From: steve@
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Graphics slow?
Date: 29 Oct 1996 11:21:29 GMT
Organization: IBM UK
Lines: 35
Message-ID: <554pbp$jho@ausnews.austin.ibm.com>
References: <Pine DOT GSO DOT 3 DOT 94 DOT 961027145010 DOT 27194A-100000 AT zippy> <32750C02 DOT 6BC0 AT bnr DOT ca>
Reply-To: schew AT vnet DOT ibm DOT com
NNTP-Posting-Host: steve.csnsg.uk.ibm.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In <32750C02 DOT 6BC0 AT bnr DOT ca>, Brad Spencer <stud73 AT bnr DOT ca> writes:
>I don';t have the original poster's address, so I'll reply here..
>
>> On Sat, 26 Oct 1996, Indrek Mandre wrote:
>> 
>> >    First I must say that I am a beginner in programming djgpp.
stuff deleted.
>> > I ported one of my programs to djgpp and used Allegro (bliting and
>> > double buffering, virtual bitmaps and so on). I tested it and
>> > it was precisely 2 times slower than on a Linux. Is this normal?
>
>"Precisely 2 times slower" sounds suspiciously like you might be waiting
>for retrace twice.  If svgalib's page-flip routine doesn't wait for
>vertical retrace and Allegro's does (I don't know if this is the case),
>then you probably have separate waits in your own code.  This would
>make your program wait an extra frame every time (twice the delay)
>with the new library.  Of course, it could be something more evil :)
>
>-- 
>------------------------------------------------------------------
>Brad Spencer - spencer AT ug DOT cs DOT dal DOT ca - in CS @ Dalhousie University
>    Currently working in a co-op position at Nortel Technology
>[Surprisingly enough, my views are not always those of my company]
>"S.M.A.K.I.B.B.F.B." - A.J. Rimmer | http://ug.cs.dal.ca/~spencer/

Indrek, Brad, I use Allegro for hardware page flipping to create a double
buffered screen and can confirm that the scroll_screen function DOES 
vsync automatically, at least with Allegro 2.1. So, if you are using
scroll_screen, remove any vsync's. 
I do not know what SVGALIB does.

(With 2.0, it vsync'd automatically on my Cirrus at home but not on my S3
equipped PC at work.)  

Steve.