//设置下面一些参数，小球移动速度1-50，数值大速度快；
var BallSpeed = 2;
var maxBallSpeed = 50;
var xMax;
var yMax;
var xPos = 0;
var yPos = 0;
var xDir = 'right';  //水平方向向右移动
var yDir = 'down'; //垂直方向向下移动
var superballRunning = true;
var tempBallSpeed;
var currentBallSrc;
var newXDir;
var newYDir;
function initializeBall() {
    if (document.all) {
        xMax = document.body.clientWidth;
        yMax = document.body.clientHeight;
        document.all("superball").style.visibility = "visible";
    }
    else if (document.layers) {
        xMax = window.innerWidth;
        yMax = window.innerHeight;
        document.layers["superball"].visibility = "show";
    }
   setTimeout('moveBall()',400);

}

function moveBall() {
   if (superballRunning == true) {
      calculatePosition();
      if (document.all) {
         document.all("superball").style.left = xPos + document.body.scrollLeft;
         document.all("superball").style.top = yPos + document.body.scrollTop;
         }
      else if (document.layers) {
         document.layers["superball"].left = xPos + pageXOffset;
         document.layers["superball"].top = yPos + pageYOffset;
         }
      }
	  setTimeout('moveBall()',30);

}

function calculatePosition() {
    if (xDir == "right") {
        if (xPos > (xMax - ballWidth - BallSpeed)) {
            xDir = "left";
        }
    }
    else if (xDir == "left") {
        if (xPos < (0 + BallSpeed)) {
            xDir = "right";
        }
    }
    if (yDir == "down") {
        if (yPos > (yMax - ballHeight - BallSpeed)) {
            yDir = "up";
        }
    }
    else if (yDir == "up") {
        if (yPos < (0 + BallSpeed)) {
            yDir = "down";
        }
    }
    if (xDir == "right") {
        xPos = xPos + BallSpeed;
    }
    else if (xDir == "left") {
        xPos = xPos - BallSpeed;
    }
    else {
        xPos = xPos;
    }
    if (yDir == "down") {
        yPos = yPos + BallSpeed;
    }
    else if (yDir == "up") {
        yPos = yPos - BallSpeed;
    }
    else {
        yPos = yPos;
    }
}