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LoopTools Circle operator does not work with the mirror modifier
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Description

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1070 with Max-Q Design/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.66

Blender Version
Broken: version: 2.83 (sub 8), branch: master, commit date: 2020-03-14 00:31, hash: rBacab7450784a
Broken: version: 2.82a is also broken
Worked: 2.81a works correctly!

Addon Information
Name: LoopTools (4, 7, 2)
Author: Bart Crouch, Vladimir Spivak (cwolf3d)

Short description of error
Trying to run Circle on verts that span across the mirror line of a mirror modifier fails.

Exact steps for others to reproduce the error

  • Open the attached .blend (will open in 2.82a as well)
  • Run the Loop Tools -> Circle operator
  • Observe nonsense

Before operator runs:

After running Circle:

Event Timeline

I don't see this as a bug, but it is because this tool, like all other tools used in editing meshes, only works on the vertices/edges/faces of the original mesh.
Supporting this has many implications:

  • What if the modifier is hidden?
  • How to deal with other modifiers?

Supporting this only for the mirror modifier would be very specific and in my view it is more of a feature request than a bug.
The result in the image is not "nonsence", it is a "circle" formed with the 4 selected vertices.

There's explicit code in the addon to handle modifiers and it worked in prior versions, as well as 2.79 (so I'll invoke the magical "regression" word to keep the bug alive :))

Perhaps the problem is that .to_mesh () returns the mesh without using the mirror modifier. Therefore, this modifier is not taken into account when calculating the circle. Need more research.

Ankit (ankitm) added a subscriber: meme man (Blast).
Ankit (ankitm) added a subscriber: Ankit (ankitm).

line 548: "mod.use_mirror_merge = False" commenting out this seems to fix it

see merged task