View source for Building using CMake - Windows

{{Main article|Building FlightGear}}
This article is intended to give an overview of '''building FlightGear on modern Windows systems'''. It was created using Windows 11 and VS 2022. It ought to be transferable to earlier versions of the Windows OS and software.

As FlightGear is now 64-bit only, the guide only describes building on a 64-bit system.

== Required software ==
* [https://cmake.org/download/ CMake for Windows]. Download and install the Windows Win64-x64 Installer.
* [https://visualstudio.microsoft.com/downloads/ Microsoft Visual Studio 2022] (MSVC). The Community version is free. There is no need for the premium versions; none of their features are required to build FlightGear. The C++ compiler will not be installed by default. You either choose this component during installation or after installation by starting MSVC and trying to create a new C++ project. The one to download is "Desktop Development with C++". Make sure to have the latest version of the Windows SDK for your Windows version and the C++ Compiler checked. As of 8/5/2025, the option to select is "MSVC 2022 64-bit".
* [https://www.qt.io/download-open-source/ Qt6] for the [[Integrated Qt Launcher]]. Download the online installer to install and choose the latest version of Qt. Leave the default Developer and Designer Tools selection - these are needed for coding and compiling. Otherwise, here is [https://www.qt.io/offline-installers Offline Qt Downloads] for the optional offline-installer versions of Qt.
* [https://git-scm.com/download/win Git] to keep your build up to date. It also simplifies downloads of components. Optional, but can't recommend it enough!

== Obtaining source ==
{{Main article|FlightGear and Git}}
Throughout this article it is assumed that you have set up git clones of the various source repositories (FlightGear, SimGear, data...).
Using an organized directory (see below) will help significantly.

The commands to run are:

{{#tag:syntaxhighlight|
{{repo link
  | site = gitlab
  | cmd  = git clone
  | proj = flightgear
  | repo = simgear
  | type = git
  | full = 1
}} simgear
{{repo link
  | site = gitlab
  | cmd  = git clone
  | proj = flightgear
  | repo = flightgear
  | type = git
  | full = 1
}} flightgear
{{repo link
  | site = gitlab
  | cmd  = git clone
  | proj = flightgear
  | repo = fgdata
  | type = git
  | full = 1
}} fgdata
{{repo link
  | site = gitlab
  | cmd  = git clone
  | proj = flightgear
  | repo = windows-3rd-party
  | type = git
  | full = 1
}} windows-3rd-party
{{repo link
  | site = gitlab
  | cmd  = git clone
  | proj = flightgear
  | repo = openscenegraph
  | type = git
  | full = 1
}} osg
| lang = "sh"
}}

After downloading these, I would suggest assembling a folder structure as below:

== Directory Tree ==
On Windows, assumptions on the directory structure are made to automate the discovery of dependencies. This recommended directory structure is described below. The components can be downloaded from the links above. If you do not use the recommended structure you will need to enter paths by hand and some parts may not input correctly.


Caveat -- spaces in the directory names will cause errors. It is best to make sure there are no spaces in the path anywhere.

<tt>
: FlightGearBuild / </tt> (Main root directory) <tt>
:: fgdata / </tt> (FlightGear data files) <tt>
:: flightgear / </tt> (FlightGear sources) <tt>
:: install / </tt> (Directory where you will install the built binaries to) <tt>
::: launch.bat / </tt> (launch script if desired, see below) <tt>
:: osg / </tt> (OSG sources) <tt>
:: simgear / </tt> (SimGear sources) <tt>
:: windows-3rd-party /
:: build.bat / </tt> (build script, see below) <tt>
:: update.bat / </tt> (update script, see below)

== Building ==
=== Scripted Compilation ===
This script will allow you to build OpenSceneGraph, SimGear and FlightGear automatically.
 
