Mail Archives: djgpp/1996/04/17/16:27:12
Xref: | news2.mv.net comp.os.msdos.djgpp:2816
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From: | Robert.Wagner
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Newsgroups: | comp.os.msdos.djgpp
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Subject: | Re: [Q] Homemade 16-bits-per-pixel gfx mode?
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Date: | 16 Apr 1996 21:40:09 -0500
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Organization: | Louisiana State University
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Lines: | 38
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Sender: | pswagn AT unix1 DOT sncc DOT lsu DOT edu
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Message-ID: | <4l1lm9$4n9l@unix1.sncc.lsu.edu>
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NNTP-Posting-Host: | unix1-t.sncc.lsu.edu
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To: | djgpp AT delorie DOT com
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DJ-Gateway: | from newsgroup comp.os.msdos.djgpp
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>I tried this out on my Cirrus VGA, and indeed something happened.. but
>it doesn't seem to be exactly like that. After some experiments, I
>found out that my VGA had entered a mode like this:
>
>- resolution: unchanged (320x200)
>- bpp: unchanged (8bpp)
>- write mode: 'direct', that is, what you write into video ram goes
> directly to the DAC, regardless of the palette settings. Actually,
> the bits in each video ram byte are organized as follows:
>
> IRRBBBGG
> ^ ^
> msb lsb
>
This seemed really fun thing to play around with, and I got the following
results:
after reading the port $3c6 four or more times, the mode you enter
depends apon what value you send to the port. Here are the unique ones I
found:
value written | resulting bitpattern | notes
--------------|-------------------------------------------
0xc0 | IRRBBBGG | same as 0x80
0xc1 | RRRBBGGG | looks nicer, more gradients
0xc8 | greyscale | this is a 256 shade greyscale!
0xc5 | strange greyscale | " with first column redscale(strange)
0xc9 | IRRRGGBB | same as 0x80 but red has 8 shades
0x90 - 0x9f | *RRBBBGG | as 0x80, but entries 128-255 are
| | the same as for normal mode 13h
--------------|----------------------|--------------------------------------
(for all of the "modes" that are 0xc?, c can be replaced with d or e).
Tweaking modes is fun :)
-Rob
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