# The Mesa 3D Graphics Library

# Compilation and Installation using Meson

## 1. Basic Usage

The Meson build system for Mesa is still under active development, and should not be used in production environments.

The meson build is currently only tested on linux, and is known to not work on macOS, Windows, and haiku. This will be fixed.

The meson program is used to configure the source directory and generates either a ninja build file or Visual Studio® build files. The latter must be enabled via the --backend switch, as ninja is the default backend on all operating systems. Meson only supports out-of-tree builds, and must be passed a directory to put built and generated sources into. We'll call that directory "build" for examples.

        meson build/

To see a description of your options you can run `meson configure` along with a build directory to view the selected options for. This will show your meson global arguments and project arguments, along with their defaults and your local settings. Moes does not currently support listing options before configure a build directory, but this feature is being discussed upstream.

        meson configure build/

With additional arguments `meson configure` is used to change options on already configured build directory. All options passed to this command are in the form -D "command"="value".

        meson configure build/ -Dprefix=/tmp/install -Dglx=true

Once you've run the initial `meson` command successfully you can use your configured backend to build the project. With ninja, the -C option can be be used to point at a directory to build.

        ninja -C build/

Without arguments, it will produce libGL.so and/or several other libraries depending on the options you have chosen. Later, if you want to rebuild for a different configuration, you should run `ninja clean` before changing the configuration, or create a new out of tree build directory for each configuration you want to build. http://mesonbuild.com/Using-multiple-build-directories.html

`Environment Variables`

  Meson supports the standard CC and CXX envrionment variables for changing the default compiler, and CFLAGS, CXXFLAGS, and LDFLAGS for setting options to the compiler and linker. The default compilers depends on your operating system. Meson supports most of the popular compilers, a complete list is available here. These arguments are consumed and stored by meson when it is initialized or re-initialized. Therefore passing them to meson configure will not do anything, and passing them to ninja will only do something if ninja decides to re-initialze meson, for example, if a meson.build file has been changed. Changing these variables will not cause all targets to be rebuilt, so running ninja clean is recomended when changing CFLAGS or CXXFLAGS. meson will never change compiler in a configured build directory.

          CC=clang CXX=clang++ meson build-clang
          ninja -C build-clang
          ninja -C build-clang clean
          touch meson.build
          CFLAGS=-Wno-typedef-redefinition ninja -C build-clang

  Meson also honors DESTDIR for installs

`LLVM`

  Meson includes upstream logic to wrap llvm-config using it's standard dependncy interface. It will search $PATH (or %PATH% on windows) for llvm-config, so using an LLVM from a non-standard path is as easy as `PATH=/path/with/llvm-config:$PATH meson build`.

`PKG_CONFIG_PATH`

  The `pkg-config` utility is a hard requirement for configuring and building Mesa on Linux and *BSD. It is used to search for external libraries on the system. This environment variable is used to control the search path for `pkg-config`. For instance, setting `PKG_CONFIG_PATH=/usr/X11R6/lib/pkgconfig` will search for package metadata in `/usr/X11R6` before the standard directories.

One of the oddities of meson is that some options are different when passed to the `meson` than to `meson configure`. These options are passed as --option=foo to `meson`, but -Doption=foo to `meson configure`. Mesa defined options are always passed as -Doption=foo.

For those coming from autotools be aware of the following:

`--buildtype/-Dbuildtype`

  This option will set the compiler debug/optimisation levels to aid debugging the Mesa libraries.

  Note that in meson this defaults to "debugoptimized", and not setting it to "release" will yield non-optimal performance and binary size. Not using "debug" may interfer with debbugging as some code and validation will be optimized away.

  For those wishing to pass their own -O option, use the "plain" buildtype, which cuases meson to inject no additional compiler arguments, only those in the C/CXXFLAGS and those that mesa itself defines.

`-Db_ndebug`

  This option controls assertions in meson projects. When set to false (the default) assertions are enabled, when set to true they are disabled. This is unrelated to the `buildtype`; setting the latter to `release` will not turn off assertions.