From:	mert0407 AT sable DOT ox DOT ac DOT uk (George Foot)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: direct video memory access?
Date:	13 Mar 1997 17:56:34 GMT
Organization:	Oxford University, England
Message-ID:	<5g9f4i$jh5@news.ox.ac.uk>
References:	<01bc2f90$4d2fb6e0$3350c5a3 AT pni>
NNTP-Posting-Host:	sable.ox.ac.uk
Lines:	36
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

pni (dbmpni AT db DOT za) wrote:
: I am using libgrx2.0 and need to direct video memory access of all video
: memory
: on a hp vectra vl series 4 p/120 with s3 trio 64v+ chipset
: functions needed include
: 1 write block of data to the screen quickly, typically this would be a row
: or column of pixels.
: 2 scroll screen up/down , left/right to achieve waterfall display effect.

: time for these operations is critical as this is a high speed real time
: data logging/display application
: any suggestions ?

What resolution are you running in? How many colours do you need? Not
many, I would presume, for data dispaly - 256 should be fine.

I personally don't know much about GRX, but I seem to remember hearing
that it hasn't been updated for ages. On this note I would suggest moving
over to Allegro, which (CMIIW) is register-compatible with the S3. The
only serious restriction is that it only does 256 colour modes at present. 
However, its graphics are very fast, and (if you want to) you can write
directly to the video memory. There are functions to draw vertical and
horizontal lines, certainly, which are very fast. 

As for the scrolling, if you use mode-X you can use hardware scrolling
with one-pixel accuracy vertically, and four-pixel accuracy horizontally. 

It also has a GUI manager which you may find useful in your application,
and handles mouse and keyboard input in a more powerful way than the libc
routines. 

http://www.talula.demon.co.uk/allegro/ for more information.

-- 
George Foot <mert0407 AT sable DOT ox DOT ac DOT uk>
Merton College, Oxford

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