比较容易理解得两个
Unity #pragma multi_compile说明（简单得代码实例说明）
https://blog.csdn.net/ak47007tiger/article/details/100007655
让我们好好聊聊Unity Shader中的multi_complie
https://zhuanlan.zhihu.com/p/77043332
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这篇很详细
unity shader 变种（多重编译 multi_compile）-
https://blog.csdn.net/yinfourever/article/details/103072057
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Unity Shader - 使用multi_compile对Shader渲染质量控制
https://blog.csdn.net/linjf520/article/details/93721871