package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class Bubbles2 extends Sprite {
        private var balls:Array;
        private var numBalls:Number=20;
        private var bounce:Number=-0.9;
        private var spring:Number=0.2;
        private var gravity:Number=1;
        public function Bubbles2() {
            init();
        }
        private function init():void {
            balls = new Array();
            for (var i:uint = 0; i < numBalls; i++) {
                var ball:Ball=new Ball(Math.random()*30+20,Math.random()*0xffffff);
                ball.x=Math.random()*stage.stageWidth;
                ball.y=Math.random()*stage.stageHeight;
                ball.vx=Math.random()*6-3;
                ball.vy=Math.random()*6-3;
                addChild(ball);
                balls.push(ball);
            }
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        private function onEnterFrame(event:Event):void {
            for (var i:uint = 0; i < numBalls - 1; i++) {
                var ball0:Ball=balls[i];
                for (var j:uint = i + 1; j < numBalls; j++) {
                    var ball1:Ball=balls[j];                    
                    var dx:Number=ball1.x-ball0.x;
                    var dy:Number=ball1.y-ball0.y;
                    var dist:Number=Math.sqrt(dx*dx+dy*dy);
                    var minDist:Number=ball0.radius+ball1.radius;
                    if (dist<minDist) {
                        /*
                        var angle:Number=Math.atan2(dy,dx);
                        var tx:Number=ball0.x+Math.cos(angle)*minDist;
                        var ty:Number=ball0.y+Math.sin(angle)*minDist;
                        */                     
                        var tx:Number=ball0.x + (dx/dist)*minDist;
                        var ty:Number=ball0.y + (dy/dist)*minDist;
                        var ax:Number = (tx - ball1.x) * spring;
                        var ay:Number = (ty - ball1.y) * spring;
                        ball0.vx-=ax;
                        ball0.vy-=ay;
                        ball1.vx+=ax;
                        ball1.vy+=ay;
                    }
                }
            }
            for (i = 0; i < numBalls; i++) {
                var ball:Ball=balls[i];
                move(ball);
            }
        }
        private function move(ball:Ball):void {
            ball.vy+=gravity;
            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;
            }
        }
    }
}