[color] Add helper functions for HSV and HSL color conversion

color.lua

@@ -38,6 +38,50 @@ function Color.lighten(r, g, b, amount)
 	return r, g, b
 end
 
+function Color.hsl(h, s, l, a)
+	a = a or 1
+	if s <= 0 then return 1, 1, 1, a end
+
+	h = h * 6
+
+	local abs = math.abs
+	local c = (1 - abs(l*2 - 1))*s
+	local x = (1 - abs(h%2 - 1))*c
+	local m = l - c*0.5
+
+	local r, g, b
+	if h < 1 then     r, g, b = c, x, 0
+	elseif h < 2 then r, g, b = x, c, 0
+	elseif h < 3 then r, g, b = 0, c, x
+	elseif h < 4 then r, g, b = 0, x, c
+	elseif h < 5 then r, g, b = x, 0, c
+	else              r, g, b = c, 0, x
+	end
+	return r+m, g+m, b+m, a
+end
+
+function Color.hsv(h, s, v, a)
+	a = a or 1
+	if s <= 0 then return v, v, v, a end
+
+	h = h * 6
+
+	local c = v * s
+	local x = (1 - math.abs(h%2 - 1))*c
+	local m = v - c
+
+	local r, g, b
+	if h < 1 then     r, g, b = c, x, 0
+	elseif h < 2 then r, g, b = x, c, 0
+	elseif h < 3 then r, g, b = 0, c, x
+	elseif h < 4 then r, g, b = 0, x, c
+	elseif h < 5 then r, g, b = x, 0, c
+	else              r, g, b = c, 0, x
+	end
+	return r+m, g+m, b+m, a
+
+end
+
 --- Given two RGB colors, calculate fade by the specified amount.
 --
 -- @number cr first color, red channel