godot-docs/contributing/development/compiling/introduction_to_the_buildsystem.rst

.. _doc_introduction_to_the_buildsystem:

Introduction to the buildsystem
===============================

.. highlight:: shell

SCons
-----

Godot uses `SCons <https://www.scons.org/>`__ to build. We love it, we are not
changing it for anything else. We constantly get requests to move the build
system to CMake, or Visual Studio, but this is not going to happen. There are
many reasons why we have chosen SCons over other alternatives, for example:

-  Godot can be compiled for a dozen different platforms: all PC
   platforms, all mobile platforms, many consoles, and WebAssembly.
-  Developers often need to compile for several of the platforms **at
   the same time**, or even different targets of the same platform. They
   can't afford reconfiguring and rebuilding the project each time.
   SCons can do this with no sweat, without breaking the builds.
-  SCons will *never* break a build no matter how many changes,
   configurations, additions, removals etc.
-  Godot's build process is not simple. Several files are generated by
   code (binders), others are parsed (shaders), and others need to offer
   customization (plugins). This requires complex logic which is easier
   to write in an actual programming language (like Python) rather than
   using a mostly macro-based language only meant for building.
-  Godot build process makes heavy use of cross-compiling tools. Each
   platform has a specific detection process, and all these must be
   handled as specific cases with special code written for each.

Please try to keep an open mind and get at least a little familiar with it if
you are planning to build Godot yourself.

Setup
-----

Please refer to the documentation for :ref:`doc_compiling_for_android`,
:ref:`doc_compiling_for_ios`,  :ref:`doc_compiling_for_linuxbsd`,
:ref:`doc_compiling_for_macos`, :ref:`doc_compiling_for_uwp`,
:ref:`doc_compiling_for_web`, and :ref:`doc_compiling_for_windows`.

Note that for **Windows/Visual Studio**, you need to use ``x86_x64 Cross Tools
Command Prompt for VS 2017`` or similar, depending on your install, instead of
the standard Windows command prompt to enter the commands below.

Platform selection
------------------

Godot's build system will begin by detecting the platforms it can build
for. If not detected, the platform will simply not appear on the list of
available platforms. The build requirements for each platform are
described in the rest of this tutorial section.

SCons is invoked by just calling ``scons``. If no platform is specified,
SCons will detect the target platform automatically based on the host platform.
It will then start building for the target platform right away.

To list the available target platforms, use ``scons platform=list``::

    scons platform=list
    scons: Reading SConscript files ...
    The following platforms are available:

        android
        javascript
        linuxbsd
        server
        windows

    Please run SCons again and select a valid platform: platform=<string>

To build for a platform (for example, ``linuxbsd``), run with the ``platform=``
(or ``p=`` to make it short) argument:

::

    scons platform=linuxbsd

This will start the build process, which will take a while. By default, Godot's
SCons setup is configured to use all CPU threads but one (to keep the system
responsive during compilation). If you want to adjust how many CPU threads SCons
will use, use the ``-j <threads>`` parameter to specify how many threads will be
used for the build.

Example for using 4 threads:

::

    scons platform=linuxbsd -j4

.. _doc_introduction_to_the_buildsystem_resulting_binary:

Resulting binary
----------------

The resulting binaries will be placed in the ``bin/`` subdirectory,
generally with this naming convention::

    godot.<platform>.<target>[.dev][.double].<arch>[.<extra_suffix>][.<ext>]

For the previous build attempt, the result would look like this::

    ls bin
    bin/godot.linuxbsd.editor.x86_64

This means that the binary is for Linux *or* \*BSD (*not* both), is not optimized, has the
whole editor compiled in, and is meant for 64 bits.

A Windows binary with the same configuration will look like this:

.. code-block:: console

    C:\godot> dir bin/
    godot.windows.editor.64.exe

Copy that binary to any location you like, as it contains the Project Manager,
editor and all means to execute the game. However, it lacks the data to export
it to the different platforms. For that the export templates are needed (which
can be either downloaded from `godotengine.org <https://godotengine.org/>`__, or
you can build them yourself).

Aside from that, there are a few standard options that can be set in all
build targets, and which will be explained below.

.. _doc_introduction_to_the_buildsystem_target:

Target
------

Target controls if the editor is contained and debug flags are used.
All builds are optimized. Each mode means:

-  **editor**: Build with editor, optimized, with debugging code (defines: ``TOOLS_ENABLED``, ``DEBUG_ENABLED``, ``-O2``/``/O2``)
-  **template_debug**: Build with C++ debugging symbols (defines: ``DEBUG_ENABLED``, ``-O2``/``/O2``)
-  **template_release**: Build without symbols (defines: ``-O3``/``/O2``)

The editor is enabled by default in all PC targets (Linux, Windows, macOS),
disabled for everything else. Disabling the editor produces a binary that can
run projects but does not include the editor or the Project Manager.

