertical rotation) can
09094 ; be expressed as 
09095 ;
09096 ;     z' :=   cos(rx) * z + sin(rx) * y    (2a)
09097 ;     y' := - sin(rx) * z + cos(rx) * y    (2b)
09098 ;
09099 ; where rx is the clockwise rotation angle around the x-axis, z and y are the
09100 ; coordinates before this rotation, and the primed coordinates z' and y' the
09101 ; coordinates after this rotation. The x-coordinate is not changed by this
09102 ; rotation.
09103 ;
09104 ; SUBROUTINE IMPLEMENTATION OVERVIEW
09105 ;
09106 ; A single call of this subroutine is able to compute one of the four
09107 ; expressions (1a)-(2b). To compute all four expressions to get the new set of
09108 ; coordinates, this subroutine has to be called four times. This is done twice
09109 ; in pairs in GAMELOOP ($A1F3) at $A391 and $A398, and at $A3AE and $A3B5,
09110 ; respectively.
09111 ;
09112 ; The first pair of calls calculates the new x and z coordinates of a space
09113 ; object due to a horizontal (left/right) rotation of our starship around the
09114 ; y-axis following expressions (1a) and (1b).
09115 ;
09116 ; The second pair of calls calculates the new y and z coordinates of the same
09117 ; space object due to a vertical (up/down) rotation of our starship around the
09118 ; x-axis following expressions (2a) and (2b).
09119 ;
09120 ; If you look at the code, you may be wondering how this calculation is actually
09121 ; executed, as there is neither a sin() nor a cos() function call. What you'll
09122 ; actually find implemented are the following calculations:
09123 ;
09124 ;     Joystick left                        Joystick right
09125 ;     ---------------------                ---------------------
09126 ;     x :=  x      + z / 64    (3a)        x :=  x      - z / 64    (4a)
09127 ;     z := -x / 64 + z         (3b)        z :=  x / 64 + z         (4b)
09128 ;
09129 ;     Joystick down                        Joystick up
09130 ;     ---------------------                ---------------------
09131 ;     y :=  y      + z / 64    (5a)        y :=  y      - z / 64    (6a)
09132 ;     z := -y / 64 + z         (5b)        z :=  y / 64 + z         (6b)
09133 ;
09134 ; CORDIC ALGORITHM
09135 ;
09136 ; When you compare expressions (1a)-(2b) with (3a)-(6b), notice the similarity
09137 ; between the expressions if you substitute
09138 ;
09139 ;     sin(ry) -> 1 / 64, 
09140 ;     cos(ry) -> 1,
09141 ;     sin(rx) -> 1 / 64, and
09142 ;     cos(rx) -> 1.
09143 ;
09144 ; From sin(ry) = 1 / 64 and sin(rx) = 1 / 64 you can derive that the rotation
09145 ; angles ry and rx by which the space object is rotated per game loop iteration
09146 ; have a constant value of 0.89 degrees, as arcsine(1 / 64) = 0.89 degrees.
09147 ;
09148 ; What about cos(ry) and cos(rx)? The substitution does not match our derived
09149 ; angle exactly, because cos(0.89 degrees) = 0.99988 and is not exactly 1.
09150 ; However, this value is so close to 1 that substituting cos(0.89 degrees) with
09151 ; 1 is a very good approximation, simplifying calculations significantly.
09152 ;
09153 ; Another significant simplification results from the division by 64, because
09154 ; the actual division operation can be replaced with a much faster bit shift
09155 ; operation.
09156 ;
09157 ; This calculation-friendly way of computing rotations is known as the "CORDIC
09158 ; (COordinate Rotation DIgital Computer)" algorithm.
09159 ;
09160 ; MINSKY ROTATION
09161 ;
09162 ; There is one more interesting mathematical subtlety: Did you notice that
09163 ; expressions (1a)-(2b) use a new (primed) pair of variables to store the
09164 ; resulting coordinates, whereas in the implemented expressions (3a)-(6b) the
09165 ; value of the first coordinate of a coordinate pair is overwritten with its new
09166 ; value and this value is used in the subsequent calculation of the second
09167 ; coordinate? For example, when the joystick is pushed left, the first call of
09168 ; this subroutine calculates the new value of x according to expression (3a),
09169 ; overwriting the old value of x. During the second call to calculate z
09170 ; according to expression (3b), the new value of x is used instead of the old
09171 ; one. Is this to save the memory needed to temporarily store the old value of
09172 ; x? But isn't this a bug? If so, why does the rotation calculation actually
09173 ; work?
09174 ;
09175 ; Have a look at the expression pair (3a) and (3b) (the other expression pairs
09176 ; (4a)-(6b) work in a similar fashion):
09177 ;
09178 ;     x :=  x      + z / 64
09179 ;     z := -x / 64 + z
09180 ;
09181 ; With the substitution 1 / 64 -> e, we get
09182 ;
09183 ;     x :=  x     + e * z
09184 ;     z := -e * x + z
09185 ;
09186 ; Note that x is calculated first and then used in the second expression. When
09187 ; using primed coordinates for the resulting coordinates after calculating the
09188 ; two expressions we get
09189 ;
09190 ;     x' := x + e * z
09191 ;     z' := -e * x' + z = -e * (x + e * z) + z = -e * x + (1 - e^2) * z
09192 ;
09193 ; or in matrix form
09194 ;
09195 ;     |x'| := | 1       e   | * |x|
09196 ;     |z'|    |-e  (1 - e^2)|   |z|
09197 ;
09198 ; Surprisingly, this turns out to be a rotation matrix, because its determinant
09199 ; is (1 * (1 - e^2) - (e * -e)) = 1.
09200 ;
09201 ; (Incidentally, the column vectors of this matrix do not form a orthogonal
09202 ; basis, as their scalar product is 1 * e + (-e * (1 - e^2)) = -e^2.
09203 ; Orthogonality holds for e = 0 only.
09204 ;
09205 ; This kind of rotation calculation is described by Marvin Minsky in ["AIM 239
09206 ; HAKMEM", Item 149, p. 73, MIT AI Lab, February 1972] and is called "Minsky
09207 ; Rotation".
09208 ;
09209 ; SUBROUTINE IMPLEMENTATION DETAILS
09210 ;
09211 ; To better understand how the implementation of this subroutine works, have
09212 ; again a look at expressions (3a)-(6b). If you rearrange the expressions a
09213 ; little their structure is always of the form
09214 ;
09215 ;     TERM1 := TERM1 SIGN TERM2 / 64
09216 ;
09217 ;     or shorter
09218 ;
09219 ;     TERM1 := TERM1 SIGN TERM3
09220 ;
09221 ;     where
09222 ;
09223 ;     TERM3 := TERM2 / 64
09224 ;     SIGN := + or -
09225 ;
09226 ; and where TERM1 and TERM2 are position vector components (coordinates). In
09227 ; fact, this is all this subroutine actually does: It simply adds (or subtracts)
09228 ; TERM2 divided by 64 to (from) TERM1. 
09229 ;
09230 ; When calling this subroutine the correct indices for the appropriate position
09231 ; vector components (coordinates) TERM1 and TERM2 are passed in the Y and X
09232 ; registers, respectively.
09233 ;
09234 ; What about SIGN between TERM1 and TERM3? Have again a look at expressions
09235 ; (3a)-(6b). To compute the two new coordinates after a rotation, the SIGN
09236 ; toggles from plus to minus and vice versa. The SIGN is initialized by
09237 ; JOYSTICKDELTA ($6D) before actually calling subroutine ROTATE ($B69B) and is
09238 ; toggled in every subsequent call of this subroutine. The initial value of SIGN
09239 ; should be positive (+) if the rotation is clockwise (the joystick is pushed
09240 ; right or up) and negative if the rotation is counter-clockwise (the joystick
09241 ; is pushed left or down), respectively. Because SIGN is always toggled you have
09242 ; to pass the already toggled value with the first call.
09243 ;
09244 ; NOTE: Unclear still are three instructions starting at address $B6AD. They
09245 ; seem to set the two least significant bits of TERM3 in a random fashion. Could
09246 ; this be some quick hack to avoid messing with exact but potentially lengthy
09247 ; two-complement's arithmetic here?
09248 ;
09249 ; INPUT
09250 ;
09251 ;   X = Position vector component index of TERM2. Used values are:
09252 ;     $00..$30 -> z-component (z-coordinate) of position vector 0..48
09253 ;     $31..$61 -> x-component (x-coordinate) of position vector 0..48
09254 ;     $62..$92 -> y-component (y-coordinate) of position vector 0..48
09255 ;
09256 ;   Y = Position vector component index of TERM1. Used values are: 
09257 ;     $00..$30 -> z-component (z-coordinate) of position vector 0..48
09258 ;     $31..$61 -> x-component (x-coordinate) of position vector 0..48
09259 ;     $62..$92 -> y-component (y-coordinate) of position vector 0..48
09260 ;
09261 ;   JOYSTICKDELTA ($6D) = Initial value of SIGN. Used values are:
09262 ;     $01 -> (= Positive) Rotate right or up
09263 ;     $FF -> (= Negative) Rotate left or down
09264
09265                                         ; TERM3 is a 24-bit value, represented by 3 bytes as
09266                                         ; $(sign)(high byte)(low byte)
09267 L.TERM3LO       = $6A                   ; TERM3 (high byte), where TERM3 := TERM2 / 64
09268 L.TERM3HI       = $6B                   ; TERM3 (low byte),  where TERM3 := TERM2 / 64
09269 L.TERM3SIGN     = $6C                   ; TERM3 (sign),      where TERM3 := TERM2 / 64
09270
09271 ROTATE          LDA ZPOSSIGN,X          ;
09272                 EOR #$01                ;
09273                 BEQ SKIP224             ; Skip if sign of TERM2 is positive
09274                 LDA #$FF                ;
09275
09276 SKIP224         STA L.TERM3HI           ; If TERM2 pos. -> TERM3 := $0000xx (= TERM2 / 256)
09277                 STA L.TERM3SIGN         ; If TERM2 neg. -> TERM3 := $FFFFxx (= TERM2 / 256)
09278                 LDA ZPOSHI,X            ; where xx := TERM2 (high byte)
09279                 STA L.TERM3LO           ;
09280
09281                 LDA RANDOM              ; (?) Hack to avoid messing with two-complement's
09282                 ORA #$BF                ; (?) arithmetic? Provides two least significant
09283                 EOR ZPOSLO,X            ; (?) bits B1..0 in TERM3.
09284
09285                 ASL A                   ; TERM3 := TERM3 * 4 (= TERM2 / 256 * 4 = TERM2 / 64)
09286                 ROL L.TERM3LO           ;
09287                 ROL L.TERM3HI           ;
09288                 ASL A                   ;
09289                 ROL L.TERM3LO           ;
09290                 ROL L.TERM3HI           ;
09291
09292                 LDA JOYSTICKDELTA       ; Toggle SIGN for next call of ROTATE
09293                 EOR #$FF                ;
09294                 STA JOYSTICKDELTA       ;
09295                 BMI SKIP225             ; If SIGN negative then subtract, else add TERM3
09296
09297 ;*** Addition ******************************************************************
09298                 CLC                     ; TERM1 := TERM1 + TERM3
09299                 LDA ZPOSLO,Y            ; (24-bit addition)
09300                 ADC L.TERM3LO           ;
09301                 STA ZPOSLO,Y            ;
09302
09303                 LDA ZPOSHI,Y            ;
09304                 ADC L.TERM3HI           ;
09305                 STA ZPOSHI,Y            ;
09306
09307                 LDA ZPOSSIGN,Y          ;
09308                 ADC L.TERM3SIGN         ;
09309                 STA ZPOSSIGN,Y          ;
09310                 RTS                     ;
09311
09312 ;*** Subtraction ***************************************************************
09313 SKIP225         SEC                     ; TERM1 := TERM1 - TERM3
09314                 LDA ZPOSLO,Y            ; (24-bit subtraction)
09315                 SBC L.TERM3LO           ;
09316                 STA ZPOSLO,Y            ;
09317
09318                 LDA ZPOSHI,Y            ;
09319                 SBC L.TERM3HI           ;
09320                 STA ZPOSHI,Y            ;
09321
09322                 LDA ZPOSSIGN,Y          ;
09323                 SBC L.TERM3SIGN         ;
09324                 STA ZPOSSIGN,Y          ;
09325                 RTS                     ;
09326
09327 ;*******************************************************************************
09328 ;*                                                                             *
09329 ;*                                SCREENCOLUMN                                 *
09330 ;*                                                                             *
09331 ;*       Calculate pixel column number from centered pixel column number       *
09332 ;*                                                                             *
09333 ;*******************************************************************************
09334
09335 ; DESCRIPTION
09336 ;
09337 ; Converts a pixel column number relative to the horizontal screen center to a
09338 ; pixel column number relative to the top-left corner of the screen and stores
09339 ; the result in table PIXELCOLUMN ($0C2A). The passed relative pixel column
09340 ; number is always positive. The sign is picked from the corresponding
09341 ; x-component of the position vector (x-coordinate).
09342 ;
09343 ; If the passed relative pixel column number is offscreen horizontally the
09344 ; calculation is skipped and code execution returns. If the position vector
09345 ; corresponding to this pixel represents a PLAYFIELD space object (star,
09346 ; explosion fragments) a new position vector is initialized before code
09347 ; execution returns. If it represents a PLAYER space object the PLAYER is pushed
09348 ; offscreen before code execution returns.
09349 ;
09350 ; NOTE: The horizontal screen center's pixel column number for PLAYFIELD space
09351 ; objects has a value of 80 = 160 PLAYFIELD pixels / 2. For PLAYER space objects
09352 ; it has a value of 125 Player/Missile (PM) pixels (from left to right: 128 PM
09353 ; pixels to the horizontal screen center - 3 PM pixels relative offset of the
09354 ; PLAYER shape's horizontal center to its left edge = 125 PM pixels).
09355 ;
09356 ; INPUT
09357 ;
09358 ;   A = Pixel column number relative to the horizontal screen center, always
09359 ;       positive. Used values are:
09360 ;     0..80 -> Regular values, pixel is onscreen
09361 ;     $FF   -> Pixel is offscreen
09362 ;
09363 ;   X = Position vector index. Used values are:
09364 ;     0..4  -> Position vector of a PLAYER space object
09365 ;     5..48 -> Position vector of a PLAYFIELD space object
09366
09367 L.PIXELCOLUMN   = $6D                   ; Saves relative pixel column number
09368
09369 SCREENCOLUMN    CMP #80                 ; If pixel is offscreen (A > 79)...
09370                 BCS SKIP233             ; ...return via initializing a new position vector
09371
09372                 STA L.PIXELCOLUMN       ; Save relative pixel column number
09373 CENTERCOLUMN    
09374                 LDA #80                 ; If PLAYFIELD space object -> A := CENTERCOL = 80
09375                 CPX #NUMSPCOBJ.PL       ; If PLAYER space object    -> A := CENTERCOL = 125
09376                 BCS SKIP226             ;
09377                 LDA #125                ;
09378
09379 SKIP226         LDY XPOSSIGN,X          ; Skip if x-coordinate positive
09380                 BNE SKIP227             ;
09381
09382                 SEC                     ; Pixel in left screen half (x-coordinate negative)
09383                 INC L.PIXELCOLUMN       ;
09384                 SBC L.PIXELCOLUMN       ;
09385                 STA PIXELCOLUMN,X       ; Pixel column := CENTERCOL - (rel. pixel column + 1)
09386                 RTS                     ; Return
09387
09388 SKIP227         CLC                     ; Pixel in right screen half (x-coordinate positive)
09389                 ADC L.PIXELCOLUMN       ;
09390                 STA PIXELCOLUMN,X       ; Pixel column := CENTERCOL + relative pixel column
09391                 RTS                     ; Return
09392
09393 ;*******************************************************************************
09394 ;*                                                                             *
09395 ;*                                  SCREENROW                                  *
09396 ;*                                                                             *
09397 ;*          Calculate pixel row number from centered pixel row number          *
09398 ;*                                                                             *
09399 ;*******************************************************************************
09400
09401 ; Converts a pixel row number relative to the vertical screen center to a pixel
09402 ; row number relative to the top-left corner of the screen and stores the result
09403 ; in table PIXELROWNEW ($0BF9). The passed relative pixel row number is always
09404 ; positive. The sign is picked from the corresponding y-component of the
09405 ; position vector (y-coordinate).
09406 ;
09407 ; If the passed relative pixel row number is offscreen vertically the
09408 ; calculation is skipped and code execution returns. If the position vector
09409 ; corresponding to this pixel represents a PLAYFIELD space object (star,
09410 ; explosion fragments) a new position vector is initialized in subroutine
09411 ; INITPOSVEC ($B764) before code execution returns. If it represents a PLAYER
09412 ; space object the PLAYER is pushed offscreen before code execution returns.
09413 ;
09414 ; NOTE: The vertical screen center's pixel row number for PLAYFIELD space
09415 ; objects has a value of 50 = 100 PLAYFIELD pixels / 2. For PLAYER space objects
09416 ; it has a value of 122 Player/Missile (PM) pixels (from top to bottom: 8 PM
09417 ; pixels to start of Display List + 16 PM pixels to begin of PLAYFIELD + 100 PM
09418 ; pixels to vertical screen center - 2 PM pixels (?) = 122 PM pixels).
