Specifying Alpha
Alpha values, like the red, green, and blue components of a color, are 8-bit values in the range [0..255]. Glide maintains a constant alpha value as part of the constant color described in the previous chapter that is set with grConstantColorValue(). Alpha values associated with vertices are set in the GrVertex structure, along with the geometric coordinates and other parameters.

Chapter 6                                                                 Next : Alpha Combine Unit