Building Libwebm

To build libwebm you must first create project files. To do this run cmake
and pass it the path to your libwebm repo.

Makefile.unix can be used as a fallback on systems that cmake does not
support.


CMake Basics

To generate project/make files for the default toolchain on your system simply
run cmake with the path to the libwebm repo:

$ cmake path/to/libwebm

On Windows the above command will produce Visual Studio project files for the
newest Visual Studio detected on the system. On Mac OS X and Linux systems, the
above command will produce a makefile.

To control what types of projects are generated the -G parameter is added to
the cmake command line. This argument must be followed by the name of a
generator. Running cmake with the --help argument will list the available
generators for your system.

On Mac OS X you would run the following command to generate Xcode projects:

$ cmake path/to/libwebm -G Xcode

On a Windows box you would run the following command to generate Visual Studio
2013 projects:

$ cmake path/to/libwebm -G "Visual Studio 12"

To generate 64-bit Windows Visual Studio 2013 projects:

$ cmake path/to/libwebm "Visual Studio 12 Win64"


CMake Makefiles: Debugging and Optimization

Unlike Visual Studio and Xcode projects, the build configuration for make builds
is controlled when you run cmake. The following examples demonstrate various
build configurations.

Omitting the build type produces makefiles that use build flags containing
neither optimization nor debug flags:
$ cmake path/to/libwebm

A makefile using release (optimized) flags is produced like this:
$ cmake path/to/libwebm -DCMAKE_BUILD_TYPE=release

A release build with debug info can be produced as well:
$ cmake path/to/libwebm -DCMAKE_BUILD_TYPE=relwithdebinfo

And your standard debug build will be produced using:
$ cmake path/to/libwebm -DCMAKE_BUILD_TYPE=debug


Tests

To enable libwebm tests add -DENABLE_TESTS=ON CMake generation command line. For
example:

$ cmake path/to/libwebm -G Xcode -DENABLE_TESTS=ON

Libwebm tests depend on googletest. By default googletest is expected to be a
sibling directory of the Libwebm repository. To change that, update your CMake
command to be similar to the following:

$ cmake path/to/libwebm -G Xcode -DENABLE_TESTS=ON \
  -DGTEST_SRC_DIR=/path/to/googletest

The tests rely upon the LIBWEBM_TEST_DATA_PATH environment variable to locate
test input. The following example demonstrates running the muxer tests from the
build directory:

$ LIBWEBM_TEST_DATA_PATH=path/to/libwebm/testing/testdata ./mkvmuxer_tests

Note: Libwebm Googletest integration was built with googletest from
      https://github.com/google/googletest.git at git revision
      ddb8012eb48bc203aa93dcc2b22c1db516302b29.


CMake Include-what-you-use integration

Include-what-you-use is an analysis tool that helps ensure libwebm includes the
C/C++ header files actually in use. To enable the integration support
ENABLE_IWYU must be turned on at cmake run time:

$ cmake path/to/libwebm -G "Unix Makefiles" -DENABLE_IWYU=ON

This adds the iwyu target to the build. To run include-what-you-use:

$ make iwyu

The following requirements must be met for ENABLE_IWYU to enable the iwyu
target:

1. include-what-you-use and iwyu_tool.py must be in your PATH.
2. A python interpreter must be on the system and available to CMake.

The values of the following variables are used to determine if the requirements
have been met. Values to the right of the equals sign are what a successful run
might look like:
  iwyu_path=/path/to/iwyu_tool.py
  iwyu_tool_path=/path/to/include-what-you-use
  PYTHONINTERP_FOUND=TRUE

An empty PYTHONINTERP_FOUND, or iwyu_path/iwyu_tool_path suffixed with NOTFOUND
are failures.

For Include-what-you-use setup instructions, see:
https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/InstructionsForUsers.md

If, when building the iwyu target, compile errors reporting failures loading
standard include files occur, one solution can be found here:
include-what-you-use/include-what-you-use#100


CMake cross compile
To cross compile libwebm for Windows using mingw-w64 run cmake with the
following arguments:

$ cmake -DCMAKE_TOOLCHAIN_FILE=path/to/libwebm/build/mingw-w64_toolchain.cmake \
  path/to/libwebm

Note1: As of this writing googletest will not build via mingw-w64 without
disabling pthreads.
googletest hash: d225acc90bc3a8c420a9bcd1f033033c1ccd7fe0

To build with tests when using mingw-w64 use the following arguments when
running CMake:

$ cmake -DCMAKE_TOOLCHAIN_FILE=path/to/libwebm/build/mingw-w64_toolchain.cmake \
  -DENABLE_TESTS=ON -Dgtest_disable_pthreads=ON path/to/libwebm

Note2: i686-w64-mingw32 is the default compiler. This can be controlled using
the MINGW_PREFIX variable:

$ cmake -DCMAKE_TOOLCHAIN_FILE=path/to/libwebm/build/mingw-w64_toolchain.cmake \
  -DMINGW_PREFIX=x86_64-w64-mingw32 path/to/libwebm