Validation of CG Models - An Introduction to Computer Graphics for Artists - page 126

Fig. 9.14 Polygon 1 has a lamina face. When rotated, it will fl icker as the software attempts to
determine which of two coincident faces is in front of the other. Face 2 is not a lamina face, and
displays properly

Fig. 9.15 In this example, the fl oor does not have locked normals, so it receives a shadow from the
character. The character's normals are locked, so it renders as a silhouette

9.3.9 Locked Normals

An object with locked normals will render as nearly black, with very faint highlights,
despite having strong lights in the scene it is a part of (Fig. 9.15 ). You will know this
has happened if your object does not seem to receive light when lights are brought
into your scene. It will receive light, but so faintly that it will barely be detectable.