::

    scons platform=<platform> target=editor/template_debug/template_release

Development and production aliases
----------------------------------

When creating builds for development (running debugging/:ref:`profiling <doc_using_cpp_profilers>`
tools), you often have different goals compared to production builds
(making binaries as fast and small as possible).

Godot provides two aliases for this purpose:

- ``dev_mode=yes`` is an alias for ``verbose=yes warnings=extra werror=yes
  tests=yes``. This enables warnings-as-errors behavior (similar to Godot's
  continuous integration setup) and also builds :ref:`unit tests
  <doc_unit_testing>` so you can run them locally.
- ``production=yes`` is an alias for ``use_static_cpp=yes debug_symbols=no
  lto=auto``. Statically linking libstdc++ allows for better binary portability
  when compiling for Linux. This alias also enables link-time optimization when
  compiling for Linux, Web and Windows with MinGW, but keeps LTO disabled when
  compiling for macOS, iOS or Windows with MSVC. This is because LTO on those
  platforms is very slow to link or has issues with the generated code.

You can manually override options from those aliases by specifying them on the
same command line with different values. For example, you can use ``scons
production=yes debug_symbols=yes`` to create production-optimized binaries with
debugging symbols included.

Dev build
---------

.. note::

    ``dev_build`` should **not** be confused with ``dev_mode``, which is an
    alias for several development-related options (see above).

When doing engine development the ``dev_build`` option can be used together
with ``target`` to enable dev-specific code. ``dev_build`` defines ``DEV_ENABLED``,
disables optimization (``-O0``/``/0d``), enables generating debug symbols, and
does not define ``NDEBUG`` (so ``assert()`` works in thirdparty libraries).

::

    scons platform=<platform> dev_build=yes

This flag appends the ``.dev`` suffix (for development) to the generated
binary name.

Debugging symbols
-----------------

By default, ``debug_symbols=no`` is used, which means **no** debugging symbols
are included in compiled binaries. Use ``debug_symbols=yes`` to include debug
symbols within compiled binaries, which allows debuggers and profilers to work
correctly. Debugging symbols are also required for Godot's crash stacktraces to
display with references to source code files and lines.

The downside is that debugging symbols are large files (significantly larger
than the binaries themselves). As a result, official binaries currently do not
include debugging symbols. This means you need to compile Godot yourself to have
access to debugging symbols.

When using ``debug_symbols=yes``, you can also use
``separate_debug_symbols=yes`` to put debug information in a separate file with
a ``.debug`` suffix. This allows distributing both files independently. Note
that on Windows, when compiling with MSVC, debugging information is *always*
written to a separate ``.pdb`` file regardless of ``separate_debug_symbols``.

.. tip::

    Use the ``strip <path/to/binary>`` command to remove debugging symbols from
    a binary you've already compiled.

Optimization level
------------------

Several compiler optimization levels can be chosen from:

- ``optimize=speed_trace`` *(default when targeting non-Web platforms)*: Favors
  execution speed at the cost of larger binary size. Optimizations may sometimes
  negatively impact debugger usage (stack traces may be less accurate. If this
  occurs to you, use ``optimize=debug`` instead.
- ``optimize=speed``: Favors even more execution speed, at the cost of even
  larger binary size compared to ``optimize=speed_trace``. Even less friendly to
  debugging compared to ``optimize=debug``, as this uses the most aggressive
  optimizations available.
- ``optimize=size`` *(default when targeting the Web platform)*: Favors small
  binaries at the cost of slower execution speed.
- ``optimize=debug``: Only enables optimizations that do not impact debugging in
  any way. This results in faster binaries than ``optimize=none``, but slower
  binaries than ``optimize=speed_trace``.
- ``optimize=none``: Do not perform any optimization. This provides the fastest
  build times, but the slowest execution times.
- ``optimize=custom`` *(advanced users only)*: Do not pass optimization
  arguments to the C/C++ compilers. You will have to pass arguments manually
  using the ``CFLAGS``, ``CCFLAGS`` and ``CXXFLAGS`` SCons options.

Architecture
------------

The ``arch`` option is meant to control the CPU or OS version intended to run the
binaries. It is focused mostly on desktop platforms and ignored everywhere
else.

Supported values for the ``arch`` option are **auto**, **x86_32**, **x86_64**,
**arm32**, **arm64**, **rv64**, **ppc32**, **ppc64** and **wasm32**.

::

    scons platform=<platform> arch={auto|x86_32|x86_64|arm32|arm64|rv64|ppc32|ppc64|wasm32}

This flag appends the value of ``arch`` to resulting binaries when
relevant.  The default value ``arch=auto`` detects the architecture
that matches the host platform.

