[ActionScript 3.0] AS3 弹性运动

 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;
         }
     }
 }