Fletch

Fletch is component of Kitware's computer vision KWIVER Project. Its purpose is to make it a little easier to obtain, configure, and build various open source projects that are KWIVER dependencies. Fletch is a pure CMake project. It does not provide any actual functionality beyond encoding the knowledge of how to obtain, configure, and build a large collection of external projects. Fletch bootstraps a computer vision software development environment by configuring various external projects to all work together nicely. Futhermore it provides this environment in a standard way across platforms: Linux, MacOS, and Windows.

Some of the bigger projects that Fletch builds are

• Caffe
• OpenCV
• VXL
• VTK
• Qt
• Ceres Solver
• Boost
• Eigen

Additionally Fletch builds other projects required by the above like

• libpng
• libtiff
• libjpeg
• HDF5
• FFmpeg
• GLog
• GFlags
• SuiteSparse

For a complete and updated list of packages see CMake/fletch-tarballs.cmake.

Motivation

When building large and complex projects it can be difficult to obtain all the required dependent libraries and get them to build and work together. Many of the projects in the first list above depend on many of the projects in the second list above. If you naively build OpevCV and VXL, for example, each may provide its own copy of libjpeg, libtiff, etc. This is not a problem for the individual projects, but when you try to build a project, like KWIVER, against both of them you end up with conflicts from linking to multiple versions of the same library.

These same problems are addressed by package managers in Linux distributions and projects like MacPorts and Brew on MacOS. However, each package manager has its own versions of each of the packages and these are specific to the package manager and to the operating system. If we make KWIVER build against Ubuntu 16.04 packages it might not build against the packaged versions provided by RHEL or even another version of Ubuntu. Futhermore, building on Windows with Visual Studio is a challenge because there is no standard package manager for Windows.

Fletch solves the above problem for KWIVER using CMake. It provides a cross-platform way to get a standardized collection of open source projects working together with the same versions on any OS. Fletch is not quite a cross-platform package manager, but it aims to fill that role for a specific set of C++ and Python packages commonly used in Computer Vision.

Overview of Directories

CMake	contains the CMake code to obtain and configure the projects
Patches	contains the patches to apply to the downloaded source code

Building Fletch

Fletch uses CMake (www.cmake.org) for easy cross-platform compilation. The minimum required version of CMake is 2.8.12, but newer versions are strongly recommended.

Currently, a compiler with at C++11 support is expected (e.g. GCC 4.8, Visual Studio 2015) is required. KWIVER requires C++11; however, Fletch may compile with older compilers.

CMake Options

Fletch provides CMake options to individually enable each project you build. Some projects will require other projects to be enabled. Unless you are looking for a minimal build, the best way to get started is to set fletch_ENABLE_ALL_PACKAGES to ON and run the CMake configure step to enable all packages. You can then individually turn off packages you don't want. It is also useful to enable fletch_BUILD_WITH_PYTHON unless you only want the C++ libraries built.

CMAKE_BUILD_TYPE	The compiler mode, usually Debug or Release
fletch_ENABLE_ALL_PACKAGES	Turn all packages on (you can turn some back off later)
fletch_BUILD_WITH_PYTHON	Build all the packages with Python support
fletch_BUILD_CXX11	Build using C++11 compiler options. This is required for KWIVER.
fletch_DOWNLOAD_DIR	This is where Fletch will cache downloaded source source code tarballs
fletch_ENABLE_ package	Enables the named package for building

Running CMake

You may run cmake directly from a shell or cmd window. On unix systems, the ccmake tool allows for interactive selection of CMake options. Available for all platforms, the CMake GUI can set the source and build directories, options, "Configure" and "Generate" the build files all with the click of a few button. When running the cmake gui, we also recommend to select the 'Grouped' and 'Advanced' options to better organize the options available.

We recommend building Fletch out of the source directory to prevent mixing source files with compiled products. Create a build directory in parallel with the Fletch source directory for each desired configuration. For example :

\fletch\src	contains the code from the git repository
\fletch\build\rel	contains the built files for the release configuration
\fletch\build\deb	contains the built files for the debug configuration

** NOTE: Windows users, there is a known issue in Qt that will cause a build error if you name a build folder 'release' or 'debug' **

The recommended CMake configuration is to enable all packages and, if desired, python.

If you are using ccmake or the CMake GUI, * Set the source and build locations * Check the option for fletch_ENABLE_ALL_PACKAGES and, if desired, fletch_ENABLE_PYTHON * Configure * Generate the build files

Running from a shell or cmd window:

mkdir fletch
cd fletch
# Pull the source into a subfolder 'src'
git clone https://github.com/Kitware/fletch.git src
# Create a folder to build in
mkdir build/rel
cd build/rel
# Note you need to provide cmake the source directory at the end (relative or absolute)
# Run CMake (it will use the system default compiler if you don't provide options or use the CMake GUI)
# Also, if using visual studio, you do no need to provide the build type
cmake -DCMAKE_BUILD_TYPE=Release -Dfletch_ENABLE_ALL_PACKAGES=ON -Dfletch_ENABLE_PYTHON=ON ../../src
# Again, python very popular option, but is optional

On Linux/OSX/MinGW, execute make

For MSVC users, open the generated fletch.sln and build the project in the configuration associated with the build folder. Even though MSVC supports building multiple configurations, you should only build one configuration per build folder. If you need multiple configurations you should create multiple subfolders and repeat the above instructions for each configuration. Also If you enable Python, please ensure that python is on your Windows PATH

Getting Help

Fletch is a component of Kitware's collection of open source tools. Please join the fletch-users mailing list to discuss Fletch or to ask for help with using Fletch.