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I use a particle system to simulate fur (for an animation). To mimic the structure of the fur I combed it back.

Unfortunately, the 'Simple Children' option spawns some shorter strands of hair which I can't explain as all of the hair particles are much longer and pointing backwards.
Those strands of hair pretty much seem to ignore their parent particles.

What am I doing wrong?

Top-down view: Hair particles from a top-down-view. The hair is combed back, but in the front are 3 strands that stand out. The area is also marked with a pink circle.

Side view: Hair particles from a side-view. Another pink circle marks the area in which the shorter hair grows.

Close up view (pointing topwards): Close up of hair particles. They are combed back.

Render results: Two render results, in which a "row" of shorter hair is visible.


Image of my particle settings.


I use blender 2.93.5 on linux.


Some of my attempts that turned out false:

  • First I thought it is caused by the emitters 'Subdivision Surface' modifier, but the 'Use Modifier Stack' option is checked and the problem also occurs when I apply the modifier.
  • Then I thought it is caused by the kink, but the undesired hair is also spawned when there is no kink at all (the hair is less prominent though).
  • Obviously I also tried to comb the hair in a different manner, but this barely affected the shorter hair.

In case anyone is wondering why I don't use the 'Interpolated Children' option: The result seemed very unpredictable with 'Hair Dynamics' activated as well (at least for this kind of animation).

UPDATE:

I did separate the fur into smaller particle systems, which made it more obvious that the problem is caused by the behaviour Allen Simpson discribed.

top-down view on all particle systems on the left, and a one of its parts on the right.

On the blenderartists forum someone suggested that it could be caused due to an excessive radius on the children.

The 'Root' parameter definitely contributes to the overall effect, but doesn't seem to be the cause of the problem.

Different 'root' values and their effects.

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  • $\begingroup$ Hm. seen things like that too, I'm not exactly sure either. If you have applied all scales to the object. I always assumed its a result of averaging over edges, hairs grow from surfaces but two angled surfaces have an egde? $\endgroup$
    – Peter
    Oct 15, 2021 at 12:39
  • $\begingroup$ you might fill a bug report at blender (you can do that from within the app). $\endgroup$
    – Peter
    Oct 15, 2021 at 12:40

1 Answer 1

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I don't know much about Hair Dynamics, but I know that Simple Children do not respect the mesh like Interpolated.

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With the amount of hair on your mesh my thinking is that these are stray roots poking through the mesh.

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