[color] Add color operations and utilities.

color.lua

@@ -0,0 +1,58 @@
+--- Utility functions to manipulate colors.
+--
+-- Colors are represented as RGB or RGBA, each channel
+-- with values in range [0, 1].
+--
+-- @module gear.color
+-- @copyright 2023 The DoubleFourteen Code Forge
+-- @author Lorenzo Cogotti
+
+local Color = {}
+
+
+--- Darken RGB color by the specified amount.
+--
+-- @number r red channel
+-- @number g green channel
+-- @number b blue channel
+-- @number amount darken factor, must be in [0,1] range.
+function Color.darken(r, g, b, amount)
+	r = r * (1 - amount)
+	g = g * (1 - amount)
+	b = b * (1 - amount)
+
+	return r, g, b
+end
+
+--- Lighten RGB color by the specified amount.
+--
+-- @number r red channel
+-- @number g green channel
+-- @number b blue channel
+-- @number amount lightening factor, must be in [0,1] range.
+function Color.lighten(r, g, b, amount)
+	r = r + (1 - r) * amount
+	g = g + (1 - g) * amount
+	b = b + (1 - b) * amount
+
+	return r, g, b
+end
+
+--- Given two RGB colors, calculate fade by the specified amount.
+--
+-- @number cr first color, red channel
+-- @number cg first color, green channel
+-- @number cb first color, blue channel
+-- @number ar second color, red channel
+-- @number ag second color, green channel
+-- @number ab second color, blue channel
+-- @number amount fading factor, must be in [0,1] range.
+function Color.fade(cr, cg, cb, ar, ag, ab, amount)
+	cr = cr + (ar - cr) * amount
+	cg = cg + (ag - cg) * amount
+	cb = cb + (ab - cb) * amount
+
+	return cr, cg, cb
+end
+
+return Color