Incorrect blend shape on mesh that is triangulated with split faces

[rcorre]

OS:

Linux 5.10.7-arch1-1

Godot version:

3.2.2.stable.custom_build.3a752ee86

Blender version:

Blender 2.91.0 build hash: b50598bc78c7

Issue description:

1. Create a cube
2. In edit mode, Mesh > Split > Faces By Edges
3. Create a base blend shape and a new blend shape (Key1)
4. In the Key1 blend shape, move all separated faces away from one another
5. Export to godot, confirm it looks correct
6. Triangulate the faces
7. In edit mode, Mesh > Split > Faces By Edges
8. Move the individual triangles away from one another
9. Export to godot, see that the tris are not properly separated

Minimal reproduction project:

The cube on the right is not triangulated and looks correct. The cube on the left is triangulated -- note that in godot it maintains a shared edge between triangles that should be split.

example.zip

[rcorre]

I just tried GLTF, and it also gets it wrong, but in a different way. In GLTF, the cube on the left looks wrong with the shapekey at 0 and right with the shapekey at 1. Now I'm unsure if this is a problem with the exporter or with Godot ...

[scurest]

Now I'm unsure if this is a problem with the exporter or with Godot ...

That's a problem with the glTF exporter. Godot looks correct; it matches when reimporting the glTF file into Blender or using a web viewer.

[julienduroure]

I just pushed a fix on blender side. You should be able to test with next build (from April 18th): https://builder.blender.org/download/