xGen density multiplier error

[sharktacos]

If the xgen density multiplier is set above 1, and you render an animation of a deforming geo (like a character moving for example) the xGen primitives will appear on different places on different frames, So if you have a character with a beard talking, the xGen hair will randomly jump around on his face on each frame. Not good.

This error is easy to reproduce:
1. make a sphere with xGen interactive groom
2. skin sphere to a joint and keyframe the scale of the joint to grow up and down.
3. set the xGen density multiplier to 2.
4 batch render

Clearly not desired behavior. Is this something that can be fixed on the side of Chaos/Vray?

[shaio]

Hi,
which V-Ray and Maya versions do you use? I'll try to reproduce it on my end and get back to you with some more information.
Thank you for the feedback.

[sharktacos]

I'm on Maya2017 update 4, using Vray 3.6. Pretty sure however that the error is also present with Maya 2018.

[shaio]

Is it possible to share a simple scene so we could take a look at the problem. I tried a few setups and wasn't able to reproduce. Maybe I'm missing something.

[sharktacos]

Yes, can I email it to you?

[shaio]

Great, please send it to ivan.shaykov@chaosgroup.com or support@chaosgroup.com (with a link to the thread). I'll check the scene as soon as I receive it.

[sharktacos]

File has been sent!

[shaio]

I received the scene and rendered a few times in batch and GUI Rendering and still without any issues. I've tried in both Maya 2017 update 5 and 2018 update 4 using V-Ray 3.60.01, V-Ray 3.60.05 and V-Ray Next beta 3 but without any success on reproducing it. Can you send me a log from Maya or a few rendered frames showcasing the Issue?

[sharktacos]

It can be hard to see. Try the following: take the scene I gave you and add a clump modifier to the xGen description. Then change the density multiplier from 2 to 10.

I'm attaching a movie file of the render with those settings. The error is quite easy to spot on it, the xgen primitives jump on random frames. See if you can replicate.

[shaio]

I see the problem. I'll setup some more tests try to reproduce it and get back to you with some more info.

[shaio]

I reproduced it now. The problem is coming form the clump modifier. I'll check with the developers and see what we can do about this. Thanks for the feedback.

[shaio]

Hi,
it seems that this is indeed an issue inside xGen and unfortunately there is nothing we can do about it. I sew that the other renders behave the same way. If I happen to find a workaround for this I'll let you know if it's helpful.

[sharktacos]

One workaround is to bake the xgen down so there is no clump modifier. There currently is no “merge layers” or “flatten layers” option in xGen, but you can effectively flatten everything by using the xGen transfer function. Definitely a bug that hopefully Autodesk will fix at some point.