Getting started with CMake

[Windows instructions at the end of this document]

(These instructions apply to Unix-like systems, including Cygwin and Mac. To

build using Visual Studio or some other IDE supported by CMake, most of the

information below still applies)

Always compile in a separate directory to the code. For example, if the

code (eg, from Git) is at /home/curt/projects/flightgear, you might create

/home/curt/projects/fgbuild. Change into the new directory, and run

    cmake ../flightgear

To generate standard Unix Makefiles in fgbuild.

Probably you want to specify an install prefix:

    cmake ../flightgear -DCMAKE_INSTALL_PREFIX=/usr

Note the install prefix is automatically searched for required libraries

and header files, so if you install PLIB, OpenSceneGraph and SimGear to the

same prefix, most configuration options are unnecessary.

If for some reason you have a dependency (or several) at a different prefix,

you can specify one or more via CMAKE_PREFIX_PATH:

    cmake ../flightgear -DCMAKE_PREFIX_PATH="/opt/local;/opt/fgfs"

(note the use of semi-colons to specify multiple prefix paths)

Standard prefixes are searched automatically (/usr, /usr/local, /opt/local)

Most dependencies also expose an environment variable to specify their

installation directory explicitly eg OSG_DIR or PLIBDIR. Any of the methods

described above will work, but specifying an INSTALL_PREFIX or PREFIX_PATH is

usually simpler.

By default, we select a release build. To create a debug build, use

    cmake ../flightgear -DCMAKE_BUILD_TYPE=Debug

(or MinSizeRel, or RelWithDbg)

Debug builds will automatically use corresponding debug builds of required

libraries, if they are available. For example you can install debug builds of

SimGear and OpenSceneGraph, and a debug FlightGear build will use them.

(Debug builds of libraries have the 'd' suffix by default - Release builds

have no additional suffix)

Note most IDE projects (eg Xcode and Visual Studio) support building all the

build types from the same project, so you can omit the CMAKE_BUILD_TYPE option

when running cmake, and simply pick the build configuration as normal in the

IDE.

It's common to have several build directories with different build

configurations, eg

    /home/curt/projects/flightgear (the git clone)

    /home/curt/projects/fgdebug

    /home/curt/projects/fgrelease

    /home/curt/projects/fg-with-svn-osg

To set an optional feature, do

    cmake ../flightgear -DFEATURE_NAME=ON 

(or 'OFF' to disable )

To see the variables that can be configured / are currently defined, you can

run one of the GUI front ends, or the following command:

    cmake ../flighgear -L

Add 'A' to see all the options (including advanced options), or 'H' to see

the help for each option (similar to running configure --help under autoconf):

    cmake ../flightgear -LH

Build Targets

For a Unix makefile build, 'make dist', 'make uninstall' and 'make test' are

all available and should work as expected. 'make clean' is also as normal,

but there is *no* 'make distclean' target. The equivalent is to completely

remove your build directory, and start with a fresh one.

Adding new files to the build

Add source files to the SOURCES list, and headers to the HEADERS list. Note

technically you only need to add source files, but omitting headers confuses

project generation and distribution / packaging targets.

For target conditional files, you can append to the SOURCES or HEADERS lists

inside an if() test, for example:

    if(APPLE)

    	list(APPEND SOURCES extraFile1.cxx extraFile2.cxx)

    endif()

Setting include directories

In any CMakeList.txt, you can do the following:

    include_directories(${PROJECT_SOURCE_DIR}/some/path)

For example, this can be done in particular subdirectory, or at the project

root, or an intermediate level.

Setting target specific compile flags, includes or defines

Use set_target_property(), for example

    set_target_property(fgfs PROPERTIES

            COMPILE_DEFINITIONS FOO BAR=1)

You can set a property on an individual source file:

    set_property(SOURCE myfile.cxx PROPERTY COMPILE_FLAGS "-Wno-unsigned-compare")

Detecting Features / Libraries

For most standard libraries (Gtk, wxWidget, Python, GDAL, Qt, libXml, Boost),

cmake provides a standard helper. To see the available modules, run:

     cmake --help-module-list

In the root CMakeLists file, use a statement like:

    find_package(OpenGL REQUIRED)

Each package helper sets various variables such aaa_FOUND, aaa_INCLUDE_DIR,

and aaa_LIBRARY. Depending on the complexity of the package, these variables

might have different names (eg, OPENSCENEGRAPH_LIBRARIES).

