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1993-04-12
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04/12/93 12:07am
This demo requires a 286+, VGA+, and about 580K+ base memory free.
SOME TECHNICAL NOTES
I know I always used to love it when a coder would put some
hints & tips in his loader (Tran/Ren for one), so I figured I would too.
The demo uses a 1280x200 virtual screen, in 320x200 Mode X. To
widen the screen, you use the Offset Register at port 03D4H, Index 13H.
Mode X is a bit harder to describe, but I can refer you to some Dr. Dobbs
articles that will tell you all about it: July, August and September 1991
issues have a column by Michael Abrash called "Graphics Programming" that
will get you started with Mode X. His version is 320x240, but Mode X is more
than that. It's an entirely different way of addressing video memory. It
allows for 4 pages in regular 320x200 (hence the 1280x200 virtual screen is
possible - and addressable :), 2 pages in 320x400.
Many people often ask me for titles of books, with which to learn
VGA programming... the one I'd most recommend is Programmer's Guide to the
EGA and VGA Cards, by Richard F. Ferraro, published by Addison-Wesley
(ISBN 0-201-57025-4). It's a great book that goes into detail with each of
the VGA registers, and doesn't skip registers that it figures you don't
need to know about, and shouldn't fuck with anyway. Apparently there might
be a new edition coming out (the one I have here is Second Edition), so you
might want to wait for that.
The MOD-playing routines are GoldPlay, by The Code Blasters. It was
a tossup between that, or the STM Interface Kit. I chose the GoldPlay
routines because they support more devices, even though the sound quality
is a bit worse. Eventually I'll get around to writing my own routines, but
right now I simply don't have the time to both code demos, and work on a
music system.
There's a serious lack of information in the demo-coding scene on the
IBM. People are so tight-lipped about the things they develop, that there are
very few demos being produced that are actually worth the time to download
(at least in North America - damn Swedes! :). Share the wealth! The more
you spread useful information, the more demos will be developed. 'Nuff said.
Anyway, if you have some questions, you'll just have to get yourself
on CRiTiCAL MASS :) . Feel free to mail me about anything. I don't profess
to be the God of Demo Coding, but if I can help out a fellow coder in need,
I will.
<T*S> [iCE]
Ottawa, Canada!