private function onEnterFrame(event:Event):void
    {
     moveBall(ball0, mouseX, mouseY);
     moveBall(ball1, ball0.x, ball0.y);
     moveBall(ball2, ball1.x, ball1.y);
     
     graphics.clear();
     graphics.lineStyle(1);
     graphics.moveTo(mouseX, mouseY);
     graphics.lineTo(ball0.x, ball0.y);
     graphics.lineTo(ball1.x, ball1.y);
     graphics.lineTo(ball2.x, ball2.y);
    }