Vray-instancing: motion blur issue?


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:

  1. Generate some PRTs of fast-moving particles

  2. Load them into a PRT loader and set that as the source for a Frost mesher

  3. 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

  4. Set the renderer to vray and enable motion blur

  5. 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.

Any ideas?

I’m using 3dsmax 2017, Frost 2.0.10 and Vray 3.60.04


Thanks, we were not aware of this.
We will try to reproduce it here and see what’s going on…


Hi Bobo,

I am posting in this post as our problem also occurs after exporting TP particles backed with PRT, and then meshed with Frost using Vray Instancing.

I believe Hristo Velev has mentioned it - we don’t have proper rotational MB, just position. And in our case, we need a good sampling of MB for rotation as it is very well seen in the shots we are working, especially the close-ups.

Do you have Idea when we can expect a fix on this as we are pressured by time?



Hey Martin,

I’m not the expert here, but can you provide us the steps by which you managed to reproduce this problem? If you’re not sure how it happened, can you strip the scene down to the bare parts and provide it (you can e-mail it to support@thinkboxsoftware.com)? That should help us reproduce your problem on this side.


Hi Eamsler,

Generally what I think is the problem is that when VRAY requests subframe samples for motion blur for Frost only interpolates Velocity and Normal but no orientation. We are using it with objects that are rotating over certain pivot for each particle, and the motion blur is simply giving straight lines as result, obviously ignoring the rotational speed. Similar to a car wheel, the MB should be less in the middle and more towards the outer radius.
I can ask Hristo to join and give more information on the topic.



You’re right: currently, Frost only accounts for the Velocity, not the Orientation.

I take it your scene is too complex to render with V-Ray instancing turned off?


We are working on a Krakatoa build for you that would allow Orientation interpolation on sub-frames (Orientation channel via Magma from interpolated Normal and Tangent vectors stored in the PRT sequence). Longer term we would like to support interpolation of the Orientation channel itself.
I hope that this would allow V-Ray to request geometry sub-samples with the complete transforms changing on each step.

I got a test build from the Krakatoa developer on Friday, but found issues. I am currently on a business trip and have not heard back about an update. I will send him this thread to keep him in the loop… :slight_smile:


Thanks, Bobo,

It is working now on the scenes where we have fewer objects and we can render them without the Vray Instances. Looking forward to the update where that could work with Vray instancing option turned on too!