Object shows seams when illuminated with directional light

[tfoller]

It could happen if computeVertexNormals() is applied an object that have seams (for uv unwrapping).
computeVertexNormals doesn’t understand that face normals, calculated along the seam, need to be averaged with face normals across it. Incorrect normals will produce a mismatch in illumination.

This might be relevant:

Is computeVertexNormals working correctly?

I have a cylinder setup, it starts with smooth transition between vertical faces: [calcVert_01] after computeVertexNormals() is applied, the smooth transition remains, except the edge between the first and the last face, where there are 3 different normals instead of 2 (or 3 matching in to 2 before): [calcVert_02] this creates a jump between normals on more complex geometries, where there shouldn’t be any: [calcVert_03]