Render VDB

[pipe_mm]

Hello


My goal is to render snow like in that demo (cat)
https://www.youtube.com/watch?v=qZKoDrw_EBA

the simulation works very well in Maya Bifrost, but now I am not able to render those particles

I am writing out a VDB sequence, reloading it via the Vray Volume grid, but without succes

here are my scene files
https://pipe.green-cloud.at/index.php/s/ddAm7QamdrsxBi8


thanks for support
Martin

[hsz]

You are not converting the pts to volume so it won't save it as a vdb unless you want to write the points as vdb points? If that is the case then I would just save it as an ABC then render the pts that way, you can still write a vdb to points if you want.
To write something into a vdb you either need an SDF or Fog (density) so after the mpm solver you need a convert to volume then pick if you want an sdf or fog then you can write a vdb. You also need more resolution, usually for fx like that. The volume grid will be able to read those. Make sure to mapped the channels correctly BF all channels starts with voxel_signed_distance, voxel_ etc etc etc. Hopefully, that helps.

[hsz]

Here you go

[pipe_mm]

Hello HSZ
that definitely helps a lot

it make total sense now.
I just started to use Bifrost yesterday, and I am hooked by its possibities.
For the points it makes sense. I still have to look into the sdf/fog node.

But for the snow I will work with a meshed version and your scene helpes a lot
so my funny Character will be able to move that mesh around.
Thanks a lot and have a great day
Martin

https://vimeo.com/677182992

[pipe_mm]

Hello HSZ
thank you once again. This really worked like a charm.

https://vimeo.com/679083130

Without you, I would not have found this direct path, over from Bifrost to Vray.
First it seems not logical, to convert a particles to Fog and then read them out as a mesh.

For anyone who tries to recreate this steps, here some points that I had to get right

*Bifrost*
the file_cache node hast to be named propperly to write frames "name_####.vdb"

*Vray Volume Grid*
- when loading the VDB sequence, one gets asked if you want to use a preset. I clicked none and had to set the switch in the 3rd Party Channels Mapping und Smoke to "voxel_fog_density"
- Meshing: the meshing is done in the Vray Volume Grid. Pretty comfortable, and speedy.
The Render Mode has to be set to Mesh and I had to set the Mes Type to Maya Mesh.
The Isosurface Level and the Smooth Particle Size drive the mesh density/smoothnes.

*Material*
I was even able to apply a displacement for the Snow. So there is a UV generated in the meshing process.

Another approach is to do the meshing inside Bifrost. This way one can render Bifrost directly without having to write a cache file.
But I assume its not so bad to write a cache between simumation and rendering.

Thanks once again, and I am looking forward to many cool effects simulated in Bifrost, rendered in Vray.
I am also shure Chaosgroup will come up with Vray Nodes inside Bifrost, to have a strong connection

Best
Martin

[pipe_mm]

I have one more Bifrost question. Its about the performance. To me this snow simulation feels super slow.
I suppose this is the normal time for granular snow simulation with a decent amount of points?

Can it be compared to the sim times of Phoenix (liquid sim with high viscosity)?

Is there a way to speed things up?
Particles per Voxel to a lower number I suppose

thnx
Martin

[pipe_mm]

I will give myself the answere:
there are two aspects
- source_mpm_snow
this is mainly controlled by the particles per voxel
- the convert_to_volume
here the "detail size" is the crucial value

for me it helped a lot, first writing a cached sequence of the sim, using a file cache node and .bob format.
this are the pure particles. once I am happy with those; I feed "convert to volume" node with this cache.

so its two calculation steps, that are better simulated one after the other to control the speed and output

[pipe_mm]

ok, dont know if anyone will ever read :d
anyhow
what really speeded up things is scaling
scaled the scene smaler by 0.1 and the whole thing runs like shizzlewizzle


I remember they preached about scene scale a 100 times, back with the old Bifrost
seems still to be valid