Re: A83: side scrolling background
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Re: A83: side scrolling background
shiftLeft:
ld hl,plotsscreen+767
ld c,64
lineLoop:
ld d,h
ld e,l
ld b,12
xor a
shiftRow:
rl (hl)
dec hl
djnz shiftRow
ld a,(de)
adc a,b
ld (de),a
dec c
jr nz,lineLoop
ret
In a message dated Tue, 30 Jan 2001 1:53:14 AM Eastern Standard Time, Harper Maddox <gte172i@prism.gatech.edu> writes:
<<
i dont see why you want it to loop, but anyways let me see if i can write
an unoptimized routine real quick. If this doesnt work, then one of you
whiz kids should correct me soon.
shiftLeft:
ld hl,plotsscreen
ld b,64
lineLoop:
ld d,(hl)
sla d ; bit we want is carried
xor a
rr a
ld e,a ; preserve offscreen bit
ld c,11
byteLoop:
inc hl
ld a,(hl)
sla a ; shift byte, shifted bit = carry
dec hl
ld d,(hl)
rl d ; shift what was in carry onto this byte
ld (hl),d
inc hl
dec c
jr nz,byteLoop
ld a,(hl)
or e
ld (hl),a
inc hl
djnz lineLoop
ret
At 12:08 AM 1/30/01 -0600, you wrote:
>I'm trying to make a side scrolling game and I'm having some trouble
>figuring out a routine that will scroll the background (a 768 btye picture)
>to the left and have it loop back around to the right. I mean, I can
>scroll it fine but I can't figure out how to make the bits that disappear
>on the left edge reappear on the right edge. I've tried about 6 different
>ways of doing this, and each time I get some stupid little bug. all I need
>is one stupid little routine to scroll the background and have it loop back
>around to the other side. can anyone help?
>
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>>