在渲染玻璃表面时候， 如果有物体在玻璃后面，类似透过手表玻璃 看到指针或者表盘； 或者水杯里面的冰块之类， 由于玻璃具有折射率，怎么渲染出玻璃里面物体的单独通道？
When rendering the glass surface, if there is an object behind the glass, such as seeing the pointer or dial through the watch glass, or ice in the water cup, how to render the separate channel of the object in the glass due to its refractive index?
