package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class Billiard1 extends Sprite {
        private var ball0:Ball;
        private var ball1:Ball;
        private var bounce:Number = -0.6;
        public function Billiard1() {
            init();
        }
         
        private function init():void {
            ball0=new Ball(40);         
            addChild(ball0);
            ball1=new Ball(20,0x0000ff);            
            addChild(ball1);                    
            ReStart();
        }
         
        private function ReStart():void{
            ball0.mass=2;
            ball0.x=50;
            ball0.y=stage.stageHeight/2;
            ball0.vx=5;
            ball1.mass=1;
            ball1.x=300;
            ball1.y=stage.stageHeight/2;
            ball1.vx=-5;        
            addEventListener(Event.ENTER_FRAME,EnterFrameHandler);  
        }
         
        private function EnterFrameHandler(event:Event):void {
            ball0.x+=ball0.vx;
            ball1.x+=ball1.vx;
            var dist:Number=ball1.x-ball0.x;
             
            //如果撞到了
            if (Math.abs(dist)<ball0.radius+ball1.radius) {
                var vdx:Number = ball0.vx - ball1.vx;
                var vx0Final:Number=((ball0.mass-ball1.mass)*ball0.vx + 2*ball1.mass*ball1.vx)/(ball0.mass+ball1.mass);
                var vx1Final:Number= vx0Final + vdx;
                ball0.vx=vx0Final;
                ball1.vx=vx1Final;
                 
                //不加下面这二句的话，从视觉效果上看，有可能会看到二个球相互撞入对方球体内了，这样就不符合物理学"刚体"模型的定义
                ball0.x+=ball0.vx;
                ball1.x+=ball1.vx;
            }
             
            //舞台边界反弹
            if (ball0.x >=stage.stageWidth-ball0.radius || ball0.x<=ball0.radius){
                ball0.x -= ball0.vx;
                ball0.vx *= bounce;
            }           
             
            if (ball1.x >=stage.stageWidth-ball1.radius || ball1.x<=ball1.radius){
                ball1.x -= ball1.vx;
                ball1.vx *= bounce;
            }
             
            trace(ball1.vx,ball0.vx);
             
            //如果二球都停了
            if (Math.abs(ball1.vx)<=0.05 && Math.abs(ball0.vx)<=0.05){
                removeEventListener(Event.ENTER_FRAME,EnterFrameHandler);   
                ReStart();
            }
        }
    }
 
}