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Cloth sim: Sewing and Self Collision issue
Confirmed, NormalPublicBUG


System Information
Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 398.36

Blender Version
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-06 00:27, hash: rB8b2b79c2108b
Worked: (optional)

Short description of error
When using sewing feature of the cloth simulator, it leaves a gap between sewn vertices. This only happens when Self Collision of the cloth is also on. In Blender 2.79 this is working correctly, i.e. there are no gaps.

Exact steps for others to reproduce the error
With the default cube, delete four side faces ("Only Faces" option, leaving the edges intact). The apply the Cloth modified in the Physics tab and use Sewing with Force 100. You can play the simulation to verify now it works correctly. After checking "Self Collision" and playing the simulation again, there are now gaps.

Event Timeline

I have attached a file to demonstrate the issue. Just open the .blend and run the animation/simulation, two frames are enough. There are two clothes with Sewing on and Sewing Force 100 (and Gravity = 0 for easier tests).

The left one is sewn perfectly. The right one has Self Collision set to On with Distance = 0.1, which breaks the sewing process. The vertices on the right are repulsed and are never sewn together, there is a gap between them. The bigger the Self Collision distance, the bigger the gap.

Sebastian Parborg (zeddb) lowered the priority of this task from 90 to 50.

@Ish Bosamiya (ish_bosamiya) is this something that might have been fixed in your GSoC branch?

No, the GSoC project will not tackle/fix this bug.

This bug is there for at least 6 months.
Is anybody still in charge of this task ?

Not really, I might take a look at it when I have time, but that might take a while.

Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Bug".Mon, Feb 3, 2:46 PM

Apparently the strength of the self collision always surpasses that of sewing, regardless of the value.