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genemedic.asm
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genemedic.asm
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; This is Gene Medic version 1.0
; by Jason H. Moore, Ph.D.
; File genemedic.asm
; Last updated 12/29/17
; Compile with DASM genemedic.asm -ogenemedic.bin -f3
; The goal of the game is to save a patient with a common
; disease such as cancer by editing mutations in their
; genes. Mutations can have known or unknown consequences upon
; editing (joystick down) with some revealed by consulting the
; electronic health record powerup (computer) or the scientific
; literature (text) power ups (joystick up). Each gene edit costs
; money that can be replenished with the money bag power up.
; The goal is to improve the patient health ("P" top score)
; before the financial resources are exhausted ("$" lower score).
; For more information see http://GeneMedic.org
; Special thanks to Andrew Davies and Darrell Spice for their
; great tutorials that helped with the development of this
; edutainment game. Thanks to countless others who posted
; useful comments and code on various websites and forums
; including the Stella mailing list and AtariAge.com.
; I also found the book "Making games for the Atari 2600"
; by Steven Hugg to be useful. I have tried to comment the code
; as much as I possibly can without writing my own book.
; Programming for the 2600 is not easy! You have been warned :)
; ****************************************************************
; Tell the assembler we are working with the 6502 processor
; ****************************************************************
PROCESSOR 6502
; ****************************************************************
; Include the vcs header file with the 2600 register and
; memory map definitions. Also include the macro file that
; has some useful functions such as 'sleep' used here.
; ****************************************************************
INCLUDE VCS.h
INCLUDE macro.h
; ****************************************************************
; Constants set here
; ****************************************************************
P0HEIGHT = 55 ; height of player 0 sprite in scanlines
PUHEIGHT = 16 ; height of powerup sprite in scanlines
SCHEIGHT = 14 ; height of the score playfield
CYTHEIGHT = 14 ; height of the cytoplasm playfield
DNAHEIGHT = 11 ; height of the DNA helix playfield
HHEIGHT = 36 ; height of the heart playfield
GHEIGHT = 14 ; height of the gene name playfield
JHEIGHT = 14 ; height of the jockey name playfield
XMAX = 150 ; max X position to right for player
XMIN = 5 ; min X position to left for player
P0XSTART = 20 ; player 0 starting X position
P0YSTART = 80 ; player 0 starting Y position
P1RESX = 38 ; player 1 starting X position for research
; powerup - in sleep cycles
P1MONX = 54 ; player 1 starting X position for money
; bag powerup - in sleep cycles
P1EHRX = 22 ; player 1 starting X position for EHR
; powerup - in sleep cycles
M0X = 28 ; missile 0 starting X position for in sleep
; cycles. This M is used to queue position
; of nucleotide to edit triggering tricorder
; graphic above player 0.
; ****************************************************************
; Tell the assembler the memory locations of our game variables.
; ds is a pseudo-op for assembler that stands for 'define space'
; ds 1 = one byte and ds 2 = two bytes. Remember that the 2600
; only has 128 bytes of RAM!
; ****************************************************************
SEG.U variables ; pseudo-op for the assembler
ORG $80 ; the starting location of RAM
P0X ds 1 ; player 0 X coordinate
P0Y ds 1 ; player 0 Y coordinate
P0Pos ds 1 ; byte for P0 fine (high nibble) and
; course (low nibble) horizontal position
P0LineColor ds 1 ; player 0 color slice for that scanline
P0GfxFlag ds 1 ; flag for which P0 graphic to use
; 1 = no tricorder
; 2 = health tricorder [+]
; 3 = harm tricorder [!]
; 4 = unknown tricorder [-]
; 5 = context dependent tricorder [::]
ResearchFlag ds 1 ; flag for drawing the research powerup
; 1 = draw, 0 = don't draw
EHRFlag ds 1 ; flag for drawing the EHR powerup
; 1 = draw, 0 = don't draw
MoneyFlag ds 1 ; flag for drawing the money bag powerup
; 1 = draw, 0 = don't draw
NewLevelFlag ds 1 ; time to draw a new playfield? This gets set
; to 1 when player reaches right side of screen
ScreenFlag ds 1 ; which screen to draw? A or B?