If there's no standard helper for a library you need, find a similar one, copy

it to CMakeModules/FindABC.cmake, and modify the code to fit. Generally this

is pretty straightforward. The built-in modules reside in the Cmake 'share'

directory, eg /usr/share/cmake/modules on Unix systems.

Note libraries support by pkg-config can be handled directly, with no need

to create a custom FindABC helper.

Adding a new executable target

    add_executable(myexecutable ${SOURCES} ${HEADERS})

    target_link_libraries(myexecutable .... libraries ... )

    install(TARGETS myexecutable RUNTIME DESTINATION bin)

(If the executable should not be installed, omit the final line above)

If you add an additional line

    add_test(testname ${EXECUTABLE_OUTPUT_PATH}/myexecutable)

Then running 'make test' will run your executable as a unit test. The

executable should return either a success or failure result code.

SPECIAL INSTRUCTIONS TO BUILD UNDER WINDOWS WITH VISUAL STUDIO

==============================================================

On Windows, assumptions on the directory structure are made to automate the discovery of dependencies.

This recommended directory structure is described below:

${MSVC_3RDPARTY_ROOT} /

      3rdParty /                 ( includes plib, fltk, zlib, libpng, libjpeg, libtiff, freetype, libsvn, gdal, ...

         bin /

         include /

         lib /

      3rdParty.x64 /             ( 64 bit version )

         ...

      boost_1_44_0 /

         boost /

      install /

         msvc100 /               ( for VS2010 32 bits, or msvc90, msvc90-64 or msvc100-64 for VS2008 32, VS2008 64 and VS2010 64 )

            OpenSceneGraph /     ( OSG CMake install

               bin /

               include /

               lib /

            SimGear /

               include /

               lib /

If you do not use the recommended structure you will need to enter paths by hand. Source and build directories can be located anywhere.

The suggested inputs to cmake are :

      MSVC_3RDPARTY_ROOT : location of the above directory structure

      CMAKE_INSTALL_PREFIX : ${MSVC_3RDPARTY_ROOT}/install/msvc100/FlightGear (or any variation for the compiler version described above )

1. Set up a work directory as described above.

2. Open the Cmake gui.

3. Set "Where is the source code" to wherever you put the FlightGear sources (from the released tarball or the git repository).

4. Set "Where to build the binaries" to an empty directory.

5. Press the "Configure" button. The first time that the project is configured, Cmake will bring up a window asking which compiler you wish to use. Normally just accept Cmakes suggestion, and press Finish. Cmake will now do a check on your system and will produce a preliminary build configuration.

6. Cmake adds new configuration variables in red. Some have a value ending with -NOTFOUND. These variables should receive your attention. Some errors will prevent FlightGear to build and others will simply invalidate some options without provoking build errors. First check the MSVC_3RDPARTY_ROOT variable. If it is not set, chances are that there will be a lot of -NOTFOUND errors. Instead of trying to fix every error individually, set that variable and press the "Configure" button again.

7. Also check the lines with a checkbox. These are build options and may impact the feature set of the built program.

8. Change the CMAKE_INSTALL_PREFIX to ${MSVC_3RDPARTY_ROOT}/install/msvc100/FlightGear because C:\Program Files is likely unwritable to ordinary Windows users and will integrate better with the above directory structure (this is mandatory for SimGear if you don't want to solve errors by hand).

10. Repeat the process until the "Generate" button is enabled.

11. Press the "Generate" button.

12. Start Visual Studio 2010 and load the FlightGear solution (FlightGear.sln) located in "Where to build the binaries" (point 4.)

13. Choose the "Release" build in the VS2010 "Generation" toolbar

14. Generate the solution.

15. If there are build errors, return to Cmake, clear remaining errors, "Configure" and "Generate"

16. When Visual Studio is able to build everything without errors, build the INSTALL project to put the product files in ${CMAKE_INSTALL_PREFIX}

17. Enjoy!

PS: When updating the source from git, it is usually unnecessary to restart Cmake as the solution is able to reconfigure itself when Cmake files are changed. Simply rebuild the solution from Visual Studio and accept the reload of updated projects. It also possible to edit CMakeList.txt files directly in Visual Studio as they also appear in the solution, and projects will be reconfigured on the next generation. To change build options or directory path, it is mandatory to use the Cmake Gui. In case of problems, locate the CMakeCache.txt in "Where to build the binaries” directory and delete it to reconfigure from scratch or use the menu item File->Delete Cache.