OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Transforming Normals

In addition to transforming vertices, we will have need to transform surface normals, that is, vectors that point in the direction perpendicular to a surface at some point. In perhaps one of the most confusing twists of terminology, normals are often required to be normalized, that is, of length 1.0. However, the “normal” meaning perpendicular and the “normal” in normalize are completely unrelated, and we will come upon needs for normalized normals when computing lighting.

Typically, when computing lighting, a vertex will have a normal associated with it, so the lighting calculation knows what direction the surface reflects light. Shaders doing these calculations appear in Chapter 7, “Light and Shadow”. Here, though, we will ...