// Formula from https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef

double RelativeLuminance(Color color) {
	auto comp = [&] (double c){
		c /= 255;
		return (c <= 0.03928) ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4);
	};
	return comp(color.GetR()) * 0.2126 + comp(color.GetG()) * 0.7152 + comp(color.GetB()) * 0.0722;
}

// Formula from https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef

double ContrastRatio(Color c1, Color c2) {
	double rl1 = RelativeLuminance(c1);
	double rl2 = RelativeLuminance(c2);
	return (max(rl1, rl2) + 0.05) / (min(rl1, rl2) + 0.05);
}