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Re: [Gnu3dkit-dev] OGL 2.0 shading

From: Philippe C . D . Robert
Subject: Re: [Gnu3dkit-dev] OGL 2.0 shading
Date: Wed, 5 Feb 2003 22:37:53 +0100


I know the interview and I also know Cg (a little, at least), but - or therefore - I think that OpenGL 2.0 SLang will be the way to go when doing OpenGL, not Cg.

For the 3DKit I believe the RenderMan Shader Language will be the best solution, it is more powerful and flexible. But of course it will be possible to implement a 3DKit OpenGL renderer backend using Cg or SLang.

This said, anyone who wants to contribute a Cg based renderer for the 3DKit will be welcome, of course, but it will probably not be me...:-)

BTW the OpenGL 2.0 work makes steady progress (there is a weekly held SIG ARB meeting), the specs are scheduled for Siggraph 2003.


On Tuesday, February 4, 2003, at 09:39  Uhr, Gerard Iglesias wrote:

Philippe C.D. Robert wrote:


did someone play with the shader compiler of the OGL 2.0 proposal form 3DLabs? If yes, could this be used as foundation or starting point for our shader compiler?

I am reading what I can around the shading language, especially I read this QA :

And found this one :

* What's the difference between an "offline" shader language (such as RenderMan) and a "real-time" shader language such as Cg? Why can't the former just be compiled directly to assembly code for GPUs?*

Not only is Cg a "real-time" shader language, Cg has been designed to be hardware friendly and hardware efficient. This means that Cg should run well on most modern GPUs. Cg is like C - C for graphics, or C for GPUs. Cg specifies data types, data connections, and arithmetic and graphics operation primitives that exist in GPUs.

RenderMan is a still higher language and is custom designed for shading, not for optimal execution on GPUs. There are several universities and tool providers who are in the process of developing a compiler that translates from RenderMan shaders to Cg code. That provides the best of both worlds. You get the high level shader focus of RenderMan combined with the runtime compilation and efficient execution of Cg on GPUs.

Cg is also more than a shading language. Cg can be used to program any function that can be run on GPUs, including geometry, physics, collision detection, and also many non-graphics tasks.

The other things are interesting to read also....

And I find their work more visible and active than the one from 3DLabs, didn't see anything new from a long time, while NVIdia promise version for OSX soon.

What do you think about this?



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