# File gtk/sample/misc/cairo-pong.rb, line 74
    def update
      @x += @dx
      @y += @dy

      # ball bouncing
      if max_y > 1
        @y = 1 - (max_y - 1)
        @dy *= -1
      elsif min_y < 0
        @y -= min_y
        @dy *= -1
      end
      
      if max_x > 1
        @x = 1 - (max_x - 1)
        @dx *= -1
      elsif min_x < 0
        @x -= min_x
        @dx *= -1
      end
    end