; this help set up alternating screens with
; different playfield graphics for sense
; of movement through the cell
PScore ds 1 ; this is the patient health score
DScore ds 1 ; this is the dollars score
DScoreFLag ds 1 ; flag to indicate whether DScore = 0
; to prevent going negative
ScoreGfx ds 1 ; holds the current score graphics line
UpFlag ds 1 ; flag for joystick moved up (for power ups)
DownFlag ds 1 ; flag for joystick moved down (for edits)
MutationFlag ds 1 ; holds info about nature of mutation
; set each screen by a random number
; 0 = no mutation
; 1 = mutation - known, helpful
; 2 = mutation - known, harmful
; 3 = mutation - unknown, helpful
; 4 = mutation - unknown, harmful
; 5 = mutation - context dependent, helpful
; 6 = mutation - context dependent, harmful
EditFlag ds 1 ; keeps track of successful edits
; so score only modified once per screen
MBUsedFlag ds 1 ; keeps track of whether money bag powerup
; has been used for that screen. Only used once.
WinFlag ds 1 ; this indicates that the player has won the game
LoseFlag ds 1 ; this indicates that the player has lost the game
EndSoundFlag ds 1 ; flag indicating final sound effects are done
; so they only play once at end of game
RandomPU ds 1 ; holds 8-bit pseudo random number for powerups
RandomMut ds 1 ; holds 8-bit pseudo random number for mutations
GameLaunchFlag ds 1 ; a flag for indicating the game has booted.
; this is used to indicate the start screen
; should be drawn until fire button pressed
SFX_LEFT ds 1 ; index for sound effect functions
SFX_RIGHT ds 1 ; index for sound effect functions
; ****************************************************************
; Tell the assembler where the origin (ORG) of the program is
; ROM is memory location $F000 to $FFFF
; ****************************************************************
SEG ; pseudo-op to set current segment
ORG $F000 ; let the assembler know start address
; ****************************************************************
; This initializes the RAM and TIA registers by writing 0s.
; It also initalizes the stack pointer to $FF. This code comes
; from Andrew Davie's tutorial. Note just clearing the RAM did
; not work well on the original 2600 hardware.
; ****************************************************************
Reset
ldx #0 ; load the X register with a 0
txa ; transfer X to accumulator
Clear
dex ; decrement X register
txs ; transfer X to stack pointer
pha ; push accumulator onto stack
bne Clear ; branch to Clear if accumulator != 0
; ****************************************************************
; This initializes the random seed for the GetRandom subroutine
; Using two different random numbers to prevent dependencies
; between powerups and mutations.
; ****************************************************************
SetRandomSeed
lda INTIM ; this is an unknown value
eor #$FF ; XOR to flip bits so seed is not 0
sta RandomPU ; Seed for GetRandomPU
lda INTIM ; this is an unknown value
eor #$FF ; XOR to flip bits so seed is not 0
sta RandomMut ; Seed for GetRandomMut
; ****************************************************************
; This initializes the game launch flag for drawing start screen
; when game is first booted.
; ****************************************************************
lda #1 ; load accumulator with a 1
sta GameLaunchFlag ; set game launch flag to draw start
; screen first time through until
; reset switch is pressed then flag=0
jmp PlayfieldInit ; bypass the next bit of code on boot
; ****************************************************************
; This is marks the place in the code to jump to when starting a
; game after fire button is pressed from start screen.
; ****************************************************************
StartHere
lda #0 ; load accumulator with a 0
sta GameLaunchFlag ; reset game launch flag so start
; screen isn't drawn anymore after
; reset switch is pressed
; ****************************************************************
; This initializes the player and playfield color registers
; ****************************************************************
PlayfieldInit
lda #$80 ; load accumulator with dark blue
sta COLUBK ; store in the background color memory
lda #1 ; load the accumulator with 1
sta CTRLPF ; storing a 1 here indicates a
; reflected playfield
lda #$1E ; Load the player 1 color
sta COLUP1 ; set player 1 color register
; ****************************************************************
; This initializes the player X and Y position.
; ****************************************************************
lda #P0XSTART ; load accumulator with X position
sta P0X ; set P0 starting X position
lda #P0YSTART ; load accumulator with Y position
sta P0Y ; set P0 starting Y position
; ****************************************************************
; This initializes the patient (top) and money (bottom) scores
; that are presented to the player as colors. Brighter yellow for
; the patient score is an indication of health. Brighter yellow
; for the money score means more resources have been spent on the
; patient. The game is over when the max patient score (win), min
; patient score (loss), or max money score (loss) are reached.
