1 - Introduction to FLTK/pyFLTK

The Fast Light Tool Kit ("FLTK", pronounced "fulltick") is a cross-platform C++ GUI toolkit for UNIX®/Linux® (X11), Microsoft® Windows®, and MacOS® X. FLTK provides modern GUI functionality without the bloat and supports 3D graphics via OpenGL® and its built-in GLUT emulation. It was originally developed by Mr. Bill Spitzak and is currently maintained by a small group of developers across the world with a central repository in the US.

History of FLTK

It has always been Bill's belief that the GUI API of all modern systems is much too high level. Toolkits (even FLTK) are not what should be provided and documented as part of an operating system. The system only has to provide arbitrary shaped but featureless windows, a powerful set of graphics drawing calls, and a simple unalterable method of delivering events to the owners of the windows. NeXT (if you ignored NextStep) provided this, but they chose to hide it and tried to push their own baroque toolkit instead.

Many of the ideas in FLTK were developed on a NeXT (but not using NextStep) in 1987 in a C toolkit Bill called "views". Here he came up with passing events downward in the tree and having the handle routine return a value indicating whether it used the event, and the table-driven menus. In general he was trying to prove that complex UI ideas could be entirely implemented in a user space toolkit, with no knowledge or support by the system.

After going to film school for a few years, Bill worked at Sun Microsystems on the (doomed) NeWS project. Here he found an even better and cleaner windowing system, and he reimplemented "views" atop that. NeWS did have an unnecessarily complex method of delivering events which hurt it. But the designers did admit that perhaps the user could write just as good of a button as they could, and officially exposed the lower level interface.

With the death of NeWS Bill realized that he would have to live with X. The biggest problem with X is the "window manager", which means that the toolkit can no longer control the window borders or drag the window around.

At Digital Domain Bill discovered another toolkit, "Forms". Forms was similar to his work, but provided many more widgets, since it was used in many real applications, rather then as theoretical work. He decided to use Forms, except he integrated his table-driven menus into it. Several very large programs were created using this version of Forms.

The need to switch to OpenGL and GLX, portability, and a desire to use C++ subclassing required a rewrite of Forms. This produced the first version of FLTK. The conversion to C++ required so many changes it made it impossible to recompile any Forms objects. Since it was incompatible anyway, Bill decided to incorporate his older ideas as much as possible by simplifying the lower level interface and the event passing mechanisim.

Bill received permission to release it for free on the Internet, with the GNU general public license. Response from Internet users indicated that the Linux market dwarfed the SGI and high-speed GL market, so he rewrote it to use X for all drawing, greatly speeding it up on these machines. That is the version you have now.

Digital Domain has since withdrawn support for FLTK. While Bill is no longer able to actively develop it, he still contributes to FLTK in his free time and is a part of the FLTK development team.

History of pyFLTK

The Python wrappers for FLTK were started in 1999 by Kevin Dahlhausen. In the beginning, development went on in parallel with the Perl wrappers, maintained by Matt Kennedy. After the year 2000, neither Kevin nor Matt had the necessary resources to continue with the wrappers and both projects went into hibernation for a while. Finally, in 2003, the Python part was picked up by Andreas Held again, who thought it a pity that the combination of such great tools, namely Python and FLTK, was not in a better shape. Finally, in 2006 the first official release of pyFltk was done on Sourceforge. Meanwhile, while not a big player in the Python GUI market, pyFltk was able to recruit a small but dedicated group of followers.


FLTK was designed to be statically linked. This was done by splitting it into many small objects and designing it so that functions that are not used do not have pointers to them in the parts that are used, and thus do not get linked in. This allows you to make an easy-to-install program or to modify FLTK to the exact requirements of your application without worrying about bloat. FLTK works fine as a shared library, though, and is now included with several Linux distributions.

Here are some of the core features unique to FLTK:

In addition, some of the features of pyFLTK:


FLTK comes with complete free source code. FLTK is available under the terms of the GNU Library General Public License with exceptions that allow for static linking. Contrary to popular belief, it can be used in commercial software - even Bill Gates could use it!

The same license applies for pyFLTK; the Windows binary of pyFLTK also include the complete FLTK libraries.

What Does "FLTK" Mean?

FLTK was originally designed to be compatible with the Forms Library written for SGI machines. In that library all the functions and structures started with "fl_". This naming was extended to all new methods and widgets in the C++ library, and this prefix was taken as the name of the library. It is almost impossible to search for "FL" on the Internet, due to the fact that it is also the abbreviation for Florida. After much debating and searching for a new name for the toolkit, which was already in use by several people, Bill came up with "FLTK", including a bogus excuse that it stands for "The Fast Light Toolkit".

Internet Resources

pyFLTK is available on Sourceforge:

pyfltk-user@lists.sourceforge.net [see instructions below]

To send a message to the pyFLTK mailing list ("pyfltk-user@lists.sourceforge.net") you must first join the list. Non-member submissions are blocked to avoid problems with unsolicited email.

To join the pyFLTK mailing list, go to https://lists.sourceforge.net/lists/listinfo/pyfltk-user and fill in the required information.

Reporting Bugs

To report a bug in pyFLTK, send an email to pyfltk-user@lists.sourceforge.net, or fill in a bug report at http://sourceforge.net/projects/pyfltk/. Please include the pyFLTK version, and operating system & version, that you are using when describing the bug or problem. We will be unable to provide any kind of help without that basic information.

For general support and questions, please use the pyFLTK mailing list at pyfltk-user@lists.sourceforge.net.