asteroids-7800/JOY.S

*         2040    180684
*
** JOY.S **
** ASTEROIDS FOR THE ATARI 3600 **
** THIS FILE CONTAINS THE JOYSTICK HANDLING ROUTINE. **

JOY:
	LDX	PLAYER
	LDA	STATE,X		;CHECK IF SHIP IS OK
	BEQ	EXECJOY		;ONLY CHECK JOYSTICK IF OK
	RTS

EXECJOY:
	LDX	OFFPLAY2	;POWER STEERING BABY!
	LDA	XVELH+24,X	;CALCULATE RATE OF TURN
	BPL	ZSTTEMP		;A VELOCITY DEPENDENT VALUE
	EOR	#$FF
	CLC
	ADC	#1
ZSTTEMP:
	STA	TEMP
	LDA	YVELH+24,X
	BPL	ZADDTEMP
	EOR	#$FF
	CLC
	ADC	#1
ZADDTEMP:
	CLC
	ADC	TEMP
	STA	TEMP
	LDA	#9
	SBC	TEMP
	STA	TEMP

	LDX	PLAYER		  ;CHECK HYPERSPACE
	LDA	HYPBUT1,X
	BMI	LDSWCH
	JSR	HYPERSPC

LDSWCH:
	LDA	SWCHAVAL	;GET JOYSTICK INPUT
	LDX	PLAYER
	BEQ	JOYONE
	ASL			;IF PLAYER2 THEN SHIFT 4 MORE
	ASL
	ASL
	ASL
JOYONE:
CKWEST:
	ASL			;SHIFT MSB INTO CARRY
	PHA			;SAVE ACC
	BCS	CKEAST		;IF SET THEN NEXT, ACTIVE LOW
	JSR	ROTLEFT		;CLEAR, ROTATE LEFT
CKEAST:
	PLA			;RESTORE ACC
	ASL			;CHECK WEST BIT
	PHA			   ;SAVE ACC
	BCS	CKSOUTH		;IF SET THEN NEXT
	JSR	ROTRIGHT	;CLEAR, ROTATE RIGHT
CKSOUTH:
	PLA
	ASL
	PHA
	BCS	CKNORTH
	JSR	DAMPX
	JSR	DAMPY
CKNORTH:
	PLA			;RESTORE ACC
	ASL			;CHECK NORTH BIT
	BCS	DAMPTHR		;IF SET THEN DAMP
	BCC	ADDTHRST	;IF CLEAR THEN THRUST


*	    ROTATE SHIP ROUTINES
ROTRIGHT:
	LDA	SHIPDIR,X
	SEC
	SBC	TEMP
	JMP	SETSDIR

ROTLEFT:
	LDA	SHIPDIR,X
	CLC
	ADC	TEMP
SETSDIR:
	STA	SHIPDIR,X
	LDY	OFFPLAY2
	LSR
	LSR
	LSR
	AND	#$FE
	CLC
	ADC	#SHIP1&255
	STA	ACYC+24,Y
	RTS

*	    DAMPEN THRUST ROUTINE
DAMPTHR:
	LDA	MODE		;IN ONE-AT-A-TIME PLAY,
	CMP	#01		; (I.E., MODES $FF AND $00),
	BMI	DAMPTN		; DON'T WORRY ABOUT OTHER PLAYER
	LDA	STATE		;ELSE MAKE SURE BOTH PLAYERS ARE OK.
	ORA	STATE+1		; IF EITHER IS NOT, IT MUST BE THE
	BNE	DAMPTN		; OTHER ONE! GO ON AS IF ONLY 1 IS OK.
	LDA	SWCHAVAL	;ELSE MAKE SURE ONLY ONE THRUST TUNE IS
	AND	THRBITS,X	; EVER PLAYING AT A TIME;
	BEQ	NODAMPTN	; (IF = 0, THEN *HE* IS THRUSTING)
DAMPTN:
	LDA	#$11		;DAMP THRUST TUNE
	JSR	KILLTUNE	; (GET RID OF THE TUNE)
NODAMPTN:

