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Alembic doesn't export custom normals correctly
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Description

System Information
Windows 10 and GTX 970
Blender Version
Broken: 2.79

Short description of error
When trying to export a mesh with custom normals as Alembic they are not exported correctly. If the mesh shading was set as smooth or flat before adding the custom normals you get that after reimporting the Alembic file.

If I try to import it in other programs like Marmoset Toolbag, 3ds Max 2016 or Maya 2018 the shading is full of errors if the box "Normals" was ticked during export, even if there were no custom normals to export.

Mesh with custom normals (I apply the Data transfer modifier before exporting):

Mesh after being reimported:

Mesh after being imported in Marmoset:

Mesh in Maya:

The mesh in the left is it without custom normals, only "smooth" but with "Normals" ticked during export, the one in the right is the one of the previous images but in 3ds Max, also with broken normals:

Exact steps for others to reproduce the error

  1. Make any type of mesh or use the one in the file.
  2. Add custom normals to it, like adding Data Transfer with a sphere overlapping the mesh to transfer its normals, like I did in the first image (remember to have Auto Smooth unselected).
  3. Apply Data Transfer or any modifiers.
  4. Export the mesh as Alembic with "Normals" selected.
  5. Reimport.

Details

Type
Bug