graphics - How to mix two ARGB pixels?

Question

How can I mix two ARGB pixels ?

Example

Here A is (Red with Alpha) and B is ( Blue with Alpha ).

Answer 1

Taken from the same Wikipedia article where you got the image:

Translating to values which range from 0 to 255:

rOut = (rA * aA / 255) + (rB * aB * (255 - aA) / (255*255))
gOut = (gA * aA / 255) + (gB * aB * (255 - aA) / (255*255))
bOut = (bA * aA / 255) + (bB * aB * (255 - aA) / (255*255))
aOut = aA + (aB * (255 - aA) / 255)