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 can use shader keywords with dynamic branching, or with Shader variants. Before you use shader keywords, it is important to understand how these techniques work, and which one is right for your project.
本页包含以下信息：
You declare shader keywords in sets. A set contains mutually exclusive keywords.
For example, the following set contains three keywords:
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:
When you declare a set of keywords, you choose whether to use them with shader variants or with dynamic branching. If you choose shader variants, you must also choose how Unity defines the keywords internally; this affects the number of variants that Unity compiles.
#define preprocessor directives.
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:
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:
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:
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：
You can enable or disable shader keywords. When you enable or disable a shader keyword, the shader displays the appropriate conditional behavior. Depending on whether the keyword work with shader variants or dynamic branching, this means that either Unity renders the appropriate shader variant, or the GPU executes the appropriate branch.
There are two ways to enable and disable 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:
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. These totals include keywords used for variants, and keywords used for dynamic branching.
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.