This page describes the use of the Bifrost feature in V-Ray for Maya.
Overview
Bifrost in Maya is a procedural framework for simulating liquid effects using a FLIP (fluid implicit particle) solver. This page discusses the use of Bifrost in conjunction with V-Ray for Maya.
Prerequisites
To render Bifrost in Maya 2015, start by turning on the meshing in the bifrostShape node AE. V-Ray does not support direct rendering of Bifrost geometry in this Maya version (Maya 2016 or next is required).
Rendering using Alembic Cache
This is the preferred way to render Biforst with V-Ray. Select the Bifrost mesh (not the bifrostShape node), and from the Cache menu, export the selection to Alembic. Don't forget to turn on the color set export from the options dialog. After the import, set the Motion Vector Color Set attribute of the mesh node to bifrostVelocity.
Note that in V-Ray for Maya 2017 and above, the velocity color set is named bifrost_velocity.
Rendering using VRayMesh
Alternatively, the Biforst mesh can be exported to V-Ray proxy mesh which provides more flexible rendering. Because Bifrost exports it's velocity information per seconds, not per frame as expected, the velocity interval must be tweaked slightly in case you need motion blur. Velocity interval end should be changed to the number of frames per second, e.g. 24.
Note that in V-Ray for Maya 2017 and above, the velocity color set is named bifrost_velocity.
Direct rendering of the Bifrost mesh
It's also possible to directly render the Bifrost mesh, but this may be slower, especially with motion blur. Because Bifrost exports it's velocity information per seconds, not per frame as expected, you must scale it using the Velocity Scale attribute of the bifrostShape node. The value must be 1/ frames per second, which for the default 24 is roughly 0.042. All three components must be set to this value.
Direct rendering of the Bifrost iso-surface (Maya 2016 and next)
To render directly the Bifrost iso-surface, disable the meshing and make sure you don't turn off Export Voxels in the Bifrost Options Extra attributes.
Rendering Bifrost as VRayMetaball (Maya 2016 and next)
To render a Bifrost liquid or foam shape as a VRayMetaball iso-surface, add Bifrost Options Extra attributes, and turn on Export Particles. Then hide the shape, so you don't render it twice. In the VRayMetaball node, select the bifrostShape node as Positive Particle System. You can also use the preview to adjust the settings.
Rendering Bifrost USD Graphs
Since V-Ray 5, update 2 (version 5.20.02), V-Ray supports rendering of Bifrost USD graphs. To render them, you need to have these minimum versions:
- Maya 2020
- Bifrost 2.4.0.0
MayaUSD 0.16.0 (USD 21.11)
Support for bifrostLiquidMaterial
V-Ray has limited support for the Bifrost Liquid Material, and the foam component of the material is not fully supported.
The reflection highlights are calculated according the Blinn shading model, not the one used in Mental Ray.
Only the Fresnel reflections are supported, and unchecking this option will cause full reflections to be calculated.
Tips for working with Bifrost meshes
If you can't get Bifrost properly load each frame from the cache, try unchecking "Enable Background Processing" from the Bifrost options and go to the first frame of the cache.