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X-mirror activated in Edit Mode missleadingly affects symmetry in Weight Paint Mode
Open, Confirmed, LowPublic

Description

System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060 3GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.35

Blender Version
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-16 23:08, hash: rB12da679fa094
Worked: (optional)

Short description of error
When you activate "x-mirror" under "Options" in Editmode and switch to Weight Paint Mode, the x-mirror stays active for all weight paint actions even if symmetry is turned off in the Symmetry options (of the weight paint tool) which is very missleading... (took me half an hour to find out why there is a mirror on all my weightpaint strokes)

If x-mirroring is turned off in Edit Mode, everything works as expected.

Exact steps for others to reproduce the error

Create a new blend file.
Subdivide the cube a couple of times.
Go to Edit Mode.
Check "X-Mirror" in the active tool settings.
Switch to Weight Paint Mode.
Switch to front view.
Add some weights with the brush to some of the verts in the cube.

--> brush strokes are mirrored even if Mirror in Symmetry is turned off

Details

Type
Bug

Event Timeline

This is also the case in 2.79 and while could be improved [I see the point where this gets confusing], I think there are just two settings that have an effect on weightpaint being mirrored: the mesh option plus the paint option, if either one is active, mirroring will take place...

I would not consider this a bug at this point, but hesitate to close yet... Other opinions? @William Reynish (billreynish), @Campbell Barton (campbellbarton) , @Brecht Van Lommel (brecht) ?
I remember a similar discussion about X-Mirror being a tool option only [and the removal of the mesh option], but the outcome was in favor of keeping the mesh option...

Philipp Oeser (lichtwerk) triaged this task as Waiting for Developer to Reproduce priority.Jun 17 2019, 10:57 AM

Sounds like a bug to me, I don't know why both options should have an effect, especially if one of them is hidden.

Weight Paint mode is super weird. We actually have two mirroring options - Symmetry and X-mirror. I don’t understand why we even have X-mirror here at all

I guess this is related to the discussion in D3869 (also see https://blenderartists.org/t/x-mirror-behavior-in-2-8-poll-and-opinions/)
So there seems to be an advantage of having this per mesh not just as a tool option... (at least for mesh editing, I assume this goes hand in hand with weightpainting as well though...)

Looks like we could do two things:

  • drop the mesh option as having an influence on weightpaint [I guess this would have users voting against, see above]?
  • display the mesh option in weightpaint tool symmetry as well?

I find it super confusing that we have both. It’s very unclear what happens if you enable one or the other, and it’s just generally confusing.

Symmetry is more powerful because we have X, Y and Z. I would just remove X-mirror from weight paint mode.

Symmetry is more powerful because we have X, Y and Z. I would just remove X-mirror from weight paint mode.

I agree.

Though I guess topological mirror may be useful? I guess it's possible to add that option in the symmetry panel, not sure how difficult it is to make it work.

Yes, true. That's the most tricky bit I suppose. Really we should ideally merge these things, so that you can do topological mirror for all axes, and have a single mirror setting, rather than the current two competing methods.

I find it super confusing that we have both. It’s very unclear what happens if you enable one or the other, and it’s just generally confusing.

Agree it's in a very bad state.

Symmetry is more powerful because we have X, Y and Z. I would just remove X-mirror from weight paint mode.

The issue with this is currently these are different features.

  • Symmetry: behave as if you are painting on the other side of the object.

    This doesn't ensure symmetrical weights, from a quick test I managed to get non-symmetrical weights (there must be some subtle difference when the mirrored brush is applied).

    This has an advantage that you can symmetrically weight paint onto an asymmetrical mesh, although I'm not sure users would take advantage of this much in practice.
  • X-Mirror: for each vertex find it's mirror, and ensure identical weights, painting onto the flipped vertex group if it ends with an extension such as .L or .R.

Given this, we might be better doing the opposite and disabling symmetry mirroring until it's as capable as the existing weight paint mirror option.

@Campbell Barton (campbellbarton)

Ok, that makes sense - seems like it's better to add Y and Z to the X Mirror option and remove Symmetry.

Adding Y & Z will require many more changes, this wouldn't be for 2.80.

Brecht Van Lommel (brecht) lowered the priority of this task from Waiting for Developer to Reproduce to Confirmed, Low.Wed, Jul 3, 4:38 PM