def window_xy x,y
      s = ""
      s << "+" if x > 0
      s << x.to_s
      s << "+" if y > 0
      s << y.to_s
      @root.geometry s
    end
def window_xy x,y
      s = ""
      s << "+" if x > 0
      s << x.to_s
      s << "+" if y > 0
      s << y.to_s
      @root.geometry s
    end
background, height, width # already defined!