// Improved Unobtrusive Javascript Image Rollover v1.0
// By Christian Watson: http://www.smileycat.com
// Based on a script by Chris Nott: http://www.dithered.com/javascript/rollovers/index.html
// license: http://creativecommons.org/licenses/by/1.0/

function isDefined(property) {
  return (typeof property != 'undefined');
}

var rolloverInitialized = false;
function rolloverInit() {

   if (!rolloverInitialized && isDefined(document.images)) {

	// Check to see if an ID has been set on BODY tag
	var bodyId = document.body.id ? document.body.id : null;
      
      // get all images (including all <input type="image">s)
      // use getElementsByTagName() if supported
      var images = new Array();
      if (isDefined(document.getElementsByTagName)) {
         images = document.getElementsByTagName('img');
         var inputs = document.getElementsByTagName('input');
         for (var i = 0; i < inputs.length; i++) {
            if (inputs[i].type == 'image') {
               images[images.length] = inputs[i];
            }
         }
      }
      
      // otherwise, use document.images and document.forms collections
      // remove if not supporting IE4, Opera 4-5
      else {
         images = document.images;
         inputs = new Array();
         for (var formIndex = 0; formIndex < document.forms.length; formIndex++) {
            for (var elementIndex = 0; elementIndex < document.forms.elements.length; elementIndex++) {
               if (isDefined(document.forms.elements[i].src)) {
                  inputs[inputs.length] = document.forms.elements[i];
               }
            }
         }
      }
      
      // get all images with '_off.' in src value excepting the one that is for the BODY

      for (var i = 0; i < images.length; i++) {
         if (images[i].src.indexOf('_off.') != -1) {

            // check for BODY image, and turn it 'on' if found
            if (images[i].src.indexOf(bodyId) != -1)
               images[i].src = images[i].src.replace(/_off\./, '_on.');
            else {

            var image = images[i];
            
            // store the off state filename in a property of the image object
            image.offImage = new Image();
            image.offImage.src = image.src;
            
            // store the on state filename in a property of the image object
            // (also preloads the on state image)
            image.onImage = new Image();
            image.onImage.imageElement = image;
            
            // add onmouseover and onmouseout event handlers once the on state image has loaded
            // Safari's onload is screwed up for off-screen images; temporary fix
            if (navigator.userAgent.toLowerCase().indexOf('safari') != - 1) {
               image.onmouseover = function() {
                  this.src = this.onImage.src;
               };
               image.onmouseout = function() {
                  this.src = this.offImage.src;
               };
            }
            else {
               image.onImage.onload = function() {
                  this.imageElement.onmouseover = function() {
                     this.src = this.onImage.src;
                  };
                  this.imageElement.onmouseout = function() {
                     this.src = this.offImage.src;
                  };
               };
            }
            
            // set src of on state image after defining onload event handler
            // so cached images (that load instantly in IE) will trigger onload
            image.onImage.src = image.src.replace(/_off\./, '_on.');

           }
         }
      }
   }
   rolloverInitialized = true;
}

// call rolloverInit when document finishes loading
if (isDefined(window.addEventListener)) {
   window.addEventListener('load', rolloverInit, false);
}
else if (isDefined(window.attachEvent)) {
   window.attachEvent('onload', rolloverInit);
}