# Which `Actor` is on screen at `x, y`?
	fun visible_at(x, y: Numeric): nullable Actor
	do
		var display = display
		assert display != null

		if not selection_calculated then draw_selection_screen

		x = x.to_i
		y = y.to_i
		y = display.height - y

		# Read selection values
		var data = once new NativeCByteArray(4)
		glReadPixels(x, y, 1, 1, gl_RGBA, gl_UNSIGNED_BYTE, data)
		assert_no_gl_error

		var r = display.red_bits
		var g = display.green_bits
		var b = display.blue_bits

		# Rebuild ID from pixel color
		var rv = data[0].to_i >> (8-r)
		var gv = data[1].to_i >> (8-g) << (r)
		var bv = data[2].to_i >> (8-b) << (r+g)
		if data[0].to_i & (2**(8-r)-1) > (2**(8-r-1)) then rv += 1
		if data[1].to_i & (2**(8-g)-1) > (2**(8-g-1)) then gv += 1 << r
		if data[2].to_i & (2**(8-b)-1) > (2**(8-b-1)) then bv += 1 << (r+g)
		var id = rv + gv + bv

		# ID 0 is the background
		if id == 0 then return null

		# Wrongful selection? This should not happen.
		if not selection_map.keys.has(id) then
			print_error "Gamnit Warning: Invalid selection {id}"
			return null
		end

		return selection_map[id]
	end