The blending state combines 
        
        
BlendEquation and BlendFunction and the
enabled flag to define the full blending state for combining source and
destination fragments when rendering.
This is a helper when using custom render states with Appearance#renderState.
Members
    Blending is enabled using additive blending, 
source(source.alpha) + destination.
    Blending is enabled using alpha blending, 
source(source.alpha) + destination(1 - source.alpha).
    Blending is disabled.
    Blending is enabled using alpha blending with premultiplied alpha, 
source + destination(1 - source.alpha).
