At runtime, you can enable or disable shaderA program that runs on the GPU. More info
See in Glossary keywords. When you enable or disable a shader keyword, Unity uses the appropriate shader variant for renderingThe process of drawing graphics to the screen (or to a render texture). By default, the main camera in Unity renders its view to the screen. More info
See in Glossary.
Changing shader variants at runtime can impact performance. If a change in keywords requires a variant to be used for the first time, it can lead to hitches while the graphics driver prepares the shader program. This can be a particular problem for large or complex shaders, or if a global keyword state change affects multiple shaders. To avoid this, ensure that you consider keyword variants in your shader loading and prewarming strategy. For more information, see Shader loading.
In Unity, there are local shader keywords and global shader keywords:
You set the scope of a shader keyword when you declare it. For more information, see Shader keywords: global and local scope.
To check the state, use [Shader.IsKeywordEnabled].
When you author your shader, you declare keywords in sets. A set contains mutually-exclusive keywords.
At runtime, Unity has no concept of these sets. It allows you to enable or disable any keyword independently, and enabling or disabling a keyword has no effect on the state of any other keyword. This means that it is possible to enable multiple keywords from the same set, or disable all the keywords in a set.
When more than one keyword in a set is enabled, or no keywords in a set are enabled, Unity chooses a variant that it considers a “good enough” match. There is no guarantee about what exactly happens, and it can lead to unintended results. It is best to avoid this situation by managing keyword state carefully.