st vs uv space

Marcin Tustin

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Jul 31, 2000, 3:00:00 AM7/31/00

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Probably another stupid question, but what is the
difference between the uv texture space, and the st surface space
(in the context of shaders, obviously)? The specification doesn't
seem to say.

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Doug Epps

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Jul 31, 2000, 3:00:00 AM7/31/00

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Marcin Tustin wrote:
>
> Probably another stupid question, but what is the
> difference between the uv texture space, and the st surface space
> (in the context of shaders, obviously)? The specification doesn't
> seem to say.

often times they are the same. (u==s, v==t)

I don't know where else in the spec it is, but in the new (3.2) spec
Table 12.1 lists all the variables predefined in a surface shader and
says:

u,v 'Surface Parameters'
s,t 'Surface Texture Parameters'

so u,v are the 'natural' surface parameters that we all know and love
from patches and NURBS.

s,t are the texture parameters.

most of the time these are the same, unless there is a
RiTextureCoordinates call somewhere that changes them.

RiTextureCoordinates lets you map each 'corner' of surface parameters to
somewhere else in texture space.

Alex Magidow

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Aug 1, 2000, 3:00:00 AM8/1/00

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What does thte RiTextureCoordinate call produce in the RIB file, might I
enquire? I've been driven ever so slightly batty trying to figure this out.

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Doug Epps

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Aug 1, 2000, 3:00:00 AM8/1/00

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Alex Magidow wrote:
>
> What does thte RiTextureCoordinate call produce in the RIB file, might I
> enquire? I've been driven ever so slightly batty trying to figure this out.
>

the c-call
RiTextureCoordinates (0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 1.0, 1.0);
would end up being
TextureCoordinates [0.0 0.0 1.0 0.0 0.0 1.0 1.0 1.0]

and those numbers should be the 'default' (ie map the unit square to the
unit square).

It's an Attribute, so it gets pushed/popped with the graphics state.

all in the spec, pg 42 (pdf page 54).
http://www.pixar.com/products/rendermandocs/toolkit/Toolkit/index.html

Kevin Bjorke

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Aug 2, 2000, 3:00:00 AM8/2/00

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Exactly what is the type of "st"?

I've often been confused by it

"varying float[2]" ??

I ask because it's so often useful to declares multiple ranks of st
parameters, and they inevitably get either written into vectors with a
throwaway third term or pairs of single floats. "st" seems to live in
its own world.

kb

Doug Epps

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Aug 2, 2000, 3:00:00 AM8/2/00

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that should be exactly what it is.
you can also get s/t data onto a primitive by doing 's' and 't'
seperately.