Re: A83: side scrolling background

To: assembly-83@lists.ticalc.org
Subject: Re: A83: side scrolling background
From: "Joe Pemberton" <dArkSk8eR@buffbody.com>
Date: Tue, 30 Jan 2001 20:42:59 -0600
Reply-To: assembly-83@lists.ticalc.org


thanks! =) I never woulda thought of that

----------------------------------------------
Original Message
From: ""<ComAsYuAre@aol.com>
Subject: Re: A83: side scrolling background
Date: Tue, 30 Jan 2001 10:13:53 EST

>
> 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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>
>
> >>
>
>
>
>

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