6. Seams between separate meshes

Why the shading breaks, and common ways to match normals.

Seam handling A As is (each mesh on its own) B Match seam vertices only C Copy from a smooth shape (range R)

Range R Weaken with distance (falloff) Light direction (left/right) Light height Toon shading Toon threshold Show vertex normals

Triangles: · Drag the view to turn it.

The upper and lower parts are separate meshes with different density. The seam vertices are at exactly the same positions.
A: each mesh averages only its own faces, so the normals disagree at the seam and a shading line appears.
B: only the seam vertices get the normal computed from the joined shape. The line disappears.
C: within range R of the seam, normals are copied from a smooth shape (a sphere here). Turn off “Weaken with distance” and the change becomes sudden at the edge of the range.