在ClipPath外部禁用对象选择-FabricJs

Question

如何禁用clipPath之外的对象选择？

var canvas = new fabric.Canvas('c');
var clipath = new fabric.Rect({ width: 400, height: 300,left:50,fill: '#eee', absolutePositioned: true, selectable: false,hoverCursor: "default",strokeWidth: 0 });

var rect = new fabric.Rect({ width: 100, height: 100, fill: 'red',left:80,top:20 });

rect.clipPath = clipath;
canvas.add(clipath);
canvas.add(rect);

<canvas id="c" width="600" height="350" style="border:1px solid #ccc"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/4.1.0/fabric.min.js"></script>