[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; 
        }
    }
}