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Bone Roll Calculation creates very unexpected results.
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Description

System Information
windows 7, nvidia

Blender Version
Broken: (example: eb4f2b4 )

Short description of error

Bone roll is going bananas when rotating a bone that has local Y aligned to global Z axis. I can add a blend file if necessary.

Exact steps for others to reproduce the error

  • Create an empty scene.
  • Add a single bone
  • enable axes display (in Object Data properties)
  • go to front view
  • verify that bone roll is set to 0
  • now "r" ...

The bone rotates instantly (jumps to) about 45 degree along its y axis, and bone roll jumps like crazy.

I expected:

  • bone roll remains at 0
  • bone does NOT rotate along its y axis.
  • bones Z axis flips such that it always points "as upwards as possible".

Go on as follows:

  • rotate the bone by 90 degrees so that its local Y axis points to global X
  • set bone roll manually to 0
  • now rotate the bone slowly by a total of 180 degrees.

The bone no longer rotates along its local Y axis(expected). While the bone rotation goes from 0 to -180, its bone roll goes up to 90 and then lowers again back to 0. And the local Z axis flips when stepping over the 90 degree angle (expected).

I expect:

  • bone roll remains at 0 all the time.

Details

Type
Bug

Event Timeline

Gaia Clary (gaiaclary) set Type to Bug.
Gaia Clary (gaiaclary) created this task.
Gaia Clary (gaiaclary) raised the priority of this task from to Needs Triage by Developer.

✘ Merged into T38843.