I kept getting "Driver Message (OpenGL, Performance, GL_CLOSE_PATH_NV, High): GPU stall due to ReadPixels", which for anyone familiar with OpenGL probably knows... usage of the glReadPixels function is typically frowned upon if at all possible, because moving framebuffer data out of the GPU and back into system memory can cause huge performance issues.

I'm not sure why they need to use this function, or if it's just not optimized enough to go without it.