glClipPlanes and flickering ..

OpenGL OpenGL: Advanced Coding
1

Hi. I’m using glClipPlane to cut out a box in my scene. Polygons lying on one of the clipPlanes will flicker on/off when I change my viewpoint.Any sugggestions to what I may be doing wrong?

2

Does it looks like z-fighting ? If so, move slitghly the clip plane along its normal, or try to fiddle with polygon offset.

3

Originally posted by ZbuffeR:
Does it looks like z-fighting ? If so, move slitghly the clip plane along its normal, or try to fiddle with polygon offset.

It is z-fighting. I have tried moving the clip plane slightly, it then works fine. The problem is that the box defining the culling is to be moved by the user, so I can’t adjust the clip planes. Is the flickering to be expected?

4

Hi bp,

Yes. This is to be expected. Traditional clipping hardware generates new triangles when it clips and those will produce slightly different interpolated depth.

Note: NVIDIA GeForceFX and QuadroFX hardware is depth-invariant with user clip planes, but this invariance is not mandated by the API.

Thanks -
Cass

5

Thanks Cass.
Helps to know the source of the problem. I’ll try to figure out som ingenious scheme to deal with it.

bp