	LDA	PLAYER
	ASL
	ASL
	TAY
	LDA	#$00
	STA	SOFTCOLR+1,Y
	JSR	DAMPX
	JSR	DAMPY

*	    CHECK THE FIRE BUTTON
CHKFIRE:
	LDX	PLAYER
	LDA	FIREBUT1,X
	BMI	FRESET
	LDA	FIRESTAT,X
	BNE	JOYBYE
	JMP	DNSHOT

FRESET:
	LDA	#0
	STA	FIRESTAT,X
JOYBYE:
	RTS

*	    ADD THRUST ROUTINE
ADDTHRST:
	LDA	#$11		;ADD THRUST SOUND
	JSR	DOTUNE2		;ONLY IF NOT ALREADY PLAYING

	LDA	PLAYER		;CHANGE COLOR OF THRUST FLAME
	ASL
	ASL
	TAY
	LDA	#$4F
	STA	SOFTCOLR+1,Y

	LDX	PLAYER
	LDA	SHIPDIR,X
	LSR
	LSR
	LSR
	LSR
	TAY

	LDX	OFFPLAY2
	LDA	XVELL+24,X
	STA	TEMP+1
	LDA	XVELH+24,X
	LSR
	ROR	TEMP+1
	LSR
	ROR	TEMP+1
	LSR
	ROR	TEMP+1
	LSR
	ROR	TEMP+1

	LDA	YVELL+24,X
	STA	TEMP+2
	LDA	YVELH+24,X
	LSR
	ROR	TEMP+2
	LSR
	ROR	TEMP+2
	LSR
	ROR	TEMP+2
	LSR
	ROR	TEMP+2

XTHRUST:
	LDA	MAXVECT,Y
	BPL	POSOXVEL

NEGOXVEL:
	LDX	TEMP+1
	BPL	ADDXVEL
	CMP	TEMP+1
	BCC	ADDXVEL
	BCS	DODAMPX

POSOXVEL:
	LDX	TEMP+1
	BMI	ADDXVEL
	CMP	TEMP+1
	BCS	ADDXVEL

DODAMPX:
	JSR	DAMPX
	JMP	YTHRUST

ADDXVEL:
	LDA	UNITVECT,Y
	ASL
	ASL
	ASL
	LDX	OFFPLAY2
	CLC
	ADC	XVELL+24,X
	STA	XVELL+24,X
	LDA	XVELH+24,X
	ADC	HUNTVECT,Y
	STA	XVELH+24,X

YTHRUST:
	TYA
	CLC
	ADC	#$10
	TAY

	LDA	MAXVECT,Y
	BPL	POSOYVEL

NEGOYVEL:
	LDX	TEMP+2
	BPL	ADDYVEL
	CMP	TEMP+2
	BCC	ADDYVEL
	BCS	DODAMPY

POSOYVEL:
	LDX	TEMP+2
	BMI	ADDYVEL
	CMP	TEMP+2
	BCS	ADDYVEL

DODAMPY:
	JSR	DAMPY
	JMP	CHKFIRE

ADDYVEL:
	LDA	UNITVECT,Y
	ASL
	ASL
	ASL
	LDX	OFFPLAY2
	CLC
	ADC	YVELL+24,X
	STA	YVELL+24,X
	LDA	YVELH+24,X
	ADC	HUNTVECT,Y
	STA	YVELH+24,X
	JMP	CHKFIRE


DNSHOT:
	LDA	MODE
	CMP	#1		;MODE - 1
	BPL	TDNSHOT		;MODES 1 AND 2 USE TDNSHOT
	LDX	#3
NEXTSHOT:
	LDA	STATUS+28,X
	BMI	THISSHOT
	DEX
	BPL	NEXTSHOT
	RTS

TDNSHOT:
	LDX	PLAYER		;ALLOW 2 SHOTS PER
	BEQ	TPLAY1		;PLAYER1 GETS 0 & 1
	LDX	#2		;PLAYER2 GETS 2 & 3
TPLAY1:
	LDA	STATUS+28,X
	BMI	THISSHOT
	INX
	LDA	STATUS+28,X
	BMI	THISSHOT
	RTS

THISSHOT:
	LDY	PLAYER
	LDA	SHIPDIR,Y
	LSR
	LSR
	LSR
	LSR
	TAY
	LDA	#SHOT
	STA	STATUS+28,X
	LDA	#$EC
	STA	SHOTCNT+2,X
	STX	TEMP		;SAVE X
	LDX	OFFPLAY2
	LDA	XPOSH+24,X
	LDX	TEMP		;RESTORE
	CLC
	ADC	SHNOSEX,Y
	CMP	#XPOSMAX
	BCC	SHXOK
	SBC	#XPOSMAX
SHXOK:
	STA	XPOSH+28,X
	LDX	OFFPLAY2
	LDA	YPOSH+24,X
	LDX	TEMP		;RESTORE
	CLC
	ADC	SHNOSEY,Y
	CMP	#YPOSMAX
	BCC	SHYOK
	SBC	#YPOSMAX
SHYOK:
	STA	YPOSH+28,X
	LDX	OFFPLAY2
	LDA	XPOSL+24,X
	LDX	TEMP
	STA	XPOSL+28,X
	LDX	OFFPLAY2
	LDA	YPOSL+24,X
	LDX	TEMP
	STA	YPOSL+28,X

