Flex ActionScript实例代码之减慢速度

package {
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.TimerEvent;
    import flash.utils.Timer;

    public class Main extends Sprite {
        private var _sprite:Sprite = new Sprite(  );
        private var _easingSpeed:Number = 0.1;
        private var _targetX:Number = 400;
        private var _targetY:Number = 200;
        private var _timer:Timer;

        public function Main(  ) {

            _sprite.graphics.beginFill(0x0000ff, 100);
            _sprite.graphics.drawCircle(0, 0, 25);
            _sprite.graphics.endFill(  );
            _sprite.x = 50;
            _sprite.y = 50;
            addChild(_sprite);
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }

        public function onEnterFrame(event:Event):void {
            var dx:Number = _targetX - _sprite.x;
            var dy:Number = _targetY - _sprite.y;
            var dist:Number = Math.sqrt(dx * dx + dy * dy);
            if(dist < 1)
            {
                _sprite.x = _targetX;
                _sprite.y = _targetY;
                _timer.stop(  );
            }
            else
            {
                var vx:Number = dx * _easingSpeed;
                var vy:Number = dy * _easingSpeed;
                _sprite.x += vx;
                _sprite.y += vy;
            }
        }
    }
}