; ****************************************************************
lda #1 ; load accumulator with 1
sta PScore ; set left score to 1
lda #1 ; load accumulator with 1
sta DScore ; set left score to 1
; ****************************************************************
; This initializes the game flags for tracking score and powerups.
; Most are set to 0 with only th P0 graphics flag set to 1.
; ****************************************************************
lda #1 ; load accumulator with flag = 1 to start
sta P0GfxFlag ; set player 0 graphic flag = 1
; this draws player without tricorder.
; tricorder comes on when P0 collides
; with M0 that is present when mutation
; flag > 0
lda #0 ; load accumulator with flag = 0 to start
sta UpFlag ; set joystick Up Flag = 0
sta DownFlag ; set joystick Down Flag = 0
sta EHRFlag ; set EHR Flag = 0
sta MoneyFlag ; set Money Bag Flag = 0
sta ResearchFlag ; set Research Flag = 0
sta ScreenFlag ; set Screen Flag = 0
sta EditFlag ; set Edit Flag = 0 to start, no edit
sta MBUsedFlag ; set Money Bag used Flag = 0 to start
sta WinFlag ; set the Win Flag = 0 to start, 1=win
sta LoseFlag ; set the Lose Flag = 0 to start, 1=lose
sta MutationFlag ; set Flag = 0, no mutation first screen
sta EndSoundFlag ; set Flag = 0 until end of game
sta NewLevelFlag ; time to draw new playfield? This gets
; set to 1 when player reaches right side
; of screen
; ****************************************************************
; The first part of a 2600 program is the vertical sync that
; tells the TV to get ready to draw a picture. The CPU needs
; to wait for three scanlines for the TV to get ready. This
; is done with VSYNC to start this process and WSYNC (x2) to
; wait for the scanlines to finish.
; ****************************************************************
VerticalSYNC ; The start of the new frame
; Main game loop starts here
lda #2 ; load the accumulator with a 2
sta VSYNC ; store 2 in VSYNC memory to start
sta WSYNC ; wait for scanline to finish
sta WSYNC ; second WSYNC (need at least 2)
lda #0 ; load the accumulator with a 0
sta VSYNC ; store 0 in VSYNC memory to end
; ****************************************************************
; The second part of a 2600 program is the vertical blank
; with an additional 37 scanlines of time before the screen
; is actually drawn on the TV. Can do some game computations
; here but must count the scanlines to add up to 37 total.
; 37 scanlines at 76 cycles each works out to be 43 ticks of
; the timer. Will set TIM64T to 43 to keep track of cycles.
; Will use this time for horizontal positioning of the sprites.
; Will also use this time for game calculations.
; ****************************************************************
lda #43 ; we have 43 ticks of the timer here
sta TIM64T ; start the timer for VBLANC
GameOverCheck1 ; check win & lose flags for game over
; if game over skip game calculations
; so no player movement during final screen
lda WinFlag ; load accumulator with Win Flag
beq GameOverCheck2 ; check lose flag if win flag = 0
jmp VerticalBLANK ; skip game calcs if flag = 1
GameOverCheck2
lda LoseFlag ; load accumulator with Lose Flag
beq NewLevelCheck ; move on to game calcs if lose flag = 0
jmp VerticalBLANK ; skip game calcs if flag = 1
NewLevelCheck ; time to draw new level with new random
; powerup and gameplay flags?
lda NewLevelFlag ; if flag = 1 then it is a new level
bne NewLevel ; if flag = 0 then do game calculations
jmp CheckWin ; but skip setting new gameplay flags
; using jmp here to avoid error due to
; a branch that is too long.
; the new level flag gets set to 1 when
; the player gets to far right side of PF
NewLevel ; start here when it is a new level
; and new flags need to be set
; e.g. new powerup flags get set here
SetEditFlag ; set this flag to 0 on new level
lda #0 ; load accumulator with a 0
sta EditFlag ; make sure Edit Flag = 0 on new screen
; this flag prevents multiple changes to
; score on same screen.
