多角度回弹

算法实现：

ActionScirpt3.0实现：

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.构建多角度回弹

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

    public class MultiAngleBounce extends Sprite
    {
        private var ball:Ball;
        private var lines:Array;
        private var numLines:int=5;
        private var gravity:Number=0.3;
        private var bounce:Number=-0.6;

        public function MultiAngleBounce ()
        {
            Init ();
        }
        private function Init ():void
        {
            ball=new Ball(20,Math.random()*0xFFFFFF);
            addChild (ball);
            ball.x=100;
            ball.y=0;

            lines=new Array();
            for (var i:int=0; i<numLines; i++)
            {
                var line:Sprite=new Sprite();
                line.graphics.lineStyle (1);
                line.graphics.moveTo (-50,0);
                line.graphics.lineTo (50,0);
                addChild (line);
                lines.push (line);
            }
            lines[0].x=100;
            lines[0].y=100;
            lines[0].rotation=30;

            lines[1].x=100;
            lines[1].y=230;
            lines[1].rotation=45;

            lines[2].x=250;
            lines[2].y=180;
            lines[2].rotation=-30;

            lines[3].x=150;
            lines[3].y=330;
            lines[3].rotation=10;

            lines[4].x=230;
            lines[4].y=250;
            lines[4].rotation=-30;

            addEventListener (Event.ENTER_FRAME,EnterFrame);
        }
        private function EnterFrame (e:Event):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;
            }
            for (var i:int=0; i<numLines; i++)
            {
                CheckLine (lines[i]);
            }
        }
        private function CheckLine (line:Sprite):void
        {
            var bounds:Rectangle=line.getBounds(this);
            if (ball.x>bounds.left && ball.x<bounds.right)
            {
                var angle:Number=line.rotation*Math.PI/180;
                var x1:Number=ball.x-line.x;
                var y1:Number=ball.y-line.y;
                var y2:Number=Math.cos(angle)*y1-Math.sin(angle)*x1;
                var vy1:Number=Math.cos(angle)* ball.vy-Math.sin(angle)*ball.vx;
                if (y2+ball.radius>0 && y2<vy1)//y2为负值
                {
                    var x2:Number=Math.cos(angle)*x1+Math.sin(angle)*y1;
                    var vx1:Number=Math.cos(angle)* ball.vx+Math.sin(angle)*ball.vy;

                    y2=-ball.radius;
                    vy1*=bounce;

                    x1=Math.cos(angle)*x2-Math.sin(angle)*y2;
                    y1=Math.cos(angle)*y2+Math.sin(angle)*x2;
                    ball.vx=Math.cos(angle)*vx1-Math.sin(angle)*vy1;
                    ball.vy=Math.cos(angle)*vy1+Math.sin(angle)*vx1;
                    ball.x=line.x+x1;
                    ball.y=line.y+y1;
                }
            }
        }
    }
}