Sprite Sprite Collision tester

sprspr.asm

.file [name="collision.prg", segments="CODE"]

.segment ZP [start=$02]
	spr_spr: .byte 0 

.segment CODE [start=$0801]
.segment CODE

BasicUpstart2(Start)
//	Our code
Start:
{
	sei
	lda #$ff 
	sta $d015 

	//	copy garbage to sprites for random placement 
	ldx #$00 
spritePos:
	lda $e000,x 
	sta $d000,x 
	inx 
	cpx #$10 
	bne spritePos

waitloop:
	lda $d012 
	cmp #$f3 
	bne waitloop

	//	joy 
	lda #$01  
	sta $d020 
	jsr JoyStick.Poll
	//	move sprites
	lda #$05 
	sta $d020 
	lda #$00 
	sta $d01e
	clc 
	lda $d000
	adc JoyStick.dx 
	sta $d000 
	clc
	lda $d001 
	adc JoyStick.dy
	sta $d001 

	//	grab collision 
	lda $d01e 
	sta spr_spr
	sta $d020 

	jmp waitloop
}


JoyStick:
{
.segment ZP
	dx:	.word 0
	dy:	.byte 0
	bt:	.byte 0
.segment CODE
	Poll:
	{
		lda #$00 
		sta dx+1
		lda $dc00     // get input from port 2 only
		ldy #0        // this routine reads and decodes the
		ldx #0        // joystick/firebutton input data in
		lsr           // the accumulator. this least significant
		bcs djr0      // 5 bits contain the switch closure
		dey           // information. if a switch is closed then it
djr0:
		lsr           // produces a zero bit. if a switch is open then
		bcs djr1      // it produces a one bit. The joystick dir-
		iny           // ections are right, left, forward, backward
djr1:
		lsr           // bit3=right, bit2=left, bit1=backward,
		bcs djr2      // bit0=forward and bit4=fire button.
		dex           // at rts time dx and dy contain 2's compliment
djr2:
    lsr           // direction numbers i.e. $ff=-1, $00=0, $01=1.
		bcs djr3      // dx=1 (move right), dx=-1 (move left),
		inx           // dx=0 (no x change). dy=-1 (move up screen),
djr3:
    lsr           // dy=0 (move down screen), dy=0 (no y change).
		stx dx        // the forward joystick position corresponds
		sty dy        // to move up the screen and the backward
		cpx #$ff
		bne pos
		stx dx+1
	pos:

		sta bt 
		rts           // position to move down screen.
	}
}