/*************************************************************************/
/* JavaScript utility - rollover */
/* Copyright 2000, Brooklyn College Academic Information & Technologies */
/* http://academic.brooklyn.cuny.edu/ait/ */
/* Michael A. Mayo | March 14, 2000 */
/* mmayo@mcauleybrooklyn.org | x5279 */
/*************************************************************************/
// This file includes code for an image swap.
/* imageBank - This is an object which allows us to easily preload and swap images.
* Usage to preload images:
* myImages = new imageBank();
* myImages.add("newImage.gif");
* myImages.add("newImage2.gif");
* myImages.add("newImage3.gif");
* ...
*
* or:
* myImages.add("newImage.gif", "newImage2.gif", "newImage3.gif", ...);
*
* Either synatax is acceptable, but the first is recommended.
*
*
* Usage to swap images:
*
* 
*
* Swap's first argument must be the name of an image anywhere in the HTML document.
* Swap's second argument must be the URL of another image that has been preloaded using the add() function.
* Swap will give you a warning if you do not preload the second argument.
*
*
* imageBank will warn you if you do things like forget to preload images or leave out quotes on function paramaters.
*
*
* All functions return true if they operate successfully, false if they do not.
*/
function imageBank() {
// Variables
this.enable_imageswap; // tells us if we should do the swap
this.loaded_images = new Array(); // holds a list of all the images we have preloaded so far
this.browser_name = navigator.appName; // we need the browser name & version to help us tell if the browser is capable of running this script
this.browser_version = parseFloat(navigator.appVersion);
// Member Functions
this.add = add; // adds images to be preloaded
this.swap = swap; // swaps 2 images
// Utility Functions
// Does the work neccecary to compare a full URL to a relative URL. Returns true if they point to the same file, false if not.
this.compareURL = compareURL;
// Constructor
// Do some browser sniffing to see whether the browser is capable of running this code.
// If the browser is Netscape or MSIE, we know it can run this script only if it's version 3.0 or higher
// Otherwise, we're not entirely sure, but if document.images is supported, run the script anyway and hope. =)
if( this.browser_name == "Netscape") {
this.enable_imageswap = (this.browser_version >= 3.0);
} else if( this.browser_name == "Microsoft Internet Explorer") {
this.enable_imageswap = (this.browser_version >= 3.0);
} else {
if( document.images ) { this.enable_imageswap = true; }
else { this.enable_imageswap = false; }
}
}
/* This is a member function of the imageBank object.
* It adds another image to be preloaded.
* Usage:
* var myImages = new imageBank();
* myImages.add("imageURL1");
* myImages.add("imageURL2");
* or:
* myImages.add("imageURL1","imageURL2","imageURL3",...);
*
* Either syntax works fine, but the first is recommended as it is harder to mess up.
* Returns true if operates sucesfuly, false otherwise.
*/
function add( ) {
// Exit immediately if we aren't supposed to run this code.
if ( ! this.enable_imageswap ) {
return false;
}
// Process each image given to function as argument
for( var i = 0; i < add.arguments.length; ++i ) {
// Check arguments to make sure user didn't input some weird variable instead
if( typeof add.arguments[i] != "string" ){
alert("Warning: non-string arguments passed to the add function.");
} else {
// Add the image to the list of loaded images
this.loaded_images[this.loaded_images.length] = new Image();
this.loaded_images[(this.loaded_images.length - 1)].src = add.arguments[i];
}
}
return true;
}
/* This is a member function of the imageBank object.
* It replaces one image in the HTML document with another.
* Usage:
*
*
*
* Swap's first argument must be the name of an image anywhere in the HTML document.
* Swap's second argument must be the URL of another image that has been preloaded using the add() function.
* Swap will give you a warning if you do not preload the second argument.
*
* Returns true if operates sucessfuly, false otherwise.
*/
function swap( image1_name, image2_url ) {
// Exit immediately if we aren't supposed to run this code
if( ! this.enable_imageswap ) {
return false;
}
// Make sure the user remembered to quote the arguments
if( (typeof image1_name != "string") || (typeof image2_url != "string") ) {
alert("Warning: one of the arguments to the swap function was not quoted. This swap will not work.");
return false;
}
// Make sure the user remembered to preload the images being swapped
var found = false;
var full_url;
for( var i = 0; !found && (i < this.loaded_images.length); ++i) {
found = compareURL(this.loaded_images[i].src, image2_url);
full_url = this.loaded_images[i].src;
}
if( !found ) {
var warning_string = "Warning: image " + image2_url + " was not preloaded using the add function. This may cause the rollover to perform poorly.";
alert(warning_string);
}
// Finally, swap the images!
document.images[image1_name].src = full_url;
return true;
}
/* This is a member function of the imageBank object.
* It is a "utility function" used by other members of imageBank.
* It is not intended to be used by the user.
*
* It compares a full URL (first argument) to a relative URL (second argument), to see if they point to the same file.
* Usage: compareURL("/a/r/c/help.html","/c/help.html");
*
*/
function compareURL(full_url, relative_url) {
var start_index = full_url.length - relative_url.length;
var end_index = full_url.length;
var converted_full_url = full_url.substring(start_index, end_index);
return( converted_full_url == relative_url );
}