WMR P3Dv5 frametimes are inconsistent and cause stutter

[whitav8]

@Beau,
I am hoping that this report with data included can help you recode version 5 so that WMR (not sure about other VR HMDs) will work without large amounts of stutter. I have tried many conditions - with and without reprojection - with single-pass and with stereo - with frame limits and without but have not had any success - there are always large amount of stutter (image surging ). I am utilizing the most recent of win 10 (2004) and Nvidia drivers ( 446.14) on my 9700K@5Ghz PC.
The data I am presenting are snapshots of frame-to-frame periods in milliseconds from FRAPS plotted in a spreadsheet so that both FPS and inter-frame deltas (the current frame period subtracted from last frame period ) can be seen. I will first start with a non Prepar3D flight simulation to show how it should look for minimal stutters. There is a general 2 or 3 millisecond noise and then occasional larger deviations which usually are from scenery loading or some complex object - especially in turns. I am using WMR reprojection=motionvector so that it should always be near 45 FPS or half the HP Reverb timing (one-third of 90Hz is also supported).

https://imgur.com/HzwzYe7

Now, the next plot is from Prepar3D version 4.5 showing reasonable but not totally smooth stutter. You can see that due to the lower performance in nonVR mode (about 80FPS), the VR FPS stays around 30 which results in some image stutter but not too hard to live with.

https://imgur.com/7qicZDo

Finally, this is an example of what I am measuring (no matter what I try ) with Version 5. There is simply way too much inconsistent frame lengths and they occur on nearly every few frames so there is much stutter. Most of us can see frame deltas of as little as 2 to 3 milliseconds especially if they continue for a few frames - certainly anything over 5 msec is very noticeable.

https://imgur.com/cxYD94A

I hope this data might help you see if there is a strategy that you can use to make the frametimes more consistent including computing a moving average and then trying to hold off at the end of a frame in order to make them repeatable. Maybe this is a problem mostly for the WMR VR user but nevertheless, consistent frametimes are very important and Vsync can't be utilized for VR. I tried using the P3D internal limiter, the Nvidia CPL limiter, and the Riva Tuner limiter - but that didn't really seem to help.

[YoYo]

Nice tests, see my thoughts also:
https://www.prepar3d.com/forum/viewtopi ... 42#p220280 .

[YoYo]

@whitav8,
maybe better it was to have it in the one topic (that you created) to show for LM this problem (as posts about this VR issue in the one topic?). Just idea ....