View Full Version : NPOT Performance drop
09-19-2006, 01:41 AM
On my ATI HW 1300 (OSX) I get a huge perf drop on NPOT textures when using VBOs and heavy geometry.
Shall the asumption be that using NPOT should give no or littel perf drop in normal cases ?
09-19-2006, 01:52 AM
Current ATI hardware can not really support everything required by the NPOT extension. Really, they only support ARB_texture_rectangle, so NPOT is just taking care of the coordinate denormalization for you, which is nice to have sometimes.
So, if you use any texture state that can not be supported by ARB_texture_rectangle (such as mipmaps, or most wrap modes) then you will drop to software rasterization.
You can avoid this software fallback on Mac OS X by setting the NoRecovery bit in your pixel format, you will just get incorrect rendering if the hardware can't do what you're asking. And you can detect if a given state vector will cause software emulation with a CGLGetParameter query. See this post (http://lists.apple.com/archives/mac-opengl/2005/Nov/msg00149.html) for details.
Side note, the OpenGL spec says nothing about performance. It is OK for some features to be implemented in software (indeed many are) so while this behavior may not be ideal, it is nothing new.
09-19-2006, 02:02 AM
Thanx a lot !
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