After asking for help (pBuffer pixel problems) in this forum two times I found the reason: it’s an NVidia driver bug and it took me a lot of hours to detect it. To spare you from this ordeal I’m posting some related infos for interested guys (sample application with VisualStudio project available):
Bug appearance:
I detected a bug in my application while rendering in a Pbuffer and then reading the Pbuffer content for further rendering. The Pbuffer containts some “missing pixels” in the drawn GL_QUAD primitive, always near the lower right or upper left corner. At these pixels the clearColor is visible. This effect is reproducable in the simple_pixel sample application of the NVidia SDK 7.0 (with some modifications).
Bug conditions:
These obscure pixels occur when:
- GL_DEPTH_TEST is on
- pixelformat supports multisampling
- viewport, orthovolume and GL_QUAD primitive are sized identically
- special sizes (e.g.400230, 200230, …)
…but not all sizes: For 720*576 everything seems to be okay. - the vertex order of the GL_QUAD primitive is counterclockwise and
starts with upper left vertex (when starting with lower left vertex it’s okay. ).
I know, its hard to believe, but it’s a fact!
Hardware / driver:
The bug occurres on:
GeForce FX5900XT, driver 5303
GeForce FX5900XT, driver 5672
GeForce FX5950Ultra, driver 5303
The bug does NOT occurre on:
GeForce FX5700, driver 5672
GeForce FX5700Ultra, driver 5672
GeForce 4 Ti4200, driver 5303
In other applications the bug also occurred with tesselated polygons.
I’m still looking for a workaround. Any ideas are highly welcome!
Ravo