AS3 斜坡角度反弹【算法】

var ball:MovieClip;
var line:MovieClip;
var gravity:Number=0.3;
var bounce:Number=-0.6;

init();

function init():void {
  ball = new Ball();
  addChild(ball);
  ball.x=100;
  ball.y=100;
  ball.vy=1;
  ball.vx=0;
  line = new MovieClip();
  line.graphics.lineStyle(1);
  line.graphics.lineTo(300, 0);
  addChild(line);
  line.x=50;
  line.y=200;
  line.vy=0;
  line.vx=0;//
  line.rotation=30;
  addEventListener(Event.ENTER_FRAME, onEnterFrameHd);
}


function onEnterFrameHd(event:Event):void {// 普通的运动代码    
  ball.vy+=gravity;
  ball.x+=ball.vx;
  ball.y+=ball.vy;
  // 获得角度及正余弦值    
  var angle:Number=line.rotation*Math.PI/180;
  var cos:Number=Math.cos(angle);
  var sin:Number=Math.sin(angle);
  // 获得 ball 与 line 的相对位置    
  var x1:Number=ball.x-line.x;
  var y1:Number=ball.y-line.y;
  // 旋转坐标    
  var y2:Number=cos*y1-sin*x1;
  // 实现反弹
  if (y2>- ball.height/2) {
    // 旋转坐标    
    var x2:Number=cos*x1+sin*y1;
    // 旋转速度向量    
    var vx1:Number=cos*ball.vx+sin*ball.vy;
    var vy1:Number=cos*ball.vy-sin*ball.vx;
    y2=- ball.height/2;
    vy1*=bounce;
    // 将一切旋转回去    
    x1=cos*x2-sin*y2;
    y1=cos*y2+sin*x2;
    ball.vx=cos*vx1-sin*vy1;
    ball.vy=cos*vy1+sin*vx1;
    ball.x=line.x+x1;
    ball.y=line.y+y1;
  }
}