sta MBUsedFlag ; reset this flag that keeps track of
; whether the money bag powerup was used
sta WSYNC ; wait for finish of scanline
SetScreenFlag ; set the flag used to track which screen
; is drawn for cyto and nuc parts of PF
; this flag alternates between 0 and 1
lda ScreenFlag ; load accumulator with flag value
beq ScreenFlagSet1 ; flag is zero so need to change to 1
ScreenFlagSet0 ; flag = 1 so change to a 0
lda #0 ; load accumulator with a 0
sta ScreenFlag ; flag is 1 so need to change to 0
jmp SetPUFlags ; done setting helix flag
ScreenFlagSet1 ; change this flag to a 1
lda #1 ; load accumulator with a 1
sta ScreenFlag ; flag is 0 so need to change to 1
SetPUFlags ; set new flags for the powerups
lda #0 ; make sure all flags are reset to 0
; when a new level starts
sta EHRFlag ; set flag to 0
sta ResearchFlag ; set flag to 0
sta MoneyFlag ; set flag to 0
jsr GetRandomPU ; generate a random number from 0-255
; number is returned in accumulator
and #%00000011 ; limit number to 0-3
tax ; transfer accumulator to X register
sta WSYNC ; wait for finish of scanline
CheckEHR ; display EHR powerup?
cpx #0 ; if Random=0 then set EHR flag to 1
bne CheckRes ; if != 1 check research powerup
lda #1 ; load accumulator with a 1
sta EHRFlag ; set flag = 1
sta WSYNC ; wait for finish of scanline
CheckRes ; display research powerup?
cpx #1 ; if Random=1 then set research flag to 1
bne CheckMon ; now check money bag powerup
lda #1 ; load accumulator with a 1
sta ResearchFlag ; set flag = 1
sta WSYNC ; wait for finish of scanline
CheckMon ; display money bag powerup?
cpx #2 ; if Random=2 then set money bag flag to 1
bne CheckDone ; done setting powerup flags
lda #1 ; load accumulator with a 1
sta MoneyFlag ; set flag = 1
sta WSYNC ; wait for finish of scanline
CheckDone ; if Random=3 then no powerup
; on that screen and all powerup
; flags = 0
lda #0 ; load accumulator with a 0
sta NewLevelFlag ; set this flag = 0 to reset this flag
; no longer a new level
SetMutFlags ; set new flags for the mutation
lda #0 ; make sure flag is reset to 0
sta MutationFlag ; set flag to 0
jsr GetRandomMut ; generate a random number from 0-255
; number is returned in accumulator
and #%00000111 ; limit number to 0-7
sta MutationFlag ; store value in mutation flag
sta WSYNC ; wait for finish of scanline
CheckWin ; is the game over? winner?
ldx PScore ; load the X register with the patient score
cpx #9 ; is the patient healed?
bne CheckLose1 ; branch if PScore != 9, not healed
lda #1 ; load accumulator with a 1
sta WinFlag ; winner! Set WinFlag = 1
jmp VerticalBLANK ; move on to draw final screen
CheckLose1 ; check for loss based on patient score = 0
sta WSYNC ; wait for finish of scanline
lda PScore ; load accumulator with the patient score
bne CheckLose2 ; branch if PScore != 0
lda #1 ; load accumulator with a 1
sta LoseFlag ; loser! Set LoseFlag = 1
jmp VerticalBLANK ; move on to draw final screen
CheckLose2 ; check for loss based on dollar score = 9
ldx DScore ; load the X register with the patient score
cpx #9 ; is the player out of money?
bne MinDScore ; branch if DScore != 9
lda #1 ; load accumulator with a 1
sta LoseFlag ; loser! Set LoseFlag = 1
jmp VerticalBLANK ; move on to draw final screen
MinDScore ; this keep the DScore from falling below 1
lda DScore ; load X register with DScore value
bne SetM0X ; branch if X != 0
lda #1 ; load accumulator with a 1
sta DScore ; store the 1 in DScore to prevent 0
SetM0X ; setting the X position for missile 0
sleep M0X ; sleep this many cycles to set M0
; in middle of screen
sta RESM0 ; trigger X position for missile 0
; this never changes and is used as
; position marker for player 0
sta WSYNC ; wait for finish of scanline
; next section sets the horizontal
; position of player 1 with unique
; X positions for each powerup.
