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Maniphest T66582

Floaty disconnected bones appearing on complex rigs
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Description

System Information
Operating system: macOS Mojave & Pop!_OS
Graphics card: AMD FirePro D700 6 GB & Iris Integrated

Blender Version
Broken: 2.80 (2019007-07 23:53) Hash: bb2abacb4b5c
Worked: Never... but sometimes..?

Short description of error
Sometimes when building complex rigs my armature will decide it dislikes a bone or bones and the bone acts as if its disconnected from the rest of the armature but sort of jiggly (See Video Below). Its very strange. Kinda neat looking but not what I am going for. This effect seems to show up and disappear and random. It remains after export to FBX and Collada if the animation is exported when the bug is showing up.

Exact steps for others to reproduce the error
I wish I could detail how this happens. It really only happens after i have been working on a rig for a while. It does seems to happen a lot with bones connected to IK constraints but its has happened to other bones at random as well.

NORA_RigLabel.blend16 MBDownload

NORA_RigLabel.blend6 MBDownload

Related Objects

Event Timeline

Alex (newyear) created this task.Jul 8 2019, 11:04 PM
Germano Cavalcante (mano-wii) added subscribers: Sergey Sharybin (sergey), Germano Cavalcante (mano-wii).Jul 9 2019, 3:03 PM

If you open the console you will see that the rig has 14 dependency cycles.
This is usually cause of delay.
But I don't have much knowledge in this area.
@Sergey Sharybin (sergey), what do you think, this is a bug?

depedency_cycles_log.txt12 KBDownload

Sergey Sharybin (sergey) added a comment.Jul 9 2019, 3:18 PM

Undefined behavior of rig when it has dependency cycle is not a bug.

There is chance it is fake/avoidable dependency cycle, but for investigation we need a simple rig, which only includes relevant parts, with as few bones as possible.

Germano Cavalcante (mano-wii) lowered the priority of this task from 90 to 30.Jul 9 2019, 3:31 PM
Alex (newyear) added a comment.Jul 9 2019, 4:27 PM

I have removed all unnecessary bones, mesh, and constraints. If anything is removed from this version of the model the floatybone issue stops happening. Looks like their are still 9 dependency cycles. Hope this helps and is not all just user error. ha ha. Thanks for taking a look at this.

Floatybones_Example.blend11 MBDownload

Floatybones_Example.blend1 MBDownload

Germano Cavalcante (mano-wii) added a comment.Jul 9 2019, 4:45 PM

@Sergey Sharybin (sergey), in the new attached file, when you move the bone near the origin and press ESC the problem is more noticeable.
But I still can't confirm if it has any fake/avoidable dependency cycle.

Alex (newyear) added a comment.EditedJul 9 2019, 4:59 PM

I have played with it a little more and gotten it down to 1 dependency cycle. This is a different area of the rig but when you move the bone (LargeLegAnchor.R) you will see that bone (LargeLegTrack.R) has the floaty bone issue. In this version file if you delete the copy rotation constraint the issue goes away but not if you just turn it off. This seems to be the same issue but is being caused by something different? Not sure.

Floatybones_Example2.blend1973 KBDownload

Floatybones_Example2.blend973 KBDownload
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Sergey Sharybin (sergey) changed the task status from Unknown Status to Unknown Status.Jul 9 2019, 5:13 PM
Sergey Sharybin (sergey) claimed this task.

In the original file from Floatybones_Example.blend bone Thigh2.L copies rotation from Thigh2Pivot.L, but at the same time Thigh2.L is parent of Thigh2Pivot.L. Rest of the cycles seems to have similar nature.

Floatybones_Example2.blend has similar situation.

This is real dependency cycle and we can not do anything about it. You'd need to find a way to rig your model without introducing such cycles.

Alex (newyear) added a comment.Jul 9 2019, 5:16 PM

Thanks again for looking at this. Glad it's just me and not a bug. ha ha. Cheers!

Germano Cavalcante (mano-wii) mentioned this in T69615: Baked Animations with 1 Frame Delay using Constraints.Oct 16 2019, 8:39 PM
Germano Cavalcante (mano-wii) mentioned this in T74061: Bone poses not updating while having multiple constraints.Feb 21 2020, 8:05 PM