ShaderVariantStripper.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using UnityEditor;
using UnityEditor.Build;
using UnityEditor.Rendering;
using UnityEngine;
using UnityEngine.Rendering;

public class ShaderVariantStripper : IPreprocessShaders
{
    public int callbackOrder { get { return 0; } }

    private const string ShaderRoot = "Assets/AssetBundle/Shader/Variant";
    private const string MaterialRoot = "Assets";

    private List<Material> m_materials;

    class EqualityComparer : IEqualityComparer<string[]>
    {
        public bool Equals(string[] x, string[] y)
        {
            Array.Sort(x);
            Array.Sort(y);
            return x.SequenceEqual(y);
        }

        public int GetHashCode(string[] obj)
        {
            int hashCode = 0;
            Array.Sort(obj);
            foreach (var e in obj)
            {
                hashCode ^= e.GetHashCode();
            }
            return hashCode;
        }
    }

    public void OnProcessShader(Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data)
    {
        var shaderPath = AssetDatabase.GetAssetPath(shader);
        if (shaderPath.StartsWith(ShaderRoot))
        {
            if (m_materials == null)
            {
                m_materials = new List<Material>();
                foreach (var path in Directory.GetFiles(MaterialRoot, "*.mat", SearchOption.AllDirectories))
                {
                    var material = AssetDatabase.LoadAssetAtPath<Material>(path);
                    if (material != null)
                    {
                        m_materials.Add(material);
                    }
                }
            }

            var validKeywords = UtilityFunction.GetShaderKeywords(shader);

            var keywordsInUse = new HashSet<string[]>(new EqualityComparer());

            keywordsInUse.UnionWith(m_materials.Where(m => m.shader == shader).Select(m => m.shaderKeywords.Where(k => validKeywords.Contains(k)).ToArray()));

            for (int i = data.Count - 1; i >= 0; i--)
            {
                var keywordSet = data[i].shaderKeywordSet;
                var enabledKeywords = keywordSet.GetShaderKeywords().Select(k => k.GetKeywordName()).ToArray();

                if (!keywordsInUse.Contains(enabledKeywords))
                {
                    data.RemoveAt(i);
                }
            }

            Debug.Log($"Build shader {shader} with {data.Count} variants");
        }
    }
}