; no fine positioning needed here
; because P1 is static
SetP1XEHR ; set powerup X pos if EHR flag = 1
lda EHRFlag ; load the accumulator with EHR flag
beq SetP1XRes ; jump to next if flag = 0
sleep P1EHRX ; delay to horizontally position sprite
sta RESP1 ; set sprite X pos by writing to RESP1
sta WSYNC ; wait for finish of scanline
jmp StartHMoveP0 ; go to next section for P0 positioning
SetP1XRes ; set powerup X pos if research flag = 1
sta WSYNC ; wait for finish of scanline
lda ResearchFlag ; load the accumulator with research flag
beq SetP1XMon ; jump to next if flag = 0
sleep P1RESX ; delay to horizontally position sprite
sta RESP1 ; set sprite X pos by writing to RESP1
sta WSYNC ; wait for finish of scanline
jmp StartHMoveP0 ; go to next section for P0 positioning
SetP1XMon ; set powerup X pos if money bag flag = 1
sta WSYNC ; wait for finish of scanline
lda MoneyFlag ; load the accumulator with money bag flag
beq StartHMoveP0 ; jump to next if flag = 0
sleep P1MONX ; delay to horizontally position sprite
sta RESP1 ; set sprite X pos by writing to RESP1
StartHMoveP0 ; process P0 horizontal move here
; this bit of code from Battlezone game
; commonly used for horizontal positioning
sta WSYNC ; wait for finish of scanline
; timing of this WSYNC and next important
; for correct horizontal movement
lda P0X ; load accumulator with P0 X position
sec ; set the carry flag
DivideLoop ; divide by 15
sbc #15 ; subtract 15
bcs DivideLoop ; branch until negative
eor #7 ; calculate the fine offset
asl ; arithmetic shift left
asl
asl
asl
sta RESP0 ; fix the course position
sta WSYNC ; wait for finish of scanline
sta HMP0 ; set the fine offset
CheckMoneyBag ; is the money bag powerup activated?
lda MoneyFlag ; check if money bag powerup present
beq CheckP0M0Col1 ; if=0 then powerup not present
lda UpFlag ; is the jostick up?
beq CheckP0M0Col1 ; if=0 then joystick not up and skip
lda MBUsedFlag ; has the money bag powerul been used?
beq MBUse ; branch to use money bag if flag = 0
jmp CheckP0M0Col1 ; jump because powerup already used
MBUse
dec DScore ; powerup activated - decrease DScore
lda #1 ; load accumulator with a 1
sta MBUsedFlag ; store the 1 in MBUsedFlag so can't use
ldy #sfxPING ; select ping sound effect
jsr SFX_TRIGGER ; execute the sound
CheckP0M0Col1 ; This checks for a P0 - M0 collision
lda #1 ; load the accumulator with a 1
sta P0GfxFlag ; set the P0 graphics flag to
; tricorder off
lda #%01000000 ; load the D6 bit in accumulator
bit CXM0P ; bit compare to what is in col register
bne Collision1 ; branch if collision = 1
jmp VerticalBLANK ; skip to Vertical BLANK if no collision
; using jmp here because branch too long
Collision1
lda MutationFlag ; load accumulator with mutation flag
tax ; transfer accumulator to X register
cpx #7 ; compare X register to 7
bne Collision2 ; branch if != 7
ldx #5 ; change the 7 to a 5
; need to do something with the 7 since
; we only have 6 choices to map below
; this creates a slight excess of context
; dependent mutations that are helpful
; this is ok because I like these best
Collision2
lda DownFlag ; load accumulator with down joystick flag
tay ; transfer accumulator to Y register
cpx #0 ; is there a mutation? no mutation = 0
bne MutationYes ; if yes process type of mutation
jmp MutationDone ; if no jump to mutation done and VBLANK
MutationYes
sta WSYNC ; wait for finish of scanline
MutKnownPos ; known helpful mutation?
cpx #1 ; is mutation flag = 1?
bne MutKnownNeg ; branch if flag != 1
lda #2 ; load the accumulator with 2
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
lda EditFlag ; load edit flag to see if edit already made
beq MKPEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MKPEdit ; let's edit if joystick is down
cpy #1 ; is joystick down? Did a tay earlier
bne MutKnownNeg ; skip if not
inc PScore ; helpful editing has occured, inc score
inc DScore ; money used to edit, inc score
ldy #sfxHELP ; select sound effect for helpful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
jmp MutationDone ; all done - move on to VBLANK
MutKnownNeg ; known harmful mutation?
cpx #2 ; is mutation flag = 2?
bne MutUnknownPos ; branch if flag != 2
lda #3 ; load the accumulator with 3
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
lda EditFlag ; load edit flag to see if edit already made
beq MKNEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MKNEdit ; let's edit if joystick is down
cpy #1 ; is joystick down?