09419 ;
09420 ; NOTE: If the position vector corresponding to the pixel represents a PLAYER
09421 ; space object the passed pixel row number is doubled because 1 PLAYFIELD pixel
09422 ; has the same height as 2 PM pixels at single-line resolution.
09423 ;
09424 ; When in Long-Range Scan view the z-coordinate takes the place of the
09425 ; y-coordinate of the Front or Aft view. If the Long-Range Scan is damaged the
09426 ; passed pixel row number is treated randomly as a negative or positive value
09427 ; (mirror effect).
09428 ;
09429 ; INPUT
09430 ;
09431 ;   A = Pixel row number relative to the vertical screen center, always
09432 ;       positive. Used values are:
09433 ;     0..50 -> Regular values, pixel is onscreen
09434 ;     $FF   -> Pixel is offscreen
09435 ;
09436 ;   X = Position vector index. Used values are:
09437 ;     0..4  -> Position vector of a PLAYER space object
09438 ;     5..48 -> Position vector of a PLAYFIELD space object
09439
09440 L.PIXELROW      = $6D                   ; Saves relative pixel row number
09441
09442 SCREENROW       CMP #50                 ; If pixel is offscreen (A > 49)...
09443                 BCS SKIP233             ; ...return via initializing a new position vector
09444
09445                 STA L.PIXELROW          ; Save relative pixel row number
09446                 LDA #50                 ; If PLAYFIELD space object -> A := CENTERROW = 50
09447                 CPX #NUMSPCOBJ.PL       ;
09448                 BCS SKIP228             ;
09449                 ASL L.PIXELROW          ; If PLAYER space object -> Double pixel row number
09450                 LDA #122                ; If PLAYER space object ->    A := CENTERROW = 122
09451
09452 SKIP228         BIT SHIPVIEW            ; Skip if not in Long-Range Scan view
09453                 BVC SKIP230             ;
09454
09455                 BIT GCSTATLRS           ; Skip if Long-Range Scan OK
09456                 BPL SKIP229             ;
09457
09458                 BIT RANDOM              ; Long-Range Scan damaged...
09459                 BVC SKIP231             ; ...branch randomly to pixel row number calculation
09460                 BVS SKIP232             ; ...(mirror effect)
09461
09462 SKIP229         LDY ZPOSSIGN,X          ;
09463                 BNE SKIP231             ; Skip if z-coordinate pos. (Long-Range Scan view)
09464                 BEQ SKIP232             ; Skip if z-coordinate neg. (Long-Range Scan view)
09465
09466 SKIP230         LDY YPOSSIGN,X          ;
09467                 BEQ SKIP232             ; Skip if y-coordinate neg. (Front or Aft view)
09468
09469 SKIP231         SEC                     ; Pixel in upper screen half (z or y coordinate pos.)
09470                 INC L.PIXELROW          ;
09471                 SBC L.PIXELROW          ;
09472                 STA PIXELROWNEW,X       ; Pixel row  := CENTERROW - (rel. pixel row + 1)
09473                 RTS                     ; Return
09474
09475 SKIP232         CLC                     ; Pixel in lower screen half (y or z coordinate neg.)
09476                 ADC L.PIXELROW          ;
09477                 STA PIXELROWNEW,X       ; Pixel row := CENTERROW + relative pixel row
09478                 RTS                     ; Return
09479
09480 SKIP233         CPX #NUMSPCOBJ.PL       ; Space object is offscreen. If it is a...
09481                 BCS INITPOSVEC          ; ...PLAYFIELD space object -> New position vector
09482                 LDA #251                ; ...PLAYER space object    -> Push PLAYER offscreen
09483                 STA PIXELROWNEW,X       ;                              Why a value of 251 (?)
09484 SKIP234         RTS                     ; Return
09485
09486 ;*******************************************************************************
09487 ;*                                                                             *
09488 ;*                                 INITPOSVEC                                  *
09489 ;*                                                                             *
09490 ;*                Initialize position vector of a space object                 *
09491 ;*                                                                             *
09492 ;*******************************************************************************
09493
09494 ; DESCRIPTION
09495 ;
09496 ; Initializes the position vector of a space object.
09497 ;
09498 ; This subroutine executes the following steps:
09499 ;
09500 ; (1)  Set the pixel row and column number to an offscreen value (= 99).
09501 ;
09502 ; (2)  If the position vector represents an explosion fragment space object then
09503 ;      return code execution immediately. This avoids generating new explosion
09504 ;      fragment space objects. They are separately initialized in subroutine
09505 ;      COPYPOSVEC ($ACAF), which is called from subroutine INITEXPL ($AC6B).
09506 ;
09507 ; (3)  Assign default values (see below) to the position vector components
09508 ;      (coordinates) depending on our starship's view.
09509 ;
09510 ; Code execution continues into subroutine RNDINVXY ($B7BE) where x and y
09511 ; coordinates are inverted randomly.
09512 ;
09513 ; After passing through this and the next subroutine RNDINVXY ($B7BE) the
09514 ; components of a position vector (coordinates) are assigned to one of the
09515 ; following values depending on our starship's view:
09516 ;
09517 ; o   FRONT VIEW
09518 ;
09519 ;     +------------+---------------------------------------+
09520 ;     | Coordinate |                 Values                |
09521 ;     +------------+---------------------------------------+
09522 ;     |     x      |  -4095..+4095 (-($0***)..+$0***) <KM> |
09523 ;     |     y      |  -4095..+4095 (-($0***)..+$0***) <KM> | 
09524 ;     |     z      |  +3840..+4095 (          +$0F**) <KM> |
09525 ;     +------------+---------------------------------------+
09526 ;
09527 ; o   AFT VIEW
09528 ;
09529 ;     +------------+---------------------------------------+
09530 ;     | Coordinate |                 Values                |
09531 ;     +------------+---------------------------------------+ 
09532 ;     |     x      |  -3840..+3840 (-($0*00)..+$0*00) <KM> |
09533 ;     |     y      |  -3840..+3840 (-($0*00)..+$0*00) <KM> |
09534 ;     |     z      |  -3968.. -128 (-($0*80)        ) <KM> |
09535 ;     +------------+---------------------------------------+ 
09536 ;     Values of x, y, and z coordinates change in increments of 256.
09537 ;     Second digit of z-coordinate is -MAX(RNDY,RNDX), where
09538 ;     RNDY := RND($00..$0F), RNDX := RND($00..$0F).
09539 ;
09540 ; o   LONG-RANGE SCAN VIEW
09541 ;
09542 ;     +------------+---------------------------------------+
09543 ;     | Coordinate |                 Values                |
09544 ;     +------------+---------------------------------------+
09545 ;     |     x      | -65535..+65535 (-($****)..$****) <KM> |
09546 ;     |     y      |  -4095..+4095  (-($0***)..$0***) <KM> |
09547 ;     |     z      | -65535..+65535 (-($****)..$****) <KM> |
09548 ;     +------------+---------------------------------------+
09549 ;
09550 ; INPUT
09551 ;
09552 ;   X = Position vector index. Used values are: 0..48.
09553
09554 L.MAXRNDXY      = $6A                   ; Saves MAX(new y-coordinate (high byte), ...
09555                                         ;  ...new x-coordinate (high byte))
09556
09557 INITPOSVEC      LDA #99                 ; Init to offscreen pixel row and column numbers
09558                 STA PIXELROWNEW,X       ;
09559                 STA PIXELCOLUMN,X       ;
09560
09561                 CPX #NUMSPCOBJ.NORM     ; Return if pos vector is explosion frag space obj
09562                 BCS SKIP234             ; This avoids creating new explosion frag space objs
09563
09564                 LDA RANDOM              ; RNDY := RND($00..$0F)
09565                 AND #$0F                ;
09566                 STA L.MAXRNDXY          ; Save RNDY
09567                 STA YPOSHI,X            ; y-coordinate (high byte) := RNDY
09568
09569                 LDA RANDOM              ; RNDX := RND($00..$0F)
09570                 AND #$0F                ;
09571                 CMP L.MAXRNDXY          ;
09572                 BCC SKIP235             ;
09573                 STA L.MAXRNDXY          ; Save MAX(RNDY,RNDX)
09574 SKIP235         STA XPOSHI,X            ; x-coordinate (high byte) := RNDX
09575
09576                 LDA #$0F                ; z-coordinate (high byte) := $0F
09577                 STA ZPOSHI,X            ;
09578
09579                 LDA SHIPVIEW            ; z-coordinate (sign) := 1 or 0 (Front or Aft view)
09580                 EOR #$01                ;
09581                 AND #$01                ;
09582                 STA ZPOSSIGN,X          ;
09583                 BNE SKIP236             ; Skip if in Front or Long-Range Scan view
09584
09585                                         ; Aft view only:
09586                 STA XPOSLO,X            ; x-coordinate (low byte) := 0
09587                 STA YPOSLO,X            ; y-coordinate (low byte) := 0
09588                 SEC                     ; z-coordinate (high byte) := -MAX(RNDY,RNDX)
09589                 SBC L.MAXRNDXY          ;
09590                 STA ZPOSHI,X            ;
09591                 LDA #$80                ; z-coordinate (low byte) := $80
09592                 STA ZPOSLO,X            ;
09593
09594 SKIP236         BIT SHIPVIEW            ; If not in Long-Range Scan view skip to RNDINVXY
09595                 BVC RNDINVXY            ;
09596
09597                                         ; Long-Range Scan view only:
09598                 LDA RANDOM              ; x-coordinate (high byte) := RND($00..$FF)
09599                 STA XPOSHI,X            ;
09600                 LDA RANDOM              ; z-coordinate (high byte) := RND($00..$FF)
09601                 STA ZPOSHI,X            ;
09602                 AND #$01                ; Invert z-coordinate randomly
09603                 STA ZPOSSIGN,X          ;
09604
09605 ;*******************************************************************************
09606 ;*                                                                             *
09607 ;*                                  RNDINVXY                                   *
09608 ;*                                                                             *
09609 ;*         Randomly invert the x and y components of a position vector         *
09610 ;*                                                                             *
09611 ;*******************************************************************************
09612
09613 ; DESCRIPTION
09614 ;
09615 ; Randomly inverts the x and y components of a position vector (x and y
09616 ; coordinates). See also subroutine INITPOSVEC ($B764).
09617 ;
09618 ; INPUT
09619 ;
09620 ;   X = Position vector index. Used values are: 0..48.
09621
09622 RNDINVXY        LDA RANDOM              ; Set sign of y-coordinate randomly
09623                 AND #$01                ;
09624                 STA YPOSSIGN,X          ;
09625                 BNE SKIP237             ; Skip if sign positive
09626
09627                 SEC                     ; Sign negative -> Calc negative y-coordinate
09628                 SBC YPOSLO,X            ; (calculate two's-complement of 16-bit value)
09629                 STA YPOSLO,X            ;
09630                 LDA #0                  ;
09631                 SBC YPOSHI,X            ;
09632                 STA YPOSHI,X            ;
09633
09634 SKIP237         LDA RANDOM              ; Set sign of x-coordinate randomly
09635                 AND #$01                ;
09636                 STA XPOSSIGN,X          ;
09637                 BNE SKIP238             ; Skip if sign positive
09638
09639                 SEC                     ; Sign negative -> Calc negative x-coordinate
09640                 SBC XPOSLO,X            ; (calculate two's-complement of 16-bit value)
09641                 STA XPOSLO,X            ;
09642                 LDA #0                  ;
09643                 SBC XPOSHI,X            ;
09644                 STA XPOSHI,X            ;
09645 SKIP238         RTS                     ; Return
09646
09647 ;*******************************************************************************
09648 ;*                                                                             *
09649 ;*                                ISSURROUNDED                                 *
09650 ;*                                                                             *
09651 ;*               Check if a sector is surrounded by Zylon units                *
09652 ;*                                                                             *
09653 ;*******************************************************************************
09654
09655 ; DESCRIPTION
09656 ;
09657 ; Checks if a sector of the Galactic Chart is surrounded by Zylon units in the
09658 ; adjacent NORTH, EAST, SOUTH, and WEST sectors.
09659 ;
09660 ; INPUT
09661 ;
09662 ;   X = Sector of Galactic Chart. Used values are: $00..$7F with, for example,
09663 ;     $00 -> NORTHWEST corner sector
09664 ;     $0F -> NORTHEAST corner sector
09665 ;     $70 -> SOUTHWEST corner sector
09666 ;     $7F -> SOUTHWEST corner sector
09667 ;
09668 ; OUTPUT
09669 ;
09670 ;   A = Returns if the sector is surrounded by Zylon units in the adjacent
09671 ;       NORTH, EAST, SOUTH, and WEST sectors.
09672 ;       0 -> Sector is not surrounded
09673 ;     > 0 -> Sector is surrounded
09674
09675 ISSURROUNDED    LDA GCMEMMAP-1,X        ; Check WEST sector
09676                 BEQ SKIP239             ;
09677                 LDA GCMEMMAP+1,X        ; Check EAST sector
09678                 BEQ SKIP239             ;
09679                 LDA GCMEMMAP-16,X       ; Check NORTH sector
09680                 BEQ SKIP239             ;
09681                 LDA GCMEMMAP+16,X       ; Check SOUTH sector
09682 SKIP239         RTS                     ; Return
09683
09684 ;*******************************************************************************
09685 ;*                                                                             *
09686 ;*                                  UPDPANEL                                   *
09687 ;*                                                                             *
09688 ;*                        Update Control Panel Display                         *
09689 ;*                                                                             *
09690 ;*******************************************************************************
09691
09692 ; DESCRIPTION
09693 ;
09694 ; This subroutine executes the following steps: 
09695 ;
09696 ; (1)  Accelerate or decelerate our starship, update the VELOCITY readout
09697 ;
09698 ;      If the new velocity value is different from the current one either
09699 ;      increment or decrement the current velocity value toward the new one.
09700 ;
09701 ;      If the Engines are damaged or destroyed (and hyperwarp is not engaged)
09702 ;      then store a random value (less or equal than the current velocity) as
09703 ;      the current velocity.
09704 ;
09705 ;      Display the updated velocity by the VELOCITY readout of the Control Panel
09706 ;      Display.
09707 ;
09708 ; (2)  Update THETA, PHI, and RANGE readouts
09709 ;
09710 ;      If the Attack Computer is working then display the x, y, and z
09711 ;      coordinates of the currently tracked space object as THETA, PHI, and
09712 ;      RANGE readout values of the Control Panel Display.
09713 ;
09714 ; (3)  Calculate overall energy consumption
09715 ;
09716 ;      Add the overall energy consumption per game loop iteration to the energy
09717 ;      counter. This value is given in energy subunits (256 energy subunits = 1
09718 ;      energy unit displayed by the 4-digit ENERGY readout of the Console Panel
09719 ;      Display). It is the total of the following items:
09720 ;
09721 ;      (1)  8 energy subunits if the Shields are up
09722 ;
09723 ;      (2)  2 energy subunits if the Attack Computer is on
09724 ;
09725 ;      (3)  1 energy subunit of the life support system
09726 ;
09727 ;      (4)  Our starship's Engines energy drain rate (depending on its velocity)
09728 ;
09729 ;      If there is a carryover of the energy counter then decrement the ENERGY
09730 ;      readout of the Control Panel Display by one energy unit after code
09731 ;      execution has continued into subroutine DECENERGY ($B86F). 
