Softlight calculation

gistfile1.txt

CGFloat calculateSoftlight(CGFloat a, CGFloat b) {
  // via http://en.wikipedia.org/wiki/Blend_modes#Soft_Light
  CGFloat f;
	
	if ( b <= 0.5 ) {
		f = a - (1 - 2 * b) * a * (1 - a);
	} else {
		CGFloat g;
 
		if (a <= 0.25) {
			g = ((16 * a - 12) * a + 4) * a;
		} else {
			g = sqrt(a);
		}
 
		f = a + (2 * b - 1) * (g - a);
	}
 
	return f;
}