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From: kevinf@infmx.UUCP (Kevin Franden)
Newsgroups: comp.sys.ibm.pc
Subject: Re: VGA, direct memory access
Summary: Use BIOS, it's easier
Keywords: How to...?
Message-ID: <953@infmx.UUCP>
Date: 27 Feb 89 21:05:07 GMT
References: <4479@freja.diku.dk>
Organization: Informix Software Inc., Menlo Park, CA.
Lines: 29

In article <4479@freja.diku.dk>, tbea@freja.diku.dk (Thomas Edlund Andersen) writes:
> 
>  I have a VGA graphics system in my PS2/50, and wants to write some fast
> video rutines for mode E (640 * 200 * 16). Therefore I would like to let
> the CPU write directly to the memory for the screen - but I can only write
>     

If all you are really interested in is fast screen writes, use the BIOS,
it is pretty darn fast and you won't have to worry about all that vert. retrace
crap.

As personal experience, I was trying to draw a box around a place on the screen
for a pop-up library I wrote for Turbo-C (Tiny-Windows if you have seen it or
use it) and used the mose efficent algolrithm I could think of.  Even in C it
was slow so I used assembly to speed it up.  

I used the BIOS call to put a char at the cursor location (it's # escapes me 
right now) and all I had to do was feed it the color,character, and video page 
(you can find the current video with another call, it's easie than assuming) 
This allowed all the flexability I needed as well as taking care of the gory
details of determining the right byte for the char and byte for the color and
the dreaded curse of the retrace flicker.  Above all it is FAST!  To draw a box
around the whole screen was "instantanous". 

hope this helps.

Kevin Franden
Informix Software Inc.
disclaimer("I said what I said and not my employer");