Lighting -- Specifying the Lighting Model

Specifying the Lighting Model

GLvoid glLightModelfv(GLenum pname, const GLfloat *params)

pname indicates which property to change
params is a Boolean value or array of RGBA values

pname	Default Value	Description
`GL_LIGHT_MODEL_AMBIENT`	(0.2, 0.2, 0.2, 1.0)	Specifies global ambient illumination; not from any particular light source
`GL_LIGHT_MODEL_LOCAL_VIEWER`	0.0 (infinite)	Specifies whether viewer is local to the scene or an infinite distance away
`GL_LIGHT_MODEL_TWO_SIDE`	0.0 (one-sided)	Specifies whether to perform lighting calculations for both the front and back surfaces

Notes:

GL_LIGHT_MODEL_AMBIENT specifies the ambient light color when no lights are on. It represents light that is not from any particular source. The default value {0.2, 0.2, 0.2, 1.0} yields a small amount of white ambient light. So, even if you do not add a specific light source to your scene, you can still see the objects in the scene.

GL_LIGHT_MODEL_LOCAL_VIEWER changes the assumptions made about the location of the viewpoint. (It does not actually move the viewpoint).

With an infinite viewpoint (the default), the direction between it and any vertex in the scene remains constant.
With a local viewpoint, the viewpoint is assumed to be at (0, 0, 0) in eye coordinates. This affects the calculations of specular highlights. The intensity of the highlight at a particular vertex depends on the normal at that vertex, the direction from the vertex to the light source, and the direction from the vertex to the viewpoint. A local viewpoint tends to yield more realistic results, but since the direction has to be calculated for each vertex, overall performance is decreased.