Building a project that uses Chrono

When you develop a C++ project and you want to use the Chrono API, you need to:

• include the necessary .h headers at compile time;
• dynamically link the necessary .dll libraries at run time.

as shown below:

This process can be made almost automatic if you use CMake for building your program, see below.

The CMake path is not the only option. For example, you could add Chrono libraries to your C++ project by manually inserting libraries in the IDE settings. However, the method described here is the one that we suggest in most cases since it is platform-independent as it draws on the CMake build tool.

# 1) Check prerequisites:

• Chrono must be already installed and built on your computer, as explained here.

# 2) Create the project directory

• Copy the template_project directory to some place and rename it as you like. For example copy from C:\workspace\chrono\template_project to C:\workspace\my_project

This will be the directory where you put your source code.

# 3) Edit the CMake script

• In the template directory there is already a CMakeLists.txt script. It will be used by CMake. Optionally you might edit it, see below.
For example, suppose you want to use also the POSTPROCESS module. You can edit CMakeLists.txt where it reads:
find_package(Chrono
COMPONENTS Irrlicht
CONFIG)
find_package(Chrono
COMPONENTS Irrlicht Postprocess
CONFIG)
The same is done for any other Chrono module. The list of available modules is: Cascade, Cosimulation, FSI, Granular, Irrlicht, Matlab, MKL, MUMPS, OpenGL, Parallel, Postprocess, Python, Vehicle. The syntax is case insensitive (in other words, any of OpenGL, OPENGL, or opengl are valid component names).

Note also that Chrono modules can be listed as required (after the COMPONENTS option) or as optional (after OPTIONAL_COMPONENTS) as in the example below:
find_package(Chrono
COMPONENTS Irrlicht
OPTIONAL_COMPONENTS Postprocess
CONFIG)
In the former case, CMake processing is stopped if Chrono was not configured and built with one of the required modules enabled. In the latter case, CMake processing continues. When listing Chrono modules as optional components, it is the responsibility of the user to appropriately check in their project code whether or not that Chrono module is in fact available; e.g., by using the macros defined in ChConfig.h (CHRONO_IRRLICHT, CHRONO_POSTPROCESS, etc) which are defined for enabled modules.

For more details, see the CMake documentation for find_package and its "Config Mode".
If you prefer to change the name of the default my_example.cpp to something more meaningful, say my_simulator.cpp, just rename that file and then change the line
add_executable(myexe my_example.cpp)
into
add_executable(myexe my_simulator.cpp)
If your program is split in multiple .cpp sources, simply list them in this line: add_executable(myexe my_simulator.cpp my_foo_source.cpp my_bar_source.cpp)
As of version 2017 15.8, Visual Studio has changed its handling of aligned memory allocation. To properly deal with aligned memory allocation for classes that have members fixed-size vectorizable Eigen objects, make sure your CMakeLists.txt retains lines 104-108:
if(${CMAKE_SYSTEM_NAME} MATCHES "Windows") if(MSVC AND${MSVC_VERSION} GREATER_EQUAL 1915)
endif()
endif()
which conditionally defines _ENABLE_EXTENDED_ALIGNED_STORAGE.

# 4) Start CMake

• Start the CMake GUI
• Use Browse source... by setting the source directory that you created, e.g. C:/workspace/my_project
• Use Browse build... by setting a new empty directory for the output project, e.g. C:/workspace/my_project_build

# 5) Configure

• Press the Configure button in CMake
• When prompted to pick a generator, select the same compiler that you used to compile Chrono;
• Important: set the Chrono_DIR variable. This is the cmake directory that you find in the directory where you built Chrono. In our example it is C:/workspace/chrono_build/cmake
• Press the Configure button again

# 6) Generate the project

• Press the Generate button in CMake. A project will be created in the build directory. In our example you will find it in C:/workspace/my_project_build

# 7) Compile the project

If you used a Visual Studio generator in CMake,

• Open the solution in Visual Studio editor (in our example double click on C:\workspace\my_project_build\my_project.sln)
• Change from Debug to Release mode, using the drop-down list in the toolbar of VisualStudio
• Use the menu Build > Build solution... to compile and link.

If you used a Unix makefile generator in CMake (ex. in Linux), you can open a shell, cd into the build directory and call make:

cd /home/john/my_project_build
make

By default all binaries (ex. myexe.exe) of your project will go into your build directory, in our example C:\workspace\my_project_build\Release (or C:\workspace\my_project_build\Debug if you decided to compile in Debug mode).

Double click on the .exe file and you should see the demo running in an interactive 3D view

# Important information for Windows users

If you are a Windows users, your project executables need to know where to find the Chrono shared libraries (i.e. those with .dll extension), otherwise they will crash as soon as you try to run them.

To make things simple, we added an auxiliary CMake target (namely COPY_DLLS) that makes a copy of the Chrono DLLs (as well as other DLL dependencies such as the Irrlicht shared library, as appropriate) in the project binaries folder (e.g. C:\workspace\my_project_build\Release). There are two different scenarios:

• Chrono_DIR is a build folder; if you followed our installation guide then C:/workspace/chrono_build is of this type; in this case you may have both Release and Debug version of Chrono (under C:/workspace/chrono_build/bin); if both are present, please mind that only Release libraries will be copied; if you want to run your project in Debug configuration then you have to manually copy the Debug libraries contained in C:/workspace/chrono_build/bin/Debug into C:/workspace/my_project_build/Debug;
• Chrono_DIR is an install folder; this is the folder type that is created by building the INSTALL target; this folder is usually C:/Program Files/Chrono and contains either Debug or Release libraries, depending on the configuration that you set when you built the INSTALL target.
The COPY_DLLS target must be re-run (i.e. rebuilt) any time the Chrono library had changed.
Your project has to be compiled with the same build configuration as Chrono. For example, if Chrono was built in Release mode, your project must also be built in Release. Note that automatic copying of Chrono DLLs as described above is hard-coded for Release builds only. For other build configuraitons (Debug, RelWithDebInfo, etc.) it is the user's responsibility to ensure the Chrono DLLs are found (e.g., by manually copying them from the Chrono build directory).

Linux users do not have to worry about copying shared libraries because the .so libraries always go into a directory that is globally visible.