# Get the component `w` of the gradient unit vector at `x`, `y`
	#
	# `w` at 0 targets the X axis, at 1 the Y axis.
	#
	# Returns a value between -1.0 and 1.0.
	#
	# Require: `w == 0 or w == 1`
	protected fun gradient_vector(x, y, w: Int): Float
	do
		assert w == 0 or w == 1

		# Use our own deterministic pseudo random number generator
		#
		# These magic prime numbers were determined good enough by
		# non-emperical experimentation. They may need to be changed/improved.
		var seed = 817721 + self.seed
		var i = seed * (x+seed) * 25111217 * (y+seed) * 72233613
		var mod = 137121
		var angle = (i.mask.abs%mod).to_f*2.0*pi/mod.to_f

		# Debug code to evaluate the efficiency of the random angle generator
		# The average of the produced angles should be at pi
		#
		#var sum = once new Container[Float](0.0)
		#var count = once new Container[Float](0.0)
		#sum.item += angle
		#count.item += 1.0
		#if count.item.to_i % 1000 == 0 then print "avg:{sum.item/count.item}/{count.item} i:{i} a:{angle} ({x}, {y}: {seed})"

		if w == 0 then return angle.cos
		return angle.sin
	end