Secondary build system: Working with CMake
==========================================

.. seealso:: This page documents how to compile godot-cpp. If you're looking to
             compile Godot instead, see
             :ref:`doc_introduction_to_the_buildsystem`.

Beside the SCons_ based build system, godot-cpp also provides a CMakeLists.txt_
file to support users that prefer using CMake_ over SCons for their build
system.

While actively supported, the CMake system is considered secondary to the
SCons build system. This means it may lack some features that are available to
projects using SCons.

.. _CMakeLists.txt: https://github.com/godotengine/godot-cpp/blob/master/CMakeLists.txt
.. _CMake: http://scons.org
.. _Scons: http://cmake.org

Introduction
------------

Compiling godot-cpp independently of an extension project is mainly for
godot-cpp developers, package maintainers, and CI/CD.

Examples of how to use CMake to consume the godot-cpp library as part of an
extension project:

* `godot-cpp-template <https://github.com/godotengine/godot-cpp-template/>`__
* `godot_roguelite <https://github.com/vorlac/godot-roguelite/>`__
* `godot-orchestrator <https://github.com/CraterCrash/godot-orchestrator/>`__

Examples for configuring godot-cpp are listed at the bottom of the page, many
of which may help with configuring your project.


CMake's ``Debug`` vs Godot's ``template_debug``
-----------------------------------------------

Something that has come up during many discussions is the conflation of a
compilation of C++ source code with debug symbols enabled, and compiling a
Godot extension with debug features enabled. The two concepts are not mutually
exclusive.

- debug_features
    Enables a pre-processor definition to selectively compile code to help
    users of a Godot extension with their own project.

    debug features are enabled in ``editor`` and ``template_debug`` builds,
    which can be specified during the configure phase like so:

    .. code-block::

        cmake -S godot-cpp -B cmake-build -DGODOTCPP_TARGET=<target choice>

- Debug
    Sets compiler flags so that debug symbols are generated to help godot
    extension developers debug their extension.

    ``Debug`` is the default build type for CMake projects, to select another
    it depends on the generator used

    For single configuration generators, add to the configure command:

    ``-DCMAKE_BUILD_TYPE=<type>``

    For multi-config generators add to the build command:

    ``--config <type>``

    where ``<type>`` is one of ``Debug``, ``Release``, ``RelWithDebInfo``,
    ``MinSizeRel``


SCons Deviations
----------------

Not all code from the SCons system can be perfectly represented in CMake, here
are the notable differences.

- debug_symbols
    Is no longer an explicit option, and is enabled when using CMake build
    configurations; ``Debug``, ``RelWithDebInfo``.

- dev_build
    Does not define ``NDEBUG`` when disabled, ``NDEBUG`` is set when using
    CMake build configurations; ``Release``, ``MinSizeRel``.

- arch
    CMake sets the architecture via the toolchain files, macOS universal is
    controlled via the ``CMAKE_OSX_ARCHITECTURES``
    property which is copied to targets when they are defined.

- debug_crt
    CMake controls linking to Windows runtime libraries by copying the value of
    ``CMAKE_MSVC_RUNTIME_LIBRARIES`` to targets as they are defined.
    godot-cpp will set this variable if it isn't already set. So, include it
    before other dependencies to have the value propagate across the projects.


Basic walkthrough
-----------------

.. topic:: Clone the git repository

    .. code-block::

        git clone https://github.com/godotengine/godot-cpp.git
        Cloning into 'godot-cpp'...
        ...


.. topic:: Configure the build

    .. code-block::

        cmake -S godot-cpp -B cmake-build -G Ninja

    ``-S`` Specifies the source directory as ``godot-cpp``

    ``-B`` Specifies the build directory as ``cmake-build``

    ``-G`` Specifies the Generator as ``Ninja``

    The source directory in this example is the source root for the freshly
    cloned godot-cpp. CMake will also interpret the first path in the command
    as the source path, or if an existing build path is specified it will
    deduce the source path from the build cache.

    The following three commands are equivalent.

    .. code-block::

        # Current working directory is the godot-cpp source root.
        cmake . -B build-dir

        # Current working directory is an empty godot-cpp/build-dir.
        cmake ../

        # Current working directory is an existing build path.
        cmake .

    The build directory is specified so that generated files do not clutter
    the source tree with build artifacts.

    CMake doesn't build the code, it generates the files that a build tool
    uses, in this case the ``Ninja`` generator creates Ninja_ build files.

    To see the list of generators run ``cmake --help``.

    .. _Ninja: https://ninja-build.org/

.. topic:: Build Options

    To list the available options use the ``-L[AH]`` command flags.

    ``A`` is for advanced, and ``H`` is for help strings:

    .. code-block::

        cmake -S godot-cpp -LH

    Options are specified on the command line when configuring, for example:

    .. code-block::

        cmake -S godot-cpp -DGODOTCPP_USE_HOT_RELOAD:BOOL=ON \
            -DGODOTCPP_PRECISION:STRING=double \
            -DCMAKE_BUILD_TYPE:STRING=Debug

    Review setting-build-variables_ and build-configurations_ for more
    information.

    .. _setting-build-variables: https://cmake.org/cmake/help/latest/guide/user-interaction/index.html#setting-build-variables
    .. _build-configurations: https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#build-configurations

    A non-exhaustive list of options:

    .. code-block::

        // Path to a custom GDExtension API JSON file.
        // (takes precedence over `GODOTCPP_GDEXTENSION_DIR`)
        // ( /path/to/custom_api_file )
        GODOTCPP_CUSTOM_API_FILE:FILEPATH=

        // Force disabling exception handling code. (ON|OFF)
        GODOTCPP_DISABLE_EXCEPTIONS:BOOL=ON

        // Path to a custom directory containing the GDExtension interface
        // header and API JSON file. ( /path/to/gdextension_dir )
        GODOTCPP_GDEXTENSION_DIR:PATH=gdextension

        // Set the floating-point precision level. (single|double)
        GODOTCPP_PRECISION:STRING=single

        // Enable the extra accounting required to support hot reload. (ON|OFF)
        GODOTCPP_USE_HOT_RELOAD:BOOL=


.. topic:: Compiling

    Tell CMake to invoke the build system it generated in the specified
    directory. The default target is ``template_debug`` and the default build
    configuration is Debug.

