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Unity Engine

OnProcessShader(Shader, ShaderSnippetData, IList<ShaderCompilerData>)

Implement this interface to receive a callback before a shader snippet is compiled.
Read time 3 minutesLast updated 10 days ago

Definition

void OnProcessShader(Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data)

Parameters

shader

Shader
The shader that Unity is about to compile.

snippet

ShaderSnippetData
Details about the specific shader code being compiled.

data

IList<ShaderCompilerData>
List of variants that Unity is about to compile for the shader.

Remarks

When you build your application, Unity compiles each shader source file into multiple shader variants. Unity creates variants for some or all the possible combinations of keywords you define in the shader source file.
You can use 
OnProcessShader
to iterate through each shader and variant Unity is about to compile, and exclude ('strip') variants that use keywords or keyword combinations you don't need. If you strip variants, you can reduce build size, build times, and how much runtime memory Unity uses.
For example, you can use 
OnProcessShader
to remove variants that use the following:
  • Keywords that aren't needed for the current target platform.
  • Combinations of keywords that are never used.
  • Keywords you only use in your debug builds.
Unity invokes the 
OnProcessShader
callback in both Player and AssetBundle builds. If there are any shaders already in the cache, then this method isn't invoked for those shaders. To ensure the callback runs for all shaders, perform a clean build. To run it for a specific shader, modify that shader or one of its dependent assets.
To help you identify keywords and variants to strip, you can check what shader variants you have in your project. For example if you declare a keyword called 
DEBUG
in your shader code using 
#pragma multi_compile _ DEBUG
, the following Editor script finds and strips shader variants that use the keyword.
The script does the following when you build your application:
  1. Creates a class that implements the 
    IPreprocessShaders
    interface.
  2. Creates an instance of 
    ShaderKeyword
    with the name of the keyword.
  3. Implements the 
    OnProcessShader
    callback function and iterates over the 
    data
    list, which contains every variant in the shader.
  4. Uses 
    data.shaderKeywordSet.IsEnabled()
    to check if each variant uses the keyword.
  5. Uses 
    data.removeAt()
    to strip a shader variant if it contains the keyword and you've disabled Development build in Build Settings.
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEditor.Build;
using UnityEditor.Rendering;

class ShaderDebugBuildPreprocessor : IPreprocessShaders
{
 ShaderKeyword m_KeywordToStrip;

 public ShaderDebugBuildPreprocessor()
 {
 m_KeywordToStrip = new ShaderKeyword("DEBUG");
 }

 // Use callbackOrder to set when Unity calls this shader preprocessor. Unity starts with the preprocessor that has the lowest callbackOrder value.
 public int callbackOrder { get { return 0; } }

 public void OnProcessShader(
 Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data)
 {

 for (int i = 0; i < data.Count; ++i)
 {
 if (data[i].shaderKeywordSet.IsEnabled(m_KeywordToStrip) && !EditorUserBuildSettings.development)
 {
 var foundKeywordSet = string.Join(" ", data[i].shaderKeywordSet.GetShaderKeywords()); 
 Debug.Log("Found keyword DEBUG in variant " + i + " of shader " + shader);
 Debug.Log("Keyword set: " + foundKeywordSet);
 data.RemoveAt(i);
 --i;
 }
 }
 }
}
You can also find local keywords. You must create the 
ShaderKeyword
instance inside the implementation of 
OnProcessShader
, so you can use the callback's 
shader
variable in the 
ShaderKeyword
constructor.
For example if you declare a local keyword called 
RED
in your shader code using 
#pragma multi_compile_local _ RED
, the following script finds and strips shader variants that use the keyword.
using System.Collections.Generic;
using UnityEditor.Build;
using UnityEditor.Rendering;
using UnityEngine;
using UnityEngine.Rendering;

class MyCustomBuildProcessor : IPreprocessShaders
{

 public int callbackOrder { get { return 0; } } 

 public void OnProcessShader(Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data)
 {

 // Create an instance of ShaderKeyword using the constructor that takes a Shader argument
 ShaderKeyword localKeywordToStrip = new ShaderKeyword(shader, "RED");

 for (int i = 0; i < data.Count; ++i)
 {
 if (data[i].shaderKeywordSet.IsEnabled(localKeywordToStrip))
 {
 data.RemoveAt(i);
 --i;
 }
 }
 }
}
If you strip a variant that a Material needs at runtime, Unity chooses an available shader variant that matches as closely as possible.
Find out about other ways you can strip shader variants.
Additional Resources: BuildPipeline.BuildPlayer, BuildPipeline.BuildAssetBundles, IPreprocessComputeShaders.