; numlines < 0 scrolls down
;
- .include "atari.inc"
- .importzp tmp1,tmp4,ptr1,ptr2
- .import mul40,_clrscr
- .export __scroll
+ .include "atari.inc"
+ .importzp tmp1,tmp4,ptr1,ptr2
+ .import __mul40,_clrscr
+ .export __scroll
-.proc __scroll
+.proc __scroll
- cmp #0
- beq jmpfin
-; cmp #$80
-; bcc up
- bpl up
+ 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
+ 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
+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 ; carry is cleared by __mul40
+ 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
projects / cc65 / blobdiff