ShaderLab 之 UNITY_INITIALIZE_OUTPUT

　　在 HLSLSupport.cginc 文件中定义了此宏：

#if defined(UNITY_COMPILER_HLSL)
#define UNITY_INITIALIZE_OUTPUT(type,name) name = (type)0;
#else
#define UNITY_INITIALIZE_OUTPUT(type,name)
#endif

　　只有在HLSL编译器编译时，它才工作，初始化name参数，否则编译器可能会报如下错误：

“Shader error in 'Jie/Test': 'vert': output parameter 'o' not completely initialized at line 37”