Color Values for Lights and Materials
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4/8/2010
Microsoft® Direct3D® Mobile describes color in terms of four components — red, green, blue, and alpha — that combine to make a final color. The D3DMCOLORVALUE C++ structure is defined to contain values for each component. Each member is a floating-point value that typically ranges from 0.0 to 1.0, inclusive. Although both lights and materials use the same structure to describe color, the values in the structure are used a little differently by each.
Color values for light sources represent the amount of a particular light component it emits. Because lights do not use an alpha component, only the red, green, and blue components of the color are relevant. You can visualize the three components as the red, green, and blue lenses on a projection television. Each lens might be off (a 0.0 value in the appropriate member), it might be as bright as possible (a 1.0 value), or it might be some level in between. The colors coming through the lenses combine to make the light's final color. A combination like R: 1.0, G: 1.0, B: 1.0 creates a white light, where R: 0.0, G: 0.0, B: 0.0 does not emit light at all. You can make a light that emits only one component, resulting in a pure red, green, or blue light, or, the light could use combinations to emit colors like yellow or purple. You can even set negative color component values to create a dark light that actually removes light from a scene. Or, you might set the components to some value larger than 1.0 to create an extremely bright light.
With materials, on the other hand, color values represent how much of a light component is reflected by a surface that is rendered with that material. A material whose color components are R: 1.0, G: 1.0, B: 1.0, A: 1.0 reflects all the light that comes its way. Likewise, a material with R: 0.0, G: 1.0, B: 0.0, A: 1.0 reflects all the green light that is directed at it. Materials have multiple reflectance values to create various types of effects. For more information, see Material Properties.
Color values for ambient light are different from those used for direct light sources and materials. For more information, see Direct Light vs. Ambient Light.