09732
09733 ;*** Accelerate or decelerate our starship *************************************
09734 UPDPANEL        LDX VELOCITYLO          ; Skip if new velocity = current velocity
09735                 CPX NEWVELOCITY         ;
09736                 BEQ SKIP241             ;
09737
09738                 BCC SKIP240             ; In/decrement current velocity toward new velocity
09739                 DEC VELOCITYLO          ;
09740                 BCS SKIP242             ;
09741 SKIP240         INC VELOCITYLO          ;
09742
09743 SKIP241         LDA WARPSTATE           ; Skip if hyperwarp engaged
09744                 BNE SKIP242             ;
09745
09746                 BIT GCSTATENG           ; Skip if Engines are OK
09747                 BPL SKIP242             ;
09748
09749                 LDA NEWVELOCITY         ; Store RND(0..current velocity) to current velocity
09750                 AND RANDOM              ;
09751                 STA VELOCITYLO          ;
09752
09753 SKIP242         LDY #VELOCD1-PANELTXT-1 ; Update digits of VELOCITY readout
09754                 JSR SHOWDIGITS          ;
09755
09756 ;*** Display coordinates of tracked space object of Control Panel Display ******
09757                 BIT GCSTATCOM           ; Skip if Attack Computer damaged or destroyed
09758                 BMI SKIP243             ;
09759
09760                 LDA #$31                ; Update THETA readout (x-coordinate)
09761                 LDY #THETAC1-PANELTXT   ;
09762                 JSR SHOWCOORD           ;
09763
09764                 LDA #$62                ; Update PHI readout (y-coordinate)
09765                 LDY #PHIC1-PANELTXT     ;
09766                 JSR SHOWCOORD           ;
09767
09768                 LDA #$00                ; Update RANGE readout (z-coordinate)
09769                 LDY #RANGEC1-PANELTXT   ;
09770                 JSR SHOWCOORD           ;
09771
09772                 LDA RANGEC1+2           ; Hack to clear RANGE digit 3 when in hyperwarp:
09773                 STA RANGEC1+3           ; Copy RANGE digit 2 to digit 3
09774                 CMP #CCS.9+1            ; Skip if digit character > '9' (= 'infinity' char)
09775                 BCS SKIP243             ;
09776
09777                 LDX TRACKDIGIT          ; Get z-coordinate (low byte) of tracked space object
09778                 LDA ZPOSLO,X            ;
09779                 LSR A                   ; ...divide it by 16...
09780                 LSR A                   ;
09781                 LSR A                   ;
09782                 LSR A                   ;
09783                 TAX                     ;
09784                 LDA MAPTOBCD99,X        ; ...map value of $00..$0F to BCD value 0..9
09785                 STA RANGEC1+3           ; ...and store it to RANGE digit 3
09786
09787 ;*** Calculate overall energy consumption **************************************
09788 SKIP243         CLC                     ;
09789                 LDA ENERGYCNT           ; Load energy counter
09790                 ADC DRAINSHIELDS        ; Add energy drain rate of Shields
09791                 ADC DRAINENGINES        ; Add energy drain rate of our starship's Engines
09792                 ADC DRAINATTCOMP        ; Add energy drain rate of Attack Computer
09793                 ADC #$01                ; Add 1 energy subunit of life support system
09794                 CMP ENERGYCNT           ;
09795                 STA ENERGYCNT           ;
09796                 BCS SKIP246             ; Return if no energy counter carryover
09797
09798                 LDX #3                  ; Will decrement third energy digit
09799
09800 ;*******************************************************************************
09801 ;*                                                                             *
09802 ;*                                  DECENERGY                                  *
09803 ;*                                                                             *
09804 ;*                               Decrease energy                               *
09805 ;*                                                                             *
09806 ;*******************************************************************************
09807
09808 ; DESCRIPTION
09809 ;
09810 ; When not in demo mode, subtract energy from the 4-digit ENERGY readout of the
09811 ; Control Panel Display. If crossing a 100-energy-unit boundary during
09812 ; subtraction the score is decremented by one unit. If the energy is zero the
09813 ; game is over.
09814 ;
09815 ; INPUT
09816 ;
09817 ;   X = ENERGY readout digit to be decremented. Used values are:
09818 ;     1 -> Subtract 100 units from ENERGY readout
09819 ;     2 -> Subtract  10 units from ENERGY readout
09820 ;     3 -> Subtract   1 unit  from ENERGY readout
09821
09822 ;*** Display ENERGY readout ****************************************************
09823 DECENERGY       BIT ISDEMOMODE          ; Return if in demo mode
09824                 BVS SKIP246             ;
09825
09826                 DEC ENERGYD1,X          ; Decrement energy digit character
09827                 LDA ENERGYD1,X          ;
09828                 CMP #CCS.COL2!CCS.0     ;
09829                 BCS SKIP246             ; Return if digit character >= '0'
09830                 LDA #CCS.COL2!CCS.9     ;
09831                 STA ENERGYD1,X          ; Store digit character '9'
09832
09833 ;*** Decrement score when crossing a 100-energy-unit boundary while subtracting 
09834                 CPX #2                  ; Skip if no crossing of 100-energy-unit boundary
09835                 BNE SKIP245             ;
09836
09837                 LDA SCORE               ; SCORE := SCORE - 1
09838                 BNE SKIP244             ;
09839                 DEC SCORE+1             ;
09840 SKIP244         DEC SCORE               ;
09841
09842 SKIP245         DEX                     ;
09843                 BPL DECENERGY           ; Next digit
09844
09845 ;*** Energy is zero, game over *************************************************
09846                 LDX #CCS.SPC            ; Clear 4-digit ENERGY readout
09847                 TXA                     ;
09848                 LDY #3                  ;
09849 LOOP079         STA ENERGYD1,Y          ;
09850                 DEY                     ;
09851                 BPL LOOP079             ;
09852
09853                 JSR SETVIEW             ; Set Front view
09854
09855                 LDY #$31                ; Set title phrase "MISSION ABORTED ZERO ENERGY"
09856                 LDX #$04                ; Set mission bonus offset
09857                 JSR GAMEOVER            ; Game over
09858
09859 SKIP246         RTS                     ; Return
09860
09861 ;*******************************************************************************
09862 ;*                                                                             *
09863 ;*                                  SHOWCOORD                                  *
09864 ;*                                                                             *
09865 ;*  Display a position vector component (coordinate) in Control Panel Display  *
09866 ;*                                                                             *
09867 ;*******************************************************************************
09868
09869 ; DESCRIPTION
09870 ;
09871 ; Displays a position vector component (coordinate) by one of the THETA, PHI, or
09872 ; RANGE readouts of the Control Panel Display.
09873 ;
09874 ; Write the sign to the Control Panel Display, then map the high byte of the
09875 ; respective coordinate (x -> THETA, y -> PHI, z -> RANGE) to a BCD-value in
09876 ; 00..99. Code execution continues into subroutine SHOWDIGITS ($B8CD) where the
09877 ; digits are actually stored in the Control Panel Display.
09878 ;
09879 ; NOTE: If the digits of either the THETA or PHI readout are to be displayed and
09880 ; the x or y position vector component (high byte) is $FF then tweak the value
09881 ; to $FE. This avoids accessing table MAPTOBCD99 ($0EE9) with an index of $FF
09882 ; that would return the special value $EA. This value represents the CCS.INF
09883 ; ($0E) and CCS.SPC ($0A) characters (see comments in subroutine INITIALIZE
09884 ; ($B3BA)) that are displayed by the RANGE readout only.
09885 ;
09886 ; INPUT
09887 ;
09888 ;   A = Position vector component (coordinate) offset. Used values are: 
09889 ;     $00 -> z-coordinate
09890 ;     $31 -> x-coordinate
09891 ;     $62 -> y-coordinate
09892 ;
09893 ;   Y = Offset into the Control Panel Display memory map. Used values are:
09894 ;     $17 -> First character (sign) of THETA readout (x-coordinate of tracked
09895 ;            space object)
09896 ;     $1D -> First character (sign) of PHI readout   (y-coordinate of tracked
09897 ;            space object)
09898 ;     $23 -> First character (sign) of RANGE readout (z-coordinate of tracked
09899 ;            space object)
09900
09901 L.SIGNCHAR      = $6A                   ; Saves sign character
09902
09903 SHOWCOORD       CLC                     ; Add index of tracked space object...
09904                 ADC TRACKDIGIT          ; ...to position vector component offset
09905                 TAX                     ; Save position vector component index
09906
09907 ;*** Display sign in Control Panel Display *************************************
09908                 LDA #CCS.PLUS           ; Save '+' (CCS.PLUS) to sign character
09909                 STA L.SIGNCHAR          ;
09910
09911                 LDA ZPOSSIGN,X          ; Prep sign of coordinate
09912                 LSR A                   ;
09913                 LDA ZPOSHI,X            ; Prep coordinate (high byte)
09914                 BCS SKIP247             ; Skip if sign is positive
09915
09916                 EOR #$FF                ; Invert coordinate (high byte)
09917                 DEC L.SIGNCHAR          ; Change saved sign character to '-' (CCS.MINUS)
09918
09919 SKIP247         TAX                     ; Save coordinate (high byte)
09920                 LDA L.SIGNCHAR          ; Store sign character in Control Panel Display
09921                 STA PANELTXT,Y          ;
09922
09923 ;*** Get RANGE digits **********************************************************
09924                 TYA                     ; Skip if RANGE is to be displayed
09925                 AND #$10                ;
09926                 BEQ SHOWDIGITS          ;
09927
09928                 CPX #$FF                ; If coordinate (high byte) = $FF decrement value
09929                 BNE SHOWDIGITS          ; This avoids output of CCS.INFINITY in...
09930                 DEX                     ; ...THETA and PHI readouts
09931
09932 ;*******************************************************************************
09933 ;*                                                                             *
09934 ;*                                 SHOWDIGITS                                  *
09935 ;*                                                                             *
09936 ;*          Display a value by a readout of the Control Panel Display          *
09937 ;*                                                                             *
09938 ;*******************************************************************************
09939
09940 ; DESCRIPTION
09941 ;
09942 ; Converts a binary value in $00..$FF to a BCD-value in 0..99 and displays it as
09943 ; a 2-digit number in the Control Panel Display.
09944 ;
09945 ; INPUT
09946 ;
09947 ;   X = Value to be displayed as a 2-digit BCD-value. Used values are: $00..$FF.
09948 ;
09949 ;   Y = Offset into the Control Panel Display memory map relative to the first
09950 ;       character of the Control Panel Display (the 'V' of the VELOCITY
09951 ;       readout). Used values are: 
09952 ;     $01 -> Character before first digit of VELOCITY readout
09953 ;     $17 -> First character (sign) of THETA readout (x-coordinate of tracked
09954 ;            space object)
09955 ;     $1D -> First character (sign) of PHI readout   (y-coordinate of tracked
09956 ;            space object)
09957 ;     $23 -> First character (sign) of RANGE readout (z-coordinate of tracked
09958 ;            space object)
09959
09960 SHOWDIGITS      LDA MAPTOBCD99,X        ; Map binary value to BCD-value
09961                 TAX                     ;
09962                 AND #$0F                ;
09963                 STA PANELTXT+2,Y        ; Store 'ones' digit in Control Panel Display
09964                 TXA                     ;
09965                 LSR A                   ;
09966                 LSR A                   ;
09967                 LSR A                   ;
09968                 LSR A                   ;
09969                 STA PANELTXT+1,Y        ; Store 'tens' digit in Control Panel Display
09970                 RTS                     ; Return
09971
09972 ;*******************************************************************************
09973 ;*                                                                             *
09974 ;*                G A M E   D A T A   ( P A R T   2   O F   2 )                *
09975 ;*                                                                             *
09976 ;*******************************************************************************
09977
09978 ;*** Color register offsets of PLAYER0..4 **************************************
09979 PLCOLOROFFTAB   .BYTE 0                               ; PLAYER0
09980                 .BYTE 1                               ; PLAYER1
09981                 .BYTE 2                               ; PLAYER2
09982                 .BYTE 3                               ; PLAYER3
09983                 .BYTE 7                               ; PLAYER4
09984
09985 ;*** Shape table 1 (PLAYER2..4) ************************************************
09986 PLSHAP1TAB      .BYTE $00                             ; ........
09987                 .BYTE $18                             ; ...##...
09988                 .BYTE $3C                             ; ..####..
09989                 .BYTE $7E                             ; .######.
09990                 .BYTE $7E                             ; .######.
09991                 .BYTE $76                             ; .###.##.
09992                 .BYTE $F7                             ; ####.###
09993                 .BYTE $DF                             ; ##.#####
09994                 .BYTE $DF                             ; ##.#####
09995                 .BYTE $FF                             ; ########
09996                 .BYTE $FF                             ; ########
09997                 .BYTE $F7                             ; ####.###
09998                 .BYTE $76                             ; .###.##.
09999                 .BYTE $7E                             ; .######.
10000                 .BYTE $7E                             ; .######.
10001                 .BYTE $3C                             ; ..####..
10002                 .BYTE $18                             ; ...##...
10003                 .BYTE $10                             ; ...#....
10004                 .BYTE $38                             ; ..###...
10005                 .BYTE $7C                             ; .#####..
10006                 .BYTE $7C                             ; .#####..
10007                 .BYTE $FE                             ; #######.
10008                 .BYTE $DE                             ; ##.####.
10009                 .BYTE $DA                             ; ##.##.#.
10010                 .BYTE $FA                             ; #####.#.
10011                 .BYTE $EE                             ; ###.###.
10012                 .BYTE $EE                             ; ###.###.
10013                 .BYTE $7C                             ; .#####..
10014                 .BYTE $7C                             ; .#####..
10015                 .BYTE $38                             ; ..###...
10016                 .BYTE $10                             ; ...#....
10017                 .BYTE $18                             ; ...##...
10018                 .BYTE $3C                             ; ..####..
10019                 .BYTE $3C                             ; ..####..
10020                 .BYTE $7E                             ; .######.
10021                 .BYTE $6E                             ; .##.###.
10022                 .BYTE $7A                             ; .####.#.
10023                 .BYTE $7E                             ; .######.
10024                 .BYTE $76                             ; .###.##.
10025                 .BYTE $7E                             ; .######.
10026                 .BYTE $3C                             ; ..####..
10027                 .BYTE $3C                             ; ..####..
10028                 .BYTE $18                             ; ...##...
10029                 .BYTE $10                             ; ...#....
10030                 .BYTE $38                             ; ..###...
10031                 .BYTE $38                             ; ..###...
10032                 .BYTE $7C                             ; .#####..
10033                 .BYTE $74                             ; .###.#..
10034                 .BYTE $7C                             ; .#####..
10035                 .BYTE $6C                             ; .##.##..
10036                 .BYTE $38                             ; ..###...
10037                 .BYTE $38                             ; ..###...
10038                 .BYTE $10                             ; ...#....
10039                 .BYTE $10                             ; ...#....
10040                 .BYTE $18                             ; ...##...
10041                 .BYTE $3C                             ; ..####..
10042                 .BYTE $2C                             ; ..#.##..
10043                 .BYTE $3C                             ; ..####..
10044                 .BYTE $3C                             ; ..####..
10045                 .BYTE $18                             ; ...##...
10046                 .BYTE $08                             ; ....#...
10047                 .BYTE $10                             ; ...#....
10048                 .BYTE $38                             ; ..###...
10049                 .BYTE $38                             ; ..###...
10050                 .BYTE $28                             ; ..#.#...
10051                 .BYTE $38                             ; ..###...
10052                 .BYTE $10                             ; ...#....
10053                 .BYTE $3C                             ; ..####..
10054                 .BYTE $3C                             ; ..####..
10055                 .BYTE $24                             ; ..#..#..
10056                 .BYTE $3C                             ; ..####..
10057                 .BYTE $7E                             ; .######.
10058                 .BYTE $7E                             ; .######.
10059                 .BYTE $7E                             ; .######.
10060                 .BYTE $5A                             ; .#.##.#.
10061                 .BYTE $FF                             ; ########
10062                 .BYTE $FF                             ; ########
10063                 .BYTE $42                             ; .#....#.
10064                 .BYTE $42                             ; .#....#.
10065                 .BYTE $42                             ; .#....#.
10066                 .BYTE $42                             ; .#....#.
10067                 .BYTE $42                             ; .#....#.
10068                 .BYTE $42                             ; .#....#.
10069                 .BYTE $1C                             ; ...###..
10070                 .BYTE $1C                             ; ...###..
10071                 .BYTE $14                             ; ...#.#..
10072                 .BYTE $3E                             ; ..#####.
10073                 .BYTE $3E                             ; ..#####.
10074                 .BYTE $3E                             ; ..#####.
10075                 .BYTE $2A                             ; ..#.#.#.
10076                 .BYTE $7F                             ; .#######
10077                 .BYTE $7F                             ; .#######
10078                 .BYTE $22                             ; ..#...#.
10079                 .BYTE $22                             ; ..#...#.
10080                 .BYTE $22                             ; ..#...#.
10081                 .BYTE $22                             ; ..#...#.
10082                 .BYTE $22                             ; ..#...#.
10083                 .BYTE $18                             ; ...##...
10084                 .BYTE $18                             ; ...##...
10085                 .BYTE $3C                             ; ..####..
10086                 .BYTE $3C                             ; ..####..
10087                 .BYTE $3C                             ; ..####..
10088                 .BYTE $3C                             ; ..####..
10089                 .BYTE $7E                             ; .######.
10090                 .BYTE $24                             ; ..#..#..
10091                 .BYTE $24                             ; ..#..#..
10092                 .BYTE $24                             ; ..#..#..
10093                 .BYTE $24                             ; ..#..#..
10094                 .BYTE $10                             ; ...#....
10095                 .BYTE $10                             ; ...#....
10096                 .BYTE $38                             ; ..###...
10097                 .BYTE $38                             ; ..###...
10098                 .BYTE $38                             ; ..###...
10099                 .BYTE $7C                             ; .#####..
10100                 .BYTE $28                             ; ..#.#...
10101                 .BYTE $28                             ; ..#.#...
10102                 .BYTE $28                             ; ..#.#...
10103                 .BYTE $18                             ; ...##...
10104                 .BYTE $18                             ; ...##...
10105                 .BYTE $3C                             ; ..####..
10106                 .BYTE $18                             ; ...##...
10107                 .BYTE $18                             ; ...##...
10108                 .BYTE $10                             ; ...#....
10109                 .BYTE $10                             ; ...#....
10110                 .BYTE $38                             ; ..###...
10111                 .BYTE $10                             ; ...#....
10112                 .BYTE $18                             ; ...##...
10113                 .BYTE $7E                             ; .######.
10114                 .BYTE $FF                             ; ########
10115                 .BYTE $FF                             ; ########
10116                 .BYTE $FF                             ; ########
10117                 .BYTE $FF                             ; ########
10118                 .BYTE $FF                             ; ########
10119                 .BYTE $E7                             ; ###..###
10120                 .BYTE $E7                             ; ###..###
10121                 .BYTE $FF                             ; ########
10122                 .BYTE $FF                             ; ########
10123                 .BYTE $FF                             ; ########
10124                 .BYTE $FF                             ; ########
10125                 .BYTE $FF                             ; ########
10126                 .BYTE $7E                             ; .######.
