Configurable light direction for polyhedra shading #49
Description
Polyhedra shading currently uses a fixed light direction along the viewing axis (camera position). The Lambertian shading formula computes cos_angle = abs(normal[2] / norm_len), so faces pointing at the viewer are brightest and edge-on faces are dimmed.
This works well for tilted views but gives nearly uniform shading when looking straight down a layer of octahedra, since all visible faces have similar angles to the viewer.
A configurable light direction (independent of the camera) would allow shading to be visible from any viewing angle. For example, a light from the top-left would give clear face brightness variation even in a top-down view.