/**
 * picLazyLoad 图片延时加载，包含背景图片
 * $(img).picLazyLoad({...})
 * data-original 预加载图片地址
 * alon
 */
;(function($){
  $.fn.imgLazyLoad = function(settings){
    var $this = $(this),
      _winScrollTop = 0,
      _winHeight = $(window).height();
    settings = $.extend({
      threshold: 0, // 提前高度加载
      placeholder: 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC',
      callback:function(){}
    }, settings||{});
    // 执行懒加载图片
    lazyLoadPic();
    // 滚动触发换图
    $(window).on('scroll',function(){
      _winScrollTop = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop;
      lazyLoadPic();
    });
    // 懒加载图片
    function lazyLoadPic(){
      $this.each(function(){
        var $self = $(this);
        if($self.is('img')){
          if($self.attr('data-original')){
            var _offsetTop = $self.offset().top;
            if((_offsetTop - settings.threshold) <= (_winHeight + _winScrollTop)){
              $self.attr('src',$self.attr('data-original'));
              $self.removeAttr('data-original');
              $self.removeClass('loadH');
              settings.callback($self);
            }
          }
        }else{
          if($self.attr('data-original')){// 默认占位图片
            if($self.css('background-image') == 'none'){
              $self.css('background-image','url('+settings.placeholder+')');
            }
            var _offsetTop = $self.offset().top;
            if((_offsetTop - settings.threshold) <= (_winHeight + _winScrollTop)){
              $self.css('background-image','url('+$self.attr('data-original')+')');
              $self.removeAttr('data-original');
              settings.callback($self);
            }
          }
        }
      });
    }
  }
})(Zepto);

$('img').imgLazyLoad({callback:function(data){
 
 })