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"Exploding" mesh deformation by Bendy Bones when Preserve Volume is on
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Kubuntu Linux 18.04
Graphics card: AMD Radeon R9 290

Blender Version
Broken: 2.61, 2.70, 2.79 release, 2.80 release, daily build 2.81 Alpha, 1eead85cdc27, 2019-08-08
Worked: none

Short description of error
Bendy bones sometimes cause "exploding" mesh deformations when armature modifier flag "Preserve volume" is on. But deforming Bendy bone itself not shows any anomaly.

Exact steps for others to reproduce the error
Open file:

Launch animation playback. Text block inside also has description.



Event Timeline

Aleksander Tarkhanov (stark) renamed this task from "Exploding" deformation by Bendy Bones when Preserve Volume is on to "Exploding" mesh deformation by Bendy Bones when Preserve Volume is on.

I can reproduce this. The "detail" of the glitchiness depends on how many bbone segments there are, but the bbone segments themselves are not moving in any unexpected way, like OP said, only the mesh. So I'm guessing the problem is where the double quaternion armature deformation from bbone segments is being applied to the mesh.

Thank you, Demeter (hope I'm not confusing your name with your family name :) ) . That bug, or what it is, looks pretty old (reproducible in every Blender version I tried - down to 2.61, at a bit different bone rotation angle though) but only in 2.80 it somehow gained prominence. I consider it critical cause you don't want your character flashing with random mesh explosions during animation and not using b-bones at all also not looks like a good thing. But with 200-300 open unsorted bug reports and few dozens new a day you, developers, sure have your hands full.