Version: 2021.3
Shader variants
Using shader keywords with C# scripts

Shader keywords

Shader keywords allow you to use conditional behavior in your shader code. You can create shaders that share some common code, but have different functionality when a given keyword is enabled or disabled. You use with Shader variants.

本页包含以下信息:

Using shader keywords

Declaring shader keywords

You declare shader keywords in sets. A set contains mutually exclusive keywords.

For example, the following set contains three keywords:

  • COLOR_RED
  • COLOR_GREEN
  • COLOR_BLUE

Note: In Shader Graph, the terminology is different: a set of keywords is called a Keyword, and the keywords in a set are called states. Internally, the functionality is the same: Unity compiles them in the same way, you work with them the same way with C# scripts, and so on.

The way that you declare shader keywords affects a number of things:

  • The type affects how Unity creates shader variants for the keywords.
  • The scope affects whether the keywords are local or global. This determines their behavior at runtime.
  • The stage affects which shader stage the keywords affect (where applicable).

Definition type: “multi compile” or “shader feature”

When you declare a set of keywords, you must also choose how Unity defines the keywords internally; this affects the number of variants that Unity compiles.

  • “multi compile” or “shader feature”: Use this to create a set of keywords for use with shader variants. Internally, Unity uses these keyword to create #define preprocessor directives.
    • “multi compile” declares a set of keywords for use with shader variants.

      Unity compiles shader variants for all keywords in the set.
    • “shader feature” declares a set of keywords for use with shader variants, and also instructs the compiler to compile variants where none of these keywords are enabled.

      Unity examines the state of your project at build time, and only compiles variants for keywords that are in use. A keyword is in use if a material that is included in the build has that keyword enabled.

Whether to choose “multi compile” or “shader feature” depends on how you use the keywords. If you use the keywords to configure materials in your project and do not change their value from C# scripts at runtime, then you should use “shader feature” to reduce the number of shader keywords and variants in your project. If you enable and disable keywords at runtime using C# scripts, then you should use “multi compile” to prevent variants being stripped in error. For more information on shader stripping, see Shader variant stripping.

Note: If you add a shader to the list of Always Included Shaders in the Graphics settings window, Unity includes all keywords from all sets in the build, even if they were declared with “shader feature”.

To set this value, see the following documentation:

Local or global scope

When you declare a set of keywords, you choose whether the keywords in the set have local or global scope. This determines whether you can override the state of this keyword at runtime using a global shader keyword.

By default, you declare keywords with global scope. This means that you can override the state of this keyword at runtime using a global shader keyword. If you declare keywords with local scope, this means that you cannot override the state of this keyword at runtime using a global shader keyword. For more information and a code example, see Using shader keywords with C# scripts.

Note: If a keyword with the same name exists in a shader source file and its dependencies, the scope of the keyword in the source file overrides the scope in the dependencies. Dependencies comprise all Shaders that are included via the Fallback command, and Passes that are included via the UsePass command.

To set this value, see the following documentation:

Stage-specific keywords

By default, Unity generates keyword variants for each stage of your shader. For example, if your shader contains a vertex stage and a fragment stage, Unity generates variants for every keyword combination for both the vertex and the fragment shader programs. If a set of keywords is only used in one of those stages, this results in identical variants for the other stage. Unity automatically identifies and deduplicates identical variants so that they do not increase build size, but they still result in wasted compilation time, increased shader loading times, and increased runtime memory usage.

To avoid this problem, when you declare a set of keywords in a hand-coded shader, you can instruct Unity to compile them only for a given shader stage. You are then responsible for ensuring that the keywords are only used in the specified shader stages.

Note: The following graphics APIs do not fully support stage-specific keywords. In OpenGL and Vulkan, at compile time, Unity automatically converts all stage-specific keyword directives to regular keyword directives. In Metal, any keyword targeting vertex stages also affects tessellation stages, and vice versa.

To set this value:

Making behavior conditional with shader keywords

You can use shader keywords to make parts of your shader conditional, so that certain behaviors only execute when a given keyword is in a given state.

为此需要执行以下操作:

启用和禁用着色器关键字

You can enable or disable shader keywords. When you enable or disable a shader keyword, Unity renders the appropriate shader variant, or the GPU executes the appropriate branch.

There are two ways to enable and disable shader keywords:

Unity’s predefined shader keywords

Unity uses predefined sets of shader keywords to generate shader variants that enable common functionality.

Unity adds the following sets of shader variant keywords at compile time:

  • By default, Unity adds this set of keywords to all graphics shader programs: STEREO_INSTANCING_ON, STEREO_MULTIVIEW_ON, STEREO_CUBEMAP_RENDER_ON, UNITY_SINGLE_PASS_STEREO. You can strip these keywords using an Editor script. For more information, see Shader variant stripping.
  • By default, Unity adds this set of keywords to the Standard Shader: LIGHTMAP_ON, DIRLIGHTMAP_COMBINED, DYNAMICLIGHTMAP_ON, LIGHTMAP_SHADOW_MIXING, SHADOWS_SHADOWMASK. You can strip these keywords using the Graphics settings window.
  • In the Built-in Render Pipeline, if your project uses tier settings that differ from each other, Unity adds this set of keywords to all graphics shaders: UNITY_HARDWARE_TIER1, UNITY_HARDWARE_TIER2, UNITY_HARDWARE_TIER3. For more information, see Graphics tiers: Graphics tiers and shader variants.

Shader keyword limits

Unity can use up to 4,294,967,294 global shader keywords. Individual shaders and compute shaders can use up to 65,534 local shader keywords.

Every keyword declared in the shader source file and its dependencies count towards this limit. Dependencies include Passes that the shader includes with UsePass, and fallbacks.

If Unity encounters a shader keyword with the same name multiple times, it only counts towards the limit once.

If a shader uses more than 128 keywords in total, it incurs a small runtime performance penalty; therefore, it is best to keep the number of keywords low. Unity always reserves 4 keywords per shader.

Shader variants
Using shader keywords with C# scripts
Copyright © 2020 Unity Technologies
优美缔软件(上海)有限公司 版权所有
"Unity"、Unity 徽标及其他 Unity 商标是 Unity Technologies 或其附属机构在美国及其他地区的商标或注册商标。其他名称或品牌是其各自所有者的商标。
公安部备案号:
31010902002961