    .. code-block::

        cmake --build cmake-build

Examples
--------

These examples, while intended for godot-cpp developers, package maintainers,
and CI/CD may help you configure your own extension project.

Practical examples for how to consume the godot-cpp library as part of an
extension project are listed in the `Introduction`_

Enabling Integration Testing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The testing target ``godot-cpp-test`` is guarded by ``GODOTCPP_ENABLE_TESTING``
which is off by default.

To configure and build the godot-cpp project to enable the integration
testing targets the command will look something like:

.. code-block::

    cmake -S godot-cpp -B cmake-build -DGODOTCPP_ENABLE_TESTING=YES
    cmake --build cmake-build --target godot-cpp-test

Windows and MSVC - Release
~~~~~~~~~~~~~~~~~~~~~~~~~~

So long as CMake is installed from the `CMake Downloads`_ page and in the PATH,
and Microsoft Visual Studio is installed with C++ support, CMake will detect
the MSVC compiler.

Note that Visual Studio is a Multi-Config Generator so the build configuration
needs to be specified at build time, for example, ``--config Release``.

.. _CMake downloads: https://cmake.org/download/

.. code-block::

    cmake -S godot-cpp -B cmake-build -DGODOTCPP_ENABLE_TESTING=YES
    cmake --build cmake-build -t godot-cpp-test --config Release


MSys2/clang64, "Ninja" - Debug
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Assumes the ``ming-w64-clang-x86_64``-toolchain is installed.

Note that Ninja is a Single-Config Generator so the build type
needs to be specified at configuration time.

Using the ``msys2/clang64`` shell:

.. code-block::

    cmake -S godot-cpp -B cmake-build -G"Ninja" \
        -DGODOTCPP_ENABLE_TESTING=YES -DCMAKE_BUILD_TYPE=Release
    cmake --build cmake-build -t godot-cpp-test

MSys2/clang64, "Ninja Multi-Config" - dev_build, Debug Symbols
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Assumes the ``ming-w64-clang-x86_64``-toolchain is installed.

This time we are choosing the 'Ninja Multi-Config' generator, so the build
type is specified at build time.

Using the ``msys2/clang64`` shell:

.. code-block::

    cmake -S godot-cpp -B cmake-build -G"Ninja Multi-Config" \
        -DGODOTCPP_ENABLE_TESTING=YES -DGODOTCPP_DEV_BUILD:BOOL=ON
    cmake --build cmake-build -t godot-cpp-test --config Debug

Emscripten for web platform
~~~~~~~~~~~~~~~~~~~~~~~~~~~

This has only been tested on Windows so far. You can use this example workflow:

- Clone and install the latest Emscripten tools to ``c:\emsdk``.
- Use ``C:\emsdk\emsdk.ps1 activate latest`` to enable the environment from
  powershell in the current shell.
- The ``emcmake.bat`` utility adds the emscripten toolchain to the CMake
  command. It can also be added manually;
  the location is listed inside the ``emcmake.bat`` file

.. code-block::

    C:\emsdk\emsdk.ps1 activate latest
    emcmake.bat cmake -S godot-cpp -B cmake-build-web -DCMAKE_BUILD_TYPE=Release
    cmake --build cmake-build-web

Android Cross Compile from Windows
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are two separate paths you can choose when configuring for android.

Use the ``CMAKE_ANDROID_*`` variables specified on the command line or in your
own toolchain file as listed in the cmake-toolchains_ documentation.

.. _cmake-toolchains: https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-android-with-the-ndk

Or use the toolchain and scripts provided by the Android SDK and make changes
using the ``ANDROID_*`` variables listed there. Where ``<version>`` is whatever
NDK version you have installed (tested with `28.1.13356709`) and ``<platform>``
is for the Android sdk platform, (tested with ``android-29``).

.. warning::

    The Android SDK website explicitly states that they do not support using
    the CMake built-in method, and recommends you stick with their toolchain
    files.

.. topic:: Using your own toolchain file as described in the CMake documentation

    .. code-block::

        cmake -S godot-cpp -B cmake-build --toolchain my_toolchain.cmake
        cmake --build cmake-build -t template_release

    Doing the equivalent on just using the command line:

    .. code-block::

        cmake -S godot-cpp -B cmake-build \
            -DCMAKE_SYSTEM_NAME=Android \
            -DCMAKE_SYSTEM_VERSION=<platform> \
            -DCMAKE_ANDROID_ARCH_ABI=<arch> \
            -DCMAKE_ANDROID_NDK=/path/to/android-ndk
        cmake --build cmake-build

.. topic:: Using the toolchain file from the Android SDK

    This defaults to the minimum supported version and armv7-a:

    .. code-block::

        cmake -S godot-cpp -B cmake-build \
            --toolchain $ANDROID_HOME/ndk/<version>/build/cmake/android.toolchain.cmake
        cmake --build cmake-build

    Specifying the Android platform and ABI:

    .. code-block::

        cmake -S godot-cpp -B cmake-build \
            --toolchain $ANDROID_HOME/ndk/<version>/build/cmake/android.toolchain.cmake \
            -DANDROID_PLATFORM:STRING=android-29 \
            -DANDROID_ABI:STRING=armeabi-v7a
        cmake --build cmake-build