Can't get 'curved' motionblur on Houdini abc particles in vrmesh node

[Dan Andersen]

We're simulating sparks in Houdini and rendering them in Maya via alembic in a vrmesh node, but are having trouble getting non-linear motion blur working. They render with curved motion blur in Mantra but once in Maya it's all straight lines no matter how high we set the geometry samples.

Anyone have experience with this sort of set up?

[vlado]

Which V-Ray version? We introduced sub-frame sampling for particles relatively recently in the nightly builds (it will go into the 3.5 update too).

Best regards,
Vlado

[Dan Andersen]

VRay build 26855. Was the sub-frame particle support introduced after that?

Should the particles have velocity baked in for each subframe or does VRay compute the velocity itself based on particle positions on subframes? (we have non-changing particle count/order so that shouldn't be a problem)

[Dan Andersen]

Okay, so we sort of managed to get it working. However it doesn't blend the substeps so you see a discrete circle for each sample.

Is this a known issue?

[vlado]

Can you show an image?

Best regards,
Vlado

[Dan Andersen]

32 geometry samples. Left is geo, right is particle


M2016 Ext1 SP5
VRay #27296

[vlado]

Yeah, that's not how it is supposed to look. Can you attach the Alembic file for this? It should be working fine, but maybe there is something else going on.

Best regards,
Vlado

[Dan Andersen]

Here are two files - one for the geo and one for the particle. They are cached with 10 substeps from Houdini.

geo_particle_alembics.abc.zip

[vlado]

Thanks for the files; we can reproduce the problem and one of the developers is looking into it.

Best regards,
Vlado

[Dan Andersen]

Thank you.

[asen.atanasov]

Hi,

this is fixed in the last few nightlies.

Best regards,
Asen

[Dan Andersen]

Awesome!