Bifrost MPM with motion Blur

[daniel_berthold]

Hello,
I'm having a big problem with the Maya Bifrost graph.
Autodesk unfortunately tells me that they can not help me with vRay so I hope here for help.
I need to simulate a snow pile, which works pretty well with the Bifrost graph. From this I need to create an Alembic sequence, which will then be rendered through a vRay proxy. The problem is that I can't get any motion vector information into it so it renders with motion blur.
Has anyone here had any experience with this and can help me out?
I've pinned a small example file that is pretty simple. However, you have to change the paths of both the Bifrost output cache and the vRay proxy.
It is created with Maya 2022.5.
I hope someone can help me.
Thanks in advance.

[hsz]

You need to transfer the point_velocity attribute in order to render motion blur, from the volume contour_dual_marching_cubes node doesn't support that out of the box so use the high-level node volume to mesh.
I left a sticky note there.

[daniel_berthold]

Wow, thank you so much.
You saved my life.
Bifrost is a really cool tool, but unfortunately it gets so technical very quickly.

[hsz]

Little by little you will see that is going to start to make sense. Is not that complicated.
The solvers are pretty straightforward, you can create your own fields, etc to control stuff in a more artistic way or use them as they are with different influences.

Also, join the discord if you want to learn more and get help

https://discord.gg/bifrost-addicts-872260298508222534

[pipe_mm]

hello,
I found this thread and its great to see that its possible to transfer velocity data to alembic.
My setup is slightly different, as I use an aero-volume-simulation driving particles/instances.
The setup is based on the Bifrost browser example "gradient advection"

so there is no "volume to mesh node"
could you take a look at the example and perhaps tell me at which point and how I can transfer the voxel_velocity?

thank you so much
Martin

(will also post this onto the Bifrost Discord)

[hsz]

Hey, you do not need to instance anything. Just save the pts and render them. Also, you forgot to turn on motion blur.

[pipe_mm]

wow - I didnt know this is possible
I will use this method for this project

still the limitation seems to be the point size
per VrayProxy loader only one constant size can be defined.

so perhaps there is another way to write the velocity data while using instanced particles

[hsz]

you need to use pscale as a property to get the right point_size.

[pipe_mm]

sorry for my ignorance, but can you explain how to set up pscale

[hsz]

It is just the same way that you set up any other property/attribute

[pipe_mm]

I want to thank you very very much hsz, this technique works like a charm.
Also passing on the data onto the Alembic format and having it seamlessly read by Vray, makes the the concept behind Bifrost and the open format 3D very attractive.
Thank so much

[hsz]

No problem.