function draw_animated_bg(startx)
	if (amplitude <= 0) return
	startx = startx or 0
	fillp(0b0101101001011010)

	local color = 1
	-- vertical lines
	local t = t()+10
	for i=startx-1,127,11 do
		local a=sin(i*t/512)*amplitude+64
		local b=cos(i*t/256)*amplitude+64
		line(
		i,
		a,
		i,
		b ,
		color)
	end

	-- horizontal lines
	for i=startx-1,127,11 do
		local a=sin(i*t/512)*amplitude+64
		local b=cos(i*t/256)*amplitude+64
		line(
		a,
		i,
		b ,
		i,
		color)
	end
end