A technique of portraying transparency when drawing
an object.
It combines the color of an object to be drawn (the source)
and the color of whatever the object is to be drawn on top of (the
destination).
The higher the blending factor of the source object, the more opaque the
object looks.
Mathematically, a blending factor is a real number between 0 and 1,
inclusive.
A 32-bit color is made up of four 8-bit channels: alpha,
red, green, and blue.
These channels are represented as (A, R, G, B).
When referring to the source, the channels are denoted as As, Rs, Gs, and Bs;
for the destination, they're Ad, Rd, Gd, and Bd.