RGB - HSV conversion

colors.adb

package body Colors is

	function To_HSV (Source : RGB) return HSV is
		Max : constant Lightness := Lightness'Max (Lightness'Max (Source.Blue, Source.Green), Source.Red);
		Min : constant Lightness := Lightness'Min (Lightness'Min (Source.Blue, Source.Green), Source.Red);
		Diff : constant Lightness := Max - Min;
		Result : HSV;
	begin
		Result.Value := Max;
		if Max > Min then
			Result.Saturation := Diff / Max;
			declare
				Temp_Hue : Hue'Base;
			begin
				if Source.Blue = Max then
					Result.Hue := 4.0 + (Source.Red - Source.Green) / Diff;
				elsif Source.Green = Max then
					Result.Hue := 2.0 + (Source.Blue - Source.Red) / Diff;
				else
					Temp_Hue := (Source.Green - Source.Blue) / Diff;
					if Temp_Hue < 0.0 then
						Temp_Hue := Temp_Hue + 6.0;
					end if;
				end if;
				Result.Hue := Temp_Hue * (2.0 * Ada.Numerics.Pi) / 6.0;
			end;
		else
			Result.Saturation := 0.0;
			Result.Hue := 0.0;
		end if;
		return Result;
	end To_HSV;

	function To_RGB (Source : HSV) return RGB is
		Diff : Lightness;
		N1, N2, N3: Lightness;
		Result : RGB;
	begin
		if Source.Saturation = 0.0 then
			Result.Red := Source.Value;
			Result.Green := Source.Value;
			Result.Blue := Source.Value;
		else
			declare
				Temp_Diff : constant Lightness'Base := Source.Hue * 6.0 / (2.0 * Ada.Numerics.Pi);
			begin
				Diff := Temp_Diff - Lightness'Floor (Temp_Diff);
			end;
			N1 := Source.Value * (1.0 - Source.Saturation);
			N2 := Source.Value * (1.0 - Source.Saturation * Diff);
			N3 := Source.Value * (1.0 - Source.Saturation * (1.0 - Diff));
			declare
				Pi : constant := Ada.Numerics.Pi;
				V : Lightness renames Source.Value;
			begin
				if    Source.Hue = 0.0            then Result.Red := V ; Result.Green := N1; Result.Blue := N1;
				elsif Source.Hue < Pi       / 3.0 then Result.Red := V ; Result.Green := N3; Result.Blue := N1;
				elsif Source.Hue = Pi       / 3.0 then Result.Red := V ; Result.Green := V ; Result.Blue := N1;
				elsif Source.Hue < Pi * 2.0 / 3.0 then Result.Red := N2; Result.Green := V ; Result.Blue := N1;
				elsif Source.Hue = Pi * 2.0 / 3.0 then Result.Red := N1; Result.Green := V ; Result.Blue := N1;
				elsif Source.Hue < Pi             then Result.Red := N1; Result.Green := V ; Result.Blue := N3;
				elsif Source.Hue = Pi             then Result.Red := N1; Result.Green := V ; Result.Blue := V;
				elsif Source.Hue < Pi * 4.0 / 3.0 then Result.Red := N1; Result.Green := N2; Result.Blue := V;
				elsif Source.Hue = Pi * 4.0 / 3.0 then Result.Red := N1; Result.Green := N1; Result.Blue := V;
				elsif Source.Hue < Pi * 5.0 / 3.0 then Result.Red := N3; Result.Green := N1; Result.Blue := V;
				elsif Source.Hue = Pi * 5.0 / 3.0 then Result.Red := V ; Result.Green := N1; Result.Blue := V;
				else                                   Result.Red := V ; Result.Green := N1; Result.Blue := N2;
				end if;
			end;
		end if;
		return Result;
	end To_RGB;

end Colors;

colors.ads

with Ada.Numerics;
package Colors is
	pragma Pure;

	subtype Lightness is Float range 0.0 .. 1.0;
	subtype Hue is Float range 0.0 .. 1.0;
	subtype Saturation is Float range 0.0 .. 2.0 * Ada.Numerics.Pi;

	type RGB is record
		Red : Lightness;
		Green : Lightness;
		Blue : Lightness;
	end record;

	type HSV is record
		Hue : Colors.Hue;
		Saturation : Colors.Saturation;
		Value : Lightness;
	end record;

	function To_HSV (Source : RGB) return HSV;
	function To_RGB (Source : HSV) return RGB;

end Colors;