From: arg AT whangomatic DOT freeserve DOT co DOT uk (Andrew R. Gillett)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Vsync!
Date: Thu, 29 Jul 1999 21:33:56 +0100
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In comp.os.msdos.djgpp, Michael Stewart wrote:
> Knutte wrote in message ...
> >A few minutes after I wrote this I tried to force Allegro to use VESA 1.0
> >instead of Autodetect. The Attempt was successful so the problem lies
> within
> >the communication between Allegro and my GFXcard.  Thank you all for the
> >help
> 
> 
> I'd be suprised if that was the case. Any problems with vsync would have
> been sorted out a long time ago.
> 
> This is the `standard' method of waiting for the vertical retrace (I would
> think Allegro will be similar if not the same). Try it and see if this
> works.
> 
> void vsync () {
>   while (inportb (0x3DA) & 8);
>   while (! (inportb (0x3DA) & 8));
> }

I already answered this question quite a while ago. Some video cards 
simply don't support vsync. It is the fault of the video card 
manufacturer. This was done with some video cards several years ago when 
Quake timedemos were an important benchmark. Disabling vsync in Quake 
gives a tiny frame rate improvement. Some video card manufacturers 
deliberately ommitted the vsync facility so that their card would always 
get a 0.1 second timedemo improvement in Quake. Pretty pathetic.

-- 
Andrew Gillett      http://argnet.fatal-design.com/     ICQ: See homepage
"I've always wanted to be a sandcastle." - Chelmer Monkton, Starship Losers