Shader variant stripping

You can prevent shader variants from being compiled. This is called stripping. Stripping unneeded variants can greatly reduce build times, file size, shader loading times, and runtime memory usage. In larger projects, or projects with complex shaders, this is a very important consideration.

If you strip a shader variant that a Material needs at runtime, Unity tries to choose a similar shader variant that’s available. To avoid this, use the following approaches:

• If you use a shader_feature keyword, don’t use the keyword to change which code branch executes at runtime.
• Check what shader variants you have to help you see which shader variants and keyword combinations Materials need at runtime.
• Add shaders to the Always Included Shaders list in Graphics settings.

Limiting shader variants when you declare shader keywords

The way that you declare shader keywords can limit the number of variants that they produce:

• Use shader_feature instead of multi_compile where possible - see conditionals in shaders.
• Ensure that you don’t define unused keywords with multi_compile.
• Indicate when shader keywords only affect a given shader stage.

For information on declaring keywords in hand-coded shaders, see Declaring and using shader keywords in HLSL. For information on declaring keywords in Shader Graph, see Shader Graph: Blackboard.

Use preprocessor macros to limit variants by platform

In Unity 2021.3 and above, you can create conditional shader code using a target platform preprocessor macro, so you can limit variants on platforms with limited memory.

The code sample does the following:

• If you build for a SHADER_API_DESKTOP platform, Unity builds variants for every possible keyword combination.
• If you build for another platform, Unity builds only variants for keyword combinations the Materials in your build use.

#ifdef SHADER_API_DESKTOP
   #pragma multi_compile _ RED GREEN BLUE WHITE
#else
   #pragma shader_feature RED GREEN BLUE WHITE
#endif

You can use target platform preprocessor macros to select between shader_feature, multi_compile and dynamic_branch. For more information on when to use each type of conditional, see Shader Conditionals.

Create user-controlled quality settings

When you build for console and mobile platforms that have limited memory, you can limit shader variants by only allowing users to switch between a small number of quality settings.

For example, if you use the keywords DYNAMIC_LIGHTING, SOFT_SHADOWS and HIGH_QUALITY_LIGHTMAPS, you can create the following:

• A ‘low quality’ setting that turns on DYNAMIC_LIGHTING.
• A ‘high quality’ setting that turns on DYNAMIC_LIGHTING, SOFT_SHADOWS and HIGH_QUALITY_LIGHTMAPS.

This means Unity won’t create shader variants for DYNAMIC_LIGHTING when it’s off, or the many different combinations of the 3 keywords being on and off.

You can use target platform preprocessor macros to conditionally create fewer quality settings and fewer variants on platforms with limited memory. For example the following code sample will allow users to switch between 8 permutations of settings on SHADER_API_DESKTOP platforms, but only 2 on SHADER_API_MOBILE platforms.

#if SHADER_API_DESKTOP
   #pragma multi_compile SHADOWS_LOW SHADOWS_HIGH
   #pragma multi_compile REFLECTIONS_LOW REFLECTIONS_HIGH
   #pragma multi_compile CAUSTICS_LOW CAUSTICS_HIGH
#elif SHADER_API_MOBILE
   #pragma multi_compile QUALITY_LOW QUALITY_HIGH
   #pragma shader_feature CAUSTICS // Uses shader_feature, so Unity strips variants that use CAUSTICS if there are no Materials that use the keyword at build time.
#endif

Stripping shader variants in the Editor UI

There are several places in the Unity Editor UI where you can configure shader stripping:

• In the Graphics Settings window, configure the settings in the Shader stripping section:

• Ensure that no unneeded shaders are included in the Always-included shaders setting.

• Strip variants relating to GPU instancing, lightmapping, and fog.

• In the Built-in Render PipelineA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
  See in Glossary, if it is not important that your Tier settings are different, ensure that they are identical to each other. For more information, see Graphics tiers.

• In the Universal Render Pipeline (URP), disable unused features in the URP Asset. For more information, see Shader stripping.

If you use the Universal Render Pipeline you can also do the following:

• In the Universal Render Pipeline Asset, disable rendering any features your project doesn’t use.
• Enable shader stripping.

If you use the High Definition Render Pipeline you can also do the following:

• In the High Definition Render Pipeline Asset, disable any rendering features your project doesn’t use.
• In the Miscellaneous section of the HDRP Global Settings Window, disable Runtime Debug Shaders.

Stripping shader variants using Editor scripts

For shader variants that you can’t strip in other ways, you can use the following APIs in an Editor script to perform build-time stripping:

• IPreprocessShaders.OnProcessShader: receive a callback before Unity compiles a graphics shader Pass into a build.
• IPreprocessComputeShaders.OnProcessComputeShader: receive a callback before Unity compiles a compute shader into a build.

For more information on this subject, see the Unity blog post Stripping scriptable shader variants