OpenGL 4 Shading Language Cookbook - Third Edition

Directional lights

We can also avoid the need to compute a light direction (s) for each vertex if we assume a directional light. A directional light source is one that has no position, only a direction. Instead of computing the direction towards the source for each vertex, a constant vector is used, which represents the direction towards the remote light source. This is a good way to model lighting from distant sources such as sunlight. We'll look at an example of this in the Shading with a directional light source recipe of Chapter 4, Lighting and Shading.