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Maniphest T69261

Hair: interpolated children with 'Long Hair' option jiggling
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Description

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.15

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Worked: (optional)

Short description of error
Child hairs jittering and jiggling, while guide hair dynamics simulation looks perfectly smooth. Simulation is cached inside blendfile.

Exact steps for others to reproduce the error
See video:

Check blendfile:

xx_hair_bug.rar21 MBDownload

Thanks
Marek

Event Timeline

Marek Hollý (asil8567) created this task.Aug 28 2019, 8:00 PM
Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to 50.Aug 29 2019, 1:25 PM
Philipp Oeser (lichtwerk) added a project: Nodes & Physics.
Philipp Oeser (lichtwerk) added a subscriber: Philipp Oeser (lichtwerk).

Can confirm this.
It seems to be the Long Hair option misbehaving here (without this hair seems "stable").
I know this might not be a suitable solution, just saying for debugging purposes...
Same goes for Simple children (also stable, also not a suitable solution).

Unfortunately the current hair system has a couple of quirks, a hair rewrite is already on the horizon.
It is even marked EOL

End of life, to be replaced with new systems

https://wiki.blender.org/wiki/Modules

But I will quickly have a look at code if I find something obvious regarding the Long Hair option...
I also think that we should keep reports open (even if EOL), this might help when rewriting the system to see were the issues were...

Philipp Oeser (lichtwerk) renamed this task from CHild hairs jiggling to Hair: interpolated children with 'Long Hair' option jiggling.Aug 29 2019, 1:26 PM
Marek Hollý (asil8567) added a comment.Aug 29 2019, 3:41 PM

Hi Philipp
Thanks for taking a care. I would be really happy if you will find some easy code fix, as this is already third version of hair in my scene, and none of them worked well... and animation deadline is quickly approaching...
Marek

Philipp Oeser (lichtwerk) added a comment.Aug 29 2019, 4:17 PM

If this is mission critical, I would suggest trying to find a way to have the hair looking good without the Long Hair option tbh [might not be easy, this affects parting].
I did have a quick look (only two places really using PART_CHILD_LONG_HAIR), but more investigation is needed... no promise here at all (sorry)

Marek Hollý (asil8567) added a comment.Aug 29 2019, 4:48 PM

Sure Phillip. I am working on backup solution. Still, thanks a lot. Marek

Dalai Felinto (dfelinto) added a project: Tracker Curfew.Dec 23 2019, 1:53 PM
Sybren A. Stüvel (sybren) changed the task status from Confirmed to Needs Information from User.Jan 27 2020, 3:14 PM
Sybren A. Stüvel (sybren) removed a project: Tracker Curfew.
Sybren A. Stüvel (sybren) added a subscriber: Sybren A. Stüvel (sybren).

This example blend file is too complex to easily debug. Please update it so that it has only the minimal ingredients required to show the issue. Currently it contains a complete rig that may or may not be relevant. Please also try to reproduce the same issue in the current daily build of Blender (https://builder.blender.org/) to see if it has already been fixed, and try older versions of Blender (2.79 or older) to see if this has always been an issue or was caused by more recent changes. All this will make it much easier for us to figure out the root cause of the issue.

Dalai Felinto (dfelinto) closed this task as Archived.Feb 6 2020, 3:50 PM
Dalai Felinto (dfelinto) claimed this task.
Dalai Felinto (dfelinto) added a subscriber: Dalai Felinto (dfelinto).

Since the hair system is marked as end-of-line I will go ahead and close as invalid.
@Marek Hollý (asil8567) if you can prodiuce the simplified sample file please add as a new report, to be filled most likely as Known Issue. (and point the old report to this one, or at least mention the Long Hair findings by Philipp).