Lit Flat Height Field.shader

// https://twitter.com/shanecelis/status/1024022967532101633
Shader "Custom/Lit Flat Height Field" {
  Properties {
    _Color ("Color", Color) = (1,1,1,1)
    _MainTex ("Albedo (RGB)", 2D) = "white" {}
    _HeightField ("Height Field", 2D) = "black" {}
    _Glossiness ("Smoothness", Range(0,1)) = 0.5
    _Metallic ("Metallic", Range(0,1)) = 0.0
  }
  SubShader {
    Tags { "RenderType"="Opaque" }
    LOD 200

    CGPROGRAM
    // Physically based Standard lighting model, and enable shadows on all light types
    #pragma surface surf Standard fullforwardshadows vertex:vert addshadow

    // Use shader model 3.0 target, to get nicer looking lighting
    #pragma target 3.0

    sampler2D _MainTex;
    sampler2D _HeightField;

    struct Input {
      float2 uv_MainTex;
      float2 uv_HeightField;
      float3 worldPos;
    };

    half _Glossiness;
    half _Metallic;
    fixed4 _Color;

    void vert( inout appdata_full v ) {
      fixed4 col = tex2Dlod(_HeightField, v.texcoord);
      // The red channel is the height of our field.
      v.vertex.y += col.r;
    }

    // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
    // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
    // #pragma instancing_options assumeuniformscaling
    UNITY_INSTANCING_BUFFER_START(Props)
      // put more per-instance properties here
    UNITY_INSTANCING_BUFFER_END(Props)

    void surf (Input IN, inout SurfaceOutputStandard o) {
      // Albedo comes from a texture tinted by color
      fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
      o.Albedo = c.rgb;
      o.Metallic = _Metallic;
      o.Smoothness = _Glossiness;
      o.Alpha = c.a;

      // Here's where we compute our normals.
      float3 normal_world = normalize(cross(ddx(IN.worldPos), ddy(IN.worldPos)));
      // TIL o.Normal is in object space.
      o.Normal = mul(unity_WorldToObject, float4(normal_world, 0)).xyz;
    }

    ENDCG
  }
  FallBack "Diffuse"
}