UGUI rectMask2d正确裁减非默认材质的UI

之前使用Mask进行裁剪，由于UI是非默认材质，对shader添加了

    _StencilComp("Stencil Comparison", Float) = 8
    _Stencil("Stencil ID", Float) = 0
    _StencilOp("Stencil Operation", Float) = 0
    _StencilWriteMask("Stencil Write Mask", Float) = 255
    _StencilReadMask("Stencil Read Mask", Float) = 255
    _ColorMask("Color Mask", Float) = 15

等代码可以正常裁剪。
为了减少drawcall数，将mask用react mask 2d替换，结果对非默认材质的UI无法裁剪。

https://www.cnblogs.com/CasualAttachment/p/7725364.html