Motion Blur Issues with Time-remapped Fluid Simulation in VRay

[k_18]

Ok, we'll be switching solvers due to time constraints.

To Chaos: I believe the entire re-time feature is ineffective for film work if we lose functional motion blur in the process. If it's technically possible to implement, it would be great to have this functionality in the future.

[Anthonyyg]

Is it an option to use the velocity pass and then multiple that in post?

[zdravko_pavlov1]

Hello,

Which version of Phoenix are you using? Is there a way to slow down your simulation through the Input panel by adjusting the Play Speed instead of rendering subframes? I understand that you are using Maya, so a solution involving TyFlow is not an option. I tried to recreate your setup in Max and was able to slow down the liquid to 0.2 and render it with correct motion blur.

The advection origin and time bend controls, which you mentioned, are part of the fire and smoke simulations and should be ignored when simulating liquids. In Max, there are two separate grids for fire/smoke and liquids. As far as I know, there used to be a unified grid handling both in Maya, but in later Phoenix versions, they were split as well.

[k_18]

Is it an option to use the velocity pass and then multiple that in post?

The velocity pass has black holes in all subframes - so it's basically the same problem why it cannot render them in the first place, unfortunately.

[k_18]

Hello,

Which version of Phoenix are you using? Is there a way to slow down your simulation through the Input panel by adjusting the Play Speed instead of rendering subframes? I understand that you are using Maya, so a solution involving TyFlow is not an option. I tried to recreate your setup in Max and was able to slow down the liquid to 0.2 and render it with correct motion blur.

The advection origin and time bend controls, which you mentioned, are part of the fire and smoke simulations and should be ignored when simulating liquids. In Max, there are two separate grids for fire/smoke and liquids. As far as I know, there used to be a unified grid handling both in Maya, but in later Phoenix versions, they were split as well.

Hi Pavlov, thanks for getting back to me. We are running V5.22.00 for VRay 6.x. Strange that it works in Max, as Chaos tech support mentioned this was not supported:

It looks like the Phoenix liquid Motion blur for sub-frames is not supported. Our advice is to keep the value to 1 in order to have correct motion blur render results in this case.
We have a note about this in our documentation https://docs.chaos.com/display/PHX4M...ing-MotionBlur
same for both 3dsMax and Maya.

We are sorry for the inconvenience that is caused by this limitation.
Hope you can workaround it that way and get the desired animation result at the end.

We used the Input->Play Speed to try slowing the sim without reverting to using sub-frames. Any other setting does not seem viable in Maya. Will have someone check a newer version to make sure, though.

[zdravko_pavlov1]

Just to clarify, I didn't render any subframes. I just slowed down the sim to 0.2.
Also, I wasn't aware that Max can even render subframes, but apparently it is possible using MaxScript. I found this thread from 2010:
https://forums.chaos.com/forum/chaos...endered-output

I'll do some additional testing and get back to you.

[zdravko_pavlov1]

Hello,
I did some research and found a way to render sub-frames in MAX. I rendered a few simulations and didn't have any motion blur artefacts.
I'm not sure what happens in Maya. It might be a Maya bug, or perhaps there's something about how Phoenix and Maya are talking to each other. I'm sure Phoenix developers will look into this.
A few things I need to point out. It doesn't matter how many substeps you had during the simulation. When you interpolate frames, you will get the same results.

Here's a short video that I recorded while I was experimenting:
https://drive.google.com/file/d/1RPX...ew?usp=sharing