Eroica · July 30, 2017 16:32 · Jul 30, 2017
diff --git a/happylittlecolors.lua b/happylittlecolors.lua
@@ -0,0 +1,236 @@
+--
+-- HappyLittleColors.lua
+--
+-- Copyright (C) 2017 Eroica
+-- 
+-- This software is provided 'as-is', without any express or implied
+-- warranty.  In no event will the authors be held liable for any damages
+-- arising from the use of this software.
+-- 
+-- Permission is granted to anyone to use this software for any purpose,
+-- including commercial applications, and to alter it and redistribute it
+-- freely, subject to the following restrictions:
+-- 
+-- 1. The origin of this software must not be misrepresented; you must not
+--    claim that you wrote the original software. If you use this software
+--    in a product, an acknowledgment in the product documentation would be
+--    appreciated but is not required.
+-- 2. Altered source versions must be plainly marked as such, and must not be
+--    misrepresented as being the original software.
+-- 3. This notice may not be removed or altered from any source distribution.
+--
+
+local class_constructor = {
+	__call = function (cls, ...)
+		local _ = cls.New(...)
+		-- Disable creation of new keys
+		cls.__newindex = function (t, k, v) return end
+		return _
+	end,
+}
+
+
+-- Forward declarations for local functions. Should improve that some day ...
+local PivotRgb
+local PivotXyz
+local ToRgb
+local XyzColor
+local LabColor
+
+
+
+
+local RgbColor = {}
+RgbColor.__index = RgbColor
+setmetatable(RgbColor, class_constructor)
+
+function RgbColor.New (r, g, b)
+	return setmetatable({R = r, G = g, B = b}, RgbColor)
+end
+
+function RgbColor.__eq (lhs, rhs)
+	return lhs.R == rhs.R and lhs.G == rhs.G and lhs.B and rhs.B
+end
+
+function RgbColor.__tostring (self)
+	return "(" .. self.R .. ", " .. self.G .. ", " .. self.B .. ")"
+end
+
+function RgbColor:Copy ()
+	return RgbColor(self.R, self.G, self.B)
+end
+
+function RgbColor:ToXyz ()
+	local r = PivotRgb(self.R / 255.0)
+	local g = PivotRgb(self.G / 255.0)
+	local b = PivotRgb(self.B / 255.0)
+
+	return XyzColor(r * 0.4124 + g * 0.3576 + b * 0.1805,
+	                r * 0.2126 + g * 0.7152 + b * 0.0722,
+	                r * 0.0193 + g * 0.1192 + b * 0.9505)
+end
+
+function RgbColor:ToLab ()
+	return self:ToXyz():ToLab()
+end
+
+
+XyzColor = {}
+XyzColor.__index = XyzColor
+setmetatable(XyzColor, class_constructor)
+
+function XyzColor.New (X, Y, Z)
+
+	-- Create closures for some constant values, otherwise one could just do
+	-- getmetatable(xyz_color).Epsilon = -1
+	local WhiteReference = {X = 95.047, Y = 100.000, Z = 108.883}
+	local Epsilon = 0.008856
+	local Kappa = 903.3
+
+	function XyzColor.WhiteReference() return WhiteReference end
+	function XyzColor.Epsilon() return Epsilon end
+	function XyzColor.Kappa() return Kappa end
+
+	return setmetatable({X = X, Y = Y, Z = Z}, XyzColor)
+end
+
+function XyzColor.__eq (lhs, rhs)
+	return lhs.X == rhs.X and lhs.Y == rhs.Y and lhs.Z and rhs.Z
+end
+
+function XyzColor.__tostring (self)
+	return "(" .. self.X .. ", " .. self.Y .. ", " .. self.Z .. ")"
+end
+
+function XyzColor:Copy ()
+	return XyzColor(self.X, self.Y, self.Z)
+end
+
+function XyzColor:ToLab ()
+	local white = self.WhiteReference()
+	local x = PivotXyz(self.X / white.X)
+    local y = PivotXyz(self.Y / white.Y)
+	local z = PivotXyz(self.Z / white.Z)
+
+	return LabColor(math.max(0, 116 * y - 16),
+	                500 * (x - y),
+	                200 * (y - z))
+end
+
+function XyzColor:ToRgb ()
+	local x = self.X / 100.0
+	local y = self.Y / 100.0
+	local z = self.Z / 100.0
+
+	local r = x * 3.2406 + y * -1.5372 + z * -0.4986
+	local g = x * -0.9689 + y * 1.8758 + z * 0.0415
+	local b = x * 0.0557 + y * -0.2040 + z * 1.0570
+
+	if r > 0.0031308 then
+		r = 1.055 * math.pow(r, 1 / 2.4) - 0.055
+	else
+		r = 12.92 * r
+	end
+
+	if g > 0.0031308 then
+		g = 1.055 * math.pow(g, 1 / 2.4) - 0.055
+	else
+		g = 12.92 * g
+	end
+
+	if b > 0.0031308 then
+		b = 1.055 * math.pow(b, 1 / 2.4) - 0.055
+	else
+		b = 12.92 * b
+	end
+
+	return RgbColor(ToRgb(r),
+	                ToRgb(g),
+	                ToRgb(b))
+end
+
+
+
+
+LabColor = {}
+LabColor.__index = LabColor
+setmetatable(LabColor, class_constructor)
+
+function LabColor.New (L, a, b)
+	return setmetatable({L = L, a = a, b = b}, LabColor)
+end
+
+function LabColor.__eq (lhs, rhs)
+	return lhs.L == rhs.L and lhs.a == rhs.a and lhs.b and rhs.b
+end
+
+function LabColor.__tostring (self)
+	return "(" .. self.L .. "," .. self.a .. "," .. self.b .. ")"
+end
+
+function LabColor:ToRgb ()
+	local y = (self.L + 16.0) / 116.0
+	local x = self.a / 500.0 + y
+	local z = y - self.b / 200.0
+
+	local white = XyzColor.WhiteReference()
+	local epsilon = XyzColor.Epsilon()
+	local kappa = XyzColor.Kappa()
+	local x3 = x * x * x;
+	local z3 = z * z * z;
+	local xyz = {}
+
+	if x3 > epsilon then
+		xyz.X = white.X * x3
+	else
+		xyz.X = white.X * (x - 16.0 / 116.0) / 7.787
+	end
+
+	if self.L > (kappa * epsilon) then
+		xyz.Y = white.Y * math.pow(((self.L + 16.0) / 116.0), 3)
+	else
+		xyz.Y = white.Y * self.L / kappa
+	end
+
+	if z3 > epsilon then
+		xyz.Z = white.Z * z3
+	else
+		xyz.Z = white.Z * (z - 16.0 / 116.0) / 7.787
+	end
+
+	return XyzColor(xyz.X, xyz.Y, xyz.Z):ToRgb()
+end
+
+
+
+
+PivotRgb = function (n)
+	if n > 0.04045 then
+		return math.pow((n + 0.055) / 1.055, 2.4) * 100.0
+	else
+		return (n/12.92) * 100.0
+	end
+end
+
+
+ToRgb = function (n)
+	local result = 255.0 * n
+	if result < 0 then return 0 end
+	if result > 255 then return 255 end
+	return math.floor(result + 0.5)
+end
+
+
+
+PivotXyz = function (n)
+	if n > XyzColor.Epsilon() then
+		return n ^ (1/3)
+	else
+		return (XyzColor.Kappa() * n + 16) / 116
+	end
+end
+
+
+return {Rgb = RgbColor,
+        Xyz = XyzColor,
+Lab = LabColor}