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UFO.S
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UFO.S
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* 2035 030784
*
*
** UFO.S **
** ASTEROIDS FOR THE ATARI 3600 **
** THIS FILE CONTAINS THE UFO HANDLING ROUTINE **
**
** TRASHES: X, Y, AC AND FIRST 7 BYTES OF TEMP.
URTS:
RTS
UFO:
LDA STATUS+25 ;CHECK STATUS OF UFO
BMI TOOFAR
JMP NOTNEW ;DON'T INITIALIZE IF ALREADY EXISTS
TOOFAR:
CMP #$FF ;IF HE'S BLOWING UP, DO NOTHING TILL
BNE URTS ; HE'S DEAD.
LDA DIFF ;IF NOVICE THEN NO UFO
BEQ URTS
LDA MODE ;CHECK STATUS OF SHIPS
CMP #1
BMI NOTTEAM
LDA STATE
AND STATE+1
BNE URTS
BEQ BRINGOUT ;BEQ = JMP
NOTTEAM:
LDX PLAYER
LDA STATE,X
BNE URTS
BRINGOUT:
LDA FRMCNT ;EVERY FORTH FRAME
AND #2
BNE URTS
LDX PLAYER
LDA ROCKTOT,X ;DON'T BRING OUT UFO IF NO ROCKS.
BEQ URTS
LDY RTIMER ;DEC RTIMER, BUT PEG AT ZERO
BEQ Z2
DEC RTIMER
Z2:
DEC EDELAY
BNE URTS
INC EDELAY ;HOLD AT ONE
CPY #0 ;DON'T CARE NUM ROCKS IF RTIMER=0
BEQ LOGG
CMP STARTNUM,X ;OR OVER NUMBER TO START
BCS URTS
;NEW UFO TIME!
LOGG:
LDA SDELAY ;EVERY TIME UFO GOES REDUCE SDELAY
SEC
SBC #6
CMP #20
BCC DIES
STA SDELAY
DIES:
LDA SDELAY
STA EDELAY
LDA #$15 ;INITIALIZE SHOT REPEATER
STA USHOTCNT
JSR NEWRAND ;SET Y POSITION TO RANDOM #
LSR ; BETWEEN $10 AND $10+$7F
ADC #$10 ; (KEEP AWAY FROM TOP AND BOTTOM)
STA YPOSH+25
LDX PALTAB+25 ;LOADER MUST USE CORRECT PAL/WIDTH
LDA MODE
CMP #1
BNE ONE
LDY #8
BPL TWO
ONE:
LDA PLAYER ; CHECK SCORE
ASL
ASL
TAY
TWO:
LDA SCORE+1,Y
CMP #2
BCS MRBILL ; IF MORE THAN 30K THAN MR BILL
LDA SDELAY ;IF SDELAY IS BIG THEN SLUGGO
BMI SLUGGO
JSR NEWRAND
STA TEMP
LDA SDELAY
LSR
CMP TEMP
BCS SLUGGO
MRBILL:
INX ;ADD ONE FOR SMALLER WIDTH STAMP
LDY #SMALLUFO
BNE NEWUFO ;UNCONDITIONAL BRANCH
SLUGGO:
LDY #LARGEUFO
NEWUFO:
STY STATUS+25
STX PALS+25
JSR NEWRAND ;GOING RIGHT OR LEFT?
LSR ; SHIFT A RANDOM BIT INTO CARRY
BCC GORIGHT ; IF BIT 0, GO RIGHT TO LEFT
LDA #XPOSMAX+4 ; ELSE LEFT TO RIGHT.
STA XPOSH+25
LDA #(-1)&255 ; XVEL -1 = LEFT TO RIGHT.
