Data Channel Interpolation
FROST acquires and interpolates relevant particle data and propagates it to the final mesh.
The Velocity Channel of incoming particles will be used to interpolate particle positions on subframes and generate Motion Blur using one of the modes described in the Motion Blur Modes topic.
In addition, the Velocity can be encoded into an arbitrary Mapping Channel (default is 2) in order to be used for visualization purposes or to acquire back using for instance the Krakatoa PRT Volume object. This allows for a round-trip of the velocity data from particle data to mesh data and back to particle data.
Note that when using a particle source like Particle Flow that does not have a Mapping Channel 1 by default, enabling Velocity->Mapping Channel 2 will cause the renderer to complain that FROST is missing UVW 1. This is because enabling Channel 2 in FROST implicitly declares Channel 1 as existing, but in this case it is not. To solve this, you can either add a Mapping operator to the Particle Flow with Channel 1 enabled to pass valid data to FROST, or change FROST to copy the Velocity to Channel 1 instead.
Color / Vertex Color Channel
The Color channel of PRT files and the Vertex Color channel of 3ds Max will be acquired and interpolated into the vertices of the iso-surface mesh or the geometry objects used to replace each particle.
The image to the right shows a Particle Flow system with varying particle velocities visualized as lines, and a FROST object showing the velocities as vertex colors on the mesh. In this particular case, the velocity was saved to a PRT file, then loaded using a Krakatoa PRT Loader and converted to a Color using a Krakatoa Channels Modifier. Had the velocities been copied into the Mapping Channel 0 of the FROST object directly, the color would have been blue due to all vectors moving up along the Z axis...
3ds Max Mapping Channels
All 99 3ds Max mapping channels will be checked for, acquired if existing and interpolated just like the Vertex Color channel into the vertices of the isosurface mesh or the geometry objects used to replace each particle.
It is a know limitation of the Vertex Color display in 3ds Max that if a Primitive is set to display any mapping channel except for Vertex Color Channel in the viewport, it will show white unless a modifier is added to the stack or the stack is collapsed to turn the primitive to Editable Mesh or Editable Poly. In the case of FROST, adding any modifier like Relax or Mesh Select will implicitly convert it to Editable Mesh on top of the stack and the Object Property "Vertex Channel Display" will be able to show in the viewports any Mapping Channel acquired by FROST.
Mapping Channels And Custom Geometry Meshing
When particles are replaced with Custom Geometry objects, a collision of mapping channels may occur. For example, both the distribution particle system and the Custom Geometry object could have the same Mapping Channel defined. If this is the case, the following rules apply:
When a Custom Geometry mesh has the same channel as the distributing particle system, the mapping channel of the particles will be used.
When a built-in Geometry shape (Plane, Tetra, Box etc.) is used and the particles contain Mapping Channel 1, the Geometry's mapping channel will be used.
You can use one of the other 99 mapping channels to avoid such collisions.
The MtlIndex channel can be passed to the FROST object to define the material assignment per particle. Regardless of being an Integer value, this channel will be interpolated when using an iso-surface meshing mode like Metaballs and will affect the face Material IDs of the final mesh.