Fabric.js画布缩放+鼠标控制问题

Question

我试图找到一种方法让鼠标控制与缩放的Fabric.js画布一起使用。

http://jsfiddle.net/mrks/Ce3XF/1/

   var canvas = new fabric.Canvas('canvas');            
   canvas.setWidth(1000);
   canvas.setHeight(1000);
   canvas.add(new fabric.Rect({fill: 'red', left: 250, top: 250, width: 250, height: 250}));

   var text = new fabric.Text('Text inside canvas', { left: 200, top: 50 });
   text.hasRotatingPoint = true;
   canvas.add(text);


   canvas.upperCanvasEl.style.width = '400px';
   canvas.upperCanvasEl.style.height = '400px';
   canvas.lowerCanvasEl.style.width = '400px';
   canvas.lowerCanvasEl.style.height = '400px';

我无法弄明白该怎么做。有什么帮助吗？