Convert HSVA to RGBA

hsva2rgba.cpp

template<class T>
T clip(const T& n, const T& lower, const T& upper) {
	return std::max(lower, std::min(n, upper));
}

typedef std::array<GLfloat, 4> Color;
//Conversion according to http://www.rapidtables.com/convert/color/hsv-to-rgb.htm
Color hsva2rgba(const Color &hsva)
{
	static const double PI = 3.14159265359;
	
	GLfloat h = fmod(fmod(hsva[0], 2 * PI) + 2 * PI, 2 * PI); // 0° <= H <= 360°
	GLfloat s = clip(hsva[1], 0.0f, 1.0f);
	GLfloat v = clip(hsva[2], 0.0f, 1.0f);
	GLfloat a = clip(hsva[3], 0.0f, 1.0f);

	float c = v * s;
	float x = c * (1.0f - fabs(fmod(h*3.0f / PI, 2.0f) - 1.0f));
	float m = v - c;

	switch (int(floor(h*3.0f / PI)))
	{
	case 0: //[0°,60°)
		return{ m + c, m + x, m, a };
	case 1: //[60°,120°)
		return{ m + x, m + c, m, a };
	case 2: //[120°,180°)
		return{ m, m + c, m + x, a };
	case 3: //[180°,240°)
		return{ m, m + x, m + c, a };
	case 4: //[240°,300°)
		return{ m + x, m, m + c, a };
	case 5: //[300°,360°)
		return{ m + c, m, m + x, a };
	}
}