package {
 
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.geom.Point;
 
    public class MultiBilliard extends Sprite {
 
        private var balls:Array;
        private var numBalls:uint=8;
        private var bounce:Number=-1.0;
 
        public function MultiBilliard() {
            init();
        }
 
        private function init():void {
            balls = new Array();
            for (var i:uint = 0; i < numBalls; i++) {
                var radius:Number=Math.random()*40+10;
                var ball:Ball=new Ball(radius,Math.random()*0xffffff);
                ball.mass=radius;
                ball.x=i*100;
                ball.y=i*50;
                ball.vx=Math.random()*10-5;
                ball.vy=Math.random()*10-5;
                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];
                ball.x+=ball.vx;
                ball.y+=ball.vy;
                checkWalls(ball);
            }
 
            for (i = 0; i < numBalls - 1; i++) {
                var ballA:Ball=balls[i];
                for (var j:Number = i + 1; j < numBalls; j++) {
                    var ballB:Ball=balls[j];
                    checkCollision(ballA, ballB);
                }
            }
        }
         
 
        //舞台边界检测
        function checkWalls(b:Ball) {
            if (b.x<b.radius) {
                b.x=b.radius;
                b.vx*=bounce;
            } else if (b.x>stage.stageWidth-b.radius) {
                b.x=stage.stageWidth-b.radius;
                b.vx*=bounce;
            }
            if (b.y<b.radius) {
                b.y=b.radius;
                b.vy*=bounce;
            } else if (b.y>stage.stageHeight-b.radius) {
                b.y=stage.stageHeight-b.radius;
                b.vy*=bounce;
            }
        }
 
        private function rotate(x:Number, y:Number, sin:Number, cos:Number, reverse:Boolean):Point {
            var result:Point = new Point();
            if (reverse) {
                result.x=x*cos+y*sin;
                result.y=y*cos-x*sin;
            } else {
                result.x=x*cos-y*sin;
                result.y=y*cos+x*sin;
            }
            return result;
        }
 
        private function checkCollision(ball0:Ball, ball1:Ball):void {
            var dx:Number=ball1.x-ball0.x;
            var dy:Number=ball1.y-ball0.y;
            var dist:Number=Math.sqrt(dx*dx+dy*dy);
            if (dist<ball0.radius+ball1.radius) {
                // 计算角度和正余弦值 
                var angle:Number=Math.atan2(dy,dx);
                var sin:Number=Math.sin(angle);
                var cos:Number=Math.cos(angle);
                // 旋转 ball0 的位置 
                var pos0:Point=new Point(0,0);
                // 旋转 ball1 的速度 
                var pos1:Point=rotate(dx,dy,sin,cos,true);
                // 旋转 ball0 的速度 
                var vel0:Point=rotate(ball0.vx,ball0.vy,sin,cos,true);
                // 旋转 ball1 的速度 
                var vel1:Point=rotate(ball1.vx,ball1.vy,sin,cos,true);
                // 碰撞的作用力 
                var vxTotal:Number=vel0.x-vel1.x;
                vel0.x = ((ball0.mass - ball1.mass) * vel0.x + 2 * ball1.mass * vel1.x) / (ball0.mass + ball1.mass);
                vel1.x = vxTotal+vel0.x;
                // 更新位置 
                var absV:Number=Math.abs(vel0.x)+Math.abs(vel1.x);
                var overlap:Number = (ball0.radius + ball1.radius) - Math.abs(pos0.x - pos1.x);
                pos0.x += vel0.x/absV*overlap;
                pos1.x += vel1.x/absV*overlap;
                // 将位置旋转回来 
                var pos0F:Object=rotate(pos0.x,pos0.y,sin,cos,false);
                var pos1F:Object=rotate(pos1.x,pos1.y,sin,cos,false);
                // 将位置调整为屏幕的实际位置 
                ball1.x=ball0.x+pos1F.x;
                ball1.y=ball0.y+pos1F.y;
                ball0.x=ball0.x+pos0F.x;
                ball0.y=ball0.y+pos0F.y;
                // 将速度旋转回来 
                var vel0F:Object=rotate(vel0.x,vel0.y,sin,cos,false);
                var vel1F:Object=rotate(vel1.x,vel1.y,sin,cos,false);
                ball0.vx=vel0F.x;
                ball0.vy=vel0F.y;
                ball1.vx=vel1F.x;
                ball1.vy=vel1F.y;
            }
        }
    }
}