particle hair combing issue 2.8 and 2.79 #62877

Closed
opened 2019-03-23 10:37:24 +01:00 by dev369 · 5 comments

System Information
Operating system: win 10 latest
Graphics card: gtx 1070

Blender Version
Broken: blender-2.80-faecac0b5e14-win64
Worked: no idea

combing particle hair is glitching under some circumstances i think issue is similar to this: https://developer.blender.org/T61226

normal uv sphere seems to work fine for combing, but if you take for example apply shinkwrap modifier on a uv sphere to make a scalp mesh from human head, this scalp will have glitched behavior when adding hair to it and trying to comb it

the issue behaves in same manner on 2.79 as well

combing-issue.blend

**System Information** Operating system: win 10 latest Graphics card: gtx 1070 **Blender Version** Broken: blender-2.80-faecac0b5e14-win64 Worked: no idea combing particle hair is glitching under some circumstances i think issue is similar to this: https://developer.blender.org/T61226 normal uv sphere seems to work fine for combing, but if you take for example apply shinkwrap modifier on a uv sphere to make a scalp mesh from human head, this scalp will have glitched behavior when adding hair to it and trying to comb it the issue behaves in same manner on 2.79 as well [combing-issue.blend](https://archive.blender.org/developer/F6869208/combing-issue.blend)
Author

Added subscriber: @dev369

Added subscriber: @dev369

Added subscribers: @JacquesLucke, @ZedDB

Added subscribers: @JacquesLucke, @ZedDB
Jacques Lucke was assigned by Sebastian Parborg 2019-03-23 19:32:55 +01:00

@JacquesLucke any idea what is going on here? The hair seem to clump together and jiggle back and forth.

@JacquesLucke any idea what is going on here? The hair seem to clump together and jiggle back and forth.
Member

Changed status from 'Open' to: 'Archived'

Changed status from 'Open' to: 'Archived'
Member

The root cause of the issue are degenerate faces (the area of some triangles is 0).
Those were probably generated by the Shrinkwrap modifier.
This leads to bad normals (see image below, which only shows a part of the mesh in the file).

In particle edit mode, the option Deflect Emitter was activated in the topbar.
This option is supposed to prevent hair-mesh intersections.
To do this, it uses the normals, to decide which hair points have to be adjusted.
Since the normals are incorrect, this does not work.

There are two possible solutions:

  • Deactive Deflect Emitter.
  • Fix the mesh topology, so that it does not have degenerate triangles anymore.

The second solution should be preferred, because degenerate faces will most probably generate other problems later in the project.

image.png

The root cause of the issue are **degenerate faces** (the area of some triangles is 0). Those were probably generated by the Shrinkwrap modifier. This leads to **bad normals** (see image below, which only shows a part of the mesh in the file). In particle edit mode, the option **Deflect Emitter** was activated in the topbar. This option is supposed to prevent hair-mesh intersections. To do this, it uses the normals, to decide which hair points have to be adjusted. Since the normals are incorrect, this does not work. There are two possible solutions: * Deactive `Deflect Emitter`. * Fix the mesh topology, so that it does not have degenerate triangles anymore. The second solution should be preferred, because degenerate faces will most probably generate other problems later in the project. ![image.png](https://archive.blender.org/developer/F6880398/image.png)
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Reference: blender/blender#62877
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