package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class Easing3D extends Sprite {      
        private var balls:Array;
        private var ballNum:Number=20;
        private var easing:Number=.1;
        private var fl:Number=250;
        private var vpX:Number=stage.stageWidth/2;
        private var vpY:Number=stage.stageHeight/2;
 
        public function Easing3D() {
            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)*500;
                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();
        }
 
        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;
            //缓动公式
            b.xpos+=dx*easing;
            b.ypos+=dy*easing;
            b.zpos+=dz*easing;
            var dist:Number=Math.sqrt(dx*dx+dy*dy+dz*dz);
            if (dist<1) {
                b.tx=(Math.random()*2-1)*200;
                b.ty=(Math.random()*2-1)*200;
                b.tz=(Math.random()*2-1)*500;
            }
            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*0.7+0.3;
                b.visible=true;
            } else {
                b.visible=false;
            }
        }
 
        //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);
            }
 
        }
 
 
    }
}