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rayt

Deform Groom curve stretching

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Hi Odforcers,

Im working on a project where I have to tear up a lawn using bullet rbd's and hair to generate grass. Ive come into a problem, or maybe a bug where the grass in the deforming rbd patches becomes very long either when moving through space,  or even at rest. I cant seem to find any other topic where this has happened before. Has anybody encountered this kind of problem with H16's hair and deform groom? Any incite would be appreciated. Id love to attach a screen shot however the content is under NDA. All I can say is imagine a bunch of curves spidering out from underneath a few selected skin patches.

Cheers!

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Guest tar

yeah - like the attached? Check your mass and physical settings, also add a substep,

WildSimHairs.png

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Thats pretty much what is happening. I am unsure where mass and substeps are. Ive been having to build the setup from scratch aat times and I dont seem to see a mass or substep attribute.

EDIT:
A colleague also noted that we are using a deform  not a simulate hair so mass and substeps are not available.

Edited by rayt

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Guest tar

haven't seen that happen and it shouldn't happen as GuideDeform is simply using an attribute interpolate I think. Check the attached.

Screen Shot 2017-11-17 at 2.42.26 PM.png

GroomedOnly.hiplc

Edited by tar

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Turns out that the issue is the collision object used to press the hair system down. Removing it fixes the odd stringy grass shapes but doesnt negate the fact that the collider is needed. Im just not sure what needs to be done. It seems that the collider in question only affects one point on each of the guides and usually sets the single point to a 90 degree angle which then messes up the groom.

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Guest tar

Trying to understand the setup, are you using 'guide collide with vdbSOP'?

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Been a week with no real success. Ive had to go over everything with a fine comb and im at a point of rebuilding a sim from scratch. Using just an rbd cube and the shelf tools I have build a simming object that works well and is fairly quick. My real question at this point is, when using a custom groom guide with multiple rbd objects, do you need a deform in your network to prevent jitters or breaking sims?

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Guest tar

I'm not following how you've set this up. A deform would be needed to lock the curves onto a RBD simulation, then the wire sim adds the dynamics to the hairs.

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Hey Ray, I had the same problem actually. I had wire simulation and collision with vdb.
Didn't solve it really, but if you'll try to use
'ray intersect' as a collision method
increase substeps
check scene scale and all parameters.
it could work

 

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It looks like Marty's setup was the key to the problem. The GroomOnly.hiplc clued me into that to have the sim behave properly is to set up an animated mesh normally with a groom deform. Then apply the sim. Asside from the occasional jump in hair length on certain areas, which im pretty sure is a substep thing, the jitter is gone. From my understanding the sim drives the deform which then drives the groom.

EDIT: if you know of a way to prevent random long groom curves I would love to hear it. Everything works well save a patch that all of a sudden becomes very long for one frame then reverts back to normal.

Edited by rayt

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