Stripping commonly unused shader variants in Unity's built-in render pipeline

//#define SHADER_COMPILATION_LOGGING //#define SKIP_SHADER_COMPILATION

using System.Collections.Generic; using UnityEditor.Build; using UnityEditor.Rendering; using UnityEngine; using UnityEngine.Rendering;

public class ShaderStripper : IPreprocessShaders { private const string LOG_FILE_PATH = "Library/Shader Compilation Results.txt";

private static readonly ShaderKeyword[] SKIPPED_VARIANTS = new ShaderKeyword[]
{
	new ShaderKeyword( "DIRECTIONAL_COOKIE" ),
	new ShaderKeyword( "POINT_COOKIE" ),
	//new ShaderKeyword( "LIGHTPROBE_SH" ), // Apparently used by lightmapping, as well
};

public int callbackOrder { get { return 0; } }

public void OnProcessShader( Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data )
{
	// Don't strip essential shaders
	string shaderName = shader.name;
	if( shaderName.StartsWith( "Hidden/" ) || shaderName.StartsWith( "Unlit/" ) || shaderName.StartsWith( "Legacy Shaders/" ) || shaderName.StartsWith( "Particles/" ) )
		return;

#if SHADER_COMPILATION_LOGGING System.IO.File.AppendAllText( LOG_FILE_PATH, "\n\n\n\n===== " + shader.name + " " + snippet.passName + " " + snippet.passType + " " + snippet.shaderType + "\n" ); #endif

	if( snippet.passType == PassType.Deferred || snippet.passType == PassType.LightPrePassBase || snippet.passType == PassType.LightPrePassFinal || snippet.passType == PassType.ScriptableRenderPipeline || snippet.passType == PassType.ScriptableRenderPipelineDefaultUnlit )
	{

#if SHADER_COMPILATION_LOGGING System.IO.File.AppendAllText( LOG_FILE_PATH, "Skipped shader variant because it uses SRP or Deferred shading\n" ); #endif

		data.Clear();
	}

	for( int i = data.Count - 1; i >= 0; --i )
	{
		bool shouldSkipShaderVariant = false;
		foreach( ShaderKeyword keywordToSkip in SKIPPED_VARIANTS )
		{
			if( data[i].shaderKeywordSet.IsEnabled( keywordToSkip ) )
			{
				shouldSkipShaderVariant = true;
				break;
			}
		}

		if( shouldSkipShaderVariant )
		{
			data.RemoveAt( i );
			continue;
		}

#if SHADER_COMPILATION_LOGGING string keywords = ""; foreach( ShaderKeyword keyword in data[i].shaderKeywordSet.GetShaderKeywords() ) keywords += keyword.GetKeywordName() + " ";

		if( keywords.Length == 0 )
			keywords = "No keywords defined";

		System.IO.File.AppendAllText( LOG_FILE_PATH, "- " + keywords + "\n" );

#endif }

#if SKIP_SHADER_COMPILATION for( int i = data.Count - 1; i >= 0; --i ) data.Clear(); #endif } }