Available blending modes for drawing.
Pixel = Source * Source.a + Dest * (1 - Source.a)
Pixel = Source + Dest.
Pixel = Source * Dest.
Pixel = Source.
http://www.sfml-dev.org/documentation/2.0/group__graphics.php#ga80c52fe2f7050d7f7573b7ed3c995388
See Implementation
Laurent Gomila, Jeremy DeHaan
Available blending modes for drawing.