package com.views

 {

     import flash.display.Sprite;

     import flash.events.Event;

     import flash.geom.Point;

     /**

      * @author Frost.Yen

      * @E-mail 871979853@qq.com

      * @create 2015-8-20 上午11:16:11

      *

      */

     [SWF(width="800",height="600")]

     public class ElasticMove extends Sprite

     {

         private const SPRING:Number=0.1;//弹性系数

         private const FRICTION:Number=0.9;//摩擦系数

         private const FEAR_DISTANCE:Number=150;//安全距离(小于该距离则发生躲避行为)

         private const MAX_AVOID_FORCE:uint=10;//最大躲避速度

         private var _destinationPoint:Point;//目标静止点(鼠标远离该物体时，物体最终会静止的坐标点)

         private var _speed:Point=new Point(0,0);//速度矢量(_speed.x即相当于vx,_speed.y即相当于vy)

         public function ElasticMove()

         {

             super();

             drawStuff();

             destinationPoint = new Point(300,300);

         }

         private function drawStuff():void {

             //默认先画一个半径为10的圆

             graphics.beginFill(Math.random() * 0xFFFFFF);

             //graphics.beginFill(0xFFFFFF);

             graphics.drawCircle(0, 0, 5);

             graphics.endFill();

         }

         //只写属性(设置目标点)

         public function set destinationPoint(value:Point):void {

             _destinationPoint=value;

             addEventListener(Event.ENTER_FRAME, enterFrameHandler);

         }

         protected function enterFrameHandler(e:Event):void {

             moveToDestination();//先移动到目标点

             avoidMouse();//躲避鼠标

             applyFriction();//应用摩擦力

             updatePosition();//更新位置

         }

         //以弹性运动方式移动到目标点

         private function moveToDestination():void {

             _speed.x += (_destinationPoint.x - x) * SPRING;

             _speed.y += (_destinationPoint.y - y) * SPRING;

         }

         //躲避鼠标

         private function avoidMouse():void {

             var currentPosition:Point=new Point(x,y);//确定当前位置

             var mousePosition:Point=new Point(stage.mouseX,stage.mouseY);//确实鼠标位置

             var distance:uint=Point.distance(currentPosition,mousePosition);//计算鼠标与当前位置的距离

             //如果低于安全距离

             if (distance<FEAR_DISTANCE) {

                 var force:Number = (1 - distance / FEAR_DISTANCE) * MAX_AVOID_FORCE;//计算(每单位时间的)躲避距离--即躲避速率

                 var gamma:Number=Math.atan2(currentPosition.y- mousePosition.y,currentPosition.x- mousePosition.x);//计算鼠标所在位置与当前位置所成的夹角

                 var avoidVector:Point=Point.polar(force,gamma);//将极坐标转换为普通(笛卡尔)坐标--其实相当于vx = force*Math.cos(gamma),vy = force*Math.sin(gamma)

                 //加速 躲避逃开

                 _speed.x+=avoidVector.x;

                 _speed.y+=avoidVector.y;

             }

         }

         //应用摩擦力

         private function applyFriction():void {

             _speed.x*=FRICTION;

             _speed.y*=FRICTION;

         }

         //最终更新自身的位置

         private function updatePosition():void {

             x+=_speed.x;

             y+=_speed.y;

         }

     }

 }