redef fun [](x, y)
	do
		var val = 0.0
		for layer in layers do
			val += layer[x, y]
		end
		return val
	end

	redef fun [](x, y)
	do
		x = x/period
		y = y/period

		# Get grid coordinates
		var x0 = if x > 0.0 then x.to_i else x.to_i - 1
		var x1 = x0 + 1
		var y0 = if y > 0.0 then y.to_i else y.to_i - 1
		var y1 = y0 + 1

		# Position in grid
		var sx = x - x0.to_f
		var sy = y - y0.to_f

		# Interpolate
		var n0 = gradient_dot_product(x0, y0, x, y)
		var n1 = gradient_dot_product(x1, y0, x, y)
		var ix0 = sx.lerp(n0, n1)
		n0 = gradient_dot_product(x0, y1, x, y)
		n1 = gradient_dot_product(x1, y1, x, y)
		var ix1 = sx.lerp(n0, n1)
		var val = sy.lerp(ix0, ix1)

		# Return value in [min...max] from val in [-1.0...1.0]
		val /= 2.0
		val += 0.5
		return val.lerp(min, max)
	end