dynamic fur

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Hello,


I got a little scene here with a torus and some wire guides.
When applying a fur system, some fur (hairs) don't follow the guides and stay right up.
What can be the reason for this rare behaviour.

Using H 9.1.218, windows xp


thanks,


bern

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dynamic_fur.hipnc (345.0 KB)

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Hello,


is this a bug or is there another way to avoid this?


thanks,


bern
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Not a bug. It has to do with the faces at the top of to torus being flat and that the fur SOP interpolates the results along the face as it randomly builds the hair.

For example, if you set the torus SOP's rows to 8 you will see that the hairs stand straight up ad the top of the torus as the dynamics are acting straight down and you have perfectly straight up hairs.

If you add some initial velocity in x or z in the Wire Object Fur DOP or put a fan force on the top blowing down to get the fur to splay outward gives you a bit better result.

Ultimately you want to comb surface point normals (with either a Point or Facet SOP followed with a Comb SOP) on the geometry before the Copy SOP to comb the hair. Don't forget to turn off “Transform cumulative” in the Copy SOP. You want to comb a part in the top of the torus hair.
There's at least one school like the old school!
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Thanks Jeff,


But when all the Wires (Wire object) are hanging down, I still get Fur hairs standing up. These hairs are also jumpy when the simulation runs….

see illustration: blue= wire dop, red= fur interpolation hairs…


bern

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fur.jpg (45.1 KB)

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Yes a perfect ring of flat faces lying on an xz plane that needs to interpolate from hairs lying one way to hairs lying the other way. Yes some of the middle hairs will be standing straight up and yes they may be a bit unstable.

Fortunately there are no real creatures that look like a low res polygon torus.

By rebuilding the torus such that there was an edge facing up (instead of a face) and by adding a slight bit of velocity in X and pushing them down a bit with a bit of noise in a fan I got them to settle down without the flipping issues. The edge facing up gives you the chance to have a real part in the hair.

Another approach is to define vertex attributes and use those to part the fur at the top. Again you need an edge at the top to get the most control over this.
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“Another approach is to define vertex attributes and use those to part the fur at the top. ”

What kind of vertex attributes would need to be applied to make the hair part?
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