starfield: some work

2025-03-09 23:29:39 +00:00 · 2021-06-11 22:35:36 -04:00 · 2021-06-11 22:35:36 -04:00 · 0fa717f912
commit 0fa717f912
parent 2babb09b9f
1 changed files with 219 additions and 0 deletions
--- a/graphics/gr/starfield/starbot.s
+++ b/graphics/gr/starfield/starbot.s
@ -0,0 +1,219 @@
+; starfield tiny -- Apple II Lores
+
+; by Vince `deater` Weaver
+
+; actually too fast
+
+; 189 bytes - original
+; 184 bytes - move DIVIDEND to A
+; 173 bytes - move variables to 0 page. limits to 16 stars but that's fine?
+; 171 bytes - adjust random # generator
+; 170 bytes - can do sty zp,x
+
+COLOR		= $30
+
+QUOTIENT	= $FA
+DIVISOR		= $FB
+DIVIDEND	= $FC
+XX		= $FD
+YY		= $FE
+FRAME		= $FF
+
+oldx		= $80
+oldy		= $90
+star_x		= $A0
+star_y		= $B0
+star_z		= $C0
+
+;oldx		= $1000
+;oldy		= $1040
+;star_x		= $2000	; should be 0, not used as we never /0
+;star_y		= $2040
+;star_z		= $2080
+
+
+LORES		= $C056		; Enable LORES graphics
+
+HGR2		= $F3D8
+HGR		= $F3E2
+PLOT		= $F800		; PLOT AT Y,A (A colors output, Y preserved)
+SETGR		= $FB40
+WAIT		= $FCA8		; delay 1/2(26+27A+5A^2) us
+
+small_starfield:
+
+	;0GR:DIMV(64,48):FORZ=1TO48:FORX=0TO64:V(X,Z)=(X*4-128)/Z+20:NEXTX,Z
+
+	jsr	HGR
+
+	; init the X/Z tables
+
+	ldy	#63	; Y==z	 for(z=1;z<64;z++) {
+xloop:
+	ldx	#0	; X==x
+zloop:
+	lda	#$ff
+	sta	QUOTIENT
+;	stx	DIVIDEND
+	sty	DIVISOR
+	txa		; DIVIDEND
+div_loop:
+	inc	QUOTIENT
+	sec
+;	lda	DIVIDEND
+	sbc	DIVISOR
+;	sta	DIVIDEND
+	bpl	div_loop
+
+	; write out quotient
+
+	lda	QUOTIENT
+	pha
+	clc
+	adc	#20
+to_smc:
+	sta	$5F80,X
+
+	inx
+	bpl	zloop	; loop until 128
+
+
+	; reverse and write out negative parts
+
+	ldx	#0
+negative_loop:
+	pla
+	eor	#$ff
+	sec
+	adc	#20
+to2_smc:
+	sta	$5F00,X
+	inx
+	bpl	negative_loop
+
+	dec	to_smc+2
+	dec	to2_smc+2
+
+	dey
+	bne	xloop
+
+
+	;===================================
+	; draw the stars
+	;===================================
+
+	bit	LORES
+	jsr	SETGR
+
+	;===================================
+	; starloop
+
+	;2FORP=0TO5
+big_loop:
+	ldx	#15
+star_loop:
+
+	;==============================
+	; get X/Z
+	;	X=V(A(P),Z(P))
+
+	; position Z
+	lda	star_z,X
+	clc
+	adc	#$20		; tables in $20-$5F
+	sta	xload_smc+2
+	sta	xload2_smc+2
+
+	; get XX
+	ldy	star_x,X
+xload_smc:
+	lda	$5F00,Y
+	sta	XX
+
+	bmi	new_star	; if <0
+	cmp	#40
+	bcs	new_star	; bge >40
+
+	;==============================
+	; get Y/Z
+	;	Y=V(B(P),Z(P))
+
+	; get YY
+
+	ldy	star_y,X
+xload2_smc:
+	lda	$5F00,Y
+	sta	YY
+
+	bmi	new_star	; if <0
+	cmp	#40
+	bcs	new_star	; bge >39
+
+	;Z(P)=Z(P)-1
+	dec	star_z,X
+	bne	draw_star	; if Z!=0, draw star
+
+new_star:
+	;IFX<0ORX>39ORY<0ORY>39ORZ(P)<1THEN
+	;	A(P)=RND(1)*64
+	;	B(P)=RND(1)*64
+	;	Z(P)=RND(1)*48+1:GOTO7
+
+	ldy	FRAME
+	lda	$F000,Y
+	sta	star_x,X	; random XX
+
+	lda	$F001,Y
+	sta	star_y,X	; random YY
+
+	lda	$F002,Y
+	and	#$3f		; random ZZ 0..63
+	ora	#$1		; avoid 0
+	sta	star_z,X
+
+	iny
+	sty	FRAME
+
+	jmp	done_star
+
+draw_star:
+
+	;4 COLOR=0
+	lda	#$00
+	sta	COLOR
+
+	;PLOT O(P),Q(P)
+
+	ldy	oldx,X
+	lda	oldy,X
+	jsr	PLOT		; PLOT AT Y,A
+
+	; COLOR=15
+	dec	COLOR
+
+	;PLOT X,Y
+	; O(P)=X:Q(P)=Y
+
+	ldy	XX
+	sty	oldx,X
+
+	lda	YY
+	sta	oldy,X
+	jsr	PLOT		; PLOT AT Y,A
+
+
+done_star:
+	;7NEXT
+
+	dex
+	bpl	star_loop
+
+	lda	#100
+	jsr	WAIT
+
+	; GOTO2
+	jmp	big_loop
+
+	; for BASIC bot load
+
+	jmp	small_starfield