Clipping planes with Cg

OpenGL
1

Hi, I have a problem with using a clipping plane in conjunction with Cg. When I enable the Cg profiles the clipping plane stops working! I recall something about needing special texture shader instructions for a clipping plane to work (“cull_fragment”, I think), but I’m not sure how to enable this from Cg. Anyone else have an idea?

Thanks,

  • Richard
2

Anyone?

3

I’ll move this thread to the shading language forum, where you might get an answer. Next time however, please post Cg questions to www.cgshaders.org.

– Tom

4

I believe user clip planes are subsumed by ARB_FRAGMENT_PROGRAM, which means that you have to implement them yourself if you use a fragment shader, either explicitly (by binding a fragment program) or implicitly (by having CG do it for you).

AFAICR, the KIL instruction is used to implement clipping planes.

5

User clip planes don’t have any interaction with ARBfp.

They should Just Work.

They’re not supported in ARBvp except in position_invariant mode.

Cass

6

I 've resolved this problem on NVidia cards by changing vertex shader with fixed pipeline.Pixel shader work ok with clipplane.So the problem maybe in conflict clipplane implementation with vertex shader.

7

Originally posted by cass:

…
They’re not supported in ARBvp except in position_invariant mode.
Cass

Well, that’s what is specified.
That is true with NVidia.
But, AFAIK, it works with ATi, even without the position_invariant option.
As far as I remember DX shaders have a “phase” keyword to explicitely define the portion of code that change the position of the vertex. The “clipping phase” may be “inserted” there.
So is it API limited or hardware limited ?

Paul

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