anchor.diff:  class Arrow extends DisplayObjectContainer{
     Shape lineVector;
     Bitmap head;
  -  Bitmap body;
     Arrow(){
       mouseEnabled = false;            
       lineVector = new Shape();
  
positive.code:     Arrow arrow = new Arrow();
      arrow.addTo(stage);
      arrow.pointTo(0, i*3 , 860 , i*3);
     }
    });
    document.querySelector('#pen').onClick.listen((e) {
  
negative.code:     arrow.pointTo(startx, starty, e.localX.toInt(), e.localY.toInt());
    });
    
    touchEndListener = background.onMouseUp.listen((e) {
     touchListener.cancel();
     touchEndListener.cancel();
     arrow.endDraw();
    });
  }
  
  