BMI STORXVEL
GORIGHT:
LDA #(XPOSMIN-4)&255
STA XPOSH+25
LDA #1 ; XVEL 1 = RIGHT TO LEFT
STORXVEL:
STA XVELH+25
LDA #0 ; LO BYTE OF XVEL SET TO ZERO
STA XVELL+25
BEQ ZYVEL ;INITIALLY UFO HAS ZERO Y VELOCITY
NOTNEW:
LDA FRMCNT
CMP #$FE
BCC NOCHNGY ;CHANGE Y VELOCITY ONLY PERIODICALLY
LDA DIFF ;FOR INTER ALWAYS STRAIGHT ACROSS
CMP #1
BEQ ZYVEL
JSR NEWRAND ;GET NEW RANDOM VALUE
CMP #$AA
BCS MOVEDN ;ONE THIRD OF THE TIME MOVE DOWN
CMP #$55
BCS MOVEUP ;ONE THIRD MOVE UP
;DON'T GO STRAIGHT IF TOO CLOSE TO TOP OR BOTTOM: AVOID CLIPPED UFO
LDA YPOSH+25
CMP #YPOSMAX-20
BCS NOCHNGY
CMP #YPOSMIN+10
BCC NOCHNGY
ZYVEL:
LDA #0 ;ONE THIRD GO STRAIGHT ACROSS
STA YVELH+25
STA YVELL+25
BEQ NOCHNGY
MOVEDN:
LDA #(-1)&255
BMI STORYVEL ;BMI = JMP
MOVEUP:
LDA #1
STORYVEL:
STA YVELH+25 ;STORE Y VELOCITY
LDA #0
STA YVELL+25
NOCHNGY:
LDA XVELH+25 ;CHECK IF UFO GOES OFF THE SCREEN
CLC
ADC XPOSH+25
CMP #XPOSMAX+4 ;UFO GOES PAST RIGHT?
BCC UCHKSHOT ; NO. CHECK IF HE MAY SHOOT.
CMP #(XPOSMIN-3)&255 ;UFO GOES PAST LEFT?
BCS UCHKSHOT ; NO. CHECK IF HE MAY SHOOT.
UFODONE:
LDA #$FF ;UFO HAS GONE OFF SCREEN: NUKE HIM
STA STATUS+25
LDA #$08 ;KILL UFO TUNES
JSR KILLTUNE
LDA #$09
JSR KILLTUNE
RTS
* CHECK TO SEE IF WE SHOULD FIRE NOW
UCHKSHOT:
LDX #1 ;HAVE 2 UFO SHOTS TO USE
UFOSHOT:
LDA STATUS+26,X ;TEST SHOT STATUS
BMI ADDUSHOT ;SEE IF SHOT IS ALREADY ON SCREEN
DEX ;YES, TRY OTHER SHOT
BPL UFOSHOT
BMI UANIMATE ;NO MORE SHOTS, JUMP TO VARY STAMPS
ADDUSHOT:
DEC USHOTCNT ;CHECK COUNTER FOR NEXT SHOT
BNE UANIMATE ;NOT TIME YET, JUMP TO VARY STAMPS
LDA #$20 ;RESET COUNTER
STA USHOTCNT
LDA #SHOT ;STORE STATUS AS SHOT
STA STATUS+26,X
LDA #$EC ;STORE COUNTER VALUE
STA SHOTCNT,X
LDA COLXPOSH+25 ;STORE SHOT POSITION AS CENTER OF UFO
CMP #XPOSMAX
BCC USTXPOS
SBC #XPOSMAX
USTXPOS:
STA XPOSH+26,X
LDA COLYPOSH+25
CMP #YPOSMAX
BCC USTYPOS
SBC #YPOSMAX
USTYPOS:
STA YPOSH+26,X
LDA #00
STA XPOSL+26,X
STA YPOSL+26,X
LDA STATUS+25 ;DETERMINE HOW TO SHOOT
CMP #SMALLUFO
BEQ AIMSHOT ;MR. BILL AIMS HIS SHOTS
JSR NEWRAND ;SLUGGO IS RANDOM
USHOOT:
AND #$1F
TAY
LDA HUSHVCTX,Y
STA XVELH+26,X
LDA USHVCTX,Y
STA XVELL+26,X
LDA HUSHVCTY,Y
STA YVELH+26,X
LDA USHVCTY,Y
STA YVELL+26,X
LDA #$0D ;PLAY UFO SHOT SOUND
JSR DOTUNE
UANIMATE:
LDA FRMCNT ;VARY UFO STAMPS WITH TIME
LSR
LSR
AND #$3 ;MASK ALL BUT 2 LSBITS
LDY STATUS+25 ;WHICH TYPE?