bne MutUnknownPos ; skip if not
dec PScore ; harmful editing has occured, dec score
inc DScore ; money used to edit, inc score
ldy #sfxHARM ; select sound effect for harmful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
jmp MutationDone ; all done - move on to VBLANK
MutUnknownPos ; unknown positive mutation - player must guess
; or use research powerup to reveal effect
cpx #3 ; is mutation flag = 3?
bne MutUnknownNeg ; branch if flag != 3
lda ResearchFlag ; now check if research powerup present
beq MUPP04 ; if=0 then powerup not present
; and player doesn't know type of mutation
lda UpFlag ; is the jostick up?
beq MUPP04 ; if=0 then not up and draw tricorder 4
; with symbol for unknown mutation
lda #2 ; load the accumulator with 2
sta P0GfxFlag ; set the P0 graphics flag
; to have right helpful tricorder visible
jmp MUPP02 ; skip the next section
MUPP04 ; draw the neutral tricorder since
; mutation unknown to player
lda #4 ; load the accumulator with 4
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
MUPP02
lda EditFlag ; load edit flag to see if edit already made
beq MUPEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MUPEdit ; let's edit if joystick is down
cpy #1 ; is joystick down?
bne MutUnknownNeg ; skip if not
inc PScore ; helpful editing has occured, inc score
inc DScore ; money used to edit, inc score
ldy #sfxHELP ; select sound effect for helpful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
jmp MutationDone ; all done - move on to VBLANK
MutUnknownNeg ; unknown positive mutation - player must guess
; or use research powerup to reveal effect
cpx #4 ; is mutation flag = 4?
bne MutContextPos ; branch if flag != 4
lda ResearchFlag ; now check if research powerup present
beq MUNP04 ; if=0 then powerup not present
; and player doesn't know type of mutation
lda UpFlag ; is the jostick up?
beq MUNP04 ; if=0 then not up and draw tricorder 4
; with symbol for context-dependent mutation
lda #3 ; load the accumulator with 3
sta P0GfxFlag ; set the P0 graphics flag
; to have right helpful tricorder visible
jmp MUNP03 ; skip the next section
MUNP04 ; draw the neutral tricorder since
; mutation unknown to player
lda #4 ; load the accumulator with 4
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
MUNP03
lda EditFlag ; load edit flag to see if edit already made
beq MUNEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MUNEdit ; let's edit if joystick is down
cpy #1 ; is joystick down?
bne MutContextPos ; skip if not
dec PScore ; harmful editing has occured, dec score
inc DScore ; money used to edit, inc score
ldy #sfxHARM ; select sound effect for harmful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
jmp MutationDone ; all done - move on to VBLANK
MutContextPos ; context-dependent positive mutation
; player must guess or use EHR powerup
cpx #5 ; is mutation flag = 5?
bne MutContextNeg ; branch if flag != 5
lda EHRFlag ; now check if EHR powerup present
beq MCPP05 ; if=0 then powerup not present
; and player doesn't know type of mutation
lda UpFlag ; is the jostick up?
beq MCPP05 ; if=0 then not up and draw tricorder 5
; with symbol for context-depentent mutation
lda #2 ; load the accumulator with 2
sta P0GfxFlag ; set the P0 graphics flag
; to have right helpful tricorder visible
jmp MCPP02 ; skip the next section
MCPP05 ; draw the neutral tricorder since
; mutation unknown to player
lda #5 ; load the accumulator with 5
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
MCPP02
lda EditFlag ; load edit flag to see if edit already made
beq MCPEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MCPEdit ; let's edit if joystick is down
cpy #1 ; is joystick down?
bne MutContextNeg ; skip if not
inc PScore ; helpful editing has occured, inc score
inc DScore ; money used to edit, inc score
ldy #sfxHELP ; select sound effect for helpful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
jmp MutationDone ; all done - move on to VBLANK
MutContextNeg ; context-dependent negative mutation
; player must guess or use EHR powerup
cpx #6 ; is mutation flag = 6?
bne MutationDone ; branch to done if flag != 6
; this allow nothing to happen when flag = 7
lda EHRFlag ; now check if EHR powerup present
beq MCNP05 ; if=0 then powerup not present
; and player doesn't know type of mutation
lda UpFlag ; is the jostick up?
