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New dependency graph Spline IK with curve control dependency cycles.
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System Information
Win7 GTX980Ti

Blender Version
Broken: 2.76 rc1 c586e30

Short description of error

With new dependency graph (blender.exe --enable-new-depsgraph) controlling a curve with Hook modifier that's targeting a bone in same armature that uses the curve for IK spline causes dependency cycle, something I would expect to work in new dependency graph.

The cycle is as follows:

Dependency cycle detected:
'BezierCurve[Object].GEOMETRY_MODIFIER(Hook-Armature)' depends on 'Armature[Object].Bone.008.BONE_DONE()' through 'Hook Modifier'
'Armature[Object].Bone.008.BONE_DONE()' depends on 'Armature[Object].Bone.008.BONE_READY()' through 'Ready -> Done'
'Armature[Object].Bone.008.BONE_READY()' depends on 'Armature[Object].Bone.008.BONE_POSE_PARENT()' through 'Pose -> Ready'
'Armature[Object].Bone.008.BONE_POSE_PARENT()' depends on 'Armature[Object].Bone.008.BONE_LOCAL()' through 'Bone Local - PoseSpace Link'
'Armature[Object].Bone.008.BONE_LOCAL()' depends on 'Armature[Object].POSE_INIT()' through 'PoseEval Source-Bone Link'
'Armature[Object].POSE_INIT()' depends on 'BezierCurve[Object].GEOMETRY_UBEREVAL()' through '[Curve.Path -> Spline IK] DepsRel'
'BezierCurve[Object].GEOMETRY_UBEREVAL()' depends on 'BezierCurve[Object].GEOMETRY_MODIFIER(Hook-Armature)' through 'Object Geometry UberEval'

Exact steps for others to reproduce the error

  • Create a Curve
  • Create Armature, extrude some bone chain and set Spline IK to the Curve
  • Add another bone in Armature, set VertexHook modifier on Curve to be controlled with this bone.


Why it is important to work

Production rigs require Spline IK for spine or tentacles. It is possible to have 2 Armatures (Control and Deform one) to solve the dependencies, but they cause problems when the Rig is linked, because you make proxy from the control armature and not the deform one, which makes editing deform armature properties (bone ID properties) impossible. Having everything in one armature is the way to go and something we hope new dependency graph should fix.



Event Timeline

Jaroslav Novotny (jerryno) raised the priority of this task from to Needs Triage by Developer.
Jaroslav Novotny (jerryno) updated the task description. (Show Details)
Sergey Sharybin (sergey) closed this task as Archived.Sep 18 2015, 2:41 PM

As mentioned in the original release notes of the depsgraph currently only armature evaluation is split into granular evaluation steps. Other objects still needs work to support all sort of weird and wonderful configuration.

So thanks for the report, but currently it's not really a bug.

I think the problem here is that the POSE_INIT component (evaluating the IK tree) is a parent for all the bones of the armature, regardless of whether they are actually part of the IK chain. The SplineIK constraint makes the pose dependent on the curve, while the curve depends on the single control bone (correctly)

Perhaps this code is a bit too greedy?$1477

Sorry for commented old report. I am solving same thing now. I am little bit confused. I understand that it is not possible use one armature for spline IK. When I tried it bone was jumping. I tried it again and it is working great. I don`t know how can I replicated this. It is working with both new and old deps graph. Do you know why it is ok?

The situation is not unsolvable per-se, it's just that the depsgraph has to make the nodes detailed enough to properly resolve the order of updates. The old depsgraph simply cannot do this, while the new depsgraph just hasn't gotten enough attention in this area.

Without a valid solution by the depsgraph the order of updates is essentially random (or rather undefined). So in some cases (often depending on selected/unselected objects) you may still get a valid update order by accident and everything seems to work fine, but then breaks on seemingly unrelated changes.