"Exploding" mesh deformation by Bendy Bones when Preserve Volume is on #68422

New Issue

Aleksander Tarkhanov · 2019-08-08T20:42:53+02:00

2019-08-08 20:42:53 +02:00

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, 1eead85cdc, 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:
bendy-bones-preserve-volume-deform-bug.blend
Launch animation playback. Text block inside also has description.

**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.![b-bone-preserve-volume-bug-illustration.jpg](https://archive.blender.org/developer/F7654866/b-bone-preserve-volume-bug-illustration.jpg) **Exact steps for others to reproduce the error** Open file: [bendy-bones-preserve-volume-deform-bug.blend](https://archive.blender.org/developer/F7654864/bendy-bones-preserve-volume-deform-bug.blend) Launch animation playback. Text block inside also has description.

Aleksander Tarkhanov commented

2019-08-08 20:42:53 +02:00

Added subscriber: @AleksanderTarkhanov

Aleksander Tarkhanov changed title from ~~"Exploding" deformation by Bendy Bones when Preserve Volume is on~~ to "Exploding" mesh deformation by Bendy Bones when Preserve Volume is on

2019-08-08 20:47:58 +02:00

Demeter Dzadik commented

2019-08-08 21:56:43 +02:00

Added subscriber: @Mets

Demeter Dzadik commented

2019-08-08 21:56:43 +02:00

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.

Aleksander Tarkhanov commented

2019-08-15 09:14:00 +02:00

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.

Sybren A. Stüvel self-assigned this 2019-12-06 13:43:55 +01:00

Sybren A. Stüvel removed their assignment 2019-12-06 15:22:08 +01:00

Sybren A. Stüvel commented

2019-12-06 15:22:08 +01:00

Added subscriber: @dr.sybren

Sybren A. Stüvel commented

2019-12-06 15:22:08 +01:00

I can't quickly solve this, don't see anything obvious exploding in the code.

Sybren A. Stüvel commented

2020-01-02 14:55:20 +01:00

As this has been in Blender for so long, and there is no quick obvious solution, I'll mark this as a known issue.

Aleksander Tarkhanov commented

2020-01-02 15:55:31 +01:00

Ah, bad. It would be fine if you'd know how to not stuck into it, but now it is a lottery. Not paralyzing my work, but still is bad to have mathematics glitch somewhere that can ruin your day. Probably I need to rebuild every twisting Bendy Bone in my rigs into two-bone setup now, painful.

I know you, developers, have your own plans for Blender and you forced to say "no" sometimes, but now I feel that filling bug reports is kind of... useless, you don't need them most of the time, even when you have more hands for the project than usual. It is somehow weird. And if I'll find and resolve the issue and will commit a patch - for what I heard, you, developers, even struggling to approve patches.

Hope you know better though. Thanks for Blender - Blender 2.8x is still great piece of software.

Ah, bad. It would be fine if you'd know how to not stuck into it, but now it is a lottery. Not paralyzing my work, but still is bad to have mathematics glitch somewhere that can ruin your day. Probably I need to rebuild every twisting Bendy Bone in my rigs into two-bone setup now, painful. I know you, developers, have your own plans for Blender and you forced to say "no" sometimes, but now I feel that filling bug reports is kind of... useless, you don't need them most of the time, even when you have more hands for the project than usual. It is somehow weird. And if I'll find and resolve the issue and will commit a patch - for what I heard, you, developers, even struggling to approve patches. Hope you know better though. Thanks for Blender - Blender 2.8x is still great piece of software.

Sybren A. Stüvel commented

2020-01-03 10:49:45 +01:00

And if I'll find and resolve the issue and will commit a patch - for what I heard, you, developers, even struggling to approve patches.

Please do. The new triaging approach is meant to free up developer time and speed up patch approval.

> And if I'll find and resolve the issue and will commit a patch - for what I heard, you, developers, even struggling to approve patches. Please do. The new triaging approach is meant to free up developer time and speed up patch approval.

Philipp Oeser removed the

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"Exploding" mesh deformation by Bendy Bones when Preserve Volume is on #68422