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Hair particle system instancing along paths gives initial shape pinch
Confirmed, LowPublicBUG


System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.59

Blender Version
Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-04-24 15:23, hash: rBa8441fc90086
Worked: (newest version of Blender that worked as expected)

Short description of error
I am trying to make shape instancing to hair system and it gives bad results according tip orientation of each hair

Exact steps for others to reproduce the error
Open this file, try to drag hair tips to different directions

Event Timeline

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Confirmed.Apr 27 2020, 9:50 PM
Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Bug".

I can confirm it but I don't know exactly how this modifier should work.
And the manual is not very clear about what type of particle it should be used for.

Apparently the modifier uses the rotation of the last segment in the strand.

@Germano Cavalcante (mano-wii) as far it bends shape along hairs and as far it have «create along path» it should use curves properly.
Yes, I know, that particles an be rendered like paths.
But this paths give the same bad results.
I am surem this option made for hairs. It even have random length (in modifier)
So if it is «work like intended», that means, the intension was veery weird.
And anyway, there should be ability to have hairs with custom shape.

I know ppl make complicated workaround for it: for example baking all pats dynamics/physics, then instance along theese paths with Animation nodes.

Brecht Van Lommel (brecht) triaged this task as Low priority.May 1 2020, 6:13 PM

I found two issues with the algorithm that is used to deform the mesh.

  1. To minimize twisting it seem to try to keep track of the hair direction from bottom to top. However, for that to work it would also have to process the vertices from bottom to top, which it doesn't. I got much better results already by simply sorting the mesh elements from bottom to top with the corresponding edit mode operator.
  2. It seems to use the orientation of the face as initial direction of the deformed mesh, instead of the initial hair segment.

After sorting the elements I don't get these weird face orientation issues anymore.