I am using glReadPixels to capture an image and print it using a QPrinter. Before I use glReadPixels everything draws very fast. After calling glReadPixels and sending the file to the printer, all of my OpenGL paints are called twice in-a-row and now take a lot of time to occur. The print statements would fly by before printing, and after printing the exact same functionality now takes 30-60 seconds instead of the 2-5 seconds before printing. The only GL call that is made during this time is glReadPixels. I read in the Red Book that glReadPixels writes to processor memory which sounds like the L1 and L2 cache. I was wondering if I was clogging up the cache and if so how can I clean it out? Or do I understand the Red Book incorrectly in what it means by processor memory? Thanks for your help!
CPU memory is main memory. glReadPixels copy the pixels to your buffer.
The problem is likely driver and hw related.
Sorry I guess I should have posted I am running this on Solaris 9. I added in Qt’s updateGL( ) calls before and after the glReadPixels call and the first call ran real fast and the second call ran real slow. updateGL( ) just makes the call to start all of the OpenGL painting calls I make in my program. So processor memory is considered my RAM and not the Cache? Thanks!
It appears that when I open a secondary Qt window that my subsequent calls to glReadPixels( ) and glBitmap( ) cause the repaints to occur very slowly. I don’t know how to fix this as I have tried many things. If anyone else has any other ideas it would be great. Thanks!