msie = navigator.appVersion.indexOf("MSIE") != -1;
ns4  = !msie && document.layers;

function swapImgRestore() { //v3.0
  var i,x,a=document.sr; for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}

function findObj(n, d) { //v4.0
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=findObj(n,d.layers[i].document);
  if(!x && document.getElementById) x=document.getElementById(n); return x;
}

function swapImage() { //v3.0
  var i,j=0,x,a=swapImage.arguments; document.sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=findObj(a[i]))!=null){document.sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}


function getScale(c, height) {
  var t = Math.sqrt(2 * height / c.gravity);
  var scale = 4 * height / sqr(t);
  return scale;
}
function sqr(x) {
  return x * x;
}
function updateBounce(c) {
  var bottom = getViewYOffset() + getViewHeight() - c.imageHeight;
  for (var i = 0; i < c.imageCount; i++) {
    var name = c.prefix + i;
    var scale = c.pScale[name];
    var x = getLayerX(name) + c.xSpeed[name];
    var y = -scale * sqr(c.pIndex[name]) + c.pHeight[name];
    if (y > 0)
      y = bottom - y;
    else
      y = bottom;
    var bounds = outOfBounds(c, x, y, c.imageWidth, c.imageHeight);
    if (bounds & 1) { // left
      x =   2 * getViewXOffset() - x;
      c.xSpeed[name] = -c.xSpeed[name] * c.elasticity;
    }
    if (bounds & 2) { // right
      x = 2 * (getViewXOffset() + getViewWidth() - c.imageWidth) - x;
      c.xSpeed[name] = -c.xSpeed[name] * c.elasticity;
    }
    moveLayer(name, x, y);
    if ((c.pIndex[name] += 0.5) > c.pLimit[name]) {
      c.xSpeed[name] *= 1 - c.friction;
      c.pIndex[name] -= Math.sqrt(c.pHeight[name] / scale);
      c.pHeight[name] = Math.max(0.25, c.pHeight[name] * c.elasticity);
      c.pIndex[name] = -(c.pLimit[name] = Math.sqrt(c.pHeight[name] / scale));
      if (c.pHeight[name] < c.restThreshold) {
        if (c.restOpt == 1) { // kick
          c.pHeight[name] = 100 + random(getViewHeight());
          c.xSpeed[name] = random(41) - 20;
          scale = (c.pScale[name] = getScale(c, c.pHeight[name]));
          c.pIndex[name] = -(c.pLimit[name] = Math.sqrt(c.pHeight[name] / scale));
        }
        else if (c.restOpt == 2) { // drop
          c.pHeight[name] = getViewHeight() + c.imageHeight + 100 + random(500);
          c.pScale[name] = getScale(c, c.pHeight[name]);
          c.xSpeed[name] = random(41) - 20;
          c.pIndex[name] = 0;
          c.pLimit[name] = Math.sqrt(c.pHeight[name] / scale);
        }
      }
    }
  }
  setTimeout('updateBounce(c' + c.uid + ')', c.updateInterval);
}


function layerSupport() {
    return document.all || document.layers || document.getElementById;
}

layers = new Array();
layerX = new Array();
layerY = new Array();
cursorX = 0;
cursorY = 0;

function getViewWidth() {
  if (!ns4)
    return document.body.clientWidth;
  else
    return window.innerWidth;
}

function getViewHeight() {
  if (!ns4)
    return document.body.clientHeight;
  else
    return window.innerHeight;
}

function getViewXOffset() {
  if (msie)
    return document.body.scrollLeft;
  else
    return window.pageXOffset;
}

function getViewYOffset() {
  if (msie)
    return document.body.scrollTop;
  else
    return window.pageYOffset;
}

function getLayerX(i) {
    return layerX[i];
}

function getLayerY(i) {
    return layerY[i];
}

function moveLayer(i, x, y) {
  layerX[i] = x;
  layerY[i] = y;
  if (msie) {
    layers[i].style.pixelLeft = x;
    layers[i].style.pixelTop = y;
  }
  else if (ns4) {
    layers[i].left = x;
    layers[i].top = y;
  }
  else {
    layers[i].style.left = x + "px";
    layers[i].style.top = y + "px";
  }
}


function outOfBounds(config, x, y, w, h) {
  var result = 0;
  
  // note that fudge factor isn't used for bottom
  if (x < getViewXOffset() - config.xFudge)
    result |= 1; // Left
  else if (x + w >= getViewXOffset() + getViewWidth() + config.xFudge)
    result |= 2; // Right
  
  if (y + h >= getViewYOffset() + getViewHeight())
    result |= 4; // Bottom
  else if (y < getViewYOffset() - config.yFudge)
    result |= 8; // Top
    
  return result;
}

function random(bound) {
  return Math.floor(Math.random() * bound);
}

function randomX(config) {
  return getViewXOffset() + random(getViewWidth() - config.imageWidth);
}

function randomY(config) {
  return getViewYOffset() - config.yFudge + random(getViewHeight() + config.yFudge - config.imageHeight);
}

function setVisible(i, show) {
   if (!ns4)
      layers[i].style.visibility = show ? "" : "hidden";
   else
      layers[i].visibility = show ? "show" : "hide";
}

function writeLayer(layercontents, name, x, y) {
    layerX[name] = x;
    layerY[name] = y;
    if (!ns4) {
      document.writeln('<div id="' + name + '" style="position:absolute;left:' + x + ';top:' + y + ';">' + layercontents + '</div>');
      if (msie)
        layers[name] = document.all[name];
      else
        layers[name] = document.getElementById(name);
    }
    else {
      document.writeln('<layer id="' + name + '" left=' + x + ' top=' + y + '>' + layercontents + '</layer>');
      layers[name] = document.layers[name];
    }
}

function writeImage(image, name, x, y) {
    layerX[name] = x;
    layerY[name] = y;
    if (!ns4) {
      document.writeln('<div id="' + name + '" style="position:absolute;left:' + x + ';top:' + y + ';"><img src="' + image + '"></div>');
      if (msie)
        layers[name] = document.all[name];
      else
        layers[name] = document.getElementById(name);
    }
    else {
      document.writeln('<layer id="' + name + '" left=' + x + ' top=' + y + '><img src="' + image + '"></layer>');
      layers[name] = document.layers[name];
    }
}

function writeImages(config) {
  for (var i = 0; i < config.imageCount; i++) {
    var startX = randomX(config);
    var startY = config.startOnScreen ? randomY(config) : -config.imageHeight;
    var name = config.prefix + i;
    writeImage(config.image, name, startX, startY);
  }
}

function cursorXY(e) {
  cursorX = msie ? (getViewXOffset() + event.clientX) : e.pageX;
  cursorY = msie ? (getViewYOffset() + event.clientY) : e.pageY;
}

function captureXY() {
  if (!msie) { document.captureEvents(Event.MOUSEMOVE); }
  document.onmousemove = cursorXY;
}

function config() {
  this.xFudge = 0;
  this.yFudge = 0;
  this.updateInterval = 50;
  this.startOnScreen = true;
  this.imageCount = 1;
}