23.2.4 Diffuse Term

The diffuse term needs to take into account whether light falls directly on the vertex, the diffuse color of the light, and the diffuse material property:

$(\max \{l \cdot n, 0\}) \ast \hbox{diffuse}_{light} \ast \hbox{diffuse}_{material}$

where:

l = (l_x, l_y, l_z) is the unit vector that points from the vertex to the light position (GL_POSITION).

n = (n_x, n_y, n_z) is the unit normal vector at the vertex.