Why not recalculate the normals for changing the value of the morph in the tangent space of geometry before the geometry begins to deform by the skin modifier (), just as it happens in 3d editors?
In the bind pose, we recalculate the normals for the morph (GPU?), Then we deform the skin.
PS:After some verification it looks like it is already happening but not like in 3d editor.
Possible 3 options:
The skin improperly transforms the normals.
The morph is incorrectly transformed into a normal.
both
https://issues.unrealengine.com/issue/UE-33456
I do not understand why the error does not require correction?
The behavior of the normals does not correspond to their behavior in the 3d editor.
Because of this, it is impossible to accurately predict the behavior of the normals in UE4
In particular when using a combination morph + skin animations