	LDA	UNITVCTX,Y
	LDX	OFFPLAY2
	CLC
	ADC	XVELH+24,X
	LDX	TEMP
	STA	XVELH+28,X
	LDX	OFFPLAY2
	LDA	XVELL+24,X
	LDX	TEMP
	STA	XVELL+28,X

	LDA	UNITVCTY,Y
	LDX	OFFPLAY2
	CLC
	ADC	YVELH+24,X
	LDX	TEMP
	STA	YVELH+28,X
	LDX	OFFPLAY2
	LDA	YVELL+24,X
	LDX	TEMP
	STA	YVELL+28,X

	LDA	#$0E		;LOAD SOUND FOR HERO SHOTS
	JSR	DOTUNE1

	LDX	PLAYER
	LDA	#1
	STA	FIRESTAT,X
	RTS


HYPERSPC:
	LDX	PLAYER		;WHICH PLAYER
	LDA	STATE,X		;STATE OF PLAYER
	BNE	NOHYPER		;IF OK THEN CONTINUE
	LDA	#2		;STATE FOR HYPERSPACE
	STA	STATE,X
	LDA	#$2C		;$29+3
	STA	TIMER,X
NOHYPER:
	RTS

DAMPX:
	LDX	OFFPLAY2
	LDA	XVELL+24,X	;IS VELOCITY ALREADY ZERO?
	ORA	XVELH+24,X	; (LOW *OR* HIGH IS CHEAP MAGNITUDE)
	BEQ	DAMPXRTS	;YES: NO DAMPING NEEDED

	;COMPUTE XVEL * 3/256
	LDA	XVELL+24,X	;FIRST COMPUTE XVEL/128
	ASL
	STA	TEMP+1
	LDA	XVELH+24,X
	ROL			;ROL IN THE CARRY BIT
	STA	TEMP
	LDA	XVELL+24,X	;THEN ADD IN XVEL / 256
	CLC
	ADC	TEMP+1
	STA	TEMP+1
	LDA	XVELH+24,X
	BPL	XHPOS
	INC	XVELH+24,X	;BORROW TO CORRECT SBC #0 BELOW
XHPOS:
	ADC	TEMP
	STA	TEMP

	LDX	PLAYER
	LDA	XVELLL,X	;ADJUST THE "NOISE" BYTE
	SEC
	SBC	TEMP+1
	STA	XVELLL,X

	LDX	OFFPLAY2
	LDA	XVELL+24,X
	SBC	TEMP
	STA	XVELL+24,X
	LDA	XVELH+24,X
	SBC	#0
	STA	XVELH+24,X

	LDA	#0
	STA	CLAMP
	LDA	XVELH+24,X	;CLAMP OFF TO STOP DRIFT
	BEQ	ZCKPOSX
	CLC
	ADC	#1
	BNE	DAMPXRTS
	LDA	XVELL+24,X	;ZCKMINX
	CMP	#(0-$20) & 255
	BCC	DAMPXRTS
	BCS	ZSETX0
ZCKPOSX:
	LDA	XVELL+24,X
	CMP	#$20
	BCS	DAMPXRTS
ZSETX0:
	LDA	#1
	STA	CLAMP

DAMPXRTS:
	RTS

DAMPY:
	LDX	OFFPLAY2
	LDA	YVELL+24,X	;IS VELOCITY ALREADY ZERO?
	ORA	YVELH+24,X	; (LOW *OR* HIGH IS CHEAP MAGNITUDE)
	BEQ	DAMPYRTS	;YES: NO DAMPING NEEDED

	;COMPUTE YVEL * 3/256
	LDA	YVELL+24,X	;FIRST COMPUTE YVEL/128
	ASL
	STA	TEMP+1
	LDA	YVELH+24,X
	ROL			;ROL IN THE CARRY BIT
	STA	TEMP
	LDA	YVELL+24,X	;THEN ADD IN YVEL / 256
	CLC
	ADC	TEMP+1
	STA	TEMP+1
	LDA	YVELH+24,X
	BPL	YHPOS
	INC	YVELH+24,X	;BORROW TO CORRECT SBC #0 BELOW
YHPOS:
	ADC	TEMP
	STA	TEMP

