Work with Bifröst meshes

You can generate a mesh from the isosurface of a Bifröst simulation for more control over the surface. The channels like velocity and vorticity can be transferred to the mesh as color sets.

The mesh is a separate object that is automatically added to the scene when you create a Bifröst simulation, but it has no polygons until you activate meshing on the bifrostShape node. This is typically done as a last step before rendering or exporting.

Meshes are not cached, but are recomputed every frame.

Generate a mesh from a Bifröst simulation

1. For best results, compute the entire simulation first.
   • To generate a user cache, see Work with Bifröst user caches.
   • To use the scratch cache, see Preview a Bifröst simulation.
2. In the Bifrost Meshing attribute group of the bifrostShape node, select Enable.

   This generates a mesh surface for the bifrostMesh object.

3. Set the other Bifrost Meshing controls as desired.

Generate a mesh from part of a Bifröst simulation

You can reduce the time needed to mesh a Bifröst simulation by specifying a Clipping mesh. For example, you can place a box around the portion of the fluid inside the camera's view to mesh only that region. The topology of the clipping mesh does not matter — only its world-aligned bounding box is considered. See Work with Bifrost Kill Volume and Clipping meshes.

Export a Bifröst mesh

You can export a bifrostMesh object as an Alembic file. See Create Alembic cache files.

To export channels like velocity as color sets, make sure that Write Color Sets is selected in the Advanced Options section of the Alembic Export window. The exported channels are:

• bifrostVelocity
• bifrostVorticity (liquid only)
• bifrostCurvature (liquid only, if enabled in the main property's Optional Channels attribute group)
• bifrostChurn (liquid only, if enabled in the main property's Optional Channels attribute group)

Note that the velocity color set values are in units per second — if you use a custom shading network then you will probably need to convert the values to units per frame.

Import a Bifröst mesh

You can import a Bifröst mesh in the same way as any other Alembic file. See Import Alembic cache files.

If you are rendering with mental ray, you can apply a Bifrost material manually. For motion blur, make sure that:

• Motion Vector Color Set is set to bifrostVelocity in the Mesh Controls attribute group of the shape node.
• Motion Blur is set to Full in the Shutter group on the Scene tab of the Render Settings window.
• Use Vertex Colors is enabled in the Translation group on the Configuration tab of the Render Settings window.