Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't drive action like a traditionally parented bone. #95896
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Reference: blender/blender#95896
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System Information
Operating system: Windows 11
Graphics card: RTX 2070
Blender Version
Broken: 3.0.0 Master
Worked: Never
Short description of error
With an action constraint driven by a local space transformation channel, rotation of any parent bone in the chain breaks evaluation.
Exact steps for others to reproduce the error
I've just made a simple 3 bone rig to test this action constraint issue and found the root cause.
Action Constraint Rotation Test.blend
Turns out the problem only happens when a Child of Constraint is used on the bone driving the action constraint. When you use a bone with a true parent to drive the action constraint this behaves as expected.
Blender_ [G__My Drive__Commissions_Koop - Jeremiah Bethune_Modular Stylized Character_Action Constraint Rotation Test.blend] 2022-02-19 17-32-06_Trim.mp4
The same problem is illustrated in this file in a character rig application:
ModularStylilzed_Character.blend
Blender_ Constraint Example Koop 2022-02-19 09-42-54.mp4
Upon rotation of any parent bone in the chain, the constraint is not evaluated the same. Even though the local transformation is exactly the same on the hand bone (which drives the action constraint). Example with root bone rotated 45 degrees:
Here's what the constraint setup looks like:
This problem happens whether I select "Local" or "Local with Parent" for the target transform type.
Added subscriber: @tyler.tofu
This comment was removed by @tyler.tofu
Action Constraint - Local Space With/Without Parent breaks w/Parent Rotationto Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't match traditionally parented driving bone.Changed status from 'Needs Triage' to: 'Confirmed'
Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't match traditionally parented driving bone.to Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't drive action like a traditionally parented bone.Changed status from 'Confirmed' to: 'Needs Triage'
Added subscriber: @OmarEmaraDev
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
It seems the Target's local space location is considered to be that after constraints are applied on the target bone. The documentation states for Local Space that:
So either the behavior is wrong or the documentation should clarify that by stating that constraints are taken into account. Tagging the appropriate module for clarification.