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Maniphest T42202

Bone Constraints: IK & Copy Scale
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Description

System Information
Windows 7 64, HD 5770

Blender Version
Broken: 95182d1 (2.72 release) + ee5936c

Short description of error
Not sure if this is a bug.

Armature Pose Mode: Bones with Copy Scale constraint cant display correct scale if their rotation has changed with IK constraint or even Copy Rotation IK.

Exact steps for others to reproduce the error

IK_Scale.blend648 KBDownload

  • Add an Armature, go into Editmode.
    • Add 2 Bones: IKbone and TARGETbone
    • Set them up for Inverse Kinematics (IK).
    • Give IKbone a Copy Scale constraint.
      • Use TARGETbone as target.

Scale and rotation of IKbone is now controlled by TARGETbone.

  • Move TARGETbone to change IKbones rotation.
  • Scale TARGETbone to change IKbones scale.

Problem:
The IKbones scale works as if it has no rotation.

Note: This applys also to bones that take rotation from an IKbone via Copy Rotation constraint. (Green bone in picture)
Its like a link to the "buggy" IK rotation, but it appears to be different.

Related Objects

Event Timeline

Karja Krähwald (karja) created this task.Oct 13 2014, 7:58 AM
Karja Krähwald (karja) raised the priority of this task from to 90.
Karja Krähwald (karja) updated the task description. (Show Details)
Karja Krähwald (karja) added a project: BF Blender.
Karja Krähwald (karja) edited a custom field.
Karja Krähwald (karja) added a subscriber: Karja Krähwald (karja).
Bastien Montagne (mont29) lowered the priority of this task from 90 to 30.Oct 13 2014, 8:00 AM
Bastien Montagne (mont29) added a subscriber: Bastien Montagne (mont29).

Please always attach a .blend file to help us reproducing the issue.

Karja Krähwald (karja) added a comment.Oct 13 2014, 8:15 AM

Was attached. (above picture :D)

Bastien Montagne (mont29) raised the priority of this task from 30 to Normal.Oct 13 2014, 8:20 AM

Meh, sorry, my bad :/

Bastien Montagne (mont29) added a subscriber: Joshua Leung (aligorith).Oct 13 2014, 8:35 AM

Ok, so this is really complex to fully understand what happens here… But imho, you are suffering a well known limitation of current constraints system - space evaluation of constraints is done from 'org' situation of the bone/object, not from previous constraint's result. This is a major limitation that tend to often breaks advanced setup compared to expected results…

Joshua, would say we can close it as known TODO?

Joshua Leung (aligorith) changed the task status from Unknown Status to Unknown Status.Oct 13 2014, 3:13 PM
Joshua Leung (aligorith) claimed this task.

The main thing you're actually seeing here is the fact that IK chains only get solved after all the other constraints in the bone have been handled. So, regardless of where you place those constraints, they'll still get evaluated first, and then the IK solver goes over the top and tries to calculate what the transforms should be.based on what it has seen.

So, I think this is probably a known todo.