How to Terrain paint with a shader?

Hi,
I'm new to the forums and this is my first post. Apologies in advance if I'm posting wrong.

Goal: I'm trying to get this simple tessellation code to work with Unity terrain so that I can paint with it. How do I do this?

Note: the code works with objects but not Unity Terrain. I'm I missing something obvious?

Not C# Code:

Code (CSharp):

1. Shader "Nature/Terrain/GroundH"
2. {
3.    Properties {
4.         _Color ("Color", Color) = (1,1,1,1)
5.         _MainTex ("Albedo (RGB)", 2D) = "white" {}
6.         _BumpMap ("Normal Map (RGB)", 2D) = "bump" {}
7.         _BumpScale ("Normal Power" , Float) = 1
8.         _Occlusion ("Occlusion Map (R)" , 2D) = "white" {}
9.         _Metallic ("Metallic (R) , Smoothness (A)" , 2D) = "black" {}
10.         _ParallaxMap ("Heightmap (A)", 2D) = "black" {}
11.         _EdgeLength ("Edge length", Range(3,50)) = 10
12.         _Parallax ("Height", Range (0.0, 1)) = .5
13.     }
14.     SubShader {
15.         Tags { "RenderType"="Opaque" }
16.         LOD 200
17.      
18.         CGPROGRAM
19.         // Physically based Standard lighting model, and enable shadows on all light types
20.      
21.         #pragma surface surf Standard fullforwardshadows vertex:disp tessellate:tessEdge
22.         #include "Tessellation.cginc"
23.      
24.         sampler2D _ParallaxMap;
25.         float _EdgeLength;
26.         fixed _Parallax;
27.         float _BumpScale;
28.         sampler2D _MainTex;
29.         sampler2D _Occlusion;
30.         sampler2D _BumpMap;
31.         sampler2D _Metallic;
32.      
33.         struct appdata {
34.             float4 vertex : POSITION;
35.             float4 tangent : TANGENT;
36.             float3 normal : NORMAL;
37.             float2 texcoord : TEXCOORD0;
38.             float2 texcoord1 : TEXCOORD1;
39.             float2 texcoord2 : TEXCOORD2;
40.         };
41.      
42.         float4 tessEdge (appdata v0, appdata v1,appdata v2)
43.         {
44.             return UnityEdgeLengthBasedTessCull (v0.vertex, v1.vertex, v2.vertex, _EdgeLength, _Parallax * 1.5f);
45.         }
46.  
47.         void disp (inout appdata v)
48.         {
49.             float d = tex2Dlod(_ParallaxMap, float4(v.texcoord.xy,0,0)).a * _Parallax;
50.             v.vertex.xyz += v.normal * d;
51.         }
52.         // Use shader model 3.0 target, to get nicer looking lighting
53.         #pragma target 3.0
54.         struct Input {
55.             float2 uv_MainTex;
56.         };
57.         fixed4 _Color;
58.         void surf (Input IN, inout SurfaceOutputStandard o) {
59.             // Albedo comes from a texture tinted by color
60.             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
61.             o.Albedo = c.rgb;
62.             // Metallic and smoothness come from slider variables
63.             fixed4 m = tex2D(_Metallic,IN.uv_MainTex);
64.             o.Metallic = m.r;
65.             o.Occlusion = tex2D(_Occlusion,IN.uv_MainTex).x;
66.             o.Smoothness = m.a;
67.             o.Normal = normalize(UnpackScaleNormal(tex2D(_BumpMap, IN.uv_MainTex), _BumpScale));
68.             o.Alpha = c.a;
69.         }
70.         ENDCG
71.     }
72.     FallBack "Diffuse"
73. }