Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't drive action like a traditionally parented bone. #95896

New Issue

Tyler Walker · 2022-02-19T19:13:52+01:00

Tyler Walker commented

2022-02-19 19:13:52 +01:00

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.

**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](https://archive.blender.org/developer/F12877097/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](https://archive.blender.org/developer/F12877101/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](https://archive.blender.org/developer/F12876154/ModularStylilzed_Character.blend) [Blender_ Constraint Example Koop 2022-02-19 09-42-54.mp4](https://archive.blender.org/developer/F12876161/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: ![image.png](https://archive.blender.org/developer/F12876157/image.png) Here's what the constraint setup looks like: ![image.png](https://archive.blender.org/developer/F12876155/image.png) This problem happens whether I select "Local" or "Local with Parent" for the target transform type.

Tyler Walker commented

2022-02-19 19:13:52 +01:00

Added subscriber: @tyler.tofu

Tyler Walker commented

2022-02-20 02:36:26 +01:00

This comment was removed by @tyler.tofu

*This comment was removed by @tyler.tofu*

Tyler Walker changed title from ~~Action Constraint - Local Space With/Without Parent breaks w/Parent Rotation~~ to Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't match traditionally parented driving bone.

2022-02-20 07:50:42 +01:00

Tyler Walker commented

2022-02-20 07:50:42 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Tyler Walker changed title from ~~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.

2022-02-20 07:52:46 +01:00

Tyler Walker commented

2022-02-20 23:21:29 +01:00

Changed status from 'Confirmed' to: 'Needs Triage'

Omar Emara commented

2022-02-21 08:42:09 +01:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-02-21 08:42:09 +01:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Omar Emara commented

2022-02-21 08:42:09 +01:00

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:

Only transformations applied to the object or bone itself are taken into account.

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.

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: > Only transformations applied to the object or bone itself are taken into account. 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.

Tyler Walker commented

2022-05-15 00:53:57 +02:00

In #95896#1311020, @OmarEmaraDev wrote:
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:

Only transformations applied to the object or bone itself are taken into account.

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.

> In #95896#1311020, @OmarEmaraDev wrote: > 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: >> Only transformations applied to the object or bone itself are taken into account. > 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.

Philipp Oeser removed the

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Action Constraint BUG - "Child of" Constraint on driving bone, local transform values don't drive action like a traditionally parented bone. #95896