Chapters 4 and 5 of the Red Book.
RGB v. Color Indexing
In OpenGL, you can specify either RGB or Color Index modes. RGB is more suitable than color mapping for Stellarium because we want to generate colors that are smoothed out, and just picking a range of indexes might get wildly different colors that so happened to be beside each other on the color map. Meanwhile, in RGB changing the individual R, G, B components vary the color in an unsurprising way.
Each component is separately considered, then summed together.
Ambient - light from no particular direction, heavily scattered
Diffuse - light from 1 direction, heavily scattered
Specular - light from 1 direction, reflected in 1 direction (shininess)
Emissive - light from the object
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