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Mirror Weights to symmetrical bone removes original weights
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Description

System Information
Windows 10 home
Geforece GTX 1080

Blender Version
Broken: 2.79b

Short description of error

Mirror vertex weights from bone.L to bone.R no longer works properly.
It will mirror over the weights, but remove the weights from the original bone.
The desired result would be to mirror the weights to .R but keep the weights on .L

Exact steps for others to reproduce the error

  • have at least two bones symmetrically positioned
  • one named bone.L the other named bone.R
  • a mesh skinned to these bones
  1. Set armature to pose mode
  2. Select mesh and enter Weight Paint mode
  3. CTRL select bone.L
  4. paint weight influences
  5. CTRL select bone.R
  6. select "Mirror" from the "Weight Tools" menu
    • The bone.L weights should now be properly mirrored to bone.R
    • The bone.L weights are gone

Details

Type
Bug

Event Timeline

Afaikt this is working as intended (unless I misunderstand something).

And to me it seems the situation is a bit different than you describe:

  • blender doesnt "remove the weights from the original bone"
  • the bone.L weights "are not gone"

Since the default of the operator is to also flip the names (Flip Group Names) it will -- as expected -- mirror the weights of bone.L to the other side (but also make that name bone.R) and make existing bone.R --> bone.L.
So weights of original bone.L are not gone but are now what was originally in bone.R.

While current behaviour might not always be desired behavior I think what you want to do is:

  • remove bone.R vertex group [you want to ditch that content anyways]
  • select bone.L vertex group and make a copy (Copy Vertex Group) -- will be named "bone.L_copy"
  • select "bone.L_copy" and mirror that vertexgroup
  • rename to "bone.R" (this will automatically be associated with the bone "bone.R" since its namebased)

aha, I see.
Apologies for the false report then.

I thought mirror was a one click solution for mirroring weights over.
I was aware of the method you described, but it seems a bit cumbersome.
Perhaps a good opportunity for an addon/script.

Best regards,
Fred

I think it's broken, even in the mirror button tool tip is described as "flipping when both sides are selected, otherwise copy from unselected". and it does not perform as it is expected at all.

Hi @Luciano Muñoz Sessarego (looch)

I think it's broken, even in the mirror button tool tip is described as "flipping when both sides are selected, otherwise copy from unselected". and it does not perform as it is expected at all.

This refers to which vertices are selected in vertex selection masking (and not which bones are selected).
Where do you think this is not "performing as expected at all"?

Btw: I agree an operator like the one desired in the report would be welcome, but still dont think there is a bug in Mirror Vertex Group [which is apparently not the same -- as far as I can see...]