Jedidiah Barber's Personal Site

FLTK Ada Binding

Git repository: Link
Estimated status: 80% complete


Another year, another lot of bugfixes. Well actually the timing is pure coincidence, but it sounds kinda nice when I put it that way.

The most vexing thing about all this is that some of the above fixes were needed due to my own oversights, and some were needed due to FLTK changing in subtle ways in the few point releases it has had since I made this binding. And I cannot tell which is which.


A few noteworthy bugfixes have been applied to the binding.

First, unbeknownst to me the Fl_Widget constructor doesn't copy the given label string inside FLTK and merely stores a pointer. This meant that declaring several Widgets in a row each with their own different label could have unexpected and erratic results. Easily fixed by ensuring the binding constructor also calls copy_label() afterwards.

And second, somehow I had made an oversight with the type assigned to Color, using a signed Integer when it really needed an unsigned modular type with 32 bits of range. Again, easily fixed but even more annoying since it was my fault to begin with.

I'm sure the other guy aside from me who takes an interest in this binding will be happy about these. You know who you are.


This binding is now complete enough for most purposes. It certainly took more effort than expected, in part due to underestimation of how much needed binding. The vast majority of useful classes are now usable in Ada, with a few exceptions such as the Fl_Browser, Fl_Help_View, Fl_Table, and Fl_Tree widgets.

Noteworthy features and modifications include:

A mapping of what C++ headers and methods correspond to what Ada packages, functions, and procedures is included. Also, the below "Hello world" code sample has been modified to work with the updated binding.


FLTK, or by its full name the Fast Light Toolkit , is a graphical widget toolkit noteworthy for being so lightweight that it is commonly statically linked. Projects that make use of it include the Dillo web browser, the FLWM X window manager, and the Equinox Desktop Environment. There are bindings for it in several languages, including Python, Perl and Ruby, but not Ada. Until now!

This is a spinoff from Adapad, and so despite not yet being complete it can be at least guaranteed to be enough to write a text editor. It's a thick, loosely coupled binding, accomplished by first exporting the interface to C, then importing that to Ada. Attempted usage of the internal C interface as a binding on its own is not supported.

A typical FLTK Hello World program in Ada:

with FLTK.Widgets.Groups.Windows, FLTK.Widgets.