server/apps/contacts/js/jquery.inview.js

/**
 * author Christopher Blum
 *    - based on the idea of Remy Sharp, http://remysharp.com/2009/01/26/element-in-view-event-plugin/
 *    - forked from http://github.com/zuk/jquery.inview/
 */
(function ($) {
  var inviewObjects = {}, viewportSize, viewportOffset,
      d = document, w = window, documentElement = d.documentElement, expando = $.expando, isFiring = false, $elements = {};

  $.event.special.inview = {
    add: function(data) {
      var inviewObject = { data: data, $element: $(this) }
      inviewObjects[data.guid + "-" + this[expando]] = inviewObject;
      var selector  = inviewObject.data.selector,
      $element  = inviewObject.$element;
      var hash = parseInt(getHash( data.guid + this[expando]));
      $elements[hash] =  selector ? $element.find(selector) : $element;
    },

    remove: function(data) {
      try { delete inviewObjects[data.guid + "-" + this[expando]]; } catch(e) {}
      try {
        var hash = parseInt(getHash(data.guid + this[expando])); 
	delete($elements[hash]);
      } catch (e){}
    }
  };

  
  function getHash(str){
    str = str+'';
    var hash = 0;
    if (str.length == 0) return hash;
    for (i = 0; i < str.length; i++) {
        char = str.charCodeAt(i);
        hash = ((hash<<5)-hash)+char;
        hash = hash & hash; // Convert to 32bit integer
    }
    return Math.abs(hash);
  }
  
  function getViewportSize() {
    var mode, domObject, size = { height: w.innerHeight, width: w.innerWidth };

    // if this is correct then return it. iPad has compat Mode, so will
    // go into check clientHeight/clientWidth (which has the wrong value).
    if (!size.height) {
      mode = d.compatMode;
      if (mode || !$.support.boxModel) { // IE, Gecko
        domObject = mode === 'CSS1Compat' ?
          documentElement : // Standards
          d.body; // Quirks
        size = {
          height: domObject.clientHeight,
          width:  domObject.clientWidth
        };
      }
    }

    return size;
  }

  function getViewportOffset() {
    return {
      top:  w.pageYOffset || documentElement.scrollTop   || d.body.scrollTop,
      left: w.pageXOffset || documentElement.scrollLeft  || d.body.scrollLeft
    };
  }

  function checkInView() {
    if (isFiring){
      return;
    }
    isFiring = true;
      viewportSize   = viewportSize   || getViewportSize();
      viewportOffset = viewportOffset || getViewportOffset();
      
      for (var i in $elements) {
        if (isNaN(parseInt(i))) {
          continue;
        }

        var $element      = $($elements[i]),
            elementSize   = { height: $element.height(), width: $element.width() },
            elementOffset = $element.offset(),
            inView        = $element.data('inview'),
            visiblePartX,
            visiblePartY,
            visiblePartsMerged;

        // Don't ask me why because I haven't figured out yet:
        // viewportOffset and viewportSize are sometimes suddenly null in Firefox 5.
        // Even though it sounds weird:
        // It seems that the execution of this function is interferred by the onresize/onscroll event
        // where viewportOffset and viewportSize are unset
        if (!viewportOffset || !viewportSize) {
	  isFiring = false;
          return;
        }
        
        if (elementOffset.top + elementSize.height > viewportOffset.top &&
            elementOffset.top < viewportOffset.top + viewportSize.height &&
            elementOffset.left + elementSize.width > viewportOffset.left &&
            elementOffset.left < viewportOffset.left + viewportSize.width) {
          visiblePartX = (viewportOffset.left > elementOffset.left ?
            'right' : (viewportOffset.left + viewportSize.width) < (elementOffset.left + elementSize.width) ?
            'left' : 'both');
          visiblePartY = (viewportOffset.top > elementOffset.top ?
            'bottom' : (viewportOffset.top + viewportSize.height) < (elementOffset.top + elementSize.height) ?
            'top' : 'both');
          visiblePartsMerged = visiblePartX + "-" + visiblePartY;
          if (!inView || inView !== visiblePartsMerged) {
            $element.data('inview', visiblePartsMerged).trigger('inview', [true, visiblePartX, visiblePartY]);
          }
        } else if (inView) {
          $element.data('inview', false).trigger('inview', [false]);
        }
      }
      isFiring = false;
  }

  $(w).bind("scroll resize", function() {
    viewportSize = viewportOffset = null;
  });

  // Use setInterval in order to also make sure this captures elements within
  // "overflow:scroll" elements or elements that appeared in the dom tree due to
  // dom manipulation and reflow
  // old: $(window).scroll(checkInView);
  //
  // By the way, iOS (iPad, iPhone, ...) seems to not execute, or at least delays
  // intervals while the user scrolls. Therefore the inview event might fire a bit late there
  setInterval(checkInView, 250);
})(jQuery);