Re: Infinite Reality, Colour matrix and pfTexEnv Component

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Brian Furtaw (brian++at++sgi.com)
Tue, 21 Jan 1997 11:41:40 -0500

On Jan 21, 3:06pm, Graham Jones wrote:
> Subject: Infinite Reality, Colour matrix and pfTexEnv Component
> Hopefully the answer to these questions should be short and simple, I
> hope someone can help me:
>
> 1) More an OpenGL question than a specific Performer question:
> The glTexImage2D manual page states that RE, RE2 and VTX graphics
> systems do not support colour matrix transformations as textures are
> loaded or read back from texture memory. Does this apply to
> InfiniteReality graphics as well? I think so, but then I may just be
> doing something wrong.

It would mention Inifinite Reality if it was to be included with the RE and
RE2.
Since it does not this feature should work unless a note further down the page
states otherwise.

>
> 2) Performer question - the pfTexEnv::setComponent call allows one
> component of an RGBA texture to be selected and used as a single
> component intensity texture. The manual says that a 16 bit RGBA texture
> could be used to provide 4 independent 4-bit intensity textures - I
> presume this is just an example, am I correct? I want to use a 32bit
> RGBA texture as separate 8 bit intensity textures as an alternative to
> the colour matrix transformation.

You are talking about the select feature read the glTexImage2D man page for the
particulars of this function here are some excerpts from the man page.

...
                 GL_DUAL_ALPHA4_SGIS, GL_DUAL_ALPHA8_SGIS,
                 GL_DUAL_ALPHA12_SGIS, GL_DUAL_ALPHA16_SGIS,
                 GL_DUAL_LUMINANCE4_SGIS, GL_DUAL_LUMINANCE8_SGIS,
                 GL_DUAL_LUMINANCE12_SGIS, GL_DUAL_LUMINANCE16_SGIS,
                 GL_DUAL_INTENSITY4_SGIS, GL_DUAL_INTENSITY8_SGIS,
                 GL_DUAL_INTENSITY12_SGIS, GL_DUAL_INTENSITY16_SGIS,
                 GL_DUAL_LUMINANCE_ALPHA4_SGIS, GL_DUAL_LUMINANCE_ALPHA8_SGIS,
                 GL_QUAD_ALPHA4_SGIS, GL_QUAD_ALPHA8_SGIS,
                 GL_QUAD_LUMINANCE4_SGIS, GL_QUAD_LUMINANCE8_SGIS,
                 GL_QUAD_INTENSITY4_SGIS, or GL_QUAD_INTENSITY8_SGIS.

...
I see 4 and 8 bit per component formats listed here so I guess you can split up
an 32bit RGBA texture into four 8bit Intensity textures.
...
     The mapping of components from the canonical RGBA to the internal storage
     formats that begin with GL_DUAL_ and GL_QUAD_ needs to be clarified.
     There are three cases. The first case is for the GL_DUAL_ formats that
     are groups of GL_ALPHA, GL_LUMINANCE, and GL_INTENSITY. The R value goes
     to the first group while the A value goes to the second group. The
     second case is for the GL_DUAL_ formats that are groups of
     GL_LUMINANCE_ALPHA. The R and G values go to the first group while the B
     and A values go to the second group. The third case is for the GL_QUAD_
     formats. The R value goes to the first group, the G value to the second
     group, the B value to the third group, and the A value to the fourth
     group.

>
> Could somebody clarify the situation here,
>
> Thanks in advance,
>
> Graham.
>
> --
> Sharp Laboratories of Europe, Phone: +44-(0)1865-747711
> Oxford Science Park, Fax: +44-(0)1865-714217
> Oxford, OX4 4GA
> England Graham.Jones++at++sharp.co.uk
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>-- End of excerpt from Graham Jones

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