CPY #SMALLUFO
BEQ UANIMSM
ASL ;BIG UFO HAS 2 BYTES PER ANIMATION
CLC
ADC #UFOL1 & 255 ;ADD IN POINTER TO BASE OF LARGE UFO
JMP USTACYC
UANIMSM:
CLC
ADC #UFOS1 & 255
USTACYC:
STA ACYC+25 ;STORE ANIMATION FRAME POINTER
RTS
AIMSHOT:
* INITIALIZE FLAGS FOR OCTANT SELECTION
LDA #0
STA TEMP+2 ;UDXNEG
STA TEMP+3 ;UDYNEG
STA TEMP+4 ;UDIAGNEG
* DETERMINE WHICH SHIP TO SHOOT AT
LDA MODE
CMP #1
BMI ZNOTTEAM ;ISSOLATE CASE OF TEAM PLAY
ZTEAM:
LDA STATE ;SEE IF BOTH ALIVE
AND STATE+1
BEQ PICKSRAN
LDA STATE ;NO, SEE WHICH IS, KNOW AT LEAST 1 IS
BNE AIMSHIP2
AIMSHIP1:
LDY #0 ;AIM AT SHIP 1
BPL COMPVECT ;BPL = JMP
PICKSRAN:
JSR NEWRAND ;PICK A SHIP RANDOMLY
ASL ;WE'RE SUCH ASL'S
BCC AIMSHIP1
AIMSHIP2:
LDY #8 ;AIM AT SHIP 2
BPL COMPVECT ;BPL = JMP HERE
ZNOTTEAM:
LDY OFFPLAY2
* COMPUTE VECTORS
COMPVECT:
LDA COLXPOSH+24,Y
SEC
SBC COLXPOSH+25 ;SUBTRACT UFO'S POSITION TO GET 'DX'
BCS UDXPOS
INC TEMP+2
EOR #$FF
; CLC ;CARRY IS CLEAR ALREADY
ADC #1
UDXPOS:
STA TEMP ;SAVE DX
LDA COLYPOSH+24,Y
SEC
SBC COLYPOSH+25 ;SUBTRACT UFO'S POSITION TO GET 'DY'
BCS UDYPOS
INC TEMP+3
EOR #$FF
; CLC
ADC #1
UDYPOS:
STA TEMP+1 ;SAVE DY
* NORMALIZE VECTOR TO CORRECT FOR ASPECT RATIO. WE ALSO SCALE DOWN TO AVOID
* OVERFLOW. ALSO, FLIP THE VECTOR TO THE FIRST OCTANT (ABOVE THE LINE Y = X).
LSR ;5/8 = 1/2 + 1/8
STA TEMP+5
LSR
LSR
CLC
ADC TEMP+5
CMP TEMP
BCS UDIAGOK ;ON CORRECT SIDE OF DIAGONAL Y = X.
INC TEMP+4 ;NOT ON CORRECT SIDE:
TAY ; SWAP DX AND DY
LDA TEMP
STY TEMP
UDIAGOK:
LSR ;SCALE DY <- DY / 4
LSR
STA TEMP+1
* COMPUTE AND SAVE "3/8 DX", TO BE USED BELOW.
LDA TEMP ;TEMP+6 <- DX/4 + DX/8
LSR
LSR
STA TEMP+5
LSR
CLC
ADC TEMP+5
STA TEMP+6
* COMPUTE CORRECT SECTOR (32TH OF CIRCLE) IN Y.
