iRolley, on October 4th 2006, 05:03 PM, said:
The Doom3 engine being much more GPU limited than CPU, I guess more load could be put on the CPU. But then I can't figure out if this would help if the GPU is already saturated.
In cases where the GPU is truly saturated and is continuously processing frames without any breather - MT GL will not help. However, what we found with WoW (and what appears to be the case with DOOM3) is that under single threaded GL on OSX, GPU saturation on OSX was rarely being attained, and so a boost results by properly spreading CPU-side work across both cores.
It is possible to set up situations where you become truly GPU limited - take a low end card and run it at maximum graphical settings - AA, aniso, trilinear, and then add in vsync for example. But for games which might have moments where they become CPU-limited (specifically in CPU-side code inside OpenGL), MT-GL offers a way to flatten out those dips or eliminate them.
MT-GL *can* raise your top end frame rate if you have your GPU running on light settings. It can also pull up your bottom end frame rates and give you less variance between top and bottom end FPS. All in all very scene and setting dependent.
In the best case MT-GL can yield a doubling of frame rates and this has been experimentally observed..
It should also be pointed out that there are other improvements in OpenGL that already appeared in 10.4.7 for Intel, that can help games - specifically the buffer-range extension and the gpu_program_parameters extension - both aimed at reducing overhead for frequent key operations. Now we have MT-GL in 10.4.8 for Intel and this is good news for us.