Set the lighting model in a Surface Shader in the Built-In Render Pipeline

Important: The Built-In Render Pipeline is deprecated and will be made obsolete in a future release.
It remains supported, including bug fixes and maintenance, through the full Unity 6.7 LTS lifecycle.
For more information on migration, refer to Migrating from the Built-In Render Pipeline to the Universal Render Pipeline and Render pipeline feature comparison.

In the Built-in Render Pipeline, when writing Surface ShadersA streamlined way of writing shaders for the Built-in Render Pipeline. More info
See in Glossary, you describe the properties of a surface (such as albedo color and normal), and a Lighting Model computes the lighting interaction.

There are two built-in lighting models: Lambert for diffuse lighting, and BlinnPhong for specular lighting. The Lighting.cginc file inside Unity defines these models (Windows: <unity install path>/Data/Resources/CGIncludes/Lighting.cginc; macOS: /Applications/Unity/Unity.app/Contents/Resources/CGIncludes/Lighting.cginc).

Sometimes you might want to use a custom lighting model. You can do this with Surface Shaders. A lighting model is simply a couple of Cg/HLSL functions that match some conventions.

Render pipeline compatibility

Feature name	Universal Render Pipeline (URP)	High Definition Render Pipeline (HDRP)	Custom SRP	Built-in Render Pipeline
Surface Shaders	No For a streamlined way of creating Shader objects in URP, see Shader Graph.	No For a streamlined way of creating Shader objects in HDRP, see Shader Graph.	No	Yes

Declaring lighting models

A lighting model consists of regular functions with names that begin Lighting. You can declare them anywhere in your shader file, or one of the included files. The functions are:

half4 Lighting<Name> (SurfaceOutput s, UnityGI gi); Use this in forward rendering paths for light models that are not dependent on the view direction.
half4 Lighting<Name> (SurfaceOutput s, half3 viewDir, UnityGI gi); Use this in forward rendering paths for light models that are dependent on the view direction.
half4 Lighting<Name>_Deferred (SurfaceOutput s, UnityGI gi, out half4 outDiffuseOcclusion, out half4 outSpecSmoothness, out half4 outNormal); Use this in deferred shading paths.

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 rendering, do not declare the _Deferred function. This ensures that Shaders that use it only compile to forward rendering.

Custom GI

Declare the following function to customize the decoding lightmap data and probes:

void Lighting<Name>_GI (SurfaceOutput s, UnityGIInput data, inout UnityGI gi);

Note that to decode standard Unity lightmaps and SH probes, you can use the built-in DecodeLightmap and ShadeSHPerPixel functions, as seen in UnityGI_Base in the UnityGlobalIllumination.cginc file inside Unity (Windows: <unity install path>/Data/Resources/CGIncludes/UnityGlobalIllumination.cginc; macOS: /Applications/Unity/Unity.app/Contents/Resources/CGIncludes/UnityGlobalIllumination.cginc_).

Example

The following is an example of a shader that uses the built-in Lambert lighting model:

  Shader "Example/Diffuse Texture" {
    Properties {
      _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader {
      Tags { "RenderType" = "Opaque" }
      CGPROGRAM
      #pragma surface surf Lambert
      
      struct Input {
          float2 uv_MainTex;
      };
      
      sampler2D _MainTex;
      
      void surf (Input IN, inout SurfaceOutput o) {
          o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
      }
      ENDCG
    }
    Fallback "Diffuse"
  }

Here’s how it looks like with a Texture and without a Texture, with one directional Light in the Scene:

Shader using a diffuse texture. Shader without a diffuse texture.

Create a surface shader in the Built-In Render Pipeline

Optimize Surface Shaders