10.8.2 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 7 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 [48].

Table 7: Parameters for Common Materials

Material	GL_ AMBIENT	GL_ DIFFUSE	GL_ SPECULAR	GL_ SHININESS
Brass	0.329412	0.780392	0.992157	27.8974
	0.223529	0.568627	0.941176
	0.027451	0.113725	0.807843
	1.0	1.0	1.0
Bronze	0.2125	0.714	0.393548	25.6
	0.1275	0.4284	0.271906
	0.054	0.18144	0.166721
	1.0	1.0	1.0
Polished	0.25	0.4	0.774597	76.8
Bronze	0.148	0.2368	0.458561
	0.06475	0.1036	0.200621
	1.0	1.0	1.0
Chrome	0.25	0.4	0.774597	76.8
	0.25	0.4	0.774597
	0.25	0.4	0.774597
	1.0	1.0	1.0
Copper	0.19125	0.7038	0.256777	12.8
	0.0735	0.27048	0.137622
	0.0225	0.0828	0.086014
	1.0	1.0	1.0
Polished	0.2295	0.5508	0.580594	51.2
Copper	0.08825	0.2118	0.223257
	0.0275	0.066	0.0695701
	1.0	1.0	1.0
Gold	0.24725	0.75164	0.628281	51.2
	0.1995	0.60648	0.555802
	0.0745	0.22648	0.366065
	1.0	1.0	1.0
Polished	0.24725	0.34615	0.797357	83.2
Gold	0.2245	0.3143	0.723991
	0.0645	0.0903	0.208006
	1.0	1.0	1.0
Pewter	0.105882	0.427451	0.333333	9.84615
	0.058824	0.470588	0.333333
	0.113725	0.541176	0.521569
	1.0	1.0	1.0

Material	GL_ AMBIENT	GL_ DIFFUSE	GL_ SPECULAR	GL_ SHININESS
Silver	0.19225	0.50754	0.508273	51.2
	0.19225	0.50754	0.508273
	0.19225	0.50754	0.508273
	1.0	1.0	1.0
Polished	0.23125	0.2775	0.773911	89.6
Silver	0.23125	0.2775	0.773911
	0.23125	0.2775	0.773911
	1.0	1.0	1.0
Emerald	0.0215	0.07568	0.633	76.8
	0.1745	0.61424	0.727811
	0.0215	0.07568	0.633
	0.55	0.55	0.55
Jade	0.135	0.54	0.316228	12.8
	0.2225	0.89	0.316228
	0.1575	0.63	0.316228
	0.95	0.95	0.95
Obsidian	0.05375	0.18275	0.332741	38.4
	0.05	0.17	0.328634
	0.06625	0.22525	0.346435
	0.82	0.82	0.82
Pearl	0.25	1.0	0.296648	11.264
	0.20725	0.829	0.296648
	0.20725	0.829	0.296648
	0.922	0.922	0.922
Ruby	0.1745	0.61424	0.727811	76.8
	0.01175	0.04136	0.626959
	0.01175	0.04136	0.626959
	0.55	0.55	0.55
Turquoise	0.1	0.396	0.297254	12.8
	0.18725	0.74151	0.30829
	0.1745	0.69102	0.306678
	0.8	0.8	0.8
Black	0.0	0.01	0.50	32
Plastic	0.0	0.01	0.50
	0.0	0.01	0.50
	1.0	1.0	1.0
Black	0.02	0.01	0.4	10
Rubber	0.02	0.01	0.4
	0.02	0.01	0.4
	1.0	1.0	1.0