glReadPixels is failing...sometimes...on just one computer
I'm using glReadPixels in my app for object picking and screen capture, and it works on all computers so far, except one. On the problem computer, glReadPixels only works intermittently. I have found that there are two conditions where glReadPixels will work correctly on this machine:
1) If I run the app in a window. In full screen, the viewport is 1690 x 984. If I reduce this to about 1592 x 930, glReadPixels will work correctly. Larger than that, and it will fail, even in a window.
2) If I place enough objects on the screen. I haven't nailed down what the threshold is, but if I put enough objects on the screen, glReadPixels starts working.
I'm pretty baffled. Has anyone experienced a problem like this? Do the workarounds I've listed suggest to anyone where things might be going wrong?