Motion Blur

[Joelaff]

I have a scene where I am having trouble getting my foam (bubbles) to motion blur.

I simulated with velocity saved for the grid, and for the foam particles. (Not saving liquid particles).

I see the velocity in Phoenix Previer (thanks for that, BTW). So we know there is velocity data in the particle cache.

I have a Foam Shader set to use the foam particles of my simulator. I have tried forcing motion blur on in the particle shader, but this did not help.

I tried increasing the motion blur multiplier in the particle shader all the way to 1000. I tried increasing motion blur in the liquid simulator to 1000.

I am rendering with VRay 5 GPU (hybrid using both CPU and GPU). I tried progressive and bucket. I am on whole frames and rendering at integer frames.

I tried both a VRayCamera (what I prefer) with motion blur enabled in the camera settings, as well as a Standard camera with motion blur enabled in the render settings.

Everything else in the scene render with motion blur.

Motion blur seems to work correctly in VRay5 (non-GPU).

Any way to get it to work in GPU?

Thanks.

[Joelaff]

Oh, darn... I found it on the features page. No Particle Motion Blur in VRayGPU. Darn it!

[Svetlin.Nikolov]

Hey, can you link me the features page you are looking at?

[Joelaff]

Here you go:

https://docs.chaosgroup.com/display/...rtedFeatures-1

[Joelaff]

I am using 4.20.00, Build ID: 20200615

[Svetlin.Nikolov]

Ah, where the is mention of particle motion blur on this page, it does not refer to the Phoenix Particle Shader.

However, motion blur with Bubble and Splash mode with V-Ray 5 GPU indeed does not work, though it works with Fog mode and it should also work with V-Ray Next and Fog mode.

We will be looking at implementing Motion Blur for Bubbles and Splashes with V-Ray 5 GPU very soon, but let me note something important - the GPU code has changed tremendously since V-Ray Next, so it was by pure chance that Fog mode of the Particle Shader renders there and for Bubbles and Splashes the new additions can be added only with the architecture of V-Ray 5 GPU...

[Joelaff]

Thanks for the explanation.

We are using some fog mode, but really need motion blur on the bubbles or they look ridiculously fake.

I was thinking of trying VRayInstancer for the bubbles. I wonder if that will motion blur in GPU. Guess I need to try.

If you get that motion blur working in a nightly anytime soon please drop me a note here or privately. That would really help us out. Thanks again.

[Svetlin.Nikolov]

Yess, try out the instancer as a workaround in the meantime. I don't have an estimate yet for the GPU bubble motion blur, so if the instancer helps work around it, it would unblock you.

[pixteur]

Has any progress been made on Phoenix FD Bubble and Splash motion blur on vray 5 GPU?
Could really use this right now as I have to simulate 1-2 second long exposures for about 10 different scenes and on CPU it's just insanely slow!
Not quite sure how to use the instancer method.

[vasil_pashov]

Hello, unfortunately, though it's know issue, we have not implemented motion blur for bubbles and splashes on V-Ray GPU. However we have just bumped the priority of the task.

[Joelaff]

For the instancer method you use something like Frost or Tyflow or VrayInstancer to instance geometry such as spheres (or something more complex) onto your particles, thus turning the particles into geometry.

If simulating something like water then Frost or Tyflow can mesh them into a fluid like object, which is often better looking that individual bubbles, though much slower and more memory intensive.

Good luck.