	LDX	PLAYER
	LDA	YVELLL,X	;ADJUST THE "NOISE" BYTE
	SEC
	SBC	TEMP+1
	STA	YVELLL,X

	LDX	OFFPLAY2
	LDA	YVELL+24,X
	SBC	TEMP
	STA	YVELL+24,X
	LDA	YVELH+24,X
	SBC	#0
	STA	YVELH+24,X

	LDA	YVELH+24,X	;CLAMP OFF TO STOP DRIFT
	BEQ	ZCKPOSY
	CLC
	ADC	#1
	BNE	DAMPYRTS
	LDA	YVELL+24,X	;ZCKMINX
	CMP	#(0-$20) & 255
	BCC	DAMPYRTS
	BCS	ZSETY0
ZCKPOSY:
	LDA	YVELL+24,X
	CMP	#$20
	BCS	DAMPYRTS
ZSETY0:
	LDA	CLAMP
	BEQ	DAMPYRTS
	LDA	#0
	STA	XVELL+24,X
	STA	XVELH+24,X
	STA	YVELL+24,X
	STA	YVELH+24,X

DAMPYRTS:
	RTS

** ROUTINE TO CHECK THE JOYSTICK AND UPDATE SOFTWARE REGISTERS. **
CKJOY:
	LDA	SWCHA		;GET VALUES FROM TIA
	STA	SWCHAVAL	;STORE IN SOFT REGISTERS

	LDX	#1		;DO PLAYERS 1 AND 0
ZNXTRJ:
	JSR	READJOY		;READ HIS JOYSTICK
	DEX
	BPL	ZNXTRJ
	LDA	FIREBUT1	;PLAYER 0 FIRE BUTTON IS STARTBUT
	STA	STARTBUT

	LDA	GAMSTATE	;CHECK IF IN AUTO PLAY STATE
	CMP	#AUTOST
	BNE	CKJOYRTS	;NO.  DON'T DO RANDOM VIOLENCE

PICKJOY:
	LDA	#$FF		;CLEAR ALL BUTTONS
	STA	FIREBUT1
	STA	FIREBUT2
	STA	HYPBUT1
	STA	HYPBUT2

	LDA	FRMCNT		;DON'T ALWAYS DO
	AND	#$0C
	BNE	CKJOYRTS
	LDA	FRMCNT		;ALTERNATE FIRING
	LSR
	AND	#1
	TAX
	LDA	#$7F
	STA	FIREBUT1,X

	JSR	NEWRAND		;RANDOM SHIP MOVEMENT
	AND	#$07
	TAX
	LDA	JOYVALS,X
	STA	SWCHAVAL

CKJOYRTS:
	RTS

* READJOY: READ JOYSTICK/BUTTONS.  ON ENTRY X = PLAYER.  Y IS TRASHED
READJOY:
	LDY	INPT4,X
	BPL	GOTONE		;IF BIT 7 IS LO, OLD-STYLE BUTTON HIT

	LDA	ONEBUT		;ARE WE ALREADY IN OLD-STYLE MODE?
	AND	RJBITS,X
	BNE	GOTONE2		;YES.  GO RIGHT TO ONE-BUTTON HANDLER.

	TXA			;OTHERWISE, COMPUTE INDEX INTO
	ASL			; PADDLE PORTS, FOR PLAYER X,
	TAY			; IN Y (X * 2)

	LDA	INPT4A,Y	;READ LEFT BUTTON
	EOR	#$FF		;INVERT THE SENSE!
	STA	FIREBUT1,X
	LDA	INPT4B,Y	; RIGHT BUTTON
	EOR	#$FF
RJSTOREH:
	STA	HYPBUT1,X

RJRTS:
	RTS

	;HERE ON OLD-STYLE SINGLE BUTTON JOYSTICK PRESS.
GOTONE:
	LDA	ONEBUT		;TURN OFF TWO-PLAYER BIT IMMEDIATELY
	ORA	RJBITS,X	; TO AVOID BURNING OUT HARDWARE
	STA	SWCHB
	STA	ONEBUT		;SAVE THE NEW VALUE
GOTONE2:
	STY	FIREBUT1,X	;Y CONTAINS CONTENTS OF INPT4 NOW
	LDA	#$FF
	STA	HYPBUT1,X	;CLEAR HYPERSPACE BUTTON
	LDA	SWCHAVAL	;CHECK JOYSTICK REGISTER
	AND	JOYTBL,X	; FOR THIS PLAYER'S
	CMP	RJSBITS,X	;  HYPERSPACE BIT
	BNE	RJRTS		;IF BIT NOT LO, THEN NO HYPERSPACE
	LDA	#$7F		;OTHERWISE, SET THE BIT LO
	BNE	RJSTOREH	;BNE = JMP


RJBITS:
	.DC.B	$04,$10		;TWO-PLAYER MODE BITS PER PLAYER
RJSBITS:
	.DC.B	$D0,$0D		;SOUTH JOYSTICK BITS PER PLAYER
THRBITS:
	.DC.B	$01,$10		;NORTH BITS PER *OTHER* PLAYER
JOYVALS:
	.DC.B	$7F,$BF,$EF,$F7,$FB,$FE,$FF,$EE ;AUTOPLAY JOYSTICK VALUES