Forums Technical Discussion why when increasing vellum substeps with wire jumps?

why when increasing vellum substeps with wire jumps?

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pelos
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i just have a ball with hairs, with sub steps of one looks great, if i do 2 sub steps now they are super jumpy and every random frames will kinda pop... shouldn't increasing the sub steps ensure this doesn't happen?

any ideas or hint?
Edited by pelos - July 28, 2023 18:11:32

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interact_vellum.hip (729.5 KB)

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tamte
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Make sure your colliders and pinned points interpolate smoothly between frames
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tamte
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in your particular case it's because the orient attribute on your hair jitters a lot even between frames

mostly because you are generating it on animated hair

to avoid that copy your hair onto the static ball and then deform using Guide Deform SOP onto the animated or deforming ball after Vellum Hair SOP
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pelos
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... is interesting even trying with the guide deforms adding an orientation, or adding a timeblend to get the substeps at geometry level still same outcome...

i try different combinations and still... with higher substeps hairs are unstable.

could this be a bug?

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tamte
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you should deform it after vellumhair1, not before, since vellumhair1 is computing the hair orient and for that to be stable it's better to compute it on rest hair
but also it is only important if you are pinning orientation to animation, which you are not doing anymore in the latest file, still good to keep in mind, especially for stiffer hair if you want them to follow root's orient

another issue is that your root point is forced into collision with the sphere, the easiest is to set disableexternal to 1 for root points
Edited by tamte - July 30, 2023 01:54:10

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hair_substeps_fix.hipnc (636.8 KB)

Tomas Slancik
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pelos
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i been analyzing the scene, since under vellum object we do have "compute missing orientation" thanks i didn't know about the
disableexternal, interesting that with one sub step doesn't consider the root very close to the surface and is all good, with substeps the root been collision does get weird. your pointwrangle deactive the root from been consider, and does work, (just on my craziness moving the lines/hairs farter (than the thickness)) did the trick as well (not that we want that but was just to check)

as always thanks for sharing your wisdom!
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tamte
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pelos
since under vellum object we do have "compute missing orientation" t
The problem is not missing orientation, but orientation that is computed on animated hair every frame using world Y as up vector
So even if it was missing recomputing wouldn't be stable
But as I mentioned, it's only important if orientation is pinned also
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Benyee
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tamte
you should deform it after vellumhair1, not before, since vellumhair1 is computing the hair orient and for that to be stable it's better to compute it on rest hair
but also it is only important if you are pinning orientation to animation, which you are not doing anymore in the latest file, still good to keep in mind, especially for stiffer hair if you want them to follow root's orient

another issue is that your root point is forced into collision with the sphere, the easiest is to set disableexternal to 1 for root points
Logically, the setup must work well, however, if pin the orientation of roots, the hairs still pop at frame 79. Is this strange issue caused by or related to roots collision or other aspects?
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tamte
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other thing you can do is change your pin constraints to soft
soft with high stiffness are always better than permanent

I usually also keep pin constraints separate from hair or cloth constraints node, that way you can control pin stiffness separately
Edited by tamte - July 31, 2023 22:42:02
Tomas Slancik
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Benyee
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Soft pin works well in this situation, perfect. It seems only hard pin for orientation causes the single frame popping, hard pin for position doesn’t affect.
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