⚠️ INCOMPLETE! Metal Shader support for CMake

This project aims to allow compiling, linking, and embedding Apple Metal shader libraries in projects using CMake, without the need to write custom build steps or be restricted to only using the Xcode project generator.

Project Setup

1. Copy the files from the cmake folder of this repo into a top-level cmake folder in your project.

2. Add that cmake folder to the CMAKE_MODULE_PATH of your project:

   # In the top-level CMakeLists.txt file for your project:
   set(CMAKE_MODULE_PATH "${CMAKE_MODULE_PATH};${CMAKE_SOURCE_DIR}/cmake")
   

3. Enable the Metal language for your project:

   enable_language(Metal)
   

   If you want to conditionally detect whether Metal can be supported, you can use check_language:

   include(CheckLanguage)
   
   check_language(Metal)
   if(CMAKE_Metal_COMPILER)
       enable_language(Metal)
   
       message(STATUS "Metal is supported")
   else()
       message(WARNING "Metal is not supported")
   endif()
   

Shader Library Setup

There are a few different ways to compose shader library targets, including some that allow sharing base definitions across multiple targets. It is recommended that your final shader libraries (the ones that should output .metallib files to be included as resources) use the MODULE library type.

Important

Shaders must be in their own CMake target!
You cannot mix them with C++ or Objective-C code sources in a library or executable target.

Metal Libraries (.metallib)

Your final shader library will need to be a .metallib file that can be included in your application as a resource. You should define these as MODULE libraries rather than SHARED libraries because they do not expose symbols that can be linked with other targets.

add_library(shaders MODULE
    shader1.metal
    shader2.metal
)

# To make it work properly in Xcode with the Xcode project generator:
set_target_properties(shaders PROPERTIES
    XCODE_PRODUCT_TYPE com.apple.product-type.metal-library
    SUFFIX ".metallib"
    PREFIX ""
)

Static Archives (.metal-ar)

Caution

This is not supported with the Xcode project generator.

You can compile shaders to a static archive as a .metal-ar file that can be linked together with other archives and shaders into a Metal library.

add_library(shader_base STATIC
    shader1.metal
    shader2.metal
)

You can then reference that archive as a link library for another target:

add_library(full_shader MODULE
    another_shader.metal
)
target_link_libraries(full_shader
    PUBLIC
    shader_base
)

Object Files (.air)

Caution

This is not supported with the Xcode project generator.

You can also compile shaders to a loose collection of .air bitcode files by defining an object library, and then include those shader objects as part of another Metal shader library.

add_library(shader_base OBJECT
    shader1.metal
    shader2.metal
)

You can then reference those objects to be linked as part of another target:

add_library(full_shader MODULE
    another_shader.metal
    $<TARGET_OBJECTS:shader_base>
)

Embedding Shaders

As a final step to make your shader library available to your application, you will need to ensure that it gets embedded as a resource.

1. First, you need to ensure that the shader library itself is built as a dependency of the application target.

   add_executable(MyApp MACOSX_BUNDLE)
   
   add_dependencies(MyApp
       shaders
   )
   

2. Then you'll need to include the shader libraries as resources:

   # NOTE: This does not work!!!
   set(MyApp_SHADER_RESOURCES
       $<TARGET_FILE:shaders>
   )
   
   set_target_properties(MyApp PROPERTIES
       RESOURCE "${MyApp_SHADER_RESOURCES}"
   )
   

   If you are using CMake 3.28 or newer, you can refer to the shader targets directly:

   set_target_properties(MyApp PROPERTIES
       XCODE_EMBED_RESOURCES shaders
   )
   

Warning

Need to figure out how to handle the resources for non-Xcode builds

Remaining Work

• Handling the target and SDK parameters
• Handling extra flags
• Testing that this works with the Windows version of the Metal tools

Licence

CMake files are distributed under the OSI-approved BSD 3-clause License. See LICENCE.txt for details.

The example project is based on sample code from Apple, under its own licence. See LICENSE.txt in the example folder for details.