So slow

OpenGL OpenGL: Advanced Coding
1

Hi,
I’m having a spot of bother with texturing. For some reason using

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );

kills the performance of my app, it eats up 100% of the CPU (as far as I’m aware it’s a hardware process so shouldn’t be touching the CPU that much?) and I’m lucky to get a handfull of frames in a minute. Yet

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );

works fine and hardly touches the CPU. Now I know using GL_LINEAR should make it a little slower, but not that much. Particularly when I can get much better performance doing my own texture filtering in a shader, something I want to avoid in this case as I’m already using a hell of a lot of instructions…I’m running it on an NVIDIA GF6800 with Forceware 81.98 on M$ Windows XP.

Any ideas why this is so slow? :confused:

Thanks

2

Originally posted by Megalomaniac:
Hi,
Any ideas why this is so slow? :confused:

You are probably using texture format for which the hw does not have filtering support so it will fallback into sw emulation.

3

Originally posted by Komat:
You are probably using texture format for which the hw does not have filtering support so it will fallback into sw emulation.
Thanks. Where could I find out what the 6800 supports?

4

Originally posted by Megalomaniac:
[quote]Originally posted by Komat:
You are probably using texture format for which the hw does not have filtering support so it will fallback into sw emulation.
Thanks. Where could I find out what the 6800 supports?[/QUOTE]Look for GPU programming guide on nVidia pages. Probably the most likely format you can use that is not supported with filtering are 32bit floating point textures.

5

This thread talks about how GL_LINEAR is not supported for 32bit float textures.

6

Thought it might be something like that, I can’t really afford to do it in the shader at the moment. Might be able to get away with 16bit though, hmmmmm time for some maths.

Thanks