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
	local v = Viewport
	if love.keyboard.isDown('lctrl') or love.keyboard.isDown('rctrl') then
		local oldzoom = v.zoom
		if dy < 0 and v.zoom > 0.2 then
			v.zoom = v.zoom - 0.1
		elseif dy > 0 then
			v.zoom = v.zoom + 0.1
		end
		local mx, my = love.mouse.getPosition()
		v.x = v.x + mx/oldzoom - mx/v.zoom
		v.y = v.y + my/oldzoom - my/v.zoom
	else
		v.x = v.x - dx * scale(500)
		v.y = v.y - dy * scale(200)
	end
	B()
end