I’ve encountered a strange issue with Frost and vray instancing (in “Geometry” meshing mode). I’m not sure if it’s a Frost issue or a V-Ray issue, but I figured I’d post here anyways.
The issue seems to be that the motion blur for Frost-generated vray instances happens in camera space, as if frost velocities vectors are first transformed into camera space before being passed to vray. I’ve been able to reproduce the issue pretty easily, using the following steps:
Generate some PRTs of fast-moving particles
Load them into a PRT loader and set that as the source for a Frost mesher
Put a camera in the scene and animate it so that it tracks one or more of the particles, so that the tracked particle moves very little within screen space
Set the renderer to vray and enable motion blur
When rendered without vray-instancing turned on, the particles will have very little motion blur (as expected, since they’re not moving much in camera space, because the camera is tracking them). But with instancing turned on, the particles have as much motion blur applied as you would expect to see if the camera was stationary.
I’m using 3dsmax 2017, Frost 2.0.10 and Vray 3.60.04