SobelNode.cs

using System.Reflection;
using UnityEditor.ShaderGraph;
using UnityEngine;

[Title("Custom", "Image", "Sobel Edge Detection")]
public class SobelNode : CodeFunctionNode
{
    public SobelNode()
    {
        name = "Sobel Edge Detection";
    }
    
    protected override MethodInfo GetFunctionToConvert()
    {
        return GetType().GetMethod("SobelFunction",
            BindingFlags.Static | BindingFlags.NonPublic);
    }

    static string SobelFunction(
        [Slot(1, Binding.MeshUV0)] Vector2 uv,
        [Slot(2, Binding.None)] SamplerState SS,
        [Slot(3, Binding.None)] out Vector4 RGB
    )
    {
        RGB = Vector4.zero;
        return @"
                {
			float2 delta = float2(0.002, 0.002);
			
			float4 hr = float4(0, 0, 0, 0);
			float4 vt = float4(0, 0, 0, 0);

			hr += _MainTex.Sample(SS, (uv + float2(-1.0, -1.0) * delta)) *  1.0;
			hr += _MainTex.Sample(SS, (uv + float2( 0.0, -1.0) * delta)) *  0.0;
			hr += _MainTex.Sample(SS, (uv + float2( 1.0, -1.0) * delta)) * -1.0;
			hr += _MainTex.Sample(SS, (uv + float2(-1.0,  0.0) * delta)) *  2.0;
			hr += _MainTex.Sample(SS, (uv + float2( 0.0,  0.0) * delta)) *  0.0;
			hr += _MainTex.Sample(SS, (uv + float2( 1.0,  0.0) * delta)) * -2.0;
			hr += _MainTex.Sample(SS, (uv + float2(-1.0,  1.0) * delta)) *  1.0;
			hr += _MainTex.Sample(SS, (uv + float2( 0.0,  1.0) * delta)) *  0.0;
			hr += _MainTex.Sample(SS, (uv + float2( 1.0,  1.0) * delta)) * -1.0;

			vt += _MainTex.Sample(SS, (uv + float2(-1.0, -1.0) * delta)) *  1.0;
			vt += _MainTex.Sample(SS, (uv + float2( 0.0, -1.0) * delta)) *  2.0;
			vt += _MainTex.Sample(SS, (uv + float2( 1.0, -1.0) * delta)) *  1.0;
			vt += _MainTex.Sample(SS, (uv + float2(-1.0,  0.0) * delta)) *  0.0;
			vt += _MainTex.Sample(SS, (uv + float2( 0.0,  0.0) * delta)) *  0.0;
			vt += _MainTex.Sample(SS, (uv + float2( 1.0,  0.0) * delta)) *  0.0;
			vt += _MainTex.Sample(SS, (uv + float2(-1.0,  1.0) * delta)) * -1.0;
			vt += _MainTex.Sample(SS, (uv + float2( 0.0,  1.0) * delta)) * -2.0;

			vt += _MainTex.Sample(SS, (uv + float2( 1.0,  1.0) * delta)) * -1.0;


			hr = sqrt((hr.r * hr.r) + (hr.g * hr.g) +  (hr.b * hr.b));
			vt = sqrt((vt.r * vt.r) + (vt.g * vt.g) +  (vt.b * vt.b));		


			RGB = sqrt(hr * hr + vt * vt);
                }
                ";
    }
}