/*! Copyright (c) 2008 Brandon Aaron (http://brandonaaron.net)
* Dual licensed under the MIT (http://www.opensource.org/licenses/mit-license.php)
* and GPL (http://www.opensource.org/licenses/gpl-license.php) licenses.
*
* Version: @VERSION
*
* Requires: jQuery 1.2+
*/
 
(function($) {
 
var elements = [], timeout;
 
$.fn.extend({
viewable: function(callback) {
this
.bind('viewable', callback)
.each(function() {
elements.push(this);
});
if ( $.isReady ) checkVisibility();
return this;
},
 
stopViewable: function() {
return this.each(function() {
var self = this;
$.each( elements, function(i, element) {
if ( self == element )
delete elements[i];
});
});
}
});
 
// Check the elements visibility
function checkVisibility() {
 
// Get necessary viewport dimensions
var winHeight = $(window).height(),
winTop = self.pageYOffset || $.boxModel && document.documentElement.scrollTop || document.body.scrollTop,
winBottom = winHeight + winTop;
 
// Loop through the elements and check to see if they are viewable
$.each(elements, function(i, element) {
if ( !element ) return;
 
// Get element top offset and height
var elTop = $(element).offset().top,
elHeight = parseInt( $(element).css('height') ),
elBottom = elTop + elHeight,
percentage = 0, hiddenTop = 0, hiddenBottom = 0;
 
// Get percentage of unviewable area
if ( elTop < winTop ) // Area above the viewport
hiddenTop = winTop-elTop;
if ( elBottom > winBottom ) // Area below the viewport
hiddenBottom = elBottom-winBottom;
 
percentage = 1 - ((hiddenTop + hiddenBottom)/elHeight);
 
// Trigger viewable event along with percentage of viewable
$(element).trigger('viewable', [ (percentage > 1 ? 1 : percentage < 0 ? 0 : parseFloat(percentage)) ]);
});
};
 
$(function() {
 
// Bind scroll function to window when document is ready
$(window)
.bind('scroll.viewable', function() {
// Clear timeout if scrolling hasn't paused
if ( timeout ) clearTimeout(timeout);
// Create timeout to run actual calculations for once scrolling has paused
timeout = setTimeout(checkVisibility, 250);
});
 
// Check to see if the element is already visible
checkVisibility();
});
 
})(jQuery);