package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class Bubbles extends Sprite {
        private var balls:Array;
        private var numBalls:Number=10;
        private var centerBall:Ball;
        private var bounce:Number=-1;
        private var spring:Number=0.2;
        public function Bubbles() {
            init();
        }
        private function init():void {
            balls=new Array  ;
            centerBall=new Ball(100,0xcccccc);
            addChild(centerBall);
            centerBall.x=stage.stageWidth/2;
            centerBall.y=stage.stageHeight/2;
            for (var i:uint=0; i<numBalls; i++) {
                var ball:Ball=new Ball(Math.random()*40+5,Math.random()*0xffffff);
                ball.x=Math.random()*stage.stageWidth;
                ball.y=Math.random()*stage.stageHeight;
                ball.vx=(Math.random()*2-1)*10;
                ball.vy=(Math.random()*2-1)*10;
                addChild(ball);
                balls.push(ball);
            }
            addEventListener(Event.ENTER_FRAME,onEnterFrame);
        }
        private function onEnterFrame(event:Event):void {
            for (var i:uint=0; i<numBalls; i++) {
                var ball:Ball=balls[i];
                move(ball);
                var dx:Number=ball.x-centerBall.x;
                var dy:Number=ball.y-centerBall.y;
                var dist:Number=Math.sqrt(dx*dx+dy*dy);
                var minDist:Number=ball.radius+centerBall.radius;
                if (dist<minDist) {
                    var angle:Number=Math.atan2(dy,dx);
                    var tx:Number=centerBall.x+Math.cos(angle)*minDist;//弹性运动的目标点x坐标
                    var ty:Number=centerBall.y+Math.sin(angle)*minDist;//弹性运动的目标点y坐标
                    ball.vx+=(tx-ball.x)*spring;
                    ball.vy+=(ty-ball.y)*spring;
                }
            }
        }
        private function move(ball:Ball):void {
            ball.x+=ball.vx;
            ball.y+=ball.vy;
            if (ball.x+ball.radius>stage.stageWidth) {
                ball.x=stage.stageWidth-ball.radius;
                ball.vx*=bounce;
            } else if (ball.x-ball.radius<0) {
                ball.x=ball.radius;
                ball.vx*=bounce;
            }
            if (ball.y+ball.radius>stage.stageHeight) {
                ball.y=stage.stageHeight-ball.radius;
                ball.vy*=bounce;
            } else if (ball.y-ball.radius<0) {
                ball.y=ball.radius;
                ball.vy*=bounce;
            }
        }
    }
}