From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: fast vbe graphics
Date: Mon, 7 Apr 1997 08:19:50 +0100
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Distribution: world
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References: <01IHEKLS7NOI92SA7U AT NICKEL DOT LAURENTIAN DOT CA>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

>I'm trying to get fast vbe 2.0 (with linear frame buffer) graphics
>at 640x480x256 yet am having some difficulties.
>
>for(int i=0; i < 307200; i+=4)
>{
>        temp = ((unsigned long)(video[i])) << 24\
>        + ((unsigned long) (video[i+1])) << 16\
>        + ((unsigned long) (video[i+2])) << 8\
>        + ((unsigned long) (video[i+3]));  

Why such a complicated approach? It's possible that gcc might optimise
that out to a single 32 bit read, but I rather doubt it! It would be a
lot more efficient to write:

    temp = ((unsigned long *)video)[i/4];

>where temp is a unsigned long and I've already done a
>_farsetsel(my_video_ds) but I'm not having much success.

Where does the my_video_ds come from? If you aren't getting anything on
the screen, I'd be suspicious of the code that sets it up. Look at
Allegro for some working LFB routines...

>I know univbe can do about 60 fps on my system at 640x480x356 but
>it uses multiple pages.  Does anyone know how to use multiple pages or

Draw to a part of video memory after the initial 640x480 page (obviously
only going to work if there is enough video ram in the machine!) and
then use the VESA set-display-start function to alter which part of the
memory is visible.


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
Beauty is a French phonetic corruption of a short cloth neck ornament.