package
  {
          import flash.display.Sprite;
          import flash.events.Event;
          
          public class @ax-animation-ch08-Spring4 extends Sprite
          {
                  private var ball:animation_ch08_Ball;
                  private var spring:Number = 0.1;
                  private var targetX:Number = stage.stageWidth / 2;
                  private var targetY:Number = stage.stageHeight / 2;
                  private var vx:Number = 0;
                  private var vy:Number = 0;
                  private var friction:Number = 0.95;
                  
                  public function @ax-animation-ch08-Spring4()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          ball = new animation_ch08_Ball();
                          addChild(ball);
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                  }
  
                  
                  private function onEnterFrame(event:Event):void
                  {
                          var dx:Number = mouseX - ball.x;
                          var dy:Number = mouseY - ball.y;
                          var ax:Number = dx * spring;
                          var ay:Number = dy * spring;
                          vx += ax;
                          vy += ay;
                          vx *= friction;
                          vy *= friction;
                          ball.x += vx;
                          ball.y += vy;
                  }
          }
  }