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b-bones interpolation error
Closed, ResolvedPublicKNOWN ISSUE


System Information
Operating system: Darwin-19.2.0-x86_64-i386-64bit 64 Bits
Graphics card: Intel(R) Iris(TM) Graphics 6100 Intel Inc. 4.1 INTEL-14.3.9

Blender Version
Broken: version: 2.82 (sub 5)

Short description of error
b-bones interpolation error on bones with different length

Exact steps for others to reproduce the error
open the attached blend file and play the animation. As the second b-bone rotates the first b-bone start flipping.

Event Timeline

discussed this with @Alexander Gavrilov (angavrilov), in his opinion it seems to be basically some kind of variation on gimbal lock or suchlike it for some reason computes the roll as +-180 degrees instead of near 0.
possibly it needs to use the proper swing+twist decomposition math (now that it is implemented elsewhere) instead of whatever it's doing now

Obviously rigify is affected by the issue.

Alexander Gavrilov (angavrilov) changed the task status from Needs Triage to Confirmed.Tue, Jan 14, 5:07 PM
Bastien Montagne (mont29) changed the subtype of this task from "Report" to "Known Issue".Wed, Jan 15, 10:49 AM

Not a bug per-se though, more like internal limitation of current code, so tagging as known issue.