Re: 16 bit color buffer

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Angus Dorbie (dorbie++at++sgi.com)
Fri, 25 Jun 1999 12:17:08 -0700

Using a luminance alpha visual is the right choice (r & a bits only).

There was a bug with the selection of visuals in performer, so you may
be running into that. It's slightly worrying because you say you appear
to get rgba12 which is not the fastest visual, rgb10 would be
prefferable for speed unrelated to your problem but generally relevant
for other readers.

Try using attributes to choose the visual.

CHeers,Angus.

Christophe Bernardi wrote:
>
> How can I increase the color buffer to 16 bit (I need only Red and
> Alpha) on Performer/opengl app, and on which hardware( IR, OCTANE, O2)?
>
> I made some tests on IR and O2:
>
> 1. with perfly -t 0xvisid and GLFORCEVISUALS set to this file sent by
> Sgi:
>
> 14
> # visualClass level rgb {R,G,B,A}Bits accum{R,G,B,A}Bits double stereo
> indexBits depthBits stencilBits aux msamples mbuffers
> #
> # overlay
> 4 1 1 5 5 5 1 0 0 0 0 0 0 15 0 0 0 0 0
> # multisample
> 4 0 3 16 0 0 16 25 0 0 25 0 0 12 23 8 0 0 0
> 4 0 1 16 0 0 16 0 0 0 0 0 0 24 23 8 0 8 1
> 4 0 1 10 10 10 0 32 32 32 0 1 0 24 16 8 0 8 1
> 4 0 1 8 8 8 8 32 32 32 32 1 0 24 16 8 0 4 1
> 4 0 1 8 8 8 8 0 0 0 0 1 0 24 15 1 0 4 1
> 4 0 1 12 12 12 12 32 32 32 32 0 0 24 16 8 0 4 1
> 4 0 1 10 10 10 0 0 0 0 0 1 0 24 23 1 0 4 1
> 4 0 1 10 10 10 0 25 25 25 0 0 1 30 0 0 0 8 1
> 4 0 1 5 5 5 1 0 0 0 0 1 0 24 15 8 0 4 1
> # truecolor visuals
> 4 0 1 12 12 12 12 32 32 32 32 0 0 24 23 8 0 0 0
> 4 0 1 12 12 12 12 32 32 32 32 1 0 24 23 8 0 0 0
> # pseudocolor visuals
> 3 0 0 0 0 0 0 0 0 0 0 0 0 12 23 8 0 0 0
> 3 0 0 0 0 0 0 0 0 0 0 1 0 12 23 8 0 0 0
>
> but when I read the red buffer it's always 12 bit on IR and 8 on O2.
> i.e. 1/2^12=.000244 precision on IR and 1/2^8 on O2.
>
> I need more information/doc on the format of this file and the relation
> with the output of glxinfo -fbcinfo.
>
> 2. with pbuffer but I don't know how to make the p bit in the drawable
> type for glxinfo -fbcinfo
>
> Remark: on O2 I have these visuals but they don't have Xid
> 0xffffffff -1 ?? . 8 . r . . 8 . . . . . . . . . . . .
> p|P 0x5c
> 0xffffffff -1 ?? . 16 . r . . 16 . . . . . . . . . . . .
> p|P 0x5d
> 0xffffffff -1 ?? . 64 . r . . 16 16 16 16 . . . . . . . . .
> p|P 0x5e
>
> Thanks,
>
> --
> ---------------------------------
> Christophe Bernardi
> Oktal
> 2, Impasse de Boudeville 31100 Toulouse
> Tel: 05 62 11 93 50
> Fax: 05 62 11 50 29
> mailto:gorbalou++at++oktal.fr
> ----------------------------------
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