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8.5.2 Modeling Material Smoothness

As mentioned before, the apparent smoothness of a material is a function of how strongly it reflects and the size of the specular highlight. This is affected by the overall magnitude of the GL_AMBIENT, GL_DIFFUSE and GL_SPECULAR parameters, and the value of GL_SHININESS. Here are some heuristics that describe useful relationships between the magnitudes of these parameters:

  1. The spectral color of the GL_AMBIENT and GL_DIFFUSE parameters should be the same.
  2. The magnitudes of GL_DIFFUSE and GL_SPECULAR should sum to a value close to one. This helps prevent color value overflow.
  3. The value of GL_SHININESS should increase as the magnitude of GL_SPECULAR approaches one.

No promise is made that these relationships, or the values in Table 3 will provide a perfect imitation of a given material. The empirical model used by OpenGL emphasizes performance, not physical exactness.

For an excellent description of material properties, see [23] for more information.

Table 3: Parameters for common materials