Reduce shader variants in custom shader code

Prevent shader variantsA verion of a shader program that Unity generates according to a specific combination of shader keywords and their status. A Shader object can contain multiple shader variants. More info
See in Glossary from being compiled in your custom shaders, to greatly reduce build times, file size, shaderA program that runs on the GPU. More info
See in Glossary loading times, and runtime memory usage.

You can also limit or remove shader variants using the Editor UI. For more information, refer to Reduce shader variants.

Limit 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 How Unity compiles branching shaders.
• Ensure that you don’t define unused keywords with multi_compile.

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

Indicate which shader keywords affect which shader stage

When you declare a keyword, Unity assumes all stages of the shader contain conditional code for that keyword.

You can add the following suffixes to indicate that only certain stages contain conditional code for a keyword, so that Unity doesn’t generate unneeded shader variants.

• _vertex
• _fragment
• _hull
• _domain
• _geometry

For example, use #pragma shader_feature_fragment RED GREEN BLUE to indicate that you use the 3 keywords to create conditional code in the fragment stage only.

Note: You can’t add these suffixes to #pragma dynamic_branch because dynamic_branch doesn’t create variants.

These suffixes might behave differently or have no effect, depending on the graphics API. For example:

• The suffixes have no effect on OpenGL, OpenGL ES or Vulkan.
• The _geometry and _raytracing suffixes have no effect on Metal. Metal treats _vertex, _hull and _domain as a single stage.

Use preprocessor macros to limit variants by platform

You can create conditional shader code using a target platform preprocessor macro, so you can limit variants on platforms with limited memory.

For example:

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

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.

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.

Reduce user-controlled quality settings by platform

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

Additional resources

• Reduce shader variants