Sometimes, you want the same shaderA program that runs on the GPU. More info
See in Glossary to do different things under different circumstances. For example, you might want to configure different settings for different materials, define functionality for different hardware, or dynamically change the behavior of shaders at runtime. You might also want to avoid executing computationally expensive code when it’s not needed, such as texture reads, vertex inputs, interpolators, or loops.
You can use conditionals to define behavior that the GPU only executes under certain conditions.
To use conditionals in your shader, you can use the following approaches:
There is no “one size fits all” approach to conditionals in shaders, and you should consider the advantages and disadvantages of each approach for a given shader, in a given project.
Which conditional to use depends on when you need the shader to switch to a different code branch:
If you don’t need a shader to switch to a different code branch at runtime, you can use conditionals that Unity only evaluates while you’re editing.
For example you can set up a property in a Material’s InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary window to make a shader do the following:
If you use this approach, shader code is simpler to write and maintain, and less likely to affect build time, file size and performance.
To do this, use one of the following:
shader_feature
to declare keywords and evaluate them in if
statements.If you use the shader_feature
keyword definition, Unity keeps shader variants used by Materials in your build, and removes (‘strips’) other shader variants. This keeps build times low and file sizes small.
Avoid using a C# script to enable or disable shader_feature
keywords at runtime, because if a Material uses a shader variant that’s missing, Unity chooses a different available variant instead. If you do need to enable or disable keywords at runtime, use one of the following approaches to make sure your build includes all the variants you need:
shader_feature
keywords you want to use.If you need to use C# scripting to make the shader switch to a different code branch at runtime, you can use conditionals that Unity evaluates both while you’re editing and at runtime.
For example you can use a C# script to make a shader do the following:
To do this, use one of the following:
multi_compile
to declare keywords and evaluate them in if
statements.If you use the multi_compile
keyword definition, Unity builds a shader variant for every possible combination of shader code branches, including combinations that aren’t used by Materials in your build. This means you can enable and disable keywords at runtime, but it might also greatly increase build time, file size, load times and memory usage. See shader variants.
Dynamic branching doesn’t create shader variants, but may mean your shaders run more slowly on the GPU, especially if any of the following are true:
You can check how many shader variants you have to see whether you can use dynamic branching without affecting GPU performance too much. See shader branching for more on the advantages and disadvantages of dynamic branching.