on.mouse_wheel_move = function(dx, dy)
	if App.shift_down() then
		-- shift+scroll wheel doesn't set dx for me; manually do so if necessary
		if dx == 0 then
			dx,dy = dy,dx
		end
	end
	if dy > 0 then
		for i = 1,math.floor(dy) do
			Viewport.y = Viewport.y - scale(200)
		end
		B()
	elseif dy < 0 then
		for i = 1,math.floor(-dy) do
			Viewport.y = Viewport.y + scale(200)
		end
		B()
	end
	if dx > 0 then
		for i = 1,math.floor(dx) do
			Viewport.x = Viewport.x - scale(500)
		end
		B()
	elseif dx < 0 then
		for i = 1,math.floor(-dx) do
			Viewport.x = Viewport.x + scale(500)
		end
		B()
	end
end