Xref: news2.mv.net comp.os.msdos.djgpp:2420
From: bram AT gig DOT nl (Bram Stolk)
Newsgroups: comp.os.msdos.djgpp
Subject: [Q] Homemade 16-bits-per-pixel gfx mode?
Date: 3 Apr 1996 10:39:23 GMT
Organization: Euronet Internet
Lines: 35
Message-ID: <4jtkgr$mfv@news.euro.net>
NNTP-Posting-Host: shadwell.gig.nl
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Hello coder,


I want to use a 16 bit per pixel mode (or else 15 bpp).
And I would like a resolution of 320x200. (or something close,
in fact 320x240 would be better because of the square pixels).

However, UNIVBE doesnt give me this mode.

Is it possible to create your own mode, without having to support
all chipsets? 
So I mean: by just using standard VGA stuff?

I already found out the following trick:

  - read the port 3c6 four times
  - write 3c6 once with value 128

What it seems to do, is halve the horiz resolution, and make it
15 bpp.

So if you do this in 320x200x8bpp,
you end up in 160x200x15bpp.
However, sometimes when I do this, the performance of screenwrites
seems to come to a halt. (e.g. 50 times slower than regular modes)

So my question is:
Can you construct a 15/16bpp mode by using a generic piece
of code, that'll work on any SVGA card?
I would like to prevent depending on VBE 2.0 drivers.

   take care,

        Bram Stolk