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Cyclic dependency when b-bones parameters are driven by a child bone
Closed, ResolvedPublic

Description

System Information
Operating system: Win 10
Graphics card: Gtx 980

Blender Version
Blender 2.8 latest build
Worked: Blender 2.79b

Short description of error
A bone parented to another bone, can't drive the parent bendy bone values (easein, easeout...) without creating a dependency cycle (resulting in one frame lag, plus crashing Blender when many bones are setup this way). Since it is a common scenario when rigging characters, to add tweak controllers on characters, and it used to work fine in Blender 2.79, I would strongly recommend to consider it as a bug instead of a "feature". It would be a pain to rig without that working properly, and would totally break existing rigs from Blender 2.79.

Exact steps for others to reproduce the error

  • Open the attached blend file:

  • The left bone is parented to the right bone. It's driving its bendy values.
  • Open the console, a dependency cycle is detected.
  • Here is the file made in Blender 2.79, works fine