* FIRST, FIGURE OUT WHICH 16TH OF THE CIRCLE.
* WE USE THE 68.2 DEGREE LINE, 'CAUSE IT'S EASIER TO COMPUTE (ATAN(5/8 / 2/8)).
LDA TEMP ;5/8 = 1/2 + 1/8
LSR
STA TEMP+5
LSR
LSR
CLC
ADC TEMP+5
LDY #0
CMP TEMP+1
BCC SECTOR01
LDY #2 ;SECTOR 2 OR 3
LDA #0
BEQ SECTOR23 ;UNCONDITIONAL BRANCH
SECTOR01:
LDA TEMP
SECTOR23:
CLC
ADC TEMP+6 ;1 + 3/8 = 11/8
CMP TEMP+1
BCC SECTOR02
SECTOR13:
INY
SECTOR02:
STY TEMP
* UNFOLD VECTOR INTO CORRECT OCTANT, QUADRANT AND HALF-SPACE
LDY TEMP+4 ;CHECK UDIAGNEG
BEQ NODIAGN
LDA #7
SEC
SBC TEMP
STA TEMP
NODIAGN:
LDY TEMP+3 ;CHECK UDYNEG
BEQ NODYNEG
LDA #15
SEC
SBC TEMP
STA TEMP
NODYNEG:
LDY TEMP+2 ;CHECK UDXNEG
BEQ NODXNEG
LDA #31
SEC
SBC TEMP
STA TEMP
NODXNEG:
; PERTERB VECTOR BY RANDOM NUMBER OF INDEX NOTCHES.
LDA UFOACC ;COMPUTE UFOACC / 2
LSR
STA TEMP+6
UTOOPOOR:
JSR NEWRAND
LDY TEMP+6
AND UFOPMASK-1,Y ;TABLE IS 1-ORIGIN (Y > 0)
CMP UFOACC
BCS UTOOPOOR ;TOO POOR A SHOT, TRY AGAIN
; CLC ;CARRY IS CLEAR
ADC TEMP ;ADD TO PRECISE VECTOR
SEC
SBC TEMP+6 ;SUBTRACT UFOACC/2 (OFFSET)
JMP USHOOT
UFOPMASK:
.DC.B $03,$07,$07,$0F ;RANGE MASKS FOR RANDOM #'S
* UFO SHOT VECTORS.
HUSHVCTX:
.DC.B $00,$00,$01,$02,$03,$03,$04,$04
.DC.B $04,$04,$04,$03,$03,$02,$01,$00
.DC.B $00,$FF,$FE,$FD,$FC,$FC,$FB,$FB
.DC.B $FB,$FB,$FB,$FC,$FC,$FD,$FE,$FF
USHVCTX:
.DC.B $00,$DB,$AD,$6E,$18,$A3,$0B,$4A
.DC.B $60,$4A,$0B,$A3,$18,$6E,$AD,$DB
.DC.B $00,$26,$54,$93,$E9,$5E,$F6,$B7
.DC.B $A1,$B7,$F6,$5E,$E9,$93,$54,$26
HUSHVCTY:
.DC.B $07,$06,$06,$05,$04,$03,$02,$01
.DC.B $00,$FE,$FD,$FC,$FB,$FA,$F9,$F9
.DC.B $F9,$F9,$F9,$FA,$FB,$FC,$FD,$FE
.DC.B $00,$01,$02,$03,$04,$05,$06,$06
USHVCTY:
.DC.B $00,$DE,$78,$D2,$F3,$E4,$AE,$5E
.DC.B $00,$A3,$53,$1D,$0E,$2F,$89,$23
.DC.B $01,$23,$89,$2F,$0E,$1D,$53,$A3
.DC.B $00,$5E,$AE,$E4,$F3,$D2,$78,$DE
.DC.B $01,$23,$89,$2F,$0E,$1D,$53,$A3
.DC.B $00,$5E,$AE,$E4,$F3,$D2,$78,$DE