Absymal glReadPixels peformance with Quadro drivers

Anyone else seeing this? Our application does picking by drawing to an offscreen framebuffer with different colors for each object, and then uses glReadPixels to find out which object was picked. With 33000 instanced spheres, the first pick is fast, then the subsequent picks takes many seconds. This is on a recent i7 with a Quadro K4000 and the 340.66 drivers. My daughter’s Sempron with a GeForce GT 610 runs circles around the K4000. That is not right.

Some more clues, I can replicate the bug on a Quadro FX 3700 with the 297.03 driver or later, but the program works with 266.45, 275.65, and 276.42. Unfortunately, the older drivers don’t support the K4000.

With the 340.66 driver, if we switch to the the “3D App - Game Development” profile, the bug goes away, but so does 3D stereo-in-a-window. And we need both stereo and glReadPixels to work. So that is not a workaround.

If the application profile affects the issue, try “Workstation - Dynamic Streaming” as well.