package {
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    public class Spring3D extends Sprite {
 
        private var balls:Array;
        private var ballNum:Number=20;
 
        private var spring:Number=.1;
        private var friction:Number=.94;
        private var fl:Number=250;
        private var vpX:Number=stage.stageWidth/2;
        private var vpY:Number=stage.stageHeight/2;
         
        var temp:Number = 0;
         
        public function Spring3D() {
            init();
        }
        private function init():void {
            balls=new Array(ballNum);
            for (var i:int=0; i<ballNum; i++) {
                balls[i]=new Ball3D(20,Math.random()*0xffffff);
                balls[i].tx=(Math.random()*2-1)*200;
                balls[i].ty=(Math.random()*2-1)*200;
                balls[i].tz=(Math.random()*2-1)*300;
                addChild(balls[i]);
            }
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
             
        }
        private function onEnterFrame(event:Event):void {
            for (var i:int=0; i<ballNum; i++) {
                move(balls[i]);
            }
            sortZ();
             
            temp++;
            if (temp>=250){
                reset();
                temp=0;
            }
            //trace(temp);
        }
 
        function move(b:Ball3D):void {
            var dx:Number=b.tx-b.xpos;
            var dy:Number=b.ty-b.ypos;
            var dz:Number=b.tz-b.zpos;
            b.vx+=dx*spring;
            b.vy+=dy*spring;
            b.vz+=dz*spring;
            b.xpos+=b.vx;
            b.ypos+=b.vy;
            b.zpos+=b.vz;
            b.vx*=friction;
            b.vy*=friction;
            b.vz*=friction;
            if (b.zpos>- fl) {
                var scale:Number = fl / (fl + b.zpos);
                b.scaleX=b.scaleY=scale;
                b.x=vpX+b.xpos*scale;
                b.y=vpY+b.ypos*scale;
                b.alpha=scale*0.8+0.2;
                b.visible=true;
            } else {
                b.visible=false;
            }
        }
 
        private function reset():void {
            for (var i:int=0; i<ballNum; i++) {
                balls[i].tx=(Math.random()*2-1)*200;
                balls[i].ty=(Math.random()*2-1)*200;
                balls[i].tz=(Math.random()*2-1)*300;
            }
        }
 
        //z轴排序  
        function sortZ():void {
            balls.sortOn("zpos", Array.DESCENDING | Array.NUMERIC);
            for (var i:uint = 0; i < ballNum; i++) {
                var b:Ball3D=balls[i];
                setChildIndex(b, i);
            }
 
        }
    }
}