Blending
Combines color of object being drawn with color in frame buffer
Makes drawn object appear transparent
Most common method:
R = A1 * R1 + (1-A1) * R2
G = A1 * G1 + (1-A1) * G2
B = A1 * B1 + (1-A1) * B2
e.g. if alpha is 0.25:
R = 0.25 * R1 + 0.75 * R2
G = 0.25 * G1 + 0.75 * G2
B = 0.25 * B1 + 0.75 * B2
next