{{collapsible script
| type   = Windows batch file
| title  = The <code>build.bat</code> script for configuring and compiling OSG, SG, and FG
| lang   = batch
| script =
SET PATH=%PATH%;%ProgramFiles%\CMake\bin
SET QT6SDK64=C:\Qt\6.x\msvc2022_64
SET CMAKE_TOOLCHAIN="Visual Studio 17 2022"
SET ROOT_DIR=C:\path\to\FlightGearBuild

md osg-build
md simgear-build
md flightgear-build

cd %ROOT_DIR%\osg-build

cmake  %ROOT_DIR%\osg -G  %CMAKE_TOOLCHAIN% -A x64 ^
                 -DACTUAL_3RDPARTY_DIR=%ROOT_DIR%\windows-3rd-party/msvc140/3rdParty.x64 ^
                 -DCMAKE_RELWITHDEBINFO_POSTFIX:STRING= ^
                 -DOSG_USE_UTF8_FILENAME:BOOL=ON ^
                 -DWIN32_USE_MP:BOOL=ON ^
                 -DCMAKE_INSTALL_PREFIX:PATH=%ROOT_DIR%\install
cmake --build . --config RelWithDebInfo --target INSTALL

cd %ROOT_DIR%\simgear-build
cmake  %ROOT_DIR%\simgear -G  %CMAKE_TOOLCHAIN% -A x64 ^
                 -DOSG_FSTREAM_EXPORT_FIXED:BOOL=ON ^
                 -DCMAKE_INSTALL_PREFIX:PATH=%ROOT_DIR%\install
cmake --build . --config RelWithDebInfo --target INSTALL

cd %ROOT_DIR%\flightgear-build
cmake  %ROOT_DIR%\flightgear -G  %CMAKE_TOOLCHAIN% -A x64 ^
                  -DCMAKE_INSTALL_PREFIX:PATH=%ROOT_DIR%\install ^
                  -DCMAKE_PREFIX_PATH=%QT6SDK64% ^
                  -DOSG_FSTREAM_EXPORT_FIXED:BOOL=ON
                    
cmake --build . --config RelWithDebInfo --target INSTALL

pause
| show  = 1
}}

{{tip | 10/2024: When using VS2022 make sure your osg has this fix applied: https://gitlab.com/flightgear/openscenegraph/-/commit/31082758036c12738467a7210a17604275a79517<ref>https://sourceforge.net/p/flightgear/mailman/message/58821522/</ref>



Some folks encountered the following problem when building flightgear:
<syntaxhighlight>
 CMake Error at CMakeLists.txt:283 (find_package):
  By not providing "FindBoost.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Boost", but
  CMake did not find one.

  Could not find a package configuration file provided by "Boost" with any of
  the following names:

    BoostConfig.cmake
    boost-config.cmake

  Add the installation prefix of "Boost" to CMAKE_PREFIX_PATH or set
  "Boost_DIR" to a directory containing one of the above files.  If "Boost"
  provides a separate development package or SDK, be sure it has been
  installed.
</syntaxhighlight>
This could be solved by doing the following in the top-level <code>CMakeLists.txt</code> of [https://sourceforge.net/p/flightgear/simgear/ci/next/tree/CMakeLists.txt#l16 simgear] and [https://sourceforge.net/p/flightgear/flightgear/ci/next/tree/CMakeLists.txt#l26 flightgear]:

In each file search for the line
<syntaxhighlight lang='CMake'>
cmake_policy(SET CMP0167 NEW)
</syntaxhighlight>
(it should be near the top of each file) and change from <code>NEW</code> to <code>OLD</code> like this<ref>https://sourceforge.net/p/flightgear/mailman/message/58815368/</ref>:
<syntaxhighlight lang='CMake'>
cmake_policy(SET CMP0167 OLD)
</syntaxhighlight>



In addition there are reports that a linking error occurs when building flightgear:
<syntaxhighlight>
pui.lib(puValue.obj) : error LNK2019: unresolved external symbol __imp_strncat referenced in function "protected: void__cdecl puValue::copy_stringval(char const *)" (?copy_stringval@puValue@@IEAAXPEBD@Z) [F:\git\flightgear-build\src\Main\fgfs.vcxproj]
F:\git\flightgear-build\src\Main\RelWithDebInfo\fgfs.exe : fatal error LNK1120: 1 unresolved externals [F:\git\flightgear-build\src\Main\fgfs.vcxproj]
</syntaxhighlight>
A workaround could be by changing the build type from <code>RelWithDebInfo</code> to <code>Release</code> when building osg, simgear and flightgear<ref>https://sourceforge.net/p/flightgear/mailman/message/58824438/</ref>:

