渲染路径-surface shader 光照函数与渲染路径

https://docs.unity3d.com/Manual/SL-SurfaceShaderLighting.html

Lighting Model declaration

Lighting model is a couple of regular functions with names starting with Lighting. They can be declared anywhere in your shader file or one of included files. The functions
are:

1. half4 Lighting<Name> (SurfaceOutput s, UnityGI gi); This is used inforward rendering
   path for light models that are not view direction dependent (e.g. diffuse).

2. half4 Lighting<Name> (SurfaceOutput s, half3 viewDir, UnityGI gi); This is used inforward
   rendering path for light models that are view direction dependent.

3. half4 Lighting<Name>_Deferred(SurfaceOutput s, UnityGI gi, out half4 outDiffuseOcclusion,
out half4 outSpecSmoothness, out half4 outNormal); This isused in deferred lighting path.

4. half4 Lighting<Name>_PrePass (SurfaceOutput s, half4 light); This
   is used in light prepass (legacy deferred) lighting path.

Note that you don’t need to declare all functions. A lighting model either uses view direction or it does not. Similarly, if the lighting model only works in forward, do not declare the _Deferred or _Prepass function.
This way, all Shaders that use it compile to forward rendering only.