I'm experiencing an occasional major slowdown inside glFlush (as told
by GL profiler) - three to five seconds. This is on OS X 10.4.9,
MacBook Pro.
This seems to be related to situations when immediately after depth
pbuffer (for shadowmaps) a regular rect pbuffer (for screenspace
texture) is used; AND the window just got resized so that a new rect
pbuffer was created. But it does not happen always, only occasionally
(but often enough... and 5 second pauses aren't nice).
The sequence of GL activity is like this:
1) activate depth pbuffer
2) render shadow casters into it
3) glFlush
4) glCopyTexSubImage2D to copy depth buffer into it's texture target
5) possibly create screen sized RECT pbuffer (regular rgba format) -
this happens whenever window size changes. In the editor that happens
quite often.
6) activate this RECT pbuffer
7) perform shadow gathering render, using the previous depth texture
to gather shadows in screenspace.
When there's no slowdown, flush takes 100 microseconds or so - which
is ok. But sometimes it takes whole 5 seconds!
My question is: what could cause this? How do I track the cause?
--
Aras Pranckevicius
Graphics programmer at unity3d.com
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