In the <code>build.bat</code> change all three occurrences of
<syntaxhighlight lang='batch'>
cmake --build . --config RelWithDebInfo --target INSTALL
</syntaxhighlight>
to
<syntaxhighlight lang='batch'>
cmake --build . --config Release --target INSTALL
</syntaxhighlight>
}}

Before starting to use the script, you need to edit the top few lines of the script. You will have to:

# Set the path to your CMake installation.
# Ensure that the path to your QT SDK is correct for your version of MSVC.
# Ensure your toolchain version matches, e.g. "Visual Studio 16 2019" for MSVC 2019 or "Visual Studio 15 2017" for MSVC 2017.
# Set ROOT_DIR to the FlightGearBuild folder you created (the above directory structure)

==== Post-compilation: Launching FlightGear ====
'''In the debugger:'''
Open flightgear-build/FlightGear.sln. You can then perform all your development / debugging directly in VS. You normally only need to run build.bat again, if you update SimGear or OSG. 

To launch FlightGear from Visual Studio, you can follow the following steps:
The first time only:
# Make sure you set your build type to RelWithDebInfo in the top bar.
# To start with the launcher, click on the small black arrow beside Local Windows Debugger to open 'fgfs debug properties'. Switch to debugging; add {{code|--launcher}} to the 'Command Arguments'. Click Apply and then OK.
# Press the green arrow (Local Windows Debugger) to start up FlightGear. 
# The first time you'll have to choose where FGDATA is -- to do this, select the 'fgdata' directory you cloned at the start.

Thereafter, simply press the green arrow directly each time you want to start. If there are any local changes, it will recompile; alternatively it will start up directly. It will take a little longer to start as it loads symbols; however you also have the benefit that any segfaults will be caught allowing you to report them!

'''As a standard .exe:'''
NB these instructions overall are intended for setting up for development; there's a slightly more convoluted process for setting up for just plain flying (e.g. taking advantage of new features for aircraft development).

Essentially, Visual Studio doesn't copy in the DLLs into the /bin/ folder. It's also not ideal to manually copy in the DLLs as it can cause all sorts of issues. However, without the DLLs FlightGear won't work; therefore, you need to set the PATH so it knows where to look for them.
This launch script should work, put into your /install/bin/ folder:
{{collapsible script
| type   = Windows batch file
| title  = The <code>launch.bat</code> script for launching flightgear
| lang   = batch
| script =
SET PATH=C:\path\to\FlightGearBuild\install\bin;C:\path\to\FlightGearBuild\windows-3rd-party\msvc140\3rdParty.x64\bin;C:\Qt\5.15.2\msvc2019_64\bin;%PATH%
SET FG_ROOT=C:\path\to\FlightGearBuild\fgdata
fgfs.exe --launcher
| show  = 1
}}

Adjust the "path\to" references to suit your own personal installation, as well as the QT5 path.

=== Updating ===
To update FlightGear, in general, just run ''git pull'' on the source directories and then re-run the build.bat script -- it will update what it needs to, relatively quickly.

{{collapsible script
| type   = Windows batch file
| title  = The <code>update.bat</code> script for updating repositories
| lang   = batch
| script =
SET ROOT_DIR=C:\path\to\FlightGearBuild

cd %ROOT_DIR%\osg
git pull

cd %ROOT_DIR%\fgdata
git pull

cd %ROOT_DIR%\flightgear
git pull

cd %ROOT_DIR%\simgear
git pull

cd %ROOT_DIR%\windows-3rd-party
git pull

pause
| show  = 1
}}

=== Changing the Configuration ===
When the SimGear/FlightGear version numbers change, or you change configuration options (e.g. toggling Compositor, changing OSG versions, changing Qt versions) you do have to re-configure in CMake. To do this, it's usually safest to delete the simgear-build and flightgear-build folders and re-run the build.bat script, to ensure the build is clean. There is no need to delete osg-build unless changing OSG version.

In case of problems, most of the time deleting the simgear-build and flightgear-build folders and re-running the build.bat script will be sufficient.

{{building}}
[[fr:compiler flightear avec CMake - Windows]]
[[Category:Windows specific]]
[[Category:Hackathon Materials]]