[cairo] Large number of glReadPixel method calls
ctuckey at verano.com
Wed Jul 28 09:13:29 PDT 2004
The latest version of Glitz gets rid of the major leak on all our
systems. However, the Matrox (XiG driver) system runs our application
very, very slowly and uses quite a bit of CPU. The XiG driver has a
great feature - we can set an environment variable and it prints out all
the GL calls that are being made. When we did this, it appears as though
a call to glReadPixels() is the bottleneck. When running our memory
leak test program (see Possible Memory Leak Using Glitz Surfaces) we see
that this method is called after every call to cairo_show_text.
Do you have any suggestions? Is the call to glReadPixels() a direct
result of what's being done in the glitz library or is it a side effect
generated by the XiG driver?
If it would be useful to you I can send the log of all the GL commands
generated by the XiG driver.
FYI, here is what the XiG support person had to say:
glReadPixels() should be used sparingly because it can cause the
entire GL rendering process to halt while it synchronizes and fetches
data from the card. I notice the ReadPixels is over a relatively
'glReadPixels(x=0, y=0, width=400, height=400, format=80e1,
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