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Issue trying to weight paint if object has mirror+armature.
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Description

System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.86

Blender Version
Broken: version: 2.82 (sub 1), branch: master, commit date: 2019-10-28 21:19, hash: rB2dab4393b08e
Broken: hash: 2.81 95f020c853d6, build date: 2019-10-14, 00:11:29

Worked: f88022b96f3a build date: 28/08/2019, 01:48

Short description of error
If an object has an armature its normal to move bones to see the effect and paint on the deform mesh, this always worked.
In the lastest builds it seems that adding a mirror modifier after the armature modifier mess up how the object its read and the stroke doesn't register that the mesh its deformed.

Exact steps for others to reproduce the error


1-Open the blend file
(it was tested using default factory settings too but it was created with my normal set up, you may see some addons active, as i said i also tested in a default settings)
2-try to paint in the blue circle(1), nothing should happen.
3-try painting in the red square(2) it should paint, as if the cylinder wasn't deformed.
4-Reload the .blend file
5-delete the mirror modifier and repeat step 2 and 3

Event Timeline

Germano Cavalcante (mano-wii) lowered the priority of this task from Needs Triage by Developer to Confirmed, Medium.

Can I confirm.
This is probably due to using a mesh_eval_deform instead of mesh_eval_final somewhere.
@Jeroen Bakker (jbakker), is this your area?

Can confirm, happens while using Mask modifier too. Please fix, super annoying.

Perhaps the same root cause as T68352.

Would be awesome if these bugs got some love, it's been a pain in the butt having to disable mirror and mask modifiers every time I go into weight paint mode. Note that I also need to change shading options when going into weight paint mode ever since 2.80. This means going into or out of weight paint mode now takes 6-8 actions (and my script to automate these actions causes crashes).

Perhaps the same root cause as T68352.
Would be awesome if these bugs got some love, it's been a pain in the butt having to disable mirror and mask modifiers every time I go into weight paint mode. Note that I also need to change shading options when going into weight paint mode ever since 2.80. This means going into or out of weight paint mode now takes 6-8 actions (and my script to automate these actions causes crashes).

Yea, also the wireframe checkbox in weight paint does nothing now but that's a whole other issue.

Mask can be moved after the Armature modifier, but mirror is a problem. This bug basically ignores all modifier starting with the first non-pure-deform modifier in the stack.

Since there fortunately was a specific 'worked' and 'broken' version pair in this report, I found which specific change broke it and reverted it.

Now it just skips those Mirror and Mask modifiers like before, which is not ideal, but better than this behavior.