Re: TEXTURE COORDINATES

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Mike Weiblen (mew++at++paradigmsim.com)
Mon, 27 Jul 1998 22:55:04 -0500

Andreas.Ekstrand++at++saab.se wrote:
>
> Hi there!
>
> I don't know if I've missed or forgotten important parts of
> the course in computer graphics a couple of years ago. What
> I do know is that I can't seem to figure out how the S, T,
> R and Q texture coordinates work.
>
> Can someone please enlighten me in this matter? What I want
> to know is what are they for, how are they calculated and
> used? I also would like to understand the texture matrix,

Texture matrices are handy for projected textures, as demonstrated by
/usr/demos/bin/projtex. By grabbing a texture matrix representing the
location of the spotlight, the spot texture can be rendered from the
observer's viewpoint as if it were projected by that spotlight.

This approach is possible because textures coords (STRQ) use the same 4D
homogeneous representation as spatial coords (XYZW). Homogenizing the
coordinates (dividing by Q or W) is what makes perspective happen.

-- mew

-- 
Mike Weiblen                  talkto:972-960-2301 x292
PARADIGM Simulation, Inc.     faxto:972-960-9049
14900 Landmark, Suite 400     mailto:mew++at++paradigmsim.com
Dallas TX 75240               http://www.paradigmsim.com
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