Version: 2021.1
Asynchronous shader compilation

Shader compilation


Every time you build your project, the Unity Editor compiles all the shaders that your build requires: every required shader variant, for every required graphics API.

When you’re working in the Unity Editor, the Editor does not compile everything upfront. This is because compiling every variant for every graphics API can take a very long time.

Instead, Unity Editor does this:

  • When it imports a shader asset, it performs some minimal processing (such as Surface Shader generation).
  • When it needs to show a shader variant, it checks the Library/ShaderCache folder.
  • If it finds a previously compiled shader variant that uses identicial source code, it uses that.
  • If it does not find a match, it compiles the required shader variant and saves the result to the cache.

Shader compilation is carried out using a process called UnityShaderCompiler. Multiple UnityShaderCompiler processes can be started (generally one per CPU core in your machine), so that at player build time shader compilation can be done in parallel. While the Editor is not compiling shaders, the compiler processes do nothing and do not consume computer resources.

The shader cache folder can become quite large, if you have a lot of shaders that are changed often. It is safe to delete this folder; it just causes Unity to recompile the shader variants.

At player build time, all the “not yet compiled” shader variants are compiled, so that they are in the game data even if the editor did not happen to use them.

Different shader compilers

Different platforms use different shader compilers for shader program compilation as follows:

  • Platforms that use DirectX use Microsoft’s FXC HLSL compiler.
  • Platforms that use OpenGL (Core & ES) use Microsoft’s FXC HLSL compiler, followed by bytecode translation into GLSL using HLSLcc.
  • Platforms that use Metal use Microsoft’s FXC HLSL compiler, followed by bytecode translation into Metal, using HLSLcc.
  • Platforms that use Vulkan use Microsoft’s FXC HLSL compiler, followed by bytecode translation into SPIR-V, using HLSLcc.
  • Other platforms, such as console platforms, use their respective compilers.
  • Surface Shaders use HLSL and MojoShader for code generation analysis step.

You can use predefined shader macros to identify which compiler Unity is using. You might want to use this if you use HLSL syntax that is supported by only one compiler, or to work around a compiler bug.

You can configure various shader compiler settings using pragma directives.

The Caching Shader Preprocessor

Shader compilation involves several steps. One of the first steps is preprocessing the shader source. By default, Unity uses the platform compiler’s preprocessor to perform this step; however, you can choose to override this and use Unity’s Caching Shader Preprocessor to perform preprocesing. The Caching Shader Preprocessor is up to 25% faster than the default preprocessors used by platform compilers.

The Caching Shader Preprocessor caches intermediate preprocessing data to speed up shader import and compilation time. The Editor reuses this cached data, and only needs to parse include files when their contents change. This makes compiling multiple variants of the same shader more efficient. Enabling the Caching Shader Preprocessor has the most noticeable effect when shaders within a project use a large set of common include files.

Note that the Caching Shader Preprocessor is experimental; it is still in active development. You can provide feedback on this experimental feature in the Unity forum.

You can enable or disable the Caching Shader Preprocessor using the Caching Shader Preprocessor checkbox in the Shader Compilation section of the Editor settings window. You can also enable or disable this feature in a C# script, using the EditorSettings.cachingShaderPreprocessor API.

Build time stripping

While building the game, Unity can detect that some of the internal shader variants are not used by the game, and exclude (“strip”) them from build data. Build-time stripping is done for:

  • For shaders that use #pragma shader_feature, Unity automatically checks whether variants are used. If none of the Materials in a build use a variant, that variant it is not included into the build. See internal shader variants documentation. The Standard shader uses this.
  • いずれのシーンでも使用されていないフォグとライトマップモードを処理するシェーダーバリアントは、ゲームデータに含まれません。この動作をオーバーライドしたい場合は、Graphics ウィンドウを参照してください。
  • You can also manually identify variants and tell Unity to exclude them from a build using using the OnProcessShader API.

上記の組み合せは、シェーダーデータサイズをしばしば大幅に減らします。例えば、完全にコンパイルした Standard シェーダーは数百メガバイトを取るでしょう。しかし、典型的なプロジェクトでは、多くの場合、わずか数メガバイトを取ることになります(しばしばアプリケーションのパッケージングプロセスによってさらに圧縮されます)。

Asynchronous shader compilation