10.8.1 Modeling Material Type

Material properties are modeled with the following OpenGL parameters:

GL_ AMBIENT

How ambient light reflects from the material surface. This is an RGBA color vector. The magnitude of each component indicates how much the light of that component is being reflected.

GL_ DIFFUSE

How diffuse reflection from light sources reflect from the material surface. This is an RGBA color vector. The magnitude of each component indicates how much the light of that component is being reflected.

GL_ SPECULAR

How specular reflection from a light source reflects from the material. This is an RGBA color vector. The magnitude of each component indicates how much the light of that component is being reflected.

GL_ EMISSION

How much of what color is being emitted from this object. This is an RGBA color vector. The magnitude of each component indicates how much light of that component is glowing from the material. Since this parameter is only useful for glowing objects, we'll ignore it in this section.

GL_ SHININESS

How mirror-like the specular reflection is from this material. This is a single integer. The larger the number, the more rapidly the specular reflection drops off as the viewing angle diverges from the reflection vector.

For lighting purposes, materials can be described by the type of material, and the smoothness of its surface. Material type is simulated by the relationship between color components of the GL_ AMBIENT, GL_ DIFFUSE and GL_ SPECULAR parameters. Surface smoothness is simulated by the overall magnitude of the GL_ AMBIENT, GL_ DIFFUSE and GL_ SPECULAR parameters, and the value of GL_ SHININESS. As the magnitude of these components get closer to one, and the GL_ SHININESS value increases, the material appears to have a smoother surface.

For lighting purposes, material type can be divided into four categories: dielectrics, metals, composites, and other materials.