Help Using Fluid in VR (HTC vive)

[josemendez]

Are you using Legacy VR or XR Plugin Management? The Fluid Renderer doesn't work with XR Plugin Management for me, not even in 2019.4. With Legacy VR I can get the fluid rendered, but the Lighting is definitely broken just as badly on a two-camera setup as one a single one.

I'm using the XR plugin in 2019.4  . It also works ok in Legacy.

Works and lighting is fine for me, are you using any other asset or special setup that might interfere with lighting?

I also noticed that using two cameras more than halves my framerate, and shows a massive CPU load compared to single camera stereo pass. Is the physics simulation also being done twice with two cameras? That doesn't make sense to me, but what other explanation could there be?

Simulation is only performed once no matter how many times you render it. However, rendering is not free at all for the CPU: you're doubling the amount of drawcalls, the amount of pipeline state changes, culling work, etc. That's why single-pass stereo was conceived, to ease the burden on the CPU. The GPU always has to render the same thing two times, no matter if you're using single-pass, multi-pass, or two cameras. This thread is related: https://forum.unity.com/threads/vr-singl...ge.425280/

Then, there's death spiraling: if your frame rate is low, physics will have to be updated more than once per frame (remember that FixedUpdate can be called, 0, 1, 2 or as many times per frame as needed to keep a constant timestep). If rendering is dragging performance enough, physics will be updated multiple times per frame and drag performance down even more. Check the amount of FixedUpdate() calls in your profiler and if there's more than 1 per frame, you need to reduce Unity's max fixed timestep setting (found in the Time manager).

I cant even get a stable 45 frames for using 90Hz with reprojection in the faucet sample scene with only 1200 particles. I can't throw any faster hardware at it either, I'm already using a 5950X and a 6900XT.

45 fps is way too low, I'd recommend using the profiler to see what the culprit is. Might be simulation, but most likely it's rendering. You can share a profiler pic if you want help interpreting its data.

It would help to know your fluid renderer settings too. Some have a noticeable impact on performance (dowscaling, for example).