We have been trying to get motion blur with FROST, but no luck!
We have tried pflow , thinking particle , prt loader and both motionblur option on frost and vray or finalrender but no luck.
Could you please give a note on what might me wrong and what we should keep in mind for motion blur.
At this point I am not really sure if it is a bug or us being new to FROST.
best regards
In Vray, try changing to:
Duration (frames): 0.9 (or something less than 1)
Interval center: 0.0
We should try to improve how motion blur is handled in Frost.
Hi Mohsen,
Try this:
*Create a Default PFlow
*Invert the Speed, enter 30.0 degrees divergence
*Increase the particle count to 1000
*Disable the Shape operator
*Frost it.
Here is frame 15 of my scene:
*In V-Ray, open the Camera rollout, enable Motion Blur and change Duration to 0.999 and Interval Center to 0.0
*Render
You should get motion blur on your Frost:
If you leave the Duration at 1.0, V-Ray will try to evaluate half a frame before the current frame and half a frame after, thus getting two different topologies and will issue a WARNING that topology is changing and not blur at all. Setting it to anything less than 1.0 (we use 0.5 here anyway) solves this.
If you leave the Interval Center at 0.5, the same will happen because the center of the interval will be between two frames and will sample both the previous and the next frame.
Obviously these are some significant restrictions, but that’s how VRay works.
Also keep in mind that the “Frame Velocity Offset” option does not produce “correct” velocities. What it does is take ONE frame (the closest to the sample time) and for each vertex, assign a velocity based on the influence of the particles contributing to that vertex. So if you have 100 slow moving particles and one very fast moving close to the same vertex, the result of the motion blur might not be exactly what you expect.
The correct motion blur is produced in “Subframe Particle Position”. In this mode, the position of each particle will be evaluated on each sub-frame, and a NEW MESH is built for that sample which can (and usually will) change topology vs. other sub-samples. So this mode produces unique meshes on each sub-sample and is best suited for Multi-Pass Motion Blur which is of course slow, but it looks right. The “Frame Velocity Offset” mode will looks wrong if used with Multi-Pass camera effect.
Alternatively, you can force VRay to evaluate a large number of Geometry Samples. The following example shows Shutter of 1.0, Interval Center 0.5 and Geometry Samples of 16. Obviously this produces 16 unique copies of the mesh (similar to MPass), and there will be a warning that the topology is changing, so the 6 sub-steps won’t be performed:
A word of WARNING: If your particle source is a PRT Loader and it is set to RETIME the sequence, this could break the Motion Blur. Let’s say you have a PRT Loader with Playback Graph set to play 2 times faster than the original sequence. If you pick this in Frost and try to use “Frame Velocity Offset”, the PRT Loader will produce two different sets of particles on the before and after sample because internally it will interpolate the existing frames and skip one, thus causing Frost to mesh two different topologies again. If you have to retime a sequence, always bake to a new PRT sequence first, then pick that in Frost and it will work as shown in the beginning…
I hope this gives you a basic idea of what is going on internally in V-Ray and Frost and you will be able to combine this knowledge to render in other renderers.
EDIT: I did get it to work with finalRender but why can’t I use values greater than 1.0? Ahh Force Tween but not as correct looking
Thanks for the Vray break down Bobo 
I can confirm that mental ray is not blurring correctly, I would consider this a bug.
First of all, it considers Frost a non-animated object so it ignores its animation unless you create some keyframes (for example I right-clicked the time slider on frame 0 and 100 and set keys for PRS to force mental ray to export Frost as animated object). This could be a Frost validity interval issue, but given that V-Ray and others work, it might be a mr issue. I have seen this with other objects as well.
Then, if you have the default Motion Segments 1, no motion blur is calculated.
If you change it to 2, two samples are created and regardless of the Shutter settings, the two are always different topologies, producing a messed up motion blur.
If I switch Frost to Geometry > Sphere, it blurs nicely because the topology is mostly correct (just like PFlow would blur)
I blame mostly mental ray here, but I think Frost should find a way to work with it to get it two identical topologies with offset vertices as needed…
I don’t have finalRender around to test…
Thank you for mentioning this. I didn’t realize that Mental Ray always requires consistent topology for at least one frame. You can’t work around this by changing the renderer settings. I will try to fix this.
I wasn’t sure if I messed something up in my mental ray setup (as I don’t use it that often, is does mblur pflow geometry quite quick and fairly nice ), that is why I edited the post.
The funny thing about final render is if the mblur value is greater than 0.999 the blur disappears yet the whole Frost object appears to shift. So enabling for tween or even trails it seems to really just be mBlurring the whole object and not really generating a 3d blur. I dunno a little wierd, will have to experiment some more when I get home.
Thanks everyone. This should be fixed in the next build. Motion blur will work in Mental Ray, and it will work using default settings in VRay.
EDIT: …or not. I’ll keep looking into this.
This is improved in the new build (1.0.2).
VRay: I think this is fixed. You can use the default VRay settings, or any duration you’d like.
Mental Ray: This works now, but you may need to make some changes to make sure Frost is considered animated. Here are two ways to do this:
Final Render: if anyone tries this, please let me know how it goes.
Cool will give it a try, I have been playing with this off and on over the weekend and I have been meaning to reply sooner, I keep getting sidetracked.
I get reasonable results using Force Tween although I should not have to enable this. I was getting a bit of object shift along with the blur effect. The Shift was equal to the duration of the blur. I have always had to enable the Frost object mBlur props in fR, I thought that was normal workflow for all renderers. Upon try it with Vray I guess it isn’t necessary to enable the mBlur of the Frost object.
In the latest build, you can turn off Force Tween, but you’ll still need to change Frost’s Object Properties -> fR-Properties -> Motion Blur to “3D Blur” or “Tween”. I assume this is normal for finalRender?
Well not really sure, what is normal 
I always enable all of my object properties that I want to apply blur too. Although I could see that since Frost is an “intermediate” object, ie it is grabbing mBlur velocities from another object, that it may not need to be enabled but:
I do not have to enable Frost mBlur in Vray. LOL I just realized they didn’t fix the with PFlow Display (Phantom) bug in Vray2.0
I have to enable the Frost Object props Motion Blur for Scanline too. If I use None in Frost it doesn’t work.
And fR works fine now thank you
3d Blur
No Blur
Great, thanks for checking!
We’ll need to make a note of the required settings for each renderer in the Frost docs. EDIT: looks like Bobo wrote up everything but finalRender already. Thanks! 
No problem, thanks for making it work 
Ohh I have been jones’n for some Docs are they available yet?
It looks like they’re still private. However, I have attached an old version of the help files in CHM format.
Note: you will need to “unblock” the help file to read it. To do this, right-click Frost.chm, and choose “Properties”. In the Frost.chm Properties window, in the General tab, find the “Security” line and click the “Unblock” button.
Frost_help.zip (657 KB)
Thanks, saved me from having to uninstall current version, install old version, copy help, uninstall old version, install new version 
Just FYI while I am on the mBlur kick, not exactly a practical application and I know maxwell handles mBlur totally different than everything else BUT it does work there too 
Thanks! This is good to know, because every renderer seems to be slightly different.
So drudging up this is somewhat related:
I would like to use RSMB vectors to blur and well my velocity pass well doesn’t seem to contain any velocity. Am I doing something wrong or is it not supported or…or…
BTW when actually rendering mBlur it looks real nice, it is just taking too long.