Ext中 renderer一般用于Grid中对列模型的渲染上 其详细信息记录在 Ext.grid.ColumnModel 中的setRenderer( Number col, Function fn ) 方法里
一、col : Number
  The column index
二、fn : Function
The function to use to process the cell's raw data to return HTML markup for the grid view. The render function is called with the following parameters:
1、value : Object
    The data value for the cell.(单元格的值)
2、metadata : Object
    An object in which you may set the following attributes一个可以设置下边两个属性的对象)
    **css : String
        A CSS class name to add to the cell's TD element.
    **attr : String
        An HTML attribute definition string to apply to the data container element within the table cell (e.g. 'style="color:red;"').
3、record : Ext.data.record
    The Ext.data.Record from which the data was extracted.
4、rowIndex : Number
    Row index(行号)
5、colIndex : Number
    Column index(列号)
6、store : Ext.data.Store
    The Ext.data.Store object from which the Record was extracted.
    (数据源对象 就是Grid的store/ds)