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Maniphest T49190

Model scaling distorts hair that uses kink
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Description

System Information
OS: Ubuntu Linux 16.04, kernel 4.4.0-34
GPU: EVGA GeForce GTX 950 FTW, driver 361.42

Blender Version
Broken: 2.77a abf6f08

Short description of error
When hair kink settings such as curl or wave are used with hair, and the emitting model is scaled, the hair becomes distorted. No change to the hair appearance occurs when kink is not being used (assuming the hair is combed, that is). The problem is likely because the kink is based on world scale instead of local or pose scale. This issue can be problematic for character models using kink, if those models are using scaling.

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps

  1. Download and open the following .blend file:
    HairKinkBug.blend598 KBDownload
  2. Observe the unscaled hair system
  3. Select the emitter sphere, then scale it down to about 0.1 scale.
  4. Zoom in and observe the distorted hair.

Event Timeline

Zauber Paracelsus (zauberexonar) created this task.Aug 29 2016, 1:42 AM
Zauber Paracelsus (zauberexonar) added a comment.Aug 29 2016, 2:49 AM

I found a simple workaround for this issue: hooking up drivers to the kink's Amplitude and Frequency properties, and in the driver multiply their desired values by the model's scale.

Sergey Sharybin (sergey) changed the task status from Unknown Status to Unknown Status.Aug 29 2016, 9:56 AM
Sergey Sharybin (sergey) claimed this task.
Sergey Sharybin (sergey) added a subscriber: Sergey Sharybin (sergey).

Thanks for the report, but unless it's a recently added regression it's not considered a bug.

Hair is planned for the whole refactor/recode for 2.8 projects so current code we don't maintian anymore.

Thanks for the report anyway.