I'm trying to speed up some code that pulls that from the framebuffer using glReadPixels.
I've created two PBO with usage set to GL_STREAM_READ_ARB. My rendering code then alternate between the two PBO and do the following:
I was under the impression that glReadPixel would return immediately, but these three lines takes about 6 ms for a 1024 x 1024 framebuffer.
Currently the code isn't doing any map/unmap so the data should never leave the GPU.
I'm using a Quadro FX 3500 with the latest drivers (169.96).
Am I doing something wrong or is this to be expected?