10127                 .BYTE $7E                             ; .######.
10128                 .BYTE $00                             ; ........
10129                 .BYTE $18                             ; ...##...
10130                 .BYTE $3C                             ; ..####..
10131                 .BYTE $7E                             ; .######.
10132                 .BYTE $FF                             ; ########
10133                 .BYTE $FF                             ; ########
10134                 .BYTE $FF                             ; ########
10135                 .BYTE $E7                             ; ###..###
10136                 .BYTE $66                             ; .##..##.
10137                 .BYTE $FF                             ; ########
10138                 .BYTE $FF                             ; ########
10139                 .BYTE $FF                             ; ########
10140                 .BYTE $FF                             ; ########
10141                 .BYTE $7E                             ; .######.
10142                 .BYTE $7E                             ; .######.
10143                 .BYTE $00                             ; ........
10144                 .BYTE $18                             ; ...##...
10145                 .BYTE $3C                             ; ..####..
10146                 .BYTE $7E                             ; .######.
10147                 .BYTE $FF                             ; ########
10148                 .BYTE $FF                             ; ########
10149                 .BYTE $E7                             ; ###..###
10150                 .BYTE $66                             ; .##..##.
10151                 .BYTE $FF                             ; ########
10152                 .BYTE $FF                             ; ########
10153                 .BYTE $FF                             ; ########
10154                 .BYTE $FF                             ; ########
10155                 .BYTE $3C                             ; ..####..
10156                 .BYTE $18                             ; ...##...
10157                 .BYTE $3C                             ; ..####..
10158                 .BYTE $FF                             ; ########
10159                 .BYTE $FF                             ; ########
10160                 .BYTE $E7                             ; ###..###
10161                 .BYTE $66                             ; .##..##.
10162                 .BYTE $FF                             ; ########
10163                 .BYTE $FF                             ; ########
10164                 .BYTE $7E                             ; .######.
10165                 .BYTE $3C                             ; ..####..
10166                 .BYTE $00                             ; ........
10167                 .BYTE $18                             ; ...##...
10168                 .BYTE $3C                             ; ..####..
10169                 .BYTE $FF                             ; ########
10170                 .BYTE $FF                             ; ########
10171                 .BYTE $FF                             ; ########
10172                 .BYTE $3C                             ; ..####..
10173                 .BYTE $18                             ; ...##...
10174                 .BYTE $18                             ; ...##...
10175                 .BYTE $3C                             ; ..####..
10176                 .BYTE $FF                             ; ########
10177                 .BYTE $3C                             ; ..####..
10178                 .BYTE $18                             ; ...##...
10179                 .BYTE $28                             ; ..#.#...
10180                 .BYTE $28                             ; ..#.#...
10181                 .BYTE $28                             ; ..#.#...
10182                 .BYTE $28                             ; ..#.#...
10183                 .BYTE $EE                             ; ###.###.
10184                 .BYTE $00                             ; ........
10185                 .BYTE $00                             ; ........
10186                 .BYTE $EE                             ; ###.###.
10187                 .BYTE $28                             ; ..#.#...
10188                 .BYTE $28                             ; ..#.#...
10189                 .BYTE $28                             ; ..#.#...
10190                 .BYTE $28                             ; ..#.#...
10191
10192 ;*** Shape table 2 (PLAYER0..1) ************************************************
10193 PLSHAP2TAB      .BYTE $00                             ; ........
10194                 .BYTE $81                             ; #......#
10195                 .BYTE $81                             ; #......#
10196                 .BYTE $81                             ; #......#
10197                 .BYTE $81                             ; #......#
10198                 .BYTE $BD                             ; #.####.#
10199                 .BYTE $FF                             ; ########
10200                 .BYTE $FF                             ; ########
10201                 .BYTE $BD                             ; #.####.#
10202                 .BYTE $81                             ; #......#
10203                 .BYTE $81                             ; #......#
10204                 .BYTE $81                             ; #......#
10205                 .BYTE $81                             ; #......#
10206                 .BYTE $82                             ; #.....#.
10207                 .BYTE $82                             ; #.....#.
10208                 .BYTE $BA                             ; #.###.#.
10209                 .BYTE $FE                             ; #######.
10210                 .BYTE $FE                             ; #######.
10211                 .BYTE $BA                             ; #.###.#.
10212                 .BYTE $82                             ; #.....#.
10213                 .BYTE $82                             ; #.....#.
10214                 .BYTE $42                             ; .#....#.
10215                 .BYTE $5A                             ; .#.##.#.
10216                 .BYTE $7E                             ; .######.
10217                 .BYTE $7E                             ; .######.
10218                 .BYTE $5A                             ; .#.##.#.
10219                 .BYTE $42                             ; .#....#.
10220                 .BYTE $44                             ; .#...#..
10221                 .BYTE $54                             ; .#.#.#..
10222                 .BYTE $7C                             ; .#####..
10223                 .BYTE $7C                             ; .#####..
10224                 .BYTE $54                             ; .#.#.#..
10225                 .BYTE $44                             ; .#...#..
10226                 .BYTE $24                             ; ..#..#..
10227                 .BYTE $3C                             ; ..####..
10228                 .BYTE $3C                             ; ..####..
10229                 .BYTE $24                             ; ..#..#..
10230                 .BYTE $28                             ; ..#.#...
10231                 .BYTE $38                             ; ..###...
10232                 .BYTE $38                             ; ..###...
10233                 .BYTE $28                             ; ..#.#...
10234                 .BYTE $18                             ; ...##...
10235                 .BYTE $18                             ; ...##...
10236                 .BYTE $10                             ; ...#....
10237                 .BYTE $10                             ; ...#....
10238                 .BYTE $E0                             ; ###.....
10239                 .BYTE $F8                             ; #####...
10240                 .BYTE $F8                             ; #####...
10241                 .BYTE $FE                             ; #######.
10242                 .BYTE $57                             ; .#.#.###
10243                 .BYTE $FE                             ; #######.
10244                 .BYTE $F8                             ; #####...
10245                 .BYTE $F8                             ; #####...
10246                 .BYTE $C0                             ; ##......
10247                 .BYTE $C0                             ; ##......
10248                 .BYTE $F0                             ; ####....
10249                 .BYTE $C0                             ; ##......
10250                 .BYTE $F0                             ; ####....
10251                 .BYTE $F0                             ; ####....
10252                 .BYTE $FC                             ; ######..
10253                 .BYTE $BE                             ; #.#####.
10254                 .BYTE $FC                             ; ######..
10255                 .BYTE $F0                             ; ####....
10256                 .BYTE $80                             ; #.......
10257                 .BYTE $80                             ; #.......
10258                 .BYTE $C0                             ; ##......
10259                 .BYTE $C0                             ; ##......
10260                 .BYTE $F0                             ; ####....
10261                 .BYTE $BC                             ; #.####..
10262                 .BYTE $F0                             ; ####....
10263                 .BYTE $C0                             ; ##......
10264                 .BYTE $07                             ; .....###
10265                 .BYTE $1F                             ; ...#####
10266                 .BYTE $1F                             ; ...#####
10267                 .BYTE $7F                             ; .#######
10268                 .BYTE $EA                             ; ###.#.#.
10269                 .BYTE $7F                             ; .#######
10270                 .BYTE $1F                             ; ...#####
10271                 .BYTE $1F                             ; ...#####
10272                 .BYTE $03                             ; ......##
10273                 .BYTE $03                             ; ......##
10274                 .BYTE $0F                             ; ....####
10275                 .BYTE $03                             ; ......##
10276                 .BYTE $0F                             ; ....####
10277                 .BYTE $0F                             ; ....####
10278                 .BYTE $3F                             ; ..######
10279                 .BYTE $7D                             ; .#####.#
10280                 .BYTE $3F                             ; ..######
10281                 .BYTE $0F                             ; ....####
10282                 .BYTE $01                             ; .......#
10283                 .BYTE $01                             ; .......#
10284                 .BYTE $03                             ; ......##
10285                 .BYTE $03                             ; ......##
10286                 .BYTE $0F                             ; ....####
10287                 .BYTE $3D                             ; ..####.#
10288                 .BYTE $0F                             ; ....####
10289                 .BYTE $03                             ; ......##
10290                 .BYTE $18                             ; ...##...
10291                 .BYTE $3C                             ; ..####..
10292                 .BYTE $7E                             ; .######.
10293                 .BYTE $7E                             ; .######.
10294                 .BYTE $DB                             ; ##.##.##
10295                 .BYTE $C3                             ; ##....##
10296                 .BYTE $81                             ; #......#
10297                 .BYTE $81                             ; #......#
10298                 .BYTE $81                             ; #......#
10299                 .BYTE $10                             ; ...#....
10300                 .BYTE $38                             ; ..###...
10301                 .BYTE $7C                             ; .#####..
10302                 .BYTE $7C                             ; .#####..
10303                 .BYTE $D6                             ; ##.#.##.
10304                 .BYTE $C6                             ; ##...##.
10305                 .BYTE $82                             ; #.....#.
10306                 .BYTE $82                             ; #.....#.
10307                 .BYTE $18                             ; ...##...
10308                 .BYTE $3C                             ; ..####..
10309                 .BYTE $3C                             ; ..####..
10310                 .BYTE $66                             ; .##..##.
10311                 .BYTE $66                             ; .##..##.
10312                 .BYTE $42                             ; .#....#.
10313                 .BYTE $42                             ; .#....#.
10314                 .BYTE $10                             ; ...#....
10315                 .BYTE $38                             ; ..###...
10316                 .BYTE $38                             ; ..###...
10317                 .BYTE $6C                             ; .##.##..
10318                 .BYTE $44                             ; .#...#..
10319                 .BYTE $44                             ; .#...#..
10320                 .BYTE $18                             ; ...##...
10321                 .BYTE $3C                             ; ..####..
10322                 .BYTE $24                             ; ..#..#..
10323                 .BYTE $24                             ; ..#..#..
10324                 .BYTE $10                             ; ...#....
10325                 .BYTE $38                             ; ..###...
10326                 .BYTE $28                             ; ..#.#...
10327                 .BYTE $18                             ; ...##...
10328                 .BYTE $3C                             ; ..####..
10329                 .BYTE $7E                             ; .######.
10330                 .BYTE $FF                             ; ########
10331                 .BYTE $18                             ; ...##...
10332                 .BYTE $18                             ; ...##...
10333                 .BYTE $FF                             ; ########
10334                 .BYTE $7E                             ; .######.
10335                 .BYTE $3C                             ; ..####..
10336                 .BYTE $18                             ; ...##...
10337                 .BYTE $10                             ; ...#....
10338                 .BYTE $38                             ; ..###...
10339                 .BYTE $7C                             ; .#####..
10340                 .BYTE $FE                             ; #######.
10341                 .BYTE $38                             ; ..###...
10342                 .BYTE $38                             ; ..###...
10343                 .BYTE $FE                             ; #######.
10344                 .BYTE $7C                             ; .#####..
10345                 .BYTE $38                             ; ..###...
10346                 .BYTE $10                             ; ...#....
10347                 .BYTE $18                             ; ...##...
10348                 .BYTE $3C                             ; ..####..
10349                 .BYTE $7E                             ; .######.
10350                 .BYTE $18                             ; ...##...
10351                 .BYTE $7E                             ; .######.
10352                 .BYTE $3C                             ; ..####..
10353                 .BYTE $18                             ; ...##...
10354                 .BYTE $10                             ; ...#....
10355                 .BYTE $38                             ; ..###...
10356                 .BYTE $7C                             ; .#####..
10357                 .BYTE $10                             ; ...#....
10358                 .BYTE $7C                             ; .#####..
10359                 .BYTE $38                             ; ..###...
10360                 .BYTE $10                             ; ...#....
10361                 .BYTE $18                             ; ...##...
10362                 .BYTE $3C                             ; ..####..
10363                 .BYTE $18                             ; ...##...
10364                 .BYTE $3C                             ; ..####..
10365                 .BYTE $18                             ; ...##...
10366                 .BYTE $10                             ; ...#....
10367                 .BYTE $38                             ; ..###...
10368                 .BYTE $38                             ; ..###...
10369                 .BYTE $10                             ; ...#....
10370
10371 ;*** Display List fragments ****************************************************
10372 ;
10373 ; LOCAL VARIABLES
10374 PFMEM.C0R0      = PFMEM+0*40                          ; Start address of PLAYFIELD row 0
10375 PFMEM.C0R5      = PFMEM+5*40                          ; Start address of PLAYFIELD row 5
10376 PFMEM.C0R17     = PFMEM+17*40                         ; Start address of PLAYFIELD row 17
10377
10378 ;*** Display List fragment for Control Panel Display (bottom text window) ******
10379 DLSTFRAG        .BYTE $8D                             ; GR7 + DLI
10380                 .BYTE $00                             ; BLK1
10381                 .BYTE $46,<PANELTXT,>PANELTXT         ; GR1 @ PANELTXT
10382                 .BYTE $20                             ; BLK3
10383                 .BYTE $06                             ; GR1
10384                 .BYTE $00                             ; BLK1
10385
10386 ;*** Display List fragment for Galactic Chart view *****************************
10387 DLSTFRAGGC      .BYTE $01,<DLSTGC,>DLSTGC             ; JMP @ DLSTGC
10388
10389 ;*** Display List fragment for Long-Range Scan view ****************************
10390 DLSTFRAGLRS     .BYTE $00                             ; BLK1
10391                 .BYTE $00                             ; BLK1
10392                 .BYTE $46,<LRSHEADER,>LRSHEADER       ; GR1 @ LRSHEADER
10393                 .BYTE $4D,<PFMEM.C0R5,>PFMEM.C0R5     ; GR7 @ PFMEM.C0R5
10394
10395 ;*** Display List fragment for Aft view ****************************************
10396 DLSTFRAGAFT     .BYTE $00                             ; BLK1
10397                 .BYTE $00                             ; BLK1
10398                 .BYTE $46,<AFTHEADER,>AFTHEADER       ; GR1 @ AFTHEADER
10399                 .BYTE $4D,<PFMEM.C0R5,>PFMEM.C0R5     ; GR7 @ PFMEM.C0R5
10400
10401 ;*** Display List fragment for Front view and Title text line ******************
10402 DLSTFRAGFRONT   .BYTE $4D,<PFMEM.C0R0,>PFMEM.C0R0     ; GR7 @ PFMEM.C0R0
10403                 .BYTE $0D                             ; GR7
10404                 .BYTE $0D                             ; GR7
10405                 .BYTE $0D                             ; GR7
10406                 .BYTE $0D                             ; GR7
10407                 .BYTE $0D                             ; GR7
10408                 .BYTE $30                             ; BLK4
10409                 .BYTE $46,<TITLETXT,>TITLETXT         ; GR1 @ TITLETXT
10410                 .BYTE $4D,<PFMEM.C0R17,>PFMEM.C0R17   ; GR7 @ PFMEM.C0R17
10411
10412 ;*** Display List fragment offsets relative to DLSTFRAG ************************
10413 DLSTFRAGOFFTAB  .BYTE DLSTFRAGFRONT-DLSTFRAG          ; Front view
10414                 .BYTE DLSTFRAGAFT-DLSTFRAG            ; Aft view
10415                 .BYTE DLSTFRAGLRS-DLSTFRAG            ; Long-Range Scan view
10416                 .BYTE DLSTFRAGGC-DLSTFRAG             ; Galactic Chart view
10417
10418 ;*** 1-byte bit patterns for 4 pixels of same color for PLAYFIELD space objects 
10419 FOURCOLORPIXEL  .BYTE $FF                             ; COLOR3
10420                 .BYTE $FF                             ; COLOR3
10421                 .BYTE $FF                             ; COLOR3
10422                 .BYTE $FF                             ; COLOR3
10423                 .BYTE $AA                             ; COLOR2
10424                 .BYTE $FF                             ; COLOR3
10425                 .BYTE $AA                             ; COLOR2
10426                 .BYTE $FF                             ; COLOR3
10427                 .BYTE $AA                             ; COLOR2
10428                 .BYTE $AA                             ; COLOR2
10429                 .BYTE $AA                             ; COLOR2
10430                 .BYTE $FF                             ; COLOR3
10431                 .BYTE $AA                             ; COLOR2
10432                 .BYTE $AA                             ; COLOR2
10433                 .BYTE $AA                             ; COLOR2
10434                 .BYTE $AA                             ; COLOR2
10435                 .BYTE $AA                             ; COLOR2
10436                 .BYTE $AA                             ; COLOR2
10437                 .BYTE $AA                             ; COLOR2
10438                 .BYTE $55                             ; COLOR1
10439                 .BYTE $55                             ; COLOR1
10440                 .BYTE $AA                             ; COLOR2
10441                 .BYTE $55                             ; COLOR1
10442                 .BYTE $AA                             ; COLOR2
10443                 .BYTE $55                             ; COLOR1
10444                 .BYTE $55                             ; COLOR1
10445                 .BYTE $55                             ; COLOR1
10446                 .BYTE $AA                             ; COLOR2
10447                 .BYTE $55                             ; COLOR1
10448                 .BYTE $55                             ; COLOR1
10449                 .BYTE $55                             ; COLOR1
10450                 .BYTE $55                             ; COLOR1
10451
10452 ;*** Masks to filter 1 pixel (2 bits) from 4 pixels (1 byte of PLAYFIELD memory)
10453 PIXELMASKTAB    .BYTE $C0                             ; ##......
10454                 .BYTE $30                             ; ..##....
