function init() {
    var ie = document.getElementById("ie");
    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");
    // ctx.drawImage(ie, 120, 120);
  
    addEventListener("mousedown", on_mousedown, false);
    addEventListener("mousemove", on_mousemove, false);
    addEventListener("mouseup", on_mouseup, false);
    draw_thumb();
  }
  </script></head>