Expensive ViewExtensionPreRenderView

Development Platform & Builds XR Development
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1

Hi,

We have a little mystery on our hands with profiling, looking at stat SceneRendering:

  • ViewExtensionPreRenderView takes up 0 ms in non-VR view, our scene plays at 90FPS on a 4K resolution, all quality settings maxed out
  • Using VR, we also easily reach 90FPS, unless we set “r.SSR.Quality 3”. Then ViewExtensionPreRenderView suddenly jumps to >15ms. With “r.SSR.Quality 2”, ViewExtensionPreRenderView takes up <4ms.

We’re using simple materials here (just opaque, no tessellation / bumpmap / parallax)… Total rendertime jumps to >22ms in a simple scene – but only in VR!

What is going on here?

2

What VR system are you using? SteamVR did some changes to its Motion Smoothing and if you have that thing turned on, it can destroy performance big time. I can’t remember exactly but I think you are doing something similar to the pipeline with “r.SSR.Quality” so when you have them both on it just leads to an order of magnitude higher performance cost

3

Hello, Did you find out how to resolve this? I’m having the same issue.

4

Hi,

It is indeed SteamVR intervening to reach 45FPS when Motion Smoothing is turned on. Effectively it seems to delay the frame to reach the desired framerate (but as soon as your scene can reach 90FPS it should stop doing that and go back to regular).

5

Thank you so much for getting back to me. I’ve been struggling to resolve this.

How did you fix it in the end? Did you have to optimise it further or did you simply just turn off motion smoothing?

6

Well in the end it’s more of a feature than a bug, so there’s no need to resolve. In my case I optimized until I didn’t drop below 90FPS anymore - but in other cases you can perhaps just leave it as-is.