bystander36
Diamond Member
- Apr 1, 2013
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Fun fact. If using AMD's version, HD3D, both left and right frames are sent at the same exact time using frame packing (same goes for Nvidia if you use HDMI). Then the monitor splits it up and displays them at exactly the same time on passive monitors, or alternately displays them on active displays. Nvidia does this too when using HDMI or passive displays.I'm fairly certain 3D vision does not render 2 frames for the same time frame, nor should it for that matter, as that would lead to wonky looking animations. 2-way SLI with 3D vision does not specifically split rendering between eyes either, but since the order on which the 2 GPUs delivers frames is fixed when using AFR, they will end up doing so as a side-effect, not by design.
Another reality is that SLI specifically ignores a 3rd GPU if used in 3D Vision. If it was strictly an AFR approach, there would be no reason to ignore the 3rd GPU.
Using AFR you get poor scaling (since the load on the CPU is basically doubled), you get micro stutter (since AFR does not have any inherent way to smooth out delivery of frames), and you get so-so compatibility (much better than SFR at least).
But rendering two frames for each eye also doubles much of the work as well. At different perspectives, the frames have to recalculate for each position. That isn't to say that some of the info could share, and some can't be shared, but the same thing happens with 3D Vision. This comes down to how well the developers utilize their resources and how much special attention is given.
There are games were the CPU load in 3D Vision is not doubled, while in others it is. It varies from game to game.
With VR SLI/crossfire you get close to perfect scaling since the rendering of the 2 frames (left eye and right eye), is far more exposed and controlled (since the VR SDK is purpose built around rendering 2 frames at a time) and as such you can do a lot more optimization of the CPU side, which is exactly what has been done (this has also been done with a few 3D vision games such as Crysis 2, but they are few and far between). You also get zero micro-stutter, since VR effectively has built in smoothing, thanks to the fact that both frames are shown at the same time instead of one after the other like what happens with AFR. Finally compatibility should be very good, since all VR games has to make use of the SDKs (only possible exception being with Nvidias auto stereo feature).
So all in all multi-GPU on VR is a completely different beast from multi-GPU with 3D vision (or multi-GPU on a normal monitor for that matter).
I do not doubt that there are improvements. Even with 3D Vision and HD3D some of that happens to some extent. Just know that it will not be perfect scaling on the CPU side. Some things have to be calculated twice.
Games specifically designed for VR will likely have great support. It's the games that tack it on that will see less scaling than you seem to expect.