magnum-bindings/doc/python/pages/building.rst

..
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..

Downloading and building
########################

.. role:: sh(code)
    :language: sh

:summary: Installation guide for the Python bindings.
:ref-prefix:
    corrade
    magnum

Building of Python bindings is a similar process to
:dox:`building Magnum itself <building>` with an additional step involving
Python setuptools. Minimal set of tools and libraries required for building is:

-   C++ compiler with good C++11 support. Compilers which are tested to have
    everything needed are **GCC** >= 4.8.1, **Clang** >= 3.3 and **MSVC**
    >= 2015. On Windows you can also use **MinGW-w64**.
-   **CMake** >= 3.1
-   **Corrade** and **Magnum** installed
    :dox:`as described in their docs <building>`
-   **Python** >= 3.5 and :gh:`pybind11 <pybind/pybind11>`

`Prepared packages`_
====================

`ArchLinux packages`_
---------------------

In ``package/archlinux`` there is a development package, similar to the ones
in Magnum itself. They allow you to build and install the package directly from
the source tree.

.. code:: sh

    git clone https://github.com/mosra/magnum-bindings && cd magnum-bindings
    cd package/archlinux
    makepkg -fp PKGBUILD

The PKGBUILD also contains a :sh:`check()` function which will run all unit
tests before packaging. That might sometimes fail or take too long, pass
``--nocheck`` to ``makepkg`` to skip that.

Once built, install the package using ``pacman``:

.. code:: sh

    sudo pacman -U magnum-bindings-*.pkg.tar.zst

`Homebrew formulas for macOS`_
------------------------------

macOS `Homebrew <https://brew.sh>`_ formulas building the latest Git revision
are in the ``package/homebrew`` directory. Either use the ``*.rb`` files
directly or use the tap at https://github.com/mosra/homebrew-magnum. This will
install the latest stable version of Magnum Bindings with all its dependencies:

.. code:: sh

    brew install mosra/magnum/magnum-bindings

But often you may want to install the latest Git revision of all Magnum
projects instead:

.. code:: sh

    brew install --HEAD mosra/magnum/corrade
    brew install --HEAD mosra/magnum/magnum
    brew install --HEAD mosra/magnum/magnum-bindings

    # If already installed, use the following to upgrade, in the same order
    brew upgrade --fetch-HEAD mosra/magnum/corrade
    brew upgrade --fetch-HEAD mosra/magnum/magnum
    brew upgrade --fetch-HEAD mosra/magnum/magnum-bindings

When installing from the ``*.rb`` files you need to install the
:dox:`Corrade <building-corrade-packages-brew>` and
:dox:`Magnum <building-packages-brew>` Homebrew packages first. If you want to
pass additional flags to CMake or ``setup.py`` or enable / disable additional
features, edit the ``*.rb`` file.

There are also Homebrew packages for
:dox:`Magnum Plugins <building-plugins-packages-brew>`,
:dox:`Magnum Integration <building-integration-packages-brew>`,
:dox:`Magnum Extras <building-extras-packages-brew>` and
:dox:`Magnum Examples <building-examples-packages-brew>`.

`Manual build`_
===============

The source is available on GitHub at https://github.com/mosra/magnum-bindings.
Clone the repository with your favorite IDE or Git GUI, download currrent
snapshot as a compressed archive or use the command line:

.. code:: sh

    git clone https://github.com/mosra/magnum-bindings.git

Assuming a Unix-based OS, the first step is to build the native libraries. The
bindings will be generated for all Corrade and Magnum libraries that are found,
ignoring the ones which aren't. If Corrade, Magnum and pybind11 are not in a
default location known to CMake, add their path to ``CMAKE_PREFIX_PATH``.

.. code:: sh

    mkdir build && cd build
    cmake .. \
        -DMAGNUM_WITH_PYTHON=ON
    make

Note that pybind11 compilation is quite time- and memory-hungry, so you might
not want to run the build on all cores on memory-constrained systems. In the
build directory, CMake will create the desired Python package layout, meaning
the bindings can be used directly if you ``cd`` into ``build/src/python/magnum``.
For installing into a system-wide location, CMake generates a ``setup.py``
containing location of all built libraries for use with Python setuptools:

.. code:: sh

    cd build/src/python/magnum
    python setup.py install # or python3, sudo might be needed

`Static build`_
---------------

In case Corrade or Magnum is built with :dox:`CORRADE_BUILD_STATIC` /
:dox:`MAGNUM_BUILD_STATIC`, the corresponding bindings are compiled into a
single dynamic module instead of one module per Corrade/Magnum library.

In this case, similarly to linking static plugins to Magnum's own command-line
utilities, you can use the ``MAGNUM_PYTHON_BINDINGS_STATIC_PLUGINS`` CMake
variable to link static plugins to the Python module, assuming Magnum, Magnum
Plugins and Magnum Bindings are all CMake subprojects. It's a
semicolon-separated list of existing CMake targets, for example
``Magnum::AnyImageImporter;MagnumPlugins::StbImageImporter``.

On Unix platforms, Python by default loads the modules in isolated namespaces.
That's a good thing to do from a security point of view, nevertheless with
static builds of Corrade and Magnum it will result in globals duplicated across
the Corrade and Magnum modules (and also any other Python modules that
use Magnum natively inside) unable to see each other in order to deduplicate
themselves, causing strange issues. To solve that, the
``MAGNUM_BUILD_PYTHON_BINDINGS_RTLD_GLOBAL`` CMake option, which is enabled by
default on static builds on Unix platforms, overrides Python's module loading
code to not load them in isolated namespaces using :ref:`sys.setdlopenflags()`.
The override then happens inside :py:`import corrade` and is in effect for the
rest of the interpreter lifetime, to affect also any potential other modules
depending on Magnum loaded later. See also
:dox:`CORRADE_BUILD_STATIC_UNIQUE_GLOBALS` and
:dox:`MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS` in Corrade and Magnum for more
information.

`Running unit tests`_
---------------------

Essential functionality of the bindings is tested using Python's builtin
``unittest`` module. The tests currently assume a CMake build directory with
all binaries already built located in a ``build/`` directory in project root,
running them is then a matter of:

.. code:: sh

    cd src/python/magnum
    python -m unittest

.. block-default:: Disabling GL tests

    If the tests detect that one of
    :ref:`platform.WindowlessApplication <platform.egl.WindowlessApplication>`\ s
    is present, GL tests (suffixed with ``_gl``) will be run as well. In order
    to disable them (for example when running on a headless CI), set the
    :sh:`$MAGNUM_SKIP_GL_TESTS` environment variable to ``ON``:

    .. code:: sh

        MAGNUM_SKIP_GL_TESTS=ON python -m unittest

For code coverage, `coverage.py <https://coverage.readthedocs.io/>`_ is used.
Get it via ``pip`` or as a system package.

.. code:: sh

    pip install coverage # sudo might be needed

Running the unit tests with coverage enabled is then a matter of executing the
following commands, the resulting HTML overview is located in
``htmlcov/index.html``:

.. code:: sh

    cd src/python/magnum
    coverage run -m unittest
    coverage html

`Continuous Integration`_
=========================

In ``package/ci/`` there is a ``circleci.yml`` file that compiles and tests the
bindings on Linux GCC 4.8 + CMake 3.5 and on macOS, online at
https://circleci.com/gh/mosra/magnum-bindings. For Windows there is an
``appveyor.yml`` testing on Windows with MSVC, online at
https://ci.appveyor.com/project/mosra/magnum-bindings. Code coverage for both
the C++ bindings code and Python side is reported to
https://codecov.io/gh/mosra/magnum-bindings.