grid 显示缩略图问题

zhujs

function thumbnail (data, metadata, record, rowIndex, columnIndex, store){var url = store.getAt(rowIndex).get('bannerUrl');var fileName = store.getAt(rowIndex).get('fileName');//qtitle标题 qtip:内容var img = "<img src='"+url+"/"+fileName+ "' width='300' height='200'>";    var displayText  = '<div ext:qtitle="" ext:qtip="'+img+'">'+data+'</div>';     return displayText;  }var cm = new Ext.grid.ColumnModel( [ new Ext.grid.RowNumberer(),//自动行号  sm,//自动行号{    header:"文件名",dataIndex:'fileName',width:135,locked:true,menuDisabled: true,sortable: true,renderer:thumbnail},{    header:"文件类型",dataIndex:'leaf',width:93,locked:true,menuDisabled: true,sortable: true,renderer:thumbnail},{header:"修改时间",dataIndex:'lastModifyDate',width:140,locked:true,menuDisabled: true,sortable: true,renderer:thumbnail},{header:"图片尺寸",dataIndex:'imgSize',width:150,locked:true,menuDisabled: true,sortable: true,renderer:thumbnail},{header:"大小",dataIndex:'fileSize',width:80,locked:true,menuDisabled: true,sortable: true,renderer:thumbnail},{header:"缩略图",width:120,locked:true,menuDisabled: true,sortable: false,dataIndex:'bannerId',renderer: function(data, metadata, record, rowIndex, columnIndex, store) {var url = store.getAt(rowIndex).get('bannerUrl');var fileName = store.getAt(rowIndex).get('fileName');    return '<div class="controlBtn">' +    '<img src="'+url+'/'+fileName+'"' +    ' width="16" height="16"' +    ' ></div>';} }]);
感觉这个方法并不是很好,因为每一列都写了renderer:thumbnail,显示图片的时候也比较慢,谢谢yourgame的帮助.不知道还有什么好的方法没?