.. _doc_buildsystem_custom_modules:

Custom modules
--------------

It's possible to compile modules residing outside of Godot's directory
tree, along with the built-in modules.

A ``custom_modules`` build option can be passed to the command line before
compiling. The option represents a comma-separated list of directory paths
containing a collection of independent C++ modules that can be seen as C++
packages, just like the built-in ``modules/`` directory.

For instance, it's possible to provide both relative, absolute, and user
directory paths containing such modules:

::

    scons custom_modules="../modules,/abs/path/to/modules,~/src/godot_modules"

.. note::

    If there's any custom module with the exact directory name as a built-in
    module, the engine will only compile the custom one. This logic can be used
    to override built-in module implementations.

.. seealso::

    :ref:`doc_custom_modules_in_cpp`

Cleaning generated files
------------------------

Sometimes, you may encounter an error due to generated files being present. You
can remove them by using ``scons --clean <options>``, where ``<options>`` is the
list of build options you've used to build Godot previously.

Alternatively, you can use ``git clean -fixd`` which will clean build artifacts
for all platforms and configurations. Beware, as this will remove all untracked
and ignored files in the repository. Don't run this command if you have
uncommitted work!

Other build options
-------------------

There are several other build options that you can use to configure the
way Godot should be built (compiler, debug options, etc.) as well as the
features to include/disable.

Check the output of ``scons --help`` for details about each option for
the version you are willing to compile.

.. _doc_overriding_build_options:

Overriding the build options
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Using a file
^^^^^^^^^^^^

The default ``custom.py`` file can be created at the root of the Godot Engine
source to initialize any SCons build options passed via the command line:

.. code-block:: python

    # custom.py

    optimize = "size"
    module_mono_enabled = "yes"
    use_llvm = "yes"
    extra_suffix = "game_title"

You can also disable some of the builtin modules before compiling, saving some
time it takes to build the engine. See :ref:`doc_optimizing_for_size` page for more details.

.. seealso::

    You can use the online
    `Godot build options generator <https://godot-build-options-generator.github.io/>`__
    to generate a ``custom.py`` file containing SCons options.
    You can then save this file and place it at the root of your Godot source directory.

Another custom file can be specified explicitly with the ``profile`` command
line option, both overriding the default build configuration:

.. code-block:: shell

    scons profile=path/to/custom.py

.. note:: Build options set from the file can be overridden by the command line
          options.

It's also possible to override the options conditionally:

.. code-block:: python

    # custom.py

    import version

    # Override options specific for Godot 3.x and 4.x versions.
    if version.major == 3:
        pass
    elif version.major == 4:
        pass

Using the SCONSFLAGS
^^^^^^^^^^^^^^^^^^^^

``SCONSFLAGS`` is an environment variable which is used by the SCons to set the
options automatically without having to supply them via the command line.

For instance, you may want to force a number of CPU threads with the
aforementioned ``-j`` option for all future builds:

.. tabs::
 .. code-tab:: bash Linux/macOS

     export SCONSFLAGS="-j4"

 .. code-tab:: bat Windows (cmd)

     set SCONSFLAGS=-j4

 .. code-tab:: powershell Windows (PowerShell)

     $env:SCONSFLAGS="-j4"

Export templates
----------------

Official export templates are downloaded from the Godot Engine site:
`godotengine.org <https://godotengine.org/>`__. However, you might want
to build them yourself (in case you want newer ones, you are using custom
modules, or simply don't trust your own shadow).

If you download the official export templates package and unzip it, you
will notice that most files are optimized binaries or packages for each
platform:

.. code-block:: none

    android_debug.apk
    android_release.apk
    web_debug.zip
    web_release.zip
    linux_server_32
    linux_server_64
    linux_x11_32_debug
    linux_x11_32_release
    linux_x11_64_debug
    linux_x11_64_release
    macos.zip
    version.txt
    windows_32_debug.exe
    windows_32_release.exe
    windows_64_debug.exe
    windows_64_release.exe

To create those yourself, follow the instructions detailed for each
platform in this same tutorial section. Each platform explains how to
create its own template.

The ``version.txt`` file should contain the corresponding Godot version
identifier. This file is used to install export templates in a version-specific
directory to avoid conflicts. For instance, if you are building export templates
for Godot 3.1.1, ``version.txt`` should contain ``3.1.1.stable`` on the first
line (and nothing else). This version identifier is based on the ``major``,
``minor``, ``patch`` (if present) and ``status`` lines of the
`version.py file in the Godot Git repository <https://github.com/godotengine/godot/blob/master/version.py>`__.

If you are developing for multiple platforms, macOS is definitely the most
convenient host platform for cross-compilation, since you can cross-compile for
almost every target (except for UWP). Linux and Windows come in second place,
but Linux has the advantage of being the easier platform to set this up.