src/lay/modules/flow.js
function(othis, scroll){
      
      //计算滚动所在容器的可视高度
      var height = notDocment ? (scroll||scrollElem).height() : $(window).height();
      var start = scrollElem.scrollTop(), end = start + height;

      that.lazyimg.elem = $(elem);

      if(othis){
        show(othis, height);
      } else {
        //计算未加载过的图片
        for(var i = 0; i < that.lazyimg.elem.length; i++){
          var item = that.lazyimg.elem.eq(i), elemTop = notDocment ? function(){
            return item.offset().top - scrollElem.offset().top + start;
          }() : item.offset().top;
          
          show(item, height);
          index = i;
          
          //如果图片的top坐标，超出了当前屏，则终止后续图片的遍历
          if(elemTop > end) break;
        }
      }
    }
function(othis, scroll){
      
      //计算滚动所在容器的可视高度
      var height = notDocment ? (scroll||scrollElem).height() : $(window).height();
      var start = scrollElem.scrollTop(), end = start + height;

      that.lazyimg.elem = $(elem);

      if(othis){
        show(othis, height);
      } else {
        //计算未加载过的图片
        for(var i = 0; i < that.lazyimg.elem.length; i++){
          var item = that.lazyimg.elem.eq(i), elemTop = notDocment ? function(){
            return item.offset().top - scrollElem.offset().top + start;
          }() : item.offset().top;
          
          show(item, height);
          index = i;
          
          //如果图片的top坐标，超出了当前屏，则终止后续图片的遍历
          if(elemTop > end) break;
        }
      }
    }
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