10455                 .BYTE $0C                             ; ....##..
10456                 .BYTE $03                             ; ......##
10457
10458 ;*** Velocity table ************************************************************
10459 VELOCITYTAB     .BYTE 0                               ; Speed 0 =   0 <KM/H>
10460                 .BYTE 1                               ; Speed 1 =   1 <KM/H>
10461                 .BYTE 2                               ; Speed 2 =   2 <KM/H>
10462                 .BYTE 4                               ; Speed 3 =   4 <KM/H>
10463                 .BYTE 8                               ; Speed 4 =   8 <KM/H>
10464                 .BYTE 16                              ; Speed 5 =  16 <KM/H>
10465                 .BYTE 32                              ; Speed 6 =  32 <KM/H>
10466                 .BYTE 64                              ; Speed 7 =  64 <KM/H>
10467                 .BYTE 96                              ; Speed 8 =  96 <KM/H>
10468                 .BYTE 112                             ; Speed 9 = 112 <KM/H>
10469
10470 ;*** Keyboard code lookup table ************************************************
10471 KEYTAB          .BYTE $F2                             ; '0'   - Speed 0
10472                 .BYTE $DF                             ; '1'   - Speed 1
10473                 .BYTE $DE                             ; '2'   - Speed 2
10474                 .BYTE $DA                             ; '3'   - Speed 3
10475                 .BYTE $D8                             ; '4'   - Speed 4
10476                 .BYTE $DD                             ; '5'   - Speed 5
10477                 .BYTE $DB                             ; '6'   - Speed 6
10478                 .BYTE $F3                             ; '7'   - Speed 7
10479                 .BYTE $F5                             ; '8'   - Speed 8
10480                 .BYTE $F0                             ; '9'   - Speed 9
10481                 .BYTE $F8                             ; 'F'   - Front view
10482                 .BYTE $FF                             ; 'A'   - Aft view
10483                 .BYTE $C0                             ; 'L'   - Long-Range Scan view
10484                 .BYTE $FD                             ; 'G'   - Galactic Chart view
10485                 .BYTE $ED                             ; 'T'   - Tracking on/off
10486                 .BYTE $FE                             ; 'S'   - Shields on/off
10487                 .BYTE $D2                             ; 'C'   - Attack Computer on/off
10488                 .BYTE $F9                             ; 'H'   - Hyperwarp
10489                 .BYTE $E5                             ; 'M'   - Manual Target Selector
10490                 .BYTE $CA                             ; 'P'   - Pause
10491                 .BYTE $E7                             ; 'INV' - Abort Mission
10492
10493 ;*** Engines energy drain rates per game loop iteration in energy subunits *****
10494 DRAINRATETAB    .BYTE 0                               ;
10495                 .BYTE 4                               ;
10496                 .BYTE 6                               ;
10497                 .BYTE 8                               ;
10498                 .BYTE 10                              ;
10499                 .BYTE 12                              ;
10500                 .BYTE 14                              ;
10501                 .BYTE 30                              ;
10502                 .BYTE 45                              ;
10503                 .BYTE 60                              ;
10504
10505 ;*** Hyperwarp energy depending on distance ************************************
10506 WARPENERGYTAB   .BYTE 10                              ; =  100 energy units
10507                 .BYTE 13                              ; =  130 energy units
10508                 .BYTE 16                              ; =  160 energy units
10509                 .BYTE 20                              ; =  200 energy units
10510                 .BYTE 23                              ; =  230 energy units
10511                 .BYTE 50                              ; =  500 energy units
10512                 .BYTE 70                              ; =  700 energy units
10513                 .BYTE 80                              ; =  800 energy units
10514                 .BYTE 90                              ; =  900 energy units
10515                 .BYTE 120                             ; = 1200 energy units
10516                 .BYTE 125                             ; = 1250 energy units
10517                 .BYTE 130                             ; = 1300 energy units
10518                 .BYTE 135                             ; = 1350 energy units
10519                 .BYTE 140                             ; = 1400 energy units
10520                 .BYTE 155                             ; = 1550 energy units
10521                 .BYTE 170                             ; = 1700 energy units
10522                 .BYTE 184                             ; = 1840 energy units
10523                 .BYTE 200                             ; = 2000 energy units
10524                 .BYTE 208                             ; = 2080 energy units
10525                 .BYTE 216                             ; = 2160 energy units
10526                 .BYTE 223                             ; = 2230 energy units
10527                 .BYTE 232                             ; = 2320 energy units
10528                 .BYTE 241                             ; = 2410 energy units
10529                 .BYTE 250                             ; = 2500 energy units
10530
10531 ;*** Joystick increments *******************************************************
10532 STICKINCTAB     .BYTE 0                               ; Centered
10533                 .BYTE 1                               ; Right or up
10534                 .BYTE -1                              ; Left or down
10535                 .BYTE 0                               ; Centered
10536
10537 ;*** 3-byte elements to draw cross hairs and Attack Computer Display ***********
10538 ;   Byte 1 : Pixel column number of line start
10539 ;   Byte 2 : Pixel row number of line start
10540 ;   Byte 3 : B7 = 0 -> Draw line to the right
10541 ;            B7 = 1 -> Draw line down
10542 ;            B6..0  -> Length of line in pixels. Possible values are: 0..127.
10543 ;
10544 ;                   #
10545 ;                   #                              4
10546 ;                   #                      ##############################
10547 ;                   #1                     #             #              #
10548 ;                   #                      #             #11            #
10549 ;                   #                      #             #              #
10550 ;                   #                      #5            #    8         #6
10551 ;                                          #      ###############       #
10552 ;                                          #      #             #       #
10553 ;         15                  16           #   7  #             #   10  #
10554 ; ###############       ###############    ########             #########
10555 ;                                          #      #12           #       #
10556 ;                                          #      #             #13     #
10557 ;                                          #      ###############       #
10558 ;                   #                      #         9   #              #
10559 ;                   #                      #             #              #
10560 ;                   #                      #             #14            #
10561 ;                   #                      #       3     #              #
10562 ;                   #2                     ##############################
10563 ;                   #
10564 ;                   #
10565 ;
10566 ;         Front/Aft Cross Hairs                Attack Computer Display
10567 ;
10568 ; LOCAL VARIABLES
10569 DOWN            = $80
10570 RIGHT           = $00
10571
10572 DRAWLINESTAB    .BYTE 80,40,DOWN!7                    ; Line 1
10573                 .BYTE 80,54,DOWN!7                    ; Line 2
10574
10575                 .BYTE 119,70,RIGHT!30                 ; Line 3
10576                 .BYTE 119,86,RIGHT!30                 ; Line 4
10577                 .BYTE 119,70,DOWN!17                  ; Line 5
10578                 .BYTE 148,70,DOWN!17                  ; Line 6
10579                 .BYTE 120,78,RIGHT!6                  ; Line 7
10580                 .BYTE 126,75,RIGHT!15                 ; Line 8
10581                 .BYTE 126,81,RIGHT!15                 ; Line 9
10582                 .BYTE 141,78,RIGHT!7                  ; Line 10
10583                 .BYTE 133,71,DOWN!4                   ; Line 11
10584                 .BYTE 126,76,DOWN!5                   ; Line 12
10585                 .BYTE 140,76,DOWN!5                   ; Line 13
10586                 .BYTE 133,82,DOWN!4                   ; Line 14
10587
10588                 .BYTE 62,50,RIGHT!15                  ; Line 15
10589                 .BYTE 84,50,RIGHT!15                  ; Line 16
10590                 .BYTE $FE                             ; End marker
10591
10592 ;*** 3-byte elements to draw our starship's shape in Long-Range Scan view ******
10593 ;
10594 ;   Line  17 18 19 20 21
10595 ;               ##
10596 ;               ##
10597 ;            ## ## ##
10598 ;         ## ## ## ## ##
10599 ;         ##    ##    ##
10600
10601                 .BYTE 78,53,DOWN!2                    ; Line 17
10602                 .BYTE 79,52,DOWN!2                    ; Line 18
10603                 .BYTE 80,50,DOWN!5                    ; Line 19
10604                 .BYTE 81,52,DOWN!2                    ; Line 20
10605                 .BYTE 82,53,DOWN!2                    ; Line 21
10606                 .BYTE $FE                             ; End marker
10607
10608 ;*** Initial x and y coordinates of a star during hyperwarp ********************
10609 ; The following two tables are used to determine the initial x and y coordinates
10610 ; (high byte) of a star during hyperwarp. An index in 0..3 picks both the x and
10611 ; y coordinate, thus 4 pairs of coordinates are possible:
10612 ;
10613 ; Y           +-------+----------------------------+----------------------------+
10614 ; ^           | Index |        x-coordinate        |        y-coordinate        |
10615 ; |           +-------+----------------------------+----------------------------+
10616 ; |.32.       |   0   | +1024..+1279 (+$04**) <KM> |  +512..+767  (+$02**) <KM> |
10617 ; |...1       |   1   | +1024..+1279 (+$04**) <KM> |  +768..+1023 (+$03**) <KM> |
10618 ; |...0       |   2   |  +768..+1023 (+$03**) <KM> | +1024..+1279 (+$04**) <KM> |
10619 ; |....       |   3   |  +512..+767  (+$02**) <KM> | +1024..+1279 (+$04**) <KM> |
10620 ; 0----->X    +-------+----------------------------+----------------------------+
10621
10622 ;*** Initial x-coordinate (high byte) of star in hyperwarp *********************
10623 WARPSTARXTAB    .BYTE $04                             ; +1024..+1279 (+$04**) <KM>
10624                 .BYTE $04                             ; +1024..+1279 (+$04**) <KM>
10625                 .BYTE $03                             ;  +768..+1023 (+$03**) <KM>
10626                 .BYTE $02                             ;  +512..+767  (+$02**) <KM>
10627
10628 ;*** Initial y-coordinate (high byte) of star in hyperwarp *********************
10629 WARPSTARYTAB    .BYTE $02                             ;  +512..+767  (+$02**) <KM>
10630                 .BYTE $03                             ;  +768..+1023 (+$03**) <KM>
10631                 .BYTE $04                             ; +1024..+1279 (+$04**) <KM>
10632                 .BYTE $04                             ; +1024..+1279 (+$04**) <KM>
10633
10634 ;*** Text of Control Panel Display (encoded in custom character set) ***********
10635 ; Row 1: "V:00 K:00 E:9999 T:0"
10636 ; Row 2: " O:-00 O:-00 R:-000 "
10637
10638 PANELTXTTAB     .BYTE CCS.V
10639                 .BYTE CCS.COLON
10640                 .BYTE CCS.0
10641                 .BYTE CCS.0
10642                 .BYTE CCS.SPC
10643                 .BYTE CCS.COL1!CCS.K
10644                 .BYTE CCS.COL1!CCS.COLON
10645                 .BYTE CCS.COL1!CCS.0
10646                 .BYTE CCS.COL1!CCS.0
10647                 .BYTE CCS.SPC
10648                 .BYTE CCS.COL2!CCS.E
10649                 .BYTE CCS.COL2!CCS.COLON
10650                 .BYTE CCS.COL2!CCS.9
10651                 .BYTE CCS.COL2!CCS.9
10652                 .BYTE CCS.COL2!CCS.9
10653                 .BYTE CCS.COL2!CCS.9
10654                 .BYTE CCS.SPC
10655                 .BYTE CCS.T
10656                 .BYTE CCS.COLON
10657                 .BYTE CCS.0
10658
10659                 .BYTE CCS.SPC
10660                 .BYTE CCS.THETA
10661                 .BYTE CCS.COLON
10662                 .BYTE CCS.MINUS
10663                 .BYTE CCS.0
10664                 .BYTE CCS.0
10665                 .BYTE CCS.SPC
10666                 .BYTE CCS.COL1!CCS.PHI
10667                 .BYTE CCS.COL1!CCS.COLON
10668                 .BYTE CCS.MINUS
10669                 .BYTE CCS.0
10670                 .BYTE CCS.0
10671                 .BYTE CCS.SPC
10672                 .BYTE CCS.COL2!CCS.R
10673                 .BYTE CCS.COL2!CCS.COLON
10674                 .BYTE CCS.MINUS
10675                 .BYTE CCS.0
10676                 .BYTE CCS.0
10677                 .BYTE CCS.0
10678                 .BYTE CCS.SPC
10679
10680 ;*** Text of Galactic Chart Panel Display **************************************
10681 ; Row 1: "WARP ENERGY:   0    "
10682 ; Row 2: "TARGETS:  DC:PESCLR "
10683 ; Row 3: "STAR DATE:00.00     "
10684
10685                 .BYTE ROM.W
10686                 .BYTE ROM.A
10687                 .BYTE ROM.R
10688                 .BYTE ROM.P
10689                 .BYTE ROM.SPC
10690                 .BYTE ROM.E
10691                 .BYTE ROM.N
10692                 .BYTE ROM.E
10693                 .BYTE ROM.R
10694                 .BYTE ROM.G
10695                 .BYTE ROM.Y
10696                 .BYTE ROM.COLON
10697                 .BYTE ROM.SPC
10698                 .BYTE ROM.SPC
10699                 .BYTE ROM.SPC
10700                 .BYTE ROM.0
10701                 .BYTE ROM.SPC
10702                 .BYTE ROM.SPC
10703                 .BYTE ROM.SPC
10704                 .BYTE ROM.SPC
10705
10706                 .BYTE CCS.COL2!ROM.T
10707                 .BYTE CCS.COL2!ROM.A
10708                 .BYTE CCS.COL2!ROM.R
10709                 .BYTE CCS.COL2!ROM.G
10710                 .BYTE CCS.COL2!ROM.E
10711                 .BYTE CCS.COL2!ROM.T
10712                 .BYTE CCS.COL2!ROM.S
10713                 .BYTE CCS.COL2!ROM.COLON
10714                 .BYTE ROM.SPC
10715                 .BYTE ROM.SPC
10716                 .BYTE ROM.D
10717                 .BYTE ROM.C
10718                 .BYTE ROM.COLON
10719                 .BYTE ROM.P
10720                 .BYTE ROM.E
10721                 .BYTE ROM.S
10722                 .BYTE ROM.C
10723                 .BYTE ROM.L
10724                 .BYTE ROM.R
10725                 .BYTE ROM.SPC
10726
10727                 .BYTE CCS.COL3!ROM.S
10728                 .BYTE CCS.COL3!ROM.T
10729                 .BYTE CCS.COL3!ROM.A
10730                 .BYTE CCS.COL3!ROM.R
10731                 .BYTE ROM.SPC
10732                 .BYTE CCS.COL3!ROM.D
10733                 .BYTE CCS.COL3!ROM.A
10734                 .BYTE CCS.COL3!ROM.T
10735                 .BYTE CCS.COL3!ROM.E
10736                 .BYTE CCS.COL3!ROM.COLON
10737                 .BYTE CCS.COL3!ROM.0
10738                 .BYTE CCS.COL3!ROM.0
10739                 .BYTE CCS.COL3!ROM.DOT
10740                 .BYTE CCS.COL3!ROM.0
10741                 .BYTE CCS.COL3!ROM.0
10742                 .BYTE ROM.SPC
10743                 .BYTE ROM.SPC
10744                 .BYTE ROM.SPC
10745                 .BYTE ROM.SPC
10746                 .BYTE ROM.SPC
10747
10748 ;*** Galactic Chart sector type table ******************************************
10749 SECTORTYPETAB   .BYTE $CF                             ; Starbase
10750                 .BYTE $04                             ; 4 Zylon ships
10751                 .BYTE $03                             ; 3 Zylon ships
10752                 .BYTE $02                             ; 1 or 2 Zylon ships
10753
10754 ;*** Phrase table **************************************************************
10755 ; Phrases consist of phrase tokens. These are bytes that encode words, segments
10756 ; (multiple words that fit into a single line of text), and how they are displayed.
10757 ;
10758 ; LOCAL VARIABLES
10759 EOP             = $40                                 ; End of phrase
10760 EOS             = $80                                 ; End of segment
10761 LONG            = $C0                                 ; Display title phrase for a long time
10762
10763                                                       ; Title Phrase Offset, Text
10764 PHRASETAB       .BYTE $00                             ; (unused)
10765                 .BYTE $05,$06,$02!EOP                 ; $01  "ATTACK COMPUTER ON"
10766                 .BYTE $05,$06,$03!EOP                 ; $04  "ATTACK COMPUTER OFF"
10767                 .BYTE $04,$02!EOP                     ; $07  "SHIELDS ON"
10768                 .BYTE $04,$03!EOP                     ; $09  "SHIELDS OFF"
10769                 .BYTE $06,$07,$02!EOP                 ; $0B  "COMPUTER TRACKING ON"
10770                 .BYTE $07,$03!EOP                     ; $0E  "TRACKING OFF"
10771                 .BYTE $08!EOP                         ; $10  "WHATS WRONG?"
