Add gfx::hue(colorf)

libs/gfx/include/psemek/gfx/color.hpp

@@ -317,6 +317,39 @@ namespace psemek::gfx
 		return generic_color{dark(c.c, darkness)};
 	}
 
+	template <typename T, std::size_t N> requires (std::is_floating_point_v<T> && (N == 3 || N == 4))
+	T hue(math::vector<T, N> const & c)
+	{
+		T max = std::max({c[0], c[1], c[2]});
+		T min = std::min({c[0], c[1], c[2]});
+		T delta = max - min;
+
+		if (delta == T{0})
+			return T{0};
+
+		T result;
+
+		if (c[0] > c[1] && c[0] > c[2])
+		{
+			result = (c[1] - c[2]) / delta;
+		}
+		else if (c[1] > c[2])
+		{
+			result = 2.f + (c[2] - c[0]) / delta;
+		}
+		else
+		{
+			result = 4.f + (c[0] - c[1]) / delta;
+		}
+
+		result *= math::rad<T>(60);
+
+		if (result < 0)
+			result += math::rad<T>(360);
+
+		return result;
+	}
+
 	std::optional<color_rgba> parse_color(std::string_view const & text);
 
 }