From:	Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DJGPP and old VGA feature
Date:	Tue, 26 Aug 2003 08:56:13 CDT
Organization:	Rice University, Houston, TX
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> Long (long...) time ago I was using a very useful feature of DJGPP.
> I'm talking about the linear frame buffer emulation for video cards
> with bank switching function only.
> Now this feature has been removed and I thought it was caused by DPMI
> server (no functions available for doing that).
> But after reading the functions available in DPMI I got the impression
> it could be done, at least a small part.

Using standard DPMI 0.9 features (which are all that are available on
most DPMI servers) you can't emulate this feature.

Using a full DPMI 1.0 server which implements most features you could
do this emulation.

I've also demonstrated how this feature could be implemented using
CWSDPMI.  It was a fun exercise, but it does have a speed penalty so
most people are not interested in it.  There are several good 
libraries that handle this automatically and much faster.

> I think it would be interesting to add a new selector by default,
> maybe called _vga_ds, in addition to _dos_ds, _my_ds, etc.
> Or I could be simply wrong and this method can't be done right now.

Direct access to the vga buffer can be done using near pointers, but
you would still need to do the bank switching yourself.

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