It returns a valid pointer, unfortunately. I think it tries to fall back to non direct mode (in fact glXIsDirect(parDisplay, *context) gives false), but then it crashes on some draw call. Someone told me there might be an error in some index buffer that gets skipped by the video card but that causes my game to crash in non direct mode. I'm still not convinced since Amnesia the game crashes as well if I don't belong to the video group. However, glxgears works just fine.
I've found this page: http://src.chromium.org/viewvc/chrom...evision=129314
where they specifically check the hardcoded path "/dev/nvidiactl" if the vendor id is nvidia's one. Right now I'm going down that path. So, I kinda found the answer, but I'm still wondering if this is a driver's bug or what.
I also checked Psychonauts, which triggers an assert:
ERROR: Assert in /home/icculus/projects/psychonauts/Source/CommonLibs/DFGraphics/OpenGLGraphics.cpp, line 2042