Compiling OpenTTD

Required/optional libraries

OpenTTD makes use of the following external libraries:

(encouraged) zlib: (de)compressing of old (0.3.0-1.0.5) savegames, content downloads, heightmaps
(encouraged) liblzma: (de)compressing of savegames (1.1.0 and later)
(encouraged) libpng: making screenshots and loading heightmaps
(optional) liblzo2: (de)compressing of old (pre 0.3.0) savegames

For Linux, the following additional libraries are used (for non-dedicated only):

libSDL2: hardware access (video, sound, mouse)
libfreetype: loading generic fonts and rendering them
libfontconfig: searching for fonts, resolving font names to actual fonts
libicu: handling of right-to-left scripts (e.g. Arabic and Persian) and natural sorting of strings

OpenTTD does not require any of the libraries to be present, but without liblzma you cannot open most recent savegames and without zlib you cannot open most older savegames or use the content downloading system.

Windows

You need Microsoft Visual Studio 2017 or more recent.

You can download the free Visual Studio Community Edition from Microsoft at https://visualstudio.microsoft.com/vs/community/.

OpenTTD needs the Platform SDK, if it isn't installed already. This can be done during installing Visual Studio, by selecting Visual C++ MFC for x86 and x64 (and possibly Visual C++ ATL for x86 and x64 depending on your version). If not, you can get download it as MS Windows Platform SDK.

Install the SDK by following the instructions as given.

Dependencies for OpenTTD on Windows are handled via vcpkg. First you need to install vcpkg by following the Quick Start instructions of their README.

After this, you can install the dependencies OpenTTD needs. We advise to use the static versions, and OpenTTD currently needs the following dependencies:

liblzma
libpng
lzo
zlib

To install both the x64 (64bit) and x86 (32bit) variants (though only one is necessary), you can use:

.\vcpkg install liblzma:x64-windows-static libpng:x64-windows-static lzo:x64-windows-static zlib:x64-windows-static
.\vcpkg install liblzma:x86-windows-static libpng:x86-windows-static lzo:x86-windows-static zlib:x86-windows-static

You can open the folder (as a CMake project). CMake will be detected, and you can compile from there. If libraries are installed but not found, you need to set VCPKG_TARGET_TRIPLET in CMake parameters. For Visual Studio 2017 you also need to set CMAKE_TOOLCHAIN_FILE. (Typical values are shown in the MSVC project file command line example)

Alternatively, you can create a MSVC project file via CMake. For this either download CMake from https://cmake.org/download/ or use the version that comes with vcpkg. After that, you can run something similar to this:

mkdir build
cd build
cmake.exe .. -G'Visual Studio 16 2019' -DCMAKE_TOOLCHAIN_FILE="<location of vcpkg>\vcpkg\scripts\buildsystems\vcpkg.cmake" -DVCPKG_TARGET_TRIPLET="x64-windows-static"

Change <location of vcpkg> to where you have installed vcpkg. After this in the build folder are MSVC project files. MSVC can rebuild the project files himself via the ZERO_CHECK project.

All other platforms

Minimum required version of CMake is 3.9. By default this produces a Debug build with assertations enabled. This is a far slower build than release builds.

mkdir build
cd build
cmake ..
make

For more information on how to use CMake (including how to make Release builds), we urge you to read their excellent manual.

CMake Options

Via CMake, several options can be influenced to get different types of builds.

-DCMAKE_BUILD_TYPE=RelWithDebInfo: build a release build. This is significant faster than a debug build, but has far less useful information in case of a crash.
-DOPTION_DEDICATED=ON: build OpenTTD without a GUI. Useful if you are running a headless server, as it requires less libraries to operate.
-DOPTION_USE_ASSERTS=OFF: disable asserts. Use with care, as assert statements capture early signs of trouble. Release builds have them disabled by default.
-DOPTION_USE_THREADS=OFF: disable the use of threads. This will block the interface in many places, and in general gives a worse experience of the game. Use with care.
-DOPTION_TOOLS_ONLY=ON: only build tools like strgen. Does not build the game itself. Useful for cross-compiling.

Supported compilers

Every compiler that is supported by CMake and supports C++17, should be able to compile OpenTTD. As the exact list of compilers changes constantly, we refer to the compiler manual to see if it supports C++17, and to CMake to see if it supports your compiler.

Compilation of base sets

To recompile the extra graphics needed to play with the original Transport Tycoon Deluxe graphics you need GRFCodec (which includes NFORenum) as well. GRFCodec can be found at https://www.openttd.org/downloads/grfcodec-releases/latest.html.

Having GRFCodec installed can cause regeneration of the .grf files, which are written in the source directory. This can leave your repository in a modified state, as different GRFCodec versions can cause binary differences in the resulting .grf files. Also translations might have been added for the base sets which are not yet included in the base set information files. To avoid this behaviour, disable GRFCodec (and NFORenum) in CMake cache (GRFCODEC_EXECUTABLE and NFORENUM_EXECUTABLE).

Developers settings

You can control some flags directly via CXXFLAGS (any combination of these flags will work fine too):

-DRANDOM_DEBUG: this helps with debugging desyncs.
-fno-inline: this avoids creating inline functions; this can make debugging a lot easier.
-O0: this disables all optimizations; this can make debugging a lot easier.
-p: this enables profiling.

Always use a clean buildfolder if you changing CXXFLAGS, as this value is otherwise cached. Example use:

CXXFLAGS="-fno-inline" cmake ..

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