full-screen scroll routine (up and down)

git-svn-id: svn://svn.cc65.org/cc65/trunk@119 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/atari/scroll.s

@@ -0,0 +1,164 @@
+;
+; Christian Groessler, June 2000
+;
+; void __fastcall__ scroll (signed char numlines);
+; numlines > 0  scrolls up
+; numlines < 0  scrolls down
+;
+
+	.include	"atari.inc"
+	.importzp	tmp1,tmp4,ptr1,ptr2
+	.import		mul40,_clrscr
+	.export		_scroll
+
+.proc	_scroll
+
+	cmp	#0
+	beq	jmpfin
+;	cmp	#$80
+;	bcc	up
+	bpl	up
+
+;scroll down
+	eor	#$ff
+	clc
+	adc	#1		; make positive
+	sta	tmp1
+
+	cmp	#24		; scroll >= the whole screen?
+	bcc	down_ok
+	jmp	_clrscr
+
+down_ok:lda	SAVMSC
+	clc
+	adc	#<(40*23)
+	sta	ptr1
+	sta	ptr2
+	lda	SAVMSC+1
+	adc	#>(40*23)
+	sta	ptr1+1		; point to last line on screen
+	sta	ptr2+1
+
+	lda	tmp1
+	jsr	mul40
+	sta	tmp4
+	lda	ptr2
+	sec
+	sbc	tmp4
+	sta	ptr2
+	stx	tmp4
+	lda	ptr2+1
+	sbc	tmp4
+	sta	ptr2+1
+
+	lda	#24		; # of lines on screen
+	sec
+	sbc	tmp1		; # of lines to move
+	tax
+
+	;very simple, could be improved
+
+scrold:	ldy	#39		; # of chars on a line - 1
+copy_d:	lda	(ptr2),y
+	sta	(ptr1),y
+	dey
+	bpl	copy_d
+	lda	ptr1
+	sec
+	sbc	#40
+	sta	ptr1
+	bcs	u1
+	dec	ptr1+1
+u1:	lda	ptr2
+	sec
+	sbc	#40
+	sta	ptr2
+	bcs	u2
+	dec	ptr2+1
+u2:	dex
+	bne	scrold
+
+	; fill new scrolled in lines with space
+
+	ldx	tmp1		; # of new lines
+fild:	lda	#0
+	ldy	#39
+fill_d:	sta	(ptr1),y
+	dey
+	bpl	fill_d
+	dex
+jmpfin:	beq	finish
+	lda	ptr1
+	sec
+	sbc	#40
+	sta	ptr1
+	bcs	u3
+	dec	ptr1+1
+u3:	jmp	fild
+
+;scroll up
+up:	sta	tmp1		; # of lines to scroll
+	cmp	#24		; scroll >= the whole screen?
+	bcc	up_ok
+	jmp	_clrscr
+
+	;multiply by 40 (xsize)
+up_ok:	jsr	mul40
+	clc
+	adc	SAVMSC		; add start of screen mem
+	sta	ptr2
+	txa
+	adc	SAVMSC+1
+	sta	ptr2+1
+	lda	SAVMSC+1
+	sta	ptr1+1
+	lda	SAVMSC
+	sta	ptr1
+	lda	#24		; # of lines on screen
+	sec
+	sbc	tmp1		; # of lines to move
+	tax
+
+	;very simple, could be improved
+
+scroll:	ldy	#39		; # of chars on a line - 1
+copy_l:	lda	(ptr2),y
+	sta	(ptr1),y
+	dey
+	bpl	copy_l
+	lda	#40
+	clc
+	adc	ptr1
+	sta	ptr1
+	bcc	l1
+	inc	ptr1+1
+l1:	lda	#40
+	clc
+	adc	ptr2
+	sta	ptr2
+	bcc	l2
+	inc	ptr2+1
+l2:	dex
+	bne	scroll
+
+	; fill new scrolled in lines with space
+
+	ldx	tmp1		; # of new lines
+fill:	lda	#0
+	ldy	#39
+fill_l:	sta	(ptr1),y
+	dey
+	bpl	fill_l
+	dex
+	beq	finish
+	lda	#40
+	clc
+	adc	ptr1
+	sta	ptr1
+	bcc	l3
+	inc	ptr1+1
+l3:	jmp	fill
+
+finish:	rts
+
+.endproc