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Rigify Meta-Human Neck Bone stretching
Confirmed, NormalPublic

Description

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.19

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-02-12 16:20, hash: rB77d23b0bd76f

Short description of error
This may not necessarily be an error, but it results in Odd if not completely wrong behavior.

  1. Create a new file.
  2. Add armature Human Metarig
  3. Generate Rigyfy Rig.
  4. Enter Pose Mode
  5. Grab neck bone, and G Z Upwards, or around.

You'll see arms, breast, clavicles, just assuming weird shapes.
https://gyazo.com/f0b77fbd8d42d36da57828e98f281aa4

I do not have an older version to test at the moment, but I'm fairly sure that in prior version moving the neck caused stretching of the neck - not all the other bones that go with it. This is an issue specifically for the Breast bones, since they scale badly.

Event Timeline

Ivan Cappiello (icappiello) changed the task status from Needs Triage to Confirmed.EditedApr 2 2020, 2:59 PM

issue confirmed. It is probably related to the new rig types.
there are some difference in how the constraints are done in this spine setup vs the old one.
to make it work again as it was before this are the required changes:

• remove constraints from ORG-spine.003

change the DEF-spine.003 constraints as follows:

• Copy Transforms (target Bone: tweak_spine.003)
• Damped Track (target Bone: tweak_spine.004)
• Stretch To (target Bone: tweak_spine.004)

EDIT:
this is not working if only spine.003 is fixed.
all the constraints on spine bones have to be moved from ORG to its DEF correspondent.
all the spine ORG-bones have to be unconnected-childs of their correspondent tweak.

@Andy (MostHostLA) if you don't need all the new FK options in the new spine, you can use a temporary fix reverting to old spine system.
In order to do so you have to:

• select neck_bone in edit mode and enable the connected option in the bone properties panel. Then go in pose mode and remove the rigify property (*spines.super_head*)
•select the first spine bone in pose mode and change the rigify property from "spines.basic_spine to" "spines.super_spine"
•generate the rig

I gave this thing a shot, but I definitely want to hear what Alexander thinks about the solution in that patch. I also proposed two alternatives, including considering this as an unsupported feature, which would be a big shame, but certainly the easiest solution. ;)

@Demeter Dzadik (Mets) i'd like to have some more information about this from @Alexander Gavrilov (angavrilov). I believe he changed the hierarchy for a reason, still this leads to an unintended behaviour (stretching and skewing).
Looking from a different angle, i believe that if the skewing/scaling issue is fixed, the general way the spine works now is pretty nice.
This has been around for a while. And is actually classified as a bug since skewing shouldn't happen. So if @Alexander Gavrilov (angavrilov) has no other clever solution right now i'd be prone to accept the patch.