弹性距离碰撞

1.构建小球精灵

package 
{
    import flash.display.Sprite;

    public class Ball extends Sprite
    {
        public var radius:Number;
        public var color:uint;
        public var vx:Number=0;
        public var vy:Number=0;

        public function Ball (radius:Number,color:uint)
        {
            this.radius=radius;
            this.color=color;
            Init ();
        }
        public function Init ():void
        {
            graphics.beginFill (color);
            graphics.drawCircle (0,0,radius);
            graphics.endFill ();
        }
    }
}

2.构建碰撞动画

package 
{
    import flash.events.Event;
    import flash.display.Sprite;

    public class Bubbles extends Sprite
    {
        private var balls:Array;
        private var bigBall:Ball;
        private var bounce:Number=-0.7;
        private var numBalls:Number=10;
        private var spring:Number=0.2;

        public function Bubbles ()
        {
            Init ();
        }
        private function Init ():void
        {
            balls=new Array();
            bigBall=new Ball(100,0xFF0000);
            addChild (bigBall);
            bigBall.x=stage.stageWidth/2;
            bigBall.y=stage.stageHeight/2;

            for (var i:int=0; i<numBalls; i++)
            {
                var ball=new Ball(Math.random()*40+5,0xffcc00);
                addChild (ball);
                ball.x=Math.random()*stage.stageWidth;
                ball.y=Math.random()*stage.stageHeight;
                ball.vx=Math.random()*6-3;
                ball.vy=Math.random()*6-3;
                balls.push (ball);
            }
            addEventListener (Event.ENTER_FRAME,EnterFrame);
        }
        private function EnterFrame (e:Event):void
        {
            for (var i:int=0; i<numBalls; i++)
            {
                var ball:Ball=balls[i];
                Move (ball);
                var dx:Number=ball.x-bigBall.x;
                var dy:Number=ball.y-bigBall.y;
                var dist:Number=Math.sqrt(dx*dx+dy*dy);
                var minDist:Number=ball.radius+bigBall.radius;
                if (dist<minDist)
                {
                    var angle:Number=Math.atan2(dy,dx);
                    var tx:Number=bigBall.x+Math.cos(angle)*minDist;
                    var ty:Number=bigBall.y+Math.sin(angle)*minDist;
                    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;
            }
        }
    }
}