A faceted sphere can look angular because each quad has its own normal. Smooth shading averages normals at model points and interpolates them across faces, producing gradual lighting changes without adding geometry. section 9.2.3
A convincing low-poly sphere
A sphere made from only a few hundred quads can appear smoothly curved onscreen. The mesh remains faceted; only the normals used for the lighting calculation change. This makes smooth shading an economical way to improve appearance. section 9.2.3
Figure 9.11 By smoothly interpolating the normals of a sphere made of quads, you make the sphere itself look smooth.
See how interpolated normals make a quad-based sphere look smooth while leaving its underlying geometry unchanged. section 9.2.3
Keep these distinctions in mind:
- Smooth shading changes shading normals, not the model’s actual vertices, faces, or silhouette. section 9.2.3
- Normal mapping goes further by altering normals from bitmap data, adding apparent detail without adding quads or triangles. section 9.2.3
