Template:Tongji China/js/jquery appear JS

/*

* jQuery appear plugin
*
* Copyright (c) 2012 Andrey Sidorov
* licensed under MIT license.
*
* https://github.com/morr/jquery.appear/
*
* Version: 0.3.3
*/

(function($) {

 var selectors = [];

 var check_binded = false;
 var check_lock = false;
 var defaults = {
   interval: 250,
   force_process: false
 }
 var $window = $(window);

 var $prior_appeared;

 function process() {
   check_lock = false;
   for (var index = 0; index < selectors.length; index++) {
     var $appeared = $(selectors[index]).filter(function() {
       return $(this).is(':appeared');
     });

     $appeared.trigger('appear', [$appeared]);

     if ($prior_appeared) {
       var $disappeared = $prior_appeared.not($appeared);
       $disappeared.trigger('disappear', [$disappeared]);
     }
     $prior_appeared = $appeared;
   }
 }

 // "appeared" custom filter
 $.expr[':']['appeared'] = function(element) {
   var $element = $(element);
   if (!$element.is(':visible')) {
     return false;
   }

   var window_left = $window.scrollLeft();
   var window_top = $window.scrollTop();
   var offset = $element.offset();
   var left = offset.left;
   var top = offset.top;

   if (top + $element.height() >= window_top &&
       top - ($element.data('appear-top-offset') || 0) <= window_top + $window.height() &&
       left + $element.width() >= window_left &&
       left - ($element.data('appear-left-offset') || 0) <= window_left + $window.width()) {
     return true;
   } else {
     return false;
   }
 }

 $.fn.extend({
   // watching for element's appearance in browser viewport
   appear: function(options) {
     var opts = $.extend({}, defaults, options || {});
     var selector = this.selector || this;
     if (!check_binded) {
       var on_check = function() {
         if (check_lock) {
           return;
         }
         check_lock = true;

         setTimeout(process, opts.interval);
       };

       $(window).scroll(on_check).resize(on_check);
       check_binded = true;
     }

     if (opts.force_process) {
       setTimeout(process, opts.interval);
     }
     selectors.push(selector);
     return $(selector);
   }
 });

 $.extend({
   // force elements's appearance check
   force_appear: function() {
     if (check_binded) {
       process();
       return true;
     };
     return false;
   }
 });

})(jQuery);