HTC Vive Frame Rate Sweep Comparison on The Gallery
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This video compare the 45 FPS and 90 FPS animation appearance when playing The Gallery on an HTC Vive.
When we use The Gallery on a GTX 970 with the High image quality preset, we can force the game to run at a 45 FPS render rate. If you do something simple like take your avatar hands and move them back and forth in front of your face while looking at the fire, you will see a 45 FPS animation. For those of us that are used to looking for these kinds of image issues, it’s pretty obvious what we were seeing. If you make the same hand motions in front of your face, but look up at the sky instead, where the game is reporting a 90 FPS performance rate, the animation is significantly smoother.
However, if you are in the 45 FPS scenario, and waving your hands in front of your view, if you also rotate your head on a static axis to the left or right, THAT movement will appear to be running at a higher frame rate. That is due to the warp capability of the OpenVR (and Oculus VR) system to slightly move the entire image on the headset with a 90Hz interval frame is missed. The result is you’ll see what appears to be 90 FPS motion to the left or right (or up or down) while the hands on the screen will be running at 45 FPS effectively.
We created video to show you this phenomenon. Using 960 FPS capture on a Sony camera, we have slowed down the animation to demonstrate the effect we are seeing. What you should look for is that with the GTX 970, the hand rotation animation will update a slower rate than the rest of the environment you can see will update, on order of 1:2.
We have zoomed in and slowed things down here to help show you the effect, and removed 9 frames of black between each frame of animation (these screens have AMAZINGLY low pixel persistence). I think the result speaks for itself. Obviously the idea of artificially creating this scenario with hands waving erratically in the air is artificial, but you would experience this same effect in any situation where the frame rate of the game is running at 45 FPS and you are interacting with the world rather than just looking around.