Lighting Model

The OpenGL lighting model distinguishes between four types of light, one of which is internal:

• Emissive

• Ambient
  • Directionless
• Diffuse
  • Intensity dependent on the angle between the light source and the surface normal.
• Specular
  • Intensity dependent on the angle between the light source, the surface normal, and the viewing direction.

The color at a vertex is computed as follows:

where

• is the emissive RGB value of the current material
• is the ambient RGB value of the lighting model, i.e. it is not associated with a specific light source
• n is the number of light sources
• is the light source constant attenuation coefficient
• is the light source linear attenuation coefficient
• is the light source quadratic attenuation coefficient
• d is the distance from the vertex to the light source
• is the ambient RGB value of the light source
• is the ambient RGB value of the material
• is the unit vector from the vertex to the light source
• is the surface normal vector
• is the diffuse RGB value of the light source
• is the diffuse RGB value of the material
• is the sum and the vector from the vertex and the viewpoint
• Sh is the specular exponent of the material
• is the specular RGB value of the light source
• is the specular RGB value of the material

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