beq MCNP05 ; if=0 then not up and draw tricorder 5
; with symbol for context-depentent mutation
lda #3 ; load the accumulator with 3
sta P0GfxFlag ; set the P0 graphics flag
; to have right helpful tricorder visible
jmp MCNP03 ; skip the next section
MCNP05 ; draw the neutral tricorder since
; mutation unknown to player
lda #5 ; load the accumulator with 5
sta P0GfxFlag ; set the P0 graphics flag
; to have right tricorder visible
MCNP03
lda EditFlag ; load edit flag to see if edit already made
beq MCNEdit ; branch if edit = 0
jmp MutationDone ; otherwise we are done
MCNEdit ; let's edit if joystick is down
cpy #1 ; is joystick down?
bne MutationDone ; skip if not
dec PScore ; harmful editing has occured, dec score
inc DScore ; money used to edit, inc score
ldy #sfxHARM ; select sound effect for harmful edit
jsr SFX_TRIGGER ; execute the sound
lda #1 ; load accumulator with a 1
sta EditFlag ; reset edit flag = 1 to indicate no more
; edits this level
sta WSYNC ; wait for finish of scanline
MutationDone ; all done checking mutations
sta CXCLR ; clear the collision registers
sta WSYNC ; wait for finish of scanline
VerticalBLANK ; The finish vertical blank loop
; This burns the scanlines left over
lda INTIM ; load timer value into accumulator
bne VerticalBLANK ; loop if timer not zero
sta WSYNC ; wait for scanline to finish
sta HMOVE ; finalize the horizontal move of P0
; this triggers execution of motion
; degree of move controlled by HMP0/1
; must be done at this point in code
sta WSYNC ; wait for scanline to finish
sta VBLANK ; store 0 in VBLANK memory to end
; and start drawing the picture by
; turning the TV beam on
; ****************************************************************
; The third part of a 2600 program is the screen drawing
; routine that is often called the kernel. This is where
; the players, missiles, and playfield are drawn. There
; are 192 scanlines to be drawn with 228 color clocks per line.
; There are 192 * 228 = 43,776 color clocks. There are 3
; machine cycles per color clock. This give 14,592 machine
; cycles. Dividing this by 64 gives 228 timer ticks. So, we store
; 228 in TIM64T to start the timer that is used to draw screen.
; We are using the Y register to keep track of 192 scanlines.
; We will draw the screen in chunks starting with the scores.
; ****************************************************************
ldy #192 ; load the Y register with 192
; this is the first scanline at top
; of the screen
lda #228 ; 228 timer ticks
sta TIM64T ; start the timer
lda #$00 ; load accumulator with PF color
sta COLUPF ; set the PF color to black
lda #%11111111 ; draw solid pattern for initial PF
sta PF0 ; set the PF0 register
sta PF1 ; set the PF1 register
sta PF2 ; set the PF2 register
DrawScreenTop ; Draw very top part of screen in black
dey ; decrement Y to burn a scanline
sta WSYNC ; wait for scanline to finish
cpy #188 ; Have 4 score scanlines passed?
bne DrawScreenTop ; loop until Y = 188 then set up the
; score part of PF
ldx PScore ; Load X with current patient score
lda PScoreColor,x ; use the score to get the PF color
sta COLUPF ; score-based color of PF for patient
dey ; burn scanline 187 to create border
sta WSYNC ; wait for scanline to finish
ldx (#SCHEIGHT-1) ; set up the score line counter
DrawPScore ; Draw score for patient health
lda PatientGfx,x ; Load patient graphics for this line
sta PF1 ; Draw the "P" for patient
SLEEP 21 ; kill time so this is only part of PF
; drawn
lda BlankGfx1,x ; Blank graphics to erase 2nd PF1
sta PF1 ; Draw the blank PF1 graphics
dex ; decrement our line counter
dey ; decrement the Y register
cpy #173 ; Have 14 score scanlines passed?
sta WSYNC ; wait for scanline to finish
bne DrawPScore ; loop until Y = 173 then set up the
; dollar score part of PF
dey ; burn scanline 172 to create border
sta WSYNC ; wait for scanline to finish
lda #$00 ; load accumulator with PF color
sta COLUPF ; set the PF color to black
DrawDivider1 ; Draw 4 scanline black divider between
; the patient and dollar scores
dey ; decrement the Y register