From: BECman <becman AT cynergy DOT com DOT au>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: [Q]: Allegro scrolling question
Date: Fri, 08 Aug 1997 10:56:20 +1000
Organization: BEC Manufacturing Pty Ltd
Lines: 25
Message-ID: <33EA6EB4.2719@cynergy.com.au>
References: <33E17022 DOT 102F AT cat DOT csiro DOT au> <5sbo6q$iri AT freenet-news DOT carleton DOT ca>
Reply-To: becman AT cynergy DOT com DOT au
NNTP-Posting-Host: cyn0507.cynergy.com.au
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

Paul Derbyshire wrote:
> 
> Jonathon Ralston (j DOT ralston AT cat DOT csiro DOT au) writes:
> > Hello Allegro programmers!
> >
> > I wanted to write a 640 x 480 x 256 horizontal scrolling program, like
> > the ex19.c demo. I increased the screen bitmap size and changed the
> > other screen size variables accordingly.  However, I found that
> > *everything* on the screen was scrolled, including the text line.
> >
> > Is it possible to scroll only *part* of the screen while in an SVGA
> > mode, e.g., a 640 x 400 window?  I noticed that ex19.c uses a mode X
> > modex_split type function.  Does this mean that the split screen
> > text/scrolling only exists in mode X?  Is there a version of
> > scroll_screen() that scrolls only part of the screen, or a BITMAP
> > buffer?
> 
> In SVGA modes? I think the only easy way to do it in SVGA is to
> keep the stuff you want to not scroll in a memory bitmap and
> blit it to the screen after each scroll. Of course it might
> then flicker a bit.

You could use a virtual buffer to create the final image
to be blitted to the "screen" bitmap. This would avoid
the flicker.