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Symmetrize and Mirror Modifier change the Normals on a Mesh
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Short description of error

Symmetrize and Mirror Modifier change the Normals on a Mesh

Exact steps for others to reproduce the error

I tried to use Symmetrize on a unsymmetrical mesh body but it ended up like in this picture:

The mesh is unsymmetrical, because it has in total 2207 vertices and the left side of it has 1105, whereas the right side has 1103 vertices.

To recreate the bug:

Simple .blend file:

I went into Edit mode and selected all the vertices and then clicked on Mesh -> Symmetrize (the destructive operation)

But also I tried the non-destructive mirror modifier, which ended up in the same result.

I have to note that the mesh is using "Custom Splits Normal Data" already applied to it.

System Information
Operating system

Blender Version
2.79 Date: 2018-04-16 16:13 Hash: eb6fe5fa94b



Event Timeline

Unfortunately operations that alter topology are not supporting Custom Split Normals:

Thanks for the report, but there is nothing new here, custom normals have never been supported with topology-editing modifiers or operations (like mirror one). Iirc, 2017 GSoC tackling editing of custom normals also added their support to mirror modifier, not sure when we'll have time to merge it in master though :|
But in general, you should never modify topology of your mesh once you have added custom normals, we might end up supporting a limited set of cases (like the mirror modifier), but this is not a good idea anyway. Custom normals are designed to support alterations of the shape (deformations), but absolutely not of the topology, this is not possible. So this is a known limitation/low priority TODO at best. ;)

sorry for the duplicate and thanks for the answer :)