10772                 .BYTE $09,$0A!EOP                     ; $11  "HYPERWARP ENGAGED"
10773                 .BYTE $0B,$0D!LONG                    ; $13  "STARBASE SURROUNDED"
10774                 .BYTE $0B,$0C!LONG                    ; $15  "STARBASE DESTROYED"
10775                 .BYTE $09,$0E!EOP                     ; $17  "HYPERWARP ABORTED"
10776                 .BYTE $09,$0F!EOP                     ; $19  "HYPERWARP COMPLETE"
10777                 .BYTE $10!LONG                        ; $1B  "HYPERSPACE"
10778                 .BYTE $11,$12!EOS                     ; $1C  "ORBIT ESTABLISHED"
10779                 .BYTE $16!EOP                         ; $1E  "STANDBY"
10780                 .BYTE $13,$0E!EOP                     ; $1F  "DOCKING ABORTED"
10781                 .BYTE $15,$0F!EOP                     ; $21  "TRANSFER COMPLETE"
10782                 .BYTE $38!EOS                         ; $23  " "
10783                 .BYTE $17!EOS                         ; $24  "STAR FLEET TO"
10784                 .BYTE $19!EOS                         ; $25  "ALL UNITS"
10785                 .BYTE $18!EOS                         ; $26  "STAR CRUISER 7"
10786                 .BYTE $0C!EOS                         ; $27  "DESTROYED"
10787                 .BYTE $1D!EOS                         ; $28  "BY ZYLON FIRE"
10788                 .BYTE $1E,$1F!EOS                     ; $29  "POSTHUMOUS RANK IS:"
10789                 .BYTE $FD                             ; $2B  "<PLACEHOLDER FOR RANK>"
10790                 .BYTE $25,$FC                         ; $2C  "CLASS <PLACEHOLDER FOR CLASS>"
10791                 .BYTE $38!EOP                         ; $2E  " "
10792                 .BYTE $1B!EOS                         ; $2F  "STAR RAIDERS"
10793                 .BYTE $20!EOP                         ; $30  "COPYRIGHT ATARI 1979"
10794                 .BYTE $38!EOS                         ; $31  " "
10795                 .BYTE $17!EOS                         ; $32  "STAR FLEET TO"
10796                 .BYTE $18!EOS                         ; $33  "STAR CRUISER 7"
10797                 .BYTE $1A,$0E!EOS                     ; $34  "MISSION ABORTED"
10798                 .BYTE $1C,$14!EOS                     ; $36  "ZERO ENERGY"
10799                 .BYTE $24,$1F!EOS                     ; $38  "NEW RANK IS"
10800                 .BYTE $FD                             ; $3A  "<PLACEHOLDER FOR RANK>"
10801                 .BYTE $25,$FC                         ; $3B  "CLASS <PLACEHOLDER FOR CLASS>"
10802                 .BYTE $27!EOS                         ; $3D  "REPORT TO BASE"
10803                 .BYTE $28!EOP                         ; $3E  "FOR TRAINING"
10804                 .BYTE $38!EOS                         ; $3F  " "
10805                 .BYTE $17!EOS                         ; $40  "STAR FLEET TO"
10806                 .BYTE $18!EOS                         ; $41  "STAR CRUISER 7"
10807                 .BYTE $1A,$0F!EOS                     ; $42  "MISSION COMPLETE"
10808                 .BYTE $24,$1F!EOS                     ; $44  "NEW RANK IS:"
10809                 .BYTE $FD                             ; $46  "<PLACEHOLDER FOR RANK>"
10810                 .BYTE $25,$FC                         ; $47  "CLASS <PLACEHOLDER FOR CLASS>"
10811                 .BYTE $26!EOP                         ; $49  "CONGRATULATIONS"
10812                 .BYTE $2C,$1A!EOP                     ; $4A  "NOVICE MISSION"
10813                 .BYTE $2E,$1A!EOP                     ; $4C  "PILOT MISSION"
10814                 .BYTE $31,$1A!EOP                     ; $4E  "WARRIOR MISSION"
10815                 .BYTE $33,$1A!EOP                     ; $50  "COMMANDER MISSION"
10816                 .BYTE $38!EOS                         ; $52  " "
10817                 .BYTE $34,$36!EOP                     ; $53  "DAMAGE CONTROL"
10818                 .BYTE $37,$35!EOS                     ; $55  "PHOTONS DAMAGED"
10819                 .BYTE $38!EOP                         ; $57  " "
10820                 .BYTE $37,$0C!EOS                     ; $58  "PHOTONS DESTROYED"
10821                 .BYTE $38!EOP                         ; $5A  " "
10822                 .BYTE $23,$35!EOS                     ; $5B  "ENGINES DAMAGED"
10823                 .BYTE $38!EOP                         ; $5D  " "
10824                 .BYTE $23,$0C!EOS                     ; $5E  "ENGINES DESTROYED"
10825                 .BYTE $38!EOP                         ; $60  " "
10826                 .BYTE $04,$35!EOS                     ; $61  "SHIELDS DAMAGED"
10827                 .BYTE $38!EOP                         ; $63  " "
10828                 .BYTE $04,$0C!EOS                     ; $64  "SHIELDS DESTROYED"
10829                 .BYTE $38!EOP                         ; $66  " "
10830                 .BYTE $06,$35!EOS                     ; $67  "COMPUTER DAMAGED"
10831                 .BYTE $38!EOP                         ; $69  " "
10832                 .BYTE $06,$0C!EOS                     ; $6A  "COMPUTER DESTROYED"
10833                 .BYTE $38!EOP                         ; $6C  " "
10834                 .BYTE $22!EOS                         ; $6D  "SECTOR SCAN"
10835                 .BYTE $35!EOP                         ; $6E  "DAMAGED"
10836                 .BYTE $22!EOS                         ; $6F  "SECTOR SCAN"
10837                 .BYTE $0C!EOP                         ; $70  "DESTROYED"
10838                 .BYTE $21!EOS                         ; $71  "SUB-SPACE RADIO"
10839                 .BYTE $35!EOP                         ; $72  "DAMAGED"
10840                 .BYTE $21!EOS                         ; $73  "SUB-SPACE RADIO"
10841                 .BYTE $0C!EOP                         ; $74  "DESTROYED"
10842                 .BYTE $01!LONG                        ; $75  "RED ALERT"
10843                 .BYTE $38!EOS                         ; $76  " "
10844                 .BYTE $17!EOS                         ; $77  "STAR FLEET TO"
10845                 .BYTE $18!EOS                         ; $78  "STAR CRUISER 7"
10846                 .BYTE $1A,$0E!EOS                     ; $79  "MISSION ABORTED"
10847                 .BYTE $24,$1F!EOS                     ; $7B  "NEW RANK IS:"
10848                 .BYTE $FD                             ; $7D  "<PLACEHOLDER FOR RANK>"
10849                 .BYTE $25,$FC                         ; $7E  "CLASS <PLACEHOLDER FOR CLASS>"
10850                 .BYTE $26!EOP                         ; $80  "CONGRATULATIONS"
10851
10852 ;*** Word table ****************************************************************
10853 ; Bit B7 of the first byte of a word is the end-of-word marker of the preceding
10854 ; word
10855 ;
10856 ; LOCAL VARIABLES
10857 EOW             = $80                                 ; End of word
10858
10859 WORDTAB         .BYTE EOW!$20,"    RED ALERT"         ; Word $01
10860                 .BYTE EOW!'O,"N"                      ; Word $02
10861                 .BYTE EOW!'O,"FF"                     ; Word $03
10862                 .BYTE EOW!'S,"HIELDS"                 ; Word $04
10863                 .BYTE EOW!'A,"TTACK"                  ; Word $05
10864                 .BYTE EOW!'C,"OMPUTER"                ; Word $06
10865                 .BYTE EOW!'T,"RACKING"                ; Word $07
10866                 .BYTE EOW!'W,"HATS WRONG?"            ; Word $08
10867                 .BYTE EOW!'H,"YPERWARP"               ; Word $09
10868                 .BYTE EOW!'E,"NGAGED"                 ; Word $0A
10869                 .BYTE EOW!'S,"TARBASE"                ; Word $0B
10870                 .BYTE EOW!'D,"ESTROYED"               ; Word $0C
10871                 .BYTE EOW!'S,"URROUNDED"              ; Word $0D
10872                 .BYTE EOW!'A,"BORTED"                 ; Word $0E
10873                 .BYTE EOW!'C,"OMPLETE"                ; Word $0F
10874                 .BYTE EOW!'H,"YPERSPACE"              ; Word $10
10875                 .BYTE EOW!'O,"RBIT"                   ; Word $11
10876                 .BYTE EOW!'E,"STABLISHED"             ; Word $12
10877                 .BYTE EOW!'D,"OCKING"                 ; Word $13
10878                 .BYTE EOW!'E,"NERGY"                  ; Word $14
10879                 .BYTE EOW!'T,"RANSFER"                ; Word $15
10880                 .BYTE EOW!'S,"TANDBY"                 ; Word $16
10881                 .BYTE EOW!'S,"TAR FLEET TO"           ; Word $17
10882                 .BYTE EOW!'S,"TAR CRUISER 7"          ; Word $18
10883                 .BYTE EOW!'A,"LL UNITS"               ; Word $19
10884                 .BYTE EOW!'M,"ISSION"                 ; Word $1A
10885                 .BYTE EOW!$20,"   STAR RAIDERS"       ; Word $1B
10886                 .BYTE EOW!'Z,"ERO"                    ; Word $1C
10887                 .BYTE EOW!'B,"Y ZYLON FIRE"           ; Word $1D
10888                 .BYTE EOW!'P,"OSTHUMOUS"              ; Word $1E
10889                 .BYTE EOW!'R,"ANK IS:"                ; Word $1F
10890                 .BYTE EOW!'C,"OPYRIGHT ATARI 1979"    ; Word $20
10891                 .BYTE EOW!'S,"UB-SPACE RADIO"         ; Word $21
10892                 .BYTE EOW!'S,"ECTOR SCAN"             ; Word $22
10893                 .BYTE EOW!'E,"NGINES"                 ; Word $23
10894                 .BYTE EOW!'N,"EW"                     ; Word $24
10895                 .BYTE EOW!'C,"LASS"                   ; Word $25
10896                 .BYTE EOW!'C,"ONGRATULATIONS"         ; Word $26
10897                 .BYTE EOW!'R,"EPORT TO BASE"          ; Word $27
10898                 .BYTE EOW!'F,"OR TRAINING"            ; Word $28
10899                 .BYTE EOW!'G,"ALACTIC COOK"           ; Word $29
10900                 .BYTE EOW!'G,"ARBAGE SCOW CAPTAIN"    ; Word $2A
10901                 .BYTE EOW!'R,"OOKIE"                  ; Word $2B
10902                 .BYTE EOW!'N,"OVICE"                  ; Word $2C
10903                 .BYTE EOW!'E,"NSIGN"                  ; Word $2D
10904                 .BYTE EOW!'P,"ILOT"                   ; Word $2E
10905                 .BYTE EOW!'A,"CE"                     ; Word $2F
10906                 .BYTE EOW!'L,"IEUTENANT"              ; Word $30
10907                 .BYTE EOW!'W,"ARRIOR"                 ; Word $31
10908                 .BYTE EOW!'C,"APTAIN"                 ; Word $32
10909                 .BYTE EOW!'C,"OMMANDER"               ; Word $33
10910                 .BYTE EOW!'D,"AMAGE"                  ; Word $34
10911                 .BYTE EOW!'D,"AMAGED"                 ; Word $35
10912                 .BYTE EOW!'C,"ONTROL"                 ; Word $36
10913                 .BYTE EOW!'P,"HOTONS"                 ; Word $37
10914                 .BYTE EOW!$20                         ; Word $38
10915                 .BYTE EOW!'S,"TAR COMMANDER"          ; Word $39
10916                 .BYTE EOW!$00                         ;
10917
10918 ;*** View modes ****************************************************************
10919 VIEWMODETAB     .BYTE $00                             ; Front view
10920                 .BYTE $01                             ; Aft view
10921                 .BYTE $40                             ; Long-Range Scan view
10922                 .BYTE $80                             ; Galactic Chart view
10923
10924 ;*** Title phrase offsets of "TRACKING OFF", "SHIELDS OFF", "COMPUTER OFF" *****
10925 MSGOFFTAB       .BYTE $0E                             ; "TRACKING OFF"
10926                 .BYTE $09                             ; "SHIELDS OFF"
10927                 .BYTE $04                             ; "COMPUTER OFF"
10928
10929 ;*** Masks to test if Tracking Computer, Shields, or Attack Computer are on ****
10930 MSGBITTAB       .BYTE $FF                             ; Mask Tracking Computer
10931                 .BYTE $08                             ; Mask Shields
10932                 .BYTE $02                             ; Mask Attack Computer
10933
10934 ;*** Title phrase offsets of "COMPUTER TRACKING ON", "SHIELDS ON", "COMPUTER ON"
10935 MSGONTAB        .BYTE $0B                             ; "COMPUTER TRACKING ON"
10936                 .BYTE $07                             ; "SHIELDS ON"
10937                 .BYTE $01                             ; "COMPUTER ON"
10938
10939 ;*** The following two tables encode the PLAYER shapes *************************
10940 ;
10941 ; PHOTON TORPEDO (shape type 0, data in shape table PLSHAP1TAB)
10942 ; Numbers at top indicate the shape table offset of the first and last shape row
10943 ;
10944 ; $01..$10  $11..$1E  $1F..$2A  $2B..$34  $35..$3C  $3D..$42  $75..$76  $7A..$7B
10945 ; ...##...  ...#....  ...##...  ...#....  ...#....  ...#....  ...##...  ...#....
10946 ; ..####..  ..###...  ..####..  ..###...  ...##...  ..###...  ...##...  ...#....
10947 ; .######.  .#####..  ..####..  ..###...  ..####..  ..###...
10948 ; .######.  .#####..  .######.  .#####..  ..#.##..  ..#.#...
10949 ; .###.##.  #######.  .##.###.  .###.#..  ..####..  ..###...
10950 ; ####.###  ##.####.  .####.#.  .#####..  ..####..  ...#....
10951 ; ##.#####  ##.##.#.  .######.  .##.##..  ...##...
10952 ; ##.#####  #####.#.  .###.##.  ..###...  ....#...
10953 ; ########  ###.###.  .######.  ..###...
10954 ; ########  ###.###.  ..####..  ...#....
10955 ; ####.###  .#####..  ..####..
10956 ; .###.##.  .#####..  ...##...
10957 ; .######.  ..###...
10958 ; .######.  ...#....
10959 ; ..####..
10960 ; ...##...
10961 ;
10962 ; ZYLON FIGHTER (shape type 1, data in shape table PLSHAP2TAB)
10963 ; Numbers at top indicate the shape table offset of the first and last shape row
10964 ;
10965 ; $01..$0C  $0D..$14  $15..$1A  $1B..$20  $21..$24  $25..$28  $29..$2A  $2B..$2C
10966 ; #......#  #.....#.  .#....#.  .#...#..  ..#..#..  ..#.#...  ...##...  ...#....
10967 ; #......#  #.....#.  .#.##.#.  .#.#.#..  ..####..  ..###...  ...##...  ...#....
10968 ; #......#  #.###.#.  .######.  .#####..  ..####..  ..###...
10969 ; #......#  #######.  .######.  .#####..  ..#..#..  ..#.#...
10970 ; #.####.#  #######.  .#.##.#.  .#.#.#..
10971 ; ########  #.###.#.  .#....#.  .#...#..
10972 ; ########  #.....#.
10973 ; #.####.#  #.....#.
10974 ; #......#
10975 ; #......#
10976 ; #......#
10977 ; #......#
10978 ;
10979 ; STARBASE RIGHT (shape type 2, data in shape table PLSHAP2TAB)
10980 ; Numbers at top indicate the shape table offset of the first and last shape row
10981 ;
10982 ; $2D..$36  $38..$40  $41..$46  $36..$38  $36       $00       $00       $00
10983 ; ###.....  ##......  ##......  ##......  ##......  ........  ........  ........
10984 ; #####...  ####....  ##......  ####....
10985 ; #####...  ####....  ####....  ##......
10986 ; #######.  ######..  #.####..
10987 ;  #.#.###  #.#####.  ####....
10988 ; #######.  ######..  ##......
10989 ; #####...  ####....
10990 ; #####...  #.......
10991 ; ##......  #.......
10992 ; ##......
10993 ;
10994 ; STARBASE CENTER (shape type 3, data in shape table PLSHAP1TAB)
10995 ; Numbers at top indicate the shape table offset of the first and last shape row
10996 ;
10997 ; $7E..$8D  $8E..$9C  $9D..$A9  $AA..$B3  $B4..$BB  $BC..$C0  $7B..$7D  $7A..$7B
10998 ; ...##...  ........  ........  ...##...  ........  ...##...  ...#....  ...#....
10999 ; .######.  ...##...  ...##...  ..####..  ...##...  ..####..  ..###...  ...#....
11000 ; ########  ..####..  ..####..  ########  ..####..  ########  ...#....
11001 ; ########  .######.  .######.  ########  ########  ..####..
11002 ; ########  ########  ########  ###..###  ########  ...##...
11003 ; ########  ########  ########  .##..##.  ########
11004 ; ########  ########  ###..###  ########  ..####..
11005 ; ###..###  ###..###  .##..##.  ########  ...##...
11006 ; ###..###  .##..##.  ########  .######.
11007 ; ########  ########  ########  ..####..
11008 ; ########  ########  ########
11009 ; ########  ########  ########
11010 ; ########  ########  ..####..
11011 ; ########  .######.
11012 ; .######.  .######.
11013 ; .######.
11014 ;
11015 ; STARBASE LEFT (shape type 4, data in shape table PLSHAP2TAB)
11016 ; Numbers at top indicate the shape table offset of the first and last shape row
11017 ;
11018 ; $47..$50  $52..$5A  $5B..$60  $50..$52  $50       $00       $00       $00
11019 ; .....###  ......##  ......##  ......##  ......##  ........  ........  ........
11020 ; ...#####  ....####  ......##  ....####
11021 ; ...#####  ....####  ....####  ......##
11022 ; .#######  ..######  ..####.#
11023 ; ###.#.#.  .#####.#  ....####
11024 ; .#######  ..######  ......##
11025 ; ...#####  ....####
11026 ; ...#####  .......#
11027 ; ......##  .......#
11028 ; ......##
11029 ;
11030 ; TRANSFER VESSEL (shape type 5, data in shape table PLSHAP1TAB)
11031 ; Numbers at top indicate the shape table offset of the first and last shape row
11032 ;
11033 ; $43..$52  $53..$60  $61..$6B  $6C..$74  $75..$79  $7A..$7D  $75..$76  $7A..$7B
11034 ; ..####..  ...###..  ...##...  ...#....  ...##...  ...#....  ...##...  ...#....
11035 ; ..####..  ...###..  ...##...  ...#....  ...##...  ...#....  ...##...  ...#....
11036 ; ..#..#..  ...#.#..  ..####..  ..###...  ..####..  ..###...
11037 ; ..####..  ..#####.  ..####..  ..###...  ...##...  ...#....
11038 ; .######.  ..#####.  ..####..  ..###...  ...##...
11039 ; .######.  ..#####.  ..####..  .#####..
11040 ; .######.  ..#.#.#.  .######.  ..#.#...
11041 ; .#.##.#.  .#######  ..#..#..  ..#.#...
11042 ; ########  .#######  ..#..#..  ..#.#...
11043 ; ########  ..#...#.  ..#..#..
11044 ; .#....#.  ..#...#.  ..#..#..
11045 ; .#....#.  ..#...#.
11046 ; .#....#.  ..#...#.
11047 ; .#....#.  ..#...#.
11048 ; .#....#.
11049 ; .#....#.
11050 ;
11051 ; METEOR (shape type 6, data in shape table PLSHAP1TAB)
11052 ; Numbers at top indicate the shape table offset of the first and last shape row
11053 ;
11054 ; $01..$10  $11..$1E  $1F..$2A  $2B..$34  $35..$3C  $3D..$42  $75..$76  $7A..$7B
11055 ; ...##...  ...#....  ...##...  ...#....  ...#....  ...#....  ...##...  ...#....
11056 ; ..####..  ..###...  ..####..  ..###...  ...##...  ..###...  ...##...  ...#....
11057 ; .######.  .#####..  ..####..  ..###...  ..####..  ..###...
11058 ; .######.  .#####..  .######.  .#####..  ..#.##..  ..#.#...
11059 ; .###.##.  #######.  .##.###.  .###.#..  ..####..  ..###...
11060 ; ####.###  ##.####.  .####.#.  .#####..  ..####..  ...#....
11061 ; ##.#####  ##.##.#.  .######.  .##.##..  ...##...
11062 ; ##.#####  #####.#.  .###.##.  ..###...  ....#...
11063 ; ########  ###.###.  .######.  ..###...
11064 ; ########  ###.###.  ..####..  ...#....
11065 ; ####.###  .#####..  ..####..
11066 ; .###.##.  .#####..  ...##...
11067 ; .######.  ..###...
11068 ; .######.  ...#....
11069 ; ..####..
11070 ; ...##...
11071 ;
11072 ; ZYLON CRUISER (shape type 7, data in shape table PLSHAP2TAB)
11073 ; Numbers at top indicate the shape table offset of the first and last shape row
11074 ;
11075 ; $61..$69  $6A..$71  $72..$78  $79..$7E  $7F..$82  $83..$85  $29..$2A  $2B..$2C
11076 ; ...##...  ...#....  ...##...  ...#....  ...##...  ...#....  ...##...  ...#....
11077 ; ..####..  ..###...  ..####..  ..###...  ..####..  ..###...  ...##...  ...#....
11078 ; .######.  .#####..  ..####..  ..###...  ..#..#..  ..#.#...
11079 ; .######.  .#####..  .##..##.  .##.##..  ..#..#..
11080 ; ##.##.##  ##.#.##.  .##..##.  .#...#..
11081 ; ##....##  ##...##.  .#....#.  .#...#..
11082 ; #......#  #.....#.  .#....#.
11083 ; #......#  #.....#.
11084 ; #......#
11085 ;
11086 ; ZYLON BASESTAR (shape type 8, data in shape table PLSHAP2TAB)
11087 ; Numbers at top indicate the shape table offset of the first and last shape row
11088 ;
11089 ; $86..$8F  $90..$99  $9A..$A0  $A1..$A7  $A8..$AC  $AD..$B0  $29..$2A  $2B..$2C
11090 ; ...##...  ...#....  ...##...  ...#....  ...##...  ...#....  ...##...  ...#....
11091 ; ..####..  ..###...  ..####..  ..###...  ..####..  ..###...  ...##...  ...#....
11092 ; .######.  .#####..  .######.  .#####..  ...##...  ..###...
11093 ; ########  #######.  ...##...  ...#....  ..####..  ...#....
11094 ; ...##...  ..###...  .######.  .#####..  ...##...
11095 ; ...##...  ..###...  ..####..  ..###...
11096 ; ########  #######.  ...##...  ...#....
11097 ; .######.  .#####..
11098 ; ..####..  ..###...
11099 ; ...##...  ...#....
11100 ;
11101 ; HYPERWARP TARGET MARKER (shape type 9, data in shape table PLSHAP1TAB)
11102 ; Numbers at top indicate the shape table offset of the first and last shape row
11103 ;
11104 ; $C1..$CC  $C1..$CC  $C1..$CC  $C1..$CC  $C1..$CC  $C1..$CC  $75..$76  $C1..$CC
11105 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ...##...  ..#.#...
11106 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ...##...  ..#.#...
11107 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11108 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11109 ; ###.###.  ###.###.  ###.###.  ###.###.  ###.###.  ###.###.            ###.###.
11110 ; ........  ........  ........  ........  ........  ........            ........
11111 ; ........  ........  ........  ........  ........  ........            ........
11112 ; ###.###.  ###.###.  ###.###.  ###.###.  ###.###.  ###.###.            ###.###.
11113 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11114 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11115 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11116 ; ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...  ..#.#...            ..#.#...
11117
11118 ;*** Shape type 0..9 offset table (10 shape cell offsets of shape type...) *****
11119 PLSHAPOFFTAB    .BYTE $01,$11,$1F,$2B,$35,$3D,$75,$7A ; ...0 into PLSHAP1TAB
11120                 .BYTE $01,$0D,$15,$1B,$21,$25,$29,$2B ; ...1 into PLSHAP2TAB
11121                 .BYTE $2D,$38,$41,$36,$36,$00,$00,$00 ; ...2 into PLSHAP2TAB
11122                 .BYTE $7E,$8E,$9D,$AA,$B4,$BC,$7B,$7A ; ...3 into PLSHAP1TAB
11123                 .BYTE $47,$52,$5B,$50,$50,$00,$00,$00 ; ...4 into PLSHAP2TAB
11124                 .BYTE $43,$53,$61,$6C,$75,$7A,$75,$7A ; ...5 into PLSHAP1TAB
11125                 .BYTE $01,$11,$1F,$2B,$35,$3D,$75,$7A ; ...6 into PLSHAP1TAB
11126                 .BYTE $61,$6A,$72,$79,$7F,$83,$29,$2B ; ...7 into PLSHAP2TAB
11127                 .BYTE $86,$90,$9A,$A1,$A8,$AD,$29,$2B ; ...8 into PLSHAP2TAB
11128                 .BYTE $C1,$C1,$C1,$C1,$C1,$C1,$75,$C1 ; ...9 into PLSHAP1TAB
11129
11130 ;*** Shape type 0..9 height table (10 shape cell heights of shape type...) *****
11131 PLSHPHEIGHTTAB  .BYTE $0F,$0D,$0B,$09,$07,$05,$01,$01 ; ...0
11132                 .BYTE $0B,$07,$05,$05,$03,$03,$01,$01 ; ...1
11133                 .BYTE $09,$08,$05,$02,$00,$00,$00,$00 ; ...2
11134                 .BYTE $0F,$0E,$0C,$09,$07,$04,$02,$01 ; ...3
11135                 .BYTE $09,$08,$05,$02,$00,$00,$00,$00 ; ...4
11136                 .BYTE $0F,$0D,$0A,$08,$04,$03,$01,$01 ; ...5
11137                 .BYTE $0F,$0D,$0B,$09,$07,$05,$01,$01 ; ...6
11138                 .BYTE $08,$07,$06,$05,$03,$02,$01,$01 ; ...7
11139                 .BYTE $09,$09,$06,$06,$04,$03,$01,$01 ; ...8
11140                 .BYTE $0B,$0B,$0B,$0B,$0B,$0B,$01,$0B ; ...9
11141
11142 ;*** Keyboard codes to switch to Front or Aft view when Tracking Computer is on 
11143 TRACKKEYSTAB    .BYTE $F8                             ; 'F' - Front view
11144                 .BYTE $FF                             ; 'A' - Aft view
11145
11146 ;*** Galactic Chart sector character codes (encoded in custom character set) ***
11147 SECTORCHARTAB   .BYTE CCS.BORDERSW                    ; Empty sector
11148                 .BYTE CCS.2ZYLONS                     ; Sector contains 1 Zylon ship
11149                 .BYTE CCS.2ZYLONS                     ; Sector contains 2 Zylon ships
11150                 .BYTE CCS.3ZYLONS                     ; Sector contains 3 Zylon ships
11151                 .BYTE CCS.4ZYLONS                     ; Sector contains 4 Zylon ships
11152                 .BYTE CCS.STARBASE                    ; Sector contains starbase
11153
11154 ;*** Mask to limit veer-off velocity of Hyperwarp Target Marker in hyperwarp ***
11155 VEERMASKTAB     .BYTE NEG!31                          ;  -31..+31  <KM/H> (unused)
11156                 .BYTE NEG!63                          ;  -63..+63  <KM/H> PILOT mission
11157                 .BYTE NEG!95                          ;  -95..+95  <KM/H> WARRIOR mission
11158                 .BYTE NEG!127                         ; -127..+127 <KM/H> COMMANDER mission
11159
11160 ;*** Horizontal PLAYER offsets for PLAYER0..1 (STARBASE LEFT, STARBASE RIGHT) **
11161 PLSTARBAOFFTAB  .BYTE -8                              ; -8 Player/Missile pixels
11162                 .BYTE 8                               ; +8 Player/Missile pixels
11163
11164 ;*** Mission bonus table *******************************************************
11165 BONUSTAB        .BYTE 80                              ; Mission complete   NOVICE mission
11166                 .BYTE 76                              ; Mission complete   PILOT mission
11167                 .BYTE 60                              ; Mission complete   WARRIOR mission
11168                 .BYTE 111                             ; Mission complete   COMMANDER mission
11169
11170                 .BYTE 60                              ; Mission aborted    NOVICE mission
11171                 .BYTE 60                              ; Mission aborted    PILOT mission
11172                 .BYTE 50                              ; Mission aborted    WARRIOR mission
11173                 .BYTE 100                             ; Mission aborted    COMMANDER mission
11174
11175                 .BYTE 40                              ; Starship destroyed NOVICE mission
11176                 .BYTE 50                              ; Starship destroyed PILOT mission
11177                 .BYTE 40                              ; Starship destroyed WARRIOR mission
11178                 .BYTE 90                              ; Starship destroyed COMMANDER mission
11179
11180 ;*** Title phrase offsets of scored class rank *********************************
11181 RANKTAB         .BYTE $29!EOS                         ; "GALACTIC COOK"
11182                 .BYTE $2A!EOS                         ; "GARBAGE SCOW CAPTAIN"
11183                 .BYTE $2A!EOS                         ; "GARBAGE SCOW CAPTAIN"
11184                 .BYTE $2B!EOS                         ; "ROOKIE"
11185                 .BYTE $2B!EOS                         ; "ROOKIE"
11186                 .BYTE $2C!EOS                         ; "NOVICE"
11187                 .BYTE $2C!EOS                         ; "NOVICE"
11188                 .BYTE $2D!EOS                         ; "ENSIGN"
11189                 .BYTE $2D!EOS                         ; "ENSIGN"
11190                 .BYTE $2E!EOS                         ; "PILOT"
11191                 .BYTE $2E!EOS                         ; "PILOT"
11192                 .BYTE $2F!EOS                         ; "ACE"
11193                 .BYTE $30!EOS                         ; "LIEUTENANT"
11194                 .BYTE $31!EOS                         ; "WARRIOR"
11195                 .BYTE $32!EOS                         ; "CAPTAIN"
11196                 .BYTE $33!EOS                         ; "COMMANDER"
11197                 .BYTE $33!EOS                         ; "COMMANDER"
11198                 .BYTE $39!EOS                         ; "STAR COMMANDER"
11199                 .BYTE $39!EOS                         ; "STAR COMMANDER"
11200
11201 ;*** Scored class number table *************************************************
11202 CLASSTAB        .BYTE CCS.COL2!ROM.5                  ; Class 5
11203                 .BYTE CCS.COL2!ROM.5                  ; Class 5
11204                 .BYTE CCS.COL2!ROM.5                  ; Class 5
11205                 .BYTE CCS.COL2!ROM.4                  ; Class 4
11206                 .BYTE CCS.COL2!ROM.4                  ; Class 4
11207                 .BYTE CCS.COL2!ROM.4                  ; Class 4
11208                 .BYTE CCS.COL2!ROM.4                  ; Class 4
11209                 .BYTE CCS.COL2!ROM.3                  ; Class 3
11210                 .BYTE CCS.COL2!ROM.3                  ; Class 3
11211                 .BYTE CCS.COL2!ROM.3                  ; Class 3
11212                 .BYTE CCS.COL2!ROM.2                  ; Class 2
11213                 .BYTE CCS.COL2!ROM.2                  ; Class 2
11214                 .BYTE CCS.COL2!ROM.2                  ; Class 2
11215                 .BYTE CCS.COL2!ROM.1                  ; Class 1
11216                 .BYTE CCS.COL2!ROM.1                  ; Class 1
11217                 .BYTE CCS.COL2!ROM.1                  ; Class 1
11218
11219 ;*** Title phrase offsets of mission level *************************************
11220 MISSIONPHRTAB   .BYTE $4A                             ; "NOVICE MISSION"
11221                 .BYTE $4C                             ; "PILOT MISSION"
11222                 .BYTE $4E                             ; "WARRIOR MISSION"
11223                 .BYTE $50                             ; "COMMANDER MISSION"
11224
11225 ;*** Damage probability of subsystems depending on mission level ***************
11226 DAMAGEPROBTAB   .BYTE 0                               ;  0% (  0:256) NOVICE mission
11227                 .BYTE 80                              ; 31% ( 80:256) PILOT mission
11228                 .BYTE 180                             ; 70% (180:256) WARRIOR mission
11229                 .BYTE 254                             ; 99% (254:256) COMMANDER mission
11230
11231 ;*** Title phrase offsets of damaged subsystems ********************************
11232 DAMAGEPHRTAB    .BYTE $55                             ; "PHOTON TORPEDOS DAMAGED"
11233                 .BYTE $5B                             ; "ENGINES DAMAGED"
11234                 .BYTE $61                             ; "SHIELDS DAMAGED"
11235                 .BYTE $67                             ; "COMPUTER DAMAGED"
11236                 .BYTE $6D                             ; "LONG RANGE SCAN DAMAGED"
11237                 .BYTE $71                             ; "SUB-SPACE RADIO DAMAGED"
11238
11239 ;*** Title phrase offsets of destroyed subsystems ******************************
11240 DESTROYPHRTAB   .BYTE $58                             ; "PHOTON TORPEDOS DESTROYED"
11241                 .BYTE $5E                             ; "ENGINES DESTROYED"
11242                 .BYTE $64                             ; "SHIELDS DESTROYED"
11243                 .BYTE $6A                             ; "COMPUTER DESTROYED"
11244                 .BYTE $6F                             ; "LONG RANGE SCAN DESTROYED"
11245                 .BYTE $73                             ; "SUB-SPACE RADIO DESTROYED"
11246
11247 ;*** 3 x 10-byte noise sound patterns (bytes 0..7 stored in reverse order) *****
11248 ;
11249 ; (9) AUDCTL        ($D208) POKEY: Audio control
11250 ; (8) AUDF3         ($D204) POKEY: Audio channel 3 frequency
11251 ; (7) NOISETORPTIM  ($DA)   Timer for PHOTON TORPEDO LAUNCHED noise sound patterns
11252 ; (6) NOISEEXPLTIM  ($DB)   Timer for SHIELD and ZYLON EXPLOSION noise sound patterns
11253 ; (5) NOISEAUDC2    ($DC)   Audio channel 1/2 control shadow register
11254 ; (4) NOISEAUDC3    ($DD)   Audio channel 3   control shadow register
11255 ; (3) NOISEAUDF1    ($DE)   Audio channel 1 frequency shadow register
11256 ; (2) NOISEAUDF2    ($DF)   Audio channel 2 frequency shadow register
11257 ; (1) NOISEFRQINC   ($E0)   Audio channel 1/2 frequency increment
11258 ; (0) NOISELIFE     ($E1)   Noise sound pattern lifetime
11259 ;
11260 ;                     (0),(1),(2),(3),(4),(5),(6),(7),(8),(9)
11261 NOISEPATTAB     .BYTE $18,$FF,$02,$00,$8A,$A0,$00,$08,$50,$00; PHOTON TORPEDO LAUNCHED
11262                 .BYTE $40,$40,$01,$03,$88,$AF,$08,$00,$50,$04; SHIELD EXPLOSION
11263                 .BYTE $30,$40,$01,$03,$84,$A8,$04,$00,$50,$04; ZYLON EXPLOSION
11264
11265 ;*** 5 x 6-byte beeper sound patterns (bytes 0..5 stored in reverse order) *****
11266 ;
11267 ; (5) BEEPFRQIND    ($D2) Running index into frequency table BEEPFRQTAB ($BF5C)
11268 ; (4) BEEPREPEAT    ($D3) Number of times the beeper sound pattern sequence is repeated - 1
11269 ; (3) BEEPTONELIFE  ($D4) Lifetime of tone in TICKs - 1
11270 ; (2) BEEPPAUSELIFE ($D5) Lifetime of pause in TICKs - 1 ($FF -> No pause)
11271 ; (1) BEEPPRIORITY  ($D6) Beeper sound pattern priority. A playing beeper sound pattern is
11272 ;                         stopped if a beeper sound pattern of higher priority is about to be
11273 ;                         played. A value of 0 indicates that no beeper sound pattern is
11274 ;                         playing at the moment.
11275 ; (0) BEEPFRQSTART  ($D7) Index to first byte of the beeper sound pattern frequency in table
11276 ;                         BEEPFRQTAB ($BF5C)
11277 ;
11278 ; Frequency-over-TICKs diagrams for all beeper sound patterns:
11279 ;
11280 ; HYPERWARP TRANSIT
11281 ;
11282 ;      FRQ
11283 ;       |
11284 ;   $18 |-4--
11285 ;       |
11286 ;   $00 |    -3-
11287 ;       +-------> TICKS
11288 ;        <13 x >
11289 ;
11290 ; RED ALERT
11291 ;
11292 ;      FRQ
11293 ;       |
11294 ;   $60 |                 --------17-------
11295 ;       |
11296 ;   $40 |--------17-------
11297 ;       |
11298 ;       +----------------------------------> TICKS
11299 ;        <-------------- 8 x ------------->
11300 ;
11301 ; ACKNOWLEDGE
11302 ;
11303 ;      FRQ
11304 ;       |
11305 ;   $10 |-3-   -3-   -3-
11306 ;       |
11307 ;   $00 |   -3-   -3-   -3-
11308 ;       +------------------> TICKS
11309 ;        <------ 1 x ----->
11310 ;
11311 ; DAMAGE REPORT (not to scale)
11312 ;
11313 ;      FRQ
11314 ;       |
11315 ;   $40 |------------33-------------
11316 ;       |
11317 ;   $20 |                           ------------33-------------
11318 ;       |
11319 ;       +------------------------------------------------------> TICKS
11320 ;        <------------------------ 3 x ----------------------->
11321 ;
11322 ; MESSAGE FROM STARBASE (not to scale)
11323 ;
11324 ;      FRQ
11325 ;       |
11326 ;   $51 |                                  -----33-----
11327 ;   $48 |-----33-----
11328 ;   $40 |                 -----33-----
11329 ;       |
11330 ;   $00 |            --9--            --9--            --9--
11331 ;       +----------------------------------------------------> TICKS
11332 ;        <---------------------- 1 x ---------------------->
11333 ;
11334 ;                     (0),(1),(2),(3),(4),(5)
11335 BEEPPATTAB      .BYTE $02,$02,$02,$03,$0C,$02         ; HYPERWARP TRANSIT
11336                 .BYTE $04,$03,$FF,$10,$07,$04         ; RED ALERT
11337                 .BYTE $07,$04,$02,$02,$00,$07         ; ACKNOWLEDGE
11338                 .BYTE $0B,$05,$FF,$20,$02,$0B         ; DAMAGE REPORT
11339                 .BYTE $0E,$06,$08,$20,$00,$0E         ; MESSAGE FROM STARBASE
11340
11341 ;*** Beeper sound pattern frequency table **************************************
11342 BEEPFRQTAB      .BYTE $10,$FF                         ; (unused) (!)
11343                 .BYTE $18,$FF                         ; HYPERWARP TRANSIT
11344                 .BYTE $40,$60,$FF                     ; RED ALERT
11345                 .BYTE $10,$10,$10,$FF                 ; ACKNOWLEDGE
11346                 .BYTE $40,$20,$FF                     ; DAMAGE REPORT
11347                 .BYTE $48,$40,$51,$FF                 ; MESSAGE FROM STARBASE
11348
11349 ;*** Shape of blip in Attack Computer Display **********************************
11350 BLIPSHAPTAB     .BYTE $84                             ; #....#..
11351                 .BYTE $B4                             ; #.##.#..
11352                 .BYTE $FC                             ; ######..
11353                 .BYTE $B4                             ; #.##.#..
11354                 .BYTE $84                             ; #....#..
11355
11356 ;*** Initial x-coordinate (high byte) of our starship's photon torpedo *********
11357 BARRELXTAB      .BYTE $FF                             ; Left barrel  = -256 (-$FF00) <KM>
11358                 .BYTE $01                             ; Right barrel = +256 (+$0100) <KM>
11359
11360 ;*** Maximum photon torpedo hit z-coordinate (high byte) ***********************
11361 HITMAXZTAB      .BYTE $0C                             ; < 3328 ($0C**) <KM>
11362                 .BYTE $0C                             ; < 3328 ($0C**) <KM>
11363                 .BYTE $0C                             ; < 3328 ($0C**) <KM>
11364                 .BYTE $0C                             ; < 3328 ($0C**) <KM>
11365                 .BYTE $0E                             ; < 3840 ($0E**) <KM>
11366                 .BYTE $0E                             ; < 3840 ($0E**) <KM>
11367                 .BYTE $0E                             ; < 3840 ($0E**) <KM>
11368                 .BYTE $20                             ; < 8448 ($20**) <KM>
11369
11370 ;*** Minimum photon torpedo hit z-coordinate (high byte) ***********************
11371 HITMINZTAB      .BYTE $00                             ; >=    0 ($00**) <KM>
11372                 .BYTE $00                             ; >=    0 ($00**) <KM>
11373                 .BYTE $00                             ; >=    0 ($00**) <KM>
11374                 .BYTE $02                             ; >=  512 ($02**) <KM>
11375                 .BYTE $04                             ; >= 1024 ($04**) <KM>
11376                 .BYTE $06                             ; >= 1536 ($06**) <KM>
11377                 .BYTE $08                             ; >= 2048 ($08**) <KM>
11378                 .BYTE $0C                             ; >= 3072 ($0C**) <KM>
11379
11380 ;*** Velocity of homing Zylon photon torpedo ***********************************
11381 ZYLONHOMVELTAB  .BYTE NEG!1                           ;  -1 <KM/H> NOVICE mission
11382                 .BYTE NEG!4                           ;  -4 <KM/H> PILOT mission
11383                 .BYTE NEG!8                           ;  -8 <KM/H> WARRIOR mission
11384                 .BYTE NEG!20                          ; -20 <KM/H> COMMANDER mission
11385
11386 ;*** Zylon shape type table ****************************************************
11387 ZYLONSHAPTAB    .BYTE SHAP.ZBASESTAR                  ; ZYLON BASESTAR
11388                 .BYTE SHAP.ZFIGHTER                   ; ZYLON FIGHTER
11389                 .BYTE SHAP.ZFIGHTER                   ; ZYLON FIGHTER
11390                 .BYTE SHAP.ZFIGHTER                   ; ZYLON FIGHTER
11391                 .BYTE SHAP.ZCRUISER                   ; ZYLON CRUISER
11392                 .BYTE SHAP.ZCRUISER                   ; ZYLON CRUISER
11393                 .BYTE SHAP.ZCRUISER                   ; ZYLON CRUISER
11394                 .BYTE SHAP.ZFIGHTER                   ; ZYLON FIGHTER
11395
11396 ;*** Zylon flight pattern table ************************************************
11397 ZYLONFLPATTAB   .BYTE 4                               ; Flight pattern 4
11398                 .BYTE 4                               ; Flight pattern 4
11399                 .BYTE 0                               ; Attack Flight Pattern 0
11400                 .BYTE 0                               ; Attack Flight Pattern 0
11401                 .BYTE 0                               ; Attack Flight Pattern 0
11402                 .BYTE 1                               ; Flight pattern 1
11403                 .BYTE 0                               ; Attack Flight Pattern 0
11404                 .BYTE 0                               ; Attack Flight Pattern 0
11405
11406 ;*** Zylon velocity table ******************************************************
11407 ZYLONVELTAB     .BYTE 62                              ; +62 <KM/H>
11408                 .BYTE 30                              ; +30 <KM/H>
11409                 .BYTE 16                              ; +16 <KM/H>
11410                 .BYTE 8                               ;  +8 <KM/H>
11411                 .BYTE 4                               ;  +4 <KM/H>
11412                 .BYTE 2                               ;  +2 <KM/H>
11413                 .BYTE 1                               ;  +1 <KM/H>
11414                 .BYTE 0                               ;   0 <KM/H>
11415                 .BYTE 0                               ;   0 <KM/H>
11416                 .BYTE NEG!1                           ;  -1 <KM/H>
11417                 .BYTE NEG!2                           ;  -2 <KM/H>
11418                 .BYTE NEG!4                           ;  -4 <KM/H>
11419                 .BYTE NEG!8                           ;  -8 <KM/H>
11420                 .BYTE NEG!16                          ; -16 <KM/H>
11421                 .BYTE NEG!30                          ; -30 <KM/H>
11422                 .BYTE NEG!62                          ; -62 <KM/H>
11423
11424 ;*** PLAYFIELD colors (including PLAYFIELD colors during DLI) ******************
11425 PFCOLORTAB      .BYTE $A6                             ; PF0COLOR    = {GREEN}
11426                 .BYTE $AA                             ; PF1COLOR    = {LIGHT GREEN}
11427                 .BYTE $AF                             ; PF2COLOR    = {VERY LIGHT GREEN}
11428                 .BYTE $00                             ; PF3COLOR    = {BLACK}
11429                 .BYTE $00                             ; BGRCOLOR    = {BLACK}
11430                 .BYTE $B8                             ; PF0COLORDLI = {LIGHT MINT}
11431                 .BYTE $5A                             ; PF1COLORDLI = {MEDIUM PINK}
11432                 .BYTE $FC                             ; PF2COLORDLI = {LIGHT ORANGE}
11433                 .BYTE $5E                             ; PF3COLORDLI = {LIGHT PINK}
11434                 .BYTE $90                             ; BGRCOLORDLI = {DARK BLUE}
11435
11436 ;*** Vicinity mask table. Confines coordinates of space objects in sector ******
11437 VICINITYMASKTAB .BYTE $FF                             ; <= 65535 ($FF**) <KM>
11438                 .BYTE $FF                             ; <= 65535 ($FF**) <KM>
11439                 .BYTE $3F                             ; <= 16383 ($3F**) <KM>
11440                 .BYTE $0F                             ; <=  4095 ($0F**) <KM>
11441                 .BYTE $3F                             ; <= 16383 ($3F**) <KM>
11442                 .BYTE $7F                             ; <= 32767 ($7F**) <KM>
11443                 .BYTE $FF                             ; <= 65535 ($FF**) <KM>
11444                 .BYTE $FF                             ; <= 65535 ($FF**) <KM>
11445
11446 ;*** Movement probability of sector types in Galactic Chart ********************
11447 MOVEPROBTAB     .BYTE 0                               ; Empty sector    0% (  0:256)
11448                 .BYTE 255                             ; 1 Zylon ship  100% (255:256)
11449                 .BYTE 255                             ; 2 Zylon ships 100% (255:256)
11450                 .BYTE 192                             ; 3 Zylon ships  75% (192:256)
11451                 .BYTE 32                              ; 4 Zylon ships  13% ( 32:256)
11452
11453 ;*** Galactic Chart sector offset to adjacent sector ***************************
11454 COMPASSOFFTAB   .BYTE -16                             ; NORTH
11455                 .BYTE -17                             ; NORTHWEST
11456                 .BYTE -1                              ; WEST
11457                 .BYTE 15                              ; SOUTHWEST
11458                 .BYTE 16                              ; SOUTH
11459                 .BYTE 17                              ; SOUTHEAST
11460                 .BYTE 1                               ; EAST
11461                 .BYTE -15                             ; NORTHEAST
11462                 .BYTE 0                               ; CENTER
11463
11464 ;*** Homing velocities of photon torpedoes 0..1 depending on distance to target 
11465 HOMVELTAB       .BYTE 0                               ;  +0 <KM/H>
11466                 .BYTE 8                               ;  +8 <KM/H>
11467                 .BYTE 16                              ; +16 <KM/H>
11468                 .BYTE 24                              ; +24 <KM/H>
11469                 .BYTE 40                              ; +40 <KM/H>
11470                 .BYTE 48                              ; +48 <KM/H>
11471                 .BYTE 56                              ; +56 <KM/H>
11472                 .BYTE 64                              ; +64 <KM/H>
11473
11474 ;*** PLAYER shape color table (bits B7..4 of color/brightness) *****************
11475 PLSHAPCOLORTAB  .BYTE $50                             ; PHOTON TORPEDO          = {PURPLE}
11476                 .BYTE $00                             ; ZYLON FIGHTER           = {GRAY}
11477                 .BYTE $20                             ; STARBASE RIGHT          = {ORANGE}
11478                 .BYTE $20                             ; STARBASE CENTER         = {ORANGE}
11479                 .BYTE $20                             ; STARBASE LEFT           = {ORANGE}
11480                 .BYTE $00                             ; TRANSFER VESSEL         = {GRAY}
11481                 .BYTE $A0                             ; METEOR                  = {GREEN}
11482                 .BYTE $00                             ; ZYLON CRUISER           = {GRAY}
11483                 .BYTE $00                             ; ZYLON BASESTAR          = {GRAY}
11484                 .BYTE $9F                             ; HYPERWARP TARGET MARKER = {SKY BLUE}
11485
11486 ;*** PLAYER shape brightness table (bits B3..0 of color/brightness) ************
11487 PLSHAPBRITTAB   .BYTE $0E                             ; ##############..
11488                 .BYTE $0E                             ; ##############..
11489                 .BYTE $0E                             ; ##############..
11490                 .BYTE $0C                             ; ############....
11491                 .BYTE $0C                             ; ############....
11492                 .BYTE $0C                             ; ############....
11493                 .BYTE $0A                             ; ##########......
11494                 .BYTE $0A                             ; ##########......
11495                 .BYTE $0A                             ; ##########......
11496                 .BYTE $08                             ; ########........
11497                 .BYTE $08                             ; ########........
11498                 .BYTE $08                             ; ########........
11499                 .BYTE $06                             ; ######..........
11500                 .BYTE $06                             ; ######..........
11501                 .BYTE $04                             ; ####............
11502                 .BYTE $04                             ; ####............
11503
11504 ;*** PHOTON TORPEDO LAUNCHED noise bit and volume (stored in reverse order) ****
11505 NOISETORPVOLTAB .BYTE $8A                             ; ##########.....
11506                 .BYTE $8F                             ; ###############
11507                 .BYTE $8D                             ; #############..
11508                 .BYTE $8B                             ; ###########....
11509                 .BYTE $89                             ; #########......
11510                 .BYTE $87                             ; #######........
11511                 .BYTE $85                             ; ######.........
11512                 .BYTE $83                             ; ###............
11513
11514 ;*** PHOTON TORPEDO LAUNCHED noise frequency table (stored in reverse order) ***
11515 NOISETORPFRQTAB .BYTE $00                             ;
11516                 .BYTE $04                             ;
11517                 .BYTE $01                             ;
11518                 .BYTE $04                             ;
11519                 .BYTE $01                             ;
11520                 .BYTE $04                             ;
11521                 .BYTE $01                             ;
11522                 .BYTE $04                             ;
11523
11524                 .BYTE $07                             ; (unused)
11525
11526                 .BYTE $00                             ; Always 0 for cartridges
11527                 .BYTE $80                             ; On SYSTEM RESET jump to INITCOLD via
11528                 .WORD INITCOLD                        ; Cartridge Initialization Address