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View Full Version : bad z-buffer readback/copy performance on ATI



dreld
11-09-2004, 10:45 PM
I asked the same question before, but meanwhile I figured it's only a problem on ATI hardware. Does anyone know how to get a decent readback/copy speed of the z-buffer on ATI hardware. I can achieve maximum 2MB/s :-(, even when I simply glCopyTexSubImage without reading back. Different z-buffer/texture formats don't seem to change much. I use an X800XT board with Catalyst 4.10.

dreld

RAMman
11-10-2004, 07:03 AM
Did you renember to disable antialising ? I get a good copy when I disable, but a very poor one with antialising on.
I belive that is why some ATI demos use pixel programs to store the pixels depth in the alpha channel, so they dont have to mess with this copy.

dreld
11-10-2004, 10:55 PM
Thanks for the reply, unfortunately I have antialiasing/multisampling always switched off anyway . Any other ideas? What's the performance you have seen in your apps? ATI: 20-40MB/s is not that much to ask for, is it?

dreld

RAMman
11-11-2004, 11:56 AM
I havent made any specific tests with the speed of copying the depth.
All I can say is that I do a glCopyTexImage2D() With GL_DEPTH_COMPONENT as the source I copy from. I copy a screensized rectangle of about 1024x768, with no significant slowdown. My app is still running at 100+ fps, depending on the complexity of my other pixel shaders. If I enable altialising in the Catalyst control center, the fps drop to around 6-7.
If you are willing to share your code, I would be happy to test it on my system as well. (Radeon 9800 XT).