Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!decvax!ucbvax!ucsd!sdcc6!sdcc8!cs178abu
From: cs178abu@sdcc8.ucsd.EDU (John Schultz)
Newsgroups: comp.sys.amiga
Subject: Re: Scrolling bitmaps (help needed)
Message-ID: <795@sdcc8.ucsd.EDU>
Date: 23 Feb 88 02:40:56 GMT
References: <595NU105451@NDSUVM1>
Reply-To: cs178abu@sdcc8.ucsd.edu.UUCP (John Schultz)
Organization: University of California, San Diego
Lines: 21
Keywords: Bitmap scroll graphics

In article <595NU105451@NDSUVM1> NU105451@NDSUVM1.BITNET (Walter Reed) writes:
>I would like to do a wrap around scroll on a bitmap.  I tried using
>
>Walter Reed

  For vertical scrolling, allocate a bitmap twice as high as the
display (for 200 lines, allocate a bitmap with a height of 400,
etc).  Set up a Dwidth of 200 lines.  Make the RP handle 400 lines.
You now have a drawing area 400 pixels tall, but you can only see
200 pixels.  Increment RyOffset then call ScrollVPort().
Notice no flicker, incredible speed and smoothness; the result of
hardware scrolling. (you don't need WaitTOF() or WaitBOVP())
  You can't increment RyOffest forever, so you'll have to set
RyOffset back to zero when it is equal to BITMAP HEIGHT / 2 (If your
Bitmap is twice as high as your viewport display).
  The last excersize is left to the reader:  How to handle the reset
situation described above.


  John