Custom data Surface Shader example in the Built-In Render Pipeline

Using a vertex modifier function, it is also possible to compute custom data in a vertex ShaderA program that runs on the GPU. More info
See in Glossary, which then will be passed to the Surface ShaderA streamlined way of writing shaders for the Built-in Render Pipeline. More info
See in Glossary function per-pixel. The same compilation directive vertex:functionName is used, but the function should take two parameters: inout appdata_full and out Input. You can fill in any Input member that is not a built-in value there.

Note: Custom Input members used in this way must not have names beginning with ‘uv’ or they won’t work properly.

The example below defines a custom float3 customColor member, which is computed in a vertex function:

  Shader "Example/Custom Vertex Data" {
    Properties {
      _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader {
      Tags { "RenderType" = "Opaque" }
      CGPROGRAM
      #pragma surface surf Lambert vertex:vert
      struct Input {
          float2 uv_MainTex;
          float3 customColor;
      };
      void vert (inout appdata_full v, out Input o) {
          UNITY_INITIALIZE_OUTPUT(Input,o);
          o.customColor = abs(v.normal);
      }
      sampler2D _MainTex;
      void surf (Input IN, inout SurfaceOutput o) {
          o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
          o.Albedo *= IN.customColor;
      }
      ENDCG
    } 
    Fallback "Diffuse"
  }

In this example customColor is set to the absolute value of the normal:

More practical uses could be computing any per-vertex data that is not provided by built-in Input variables; or optimizing Shader computations. For example, it’s possible to compute Rim lighting at the GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary’s vertices, instead of doing that in the Surface Shader per-pixel.