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dronus
09-19-2005, 01:16 AM
a beginners question
if no GLSL is used, the GPU uses some "standard" pixel/vertex-codes, right? Those which render the standard goraud-shading, textures and the standard GL_LIGHT lights.
So if i place a pixel-shader only in GLSL are there any rules in which way the default data is given?
Is there a chance to know the default vertex or pixel programs generated if no GLSL is used?

Thanks very much

Nicolas Lelong
09-19-2005, 01:52 AM
You can have a look (and use?) at ShaderGen, a tool developed by 3DLabs that generates GLSL code to reproduced fixed-function pipeline given enabled states.

http://developer.3dlabs.com/downloads/shadergen/index.htm

dronus
09-19-2005, 02:43 AM
thanks, this helped much to understand.
i guess i'm right that the real original shading is decided by the GPU itself, so i cannot combine a self written pixel shader alone while leaving gl do the vertex processing or light calculation?

V-man
09-19-2005, 03:28 AM
if no GLSL is used, the GPU uses some "standard" pixel/vertex-codes, right? It's called the fixed pipe (FP) as oppposed to the programmable pipe (PP).
Sometime the FP is called a fixed function.

GPU design information is mostly secret. I suspect that information like this is mostly a guess/rumors. A GPU can have a real FF.

If you upload a fragment shader (this is the term used in GL. Pixels seems incorrect)
but no vs, then the FP runs for the vertex section. You get the "default data" like primary color, secondary color, texcoords.

dronus
09-19-2005, 03:38 AM
ok, that sounds nice, i didn't expected useful information without a vertex shader.
thank very much

Relic
09-19-2005, 04:35 AM
Typo in V-man's post:
"If you upload a fragment shader (this is the term used in GL. Pixels seems incorrect)
but no vs, then the FP runs for the fragment section. You get the "default data" like primary color, secondary color, texcoords as input into your fragment shader.