GLSL geometry- and multipass-shaders (nogo?)

Apprentice
Posts: 11
Joined: 2008.05
Post: #1
Hello,

I am just learning GLSL and would like to clarify couple of things.

1) Geometry Shaders

I tried simple geometry shader "Hello World" with GLSLEditorSample (among with corresponding vertex & fragment shaders). It seems that geometry shader is detected and supported but as soon as it's attached the vertex-shader falls back to software. (alu iMac with ati 2600 pro & Leopard).

What's the case here? The shader-editor doesn't support geometry-unit? Leopard doesn't support it? driver? hardware? I believe R600 does support geometry shaders so that shouldn't be the case here.


2) Multipass shaders
Is there any way to use multipass shaders with Quartz Composer, GLSLEditorSample or older OpenGL Shader Builder ? (i.e. two or more fragment/vertex-shaders at the same time. one getting output fro previous one).

Thank You.

-mcMike
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Luminary
Posts: 5,143
Joined: 2002.04
Post: #2
That card does support geometry shaders, so maybe you're hitting some hardware limitation. Have you got 10.5.2 + LGU1?

(for people without Radeon 2x00s or GeForce 8x00s, 10.5.2 + LGU1 also adds software support for geometry shaders on all renderers).

If you want to chain shaders together I think you'll need to write your own harness. Shouldn't be difficult, given the source to GLSLEditorSample Wink
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Sage
Posts: 1,232
Joined: 2002.10
Post: #3
2600 hardware supports geometry shader, but driver does not yet accelerate it. To be addressed in a future update.

Currently (10.5.2 + LGU1), only GeForce 8+ expose hardware acceleration. All other drivers fall back to software.
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Apprentice
Posts: 11
Joined: 2008.05
Post: #4
OneSadCookie Wrote:That card does support geometry shaders, so maybe you're hitting some hardware limitation. Have you got 10.5.2 + LGU1?

Yes. 10.5.2 and if by LGU1 you refer to Leopard Graphics Update I have that too.

OneSadCookie Wrote:If you want to chain shaders together I think you'll need to write your own harness. Shouldn't be difficult, given the source to GLSLEditorSample Wink
I know but I am still in process to experiment shaders in general with QC and GLSEdit just to learn stuff. I also have to catch up my ancient (1.0) OpenGL-knowledge back to decent level before moving to cocoa+ogl+shaders.
One thing at time Wink

arekkusu; Thanks for info!
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