Bifrost motion blur render issue, Arnold

[reniferziolo]

Hello everyone,

really  struggling here with my bitfrost simulation.  I did cache both simulation and mesh and would like to render it with the motion blur. Still i am getting this error:

| Number of normals changed between motion steps: 965390 -> 944318

etc

Any help appreciated, thanks

[Grahame_Fuller]

Hello,

It's expected that the number of normals changes in a Bifrost liquid mesh, because the liquid shape gets remeshed every frame as the simulation updates. Instead comparing vertices between frames, Bifrost has the bifrostVelocity color set for motion blur. Make sure that bifrostVelocity is set as the Motion Vector Color Set in the bifrostLiquid1MeshShape's Mesh Controls attributes.

Does it render correctly in spite of the logged error? Take a frame where the liquid is moving fairly fast, and compare the results with motion blur on and off. If the motion blur renders properly, you can ignore the error.

Did you use the built-in Bifrost caching for the mesh, or did you export to Alembic? In the case of Alembic, you need to activate Write Color Sets in the Alembic Export options. Then when import the Alembic, also make sure to set Motion Vector Color Set to bifrostVelocity.

I hope that helps,

gray

[reniferziolo]

Hello,
Motion blur doesnt render at all and I did use the bulit in cashing. I will
try your suggestions and let you know.

Thanks!

[reniferziolo]

these are the default settings. Am I supposed to change anything? I am also checking the alembic export now.

[Grahame_Fuller · Accepted solution]

Hi,

One more thing to check: In the Arnold section of the bifrostLiquidMeshShape's attributes, set Motion Vector Source to bifrost_velocity. Motion Vector Unit should be per second. You may need to toggle motion blur off and on again in the Render Settings.

If that does not work, then any mor information that you can provide would be useful: version of Maya, version of MtoA, etc. If you can provide a small scene that demonstrates the issue, that would be great.

I hope that helps,

gray

[reniferziolo]

That was it, thank you!

[Anonymous]

Hello,

I met the same problem here indicating Normal issue. But I wasn't using Bifrost. I created the fluid in Houdini and import it into Maya to export with Arnold. How do I fix this problem?