Posted By
Csabo
on 2024-11-16
08:13:34
|  Re: Scrolling a bitmap
Sorry, I missed your reply. It's fairly simple to use, you can set it at any time. Here's a basic example of scrolling the entire bitmap up:
org $1001-2
dw $1001
ptr = $D0
db $24,$40,$00,$00,$DE,$31,$2C,$31,$3A,$E2,$31,$2C,$31,$36,$30,$2C
db $39,$39,$2C,$39,$39,$2C,$2C,$2C,$2C,$2C,$31,$31,$3A
db $9E
db "0"+(start/1000)%10,"0"+(start/100)%10,"0"+(start/10)%10,"0"+start%10
db 0,0,0
start sei
;
lda #0
sta ptr
sta ptr+1
;
loop lda #$03
cmp $FF1D
bne *-3
lda #$02
cmp $FF1D
bne *-3
cmp $FF1D
beq *-3
;
lda ptr
sta $FF1B
lda ptr+1
sta $FF1A
;
lda ptr
clc
adc #40
sta ptr
lda ptr+1
adc #0
sta ptr+1
;
jmp loop
;eof
You can download the PRG and run it to see it in action. Adding 40 to the offset is exactly one line, but you can replace that with any number.
This, combined with soft scrolling via $FF06 would allow you to scroll the entire screen, all you have to do is make sure you draw the new part that's being scrolled in. |
