I'm having some strange issues with motion blur when combining a rigged character and some cached vellum cloth.

Without motion blur the frame looks fine, but when I activate motion blur in Redshift I can see the skin “blurring” though the cloth. As if the motion blur for both objects is calculated in a different way.

At first I was using an MDD cached character from Softimage, and a vellum cache for the cloth simulation. So I thought this was a difference between the way MDD and Houdini cache is handled. So instead of using MDD cache I loaded the FBX rig and re-cached the cloth.

But the problem persists.

Anyone noticed something similar and has a solution ?

Thanks.

R.

Just in case someone else runs into this.

Found that the mesh deformation velocity attribute is disabled by default. So no motion blur for cached meshes until you turn that on.

Go figure.

Why would you turn that off by default ?? By enabling motion blur in the render settings one would expect it to work for all objects by default, no for some and others not.

R.

toonafish
Found that the mesh deformation velocity attribute is disabled by default. So no motion blur for cached meshes until you turn that on.

as long as your geometry is deforming, it should be doing Deformation Motion blur and not requiring velocity
you have to have at least 2 Geo Time Samples on Mantra however, which is 1 by default

but since your deforming body has motion blur I'd assume you set it to at least 2
and also assume your cloth is just deforming and has constant topology, then you should just need to make sure it's being interpolated between frames
obviously you can go for velocity motion blur, but just in case you need deformation blur with multiple nonlinear samples

Hey thanks, I'm using Redshift.

It's a cached cloth object that's not deforming or moving in any other way. So all Motionblur is coming from deformation. So when “Mesh Deformation Blur From Velocity Attribute” = off, no motion blur whatsoever.

The strange thing is that when I load an MDD cached file, that's not deforming in any other way as well. I get motion blur with the “Mesh Deformation Blur From Velocity Attribute” being off.

Go figure.

R.

toonafish
… cached cloth object that's not deforming

toonafish
…So all Motionblur is coming from deformation

so it is deforming
deforming simply means that the topology is consistent and only the point poisitions are simply changing over time

you shouldn't need “Mesh Deformation Blur From Velocity Attribute” for that, but as I said make sure your geo is interpolating between frames, .mdd and .abc loaders may do that for you, but if you are loading a sequence of .bgeosc files it will not interpolate automatically, so maybe add Time Blend SOP to see if it helps
but again if you are using linear motion blur anyway and already baked velocity works for you, you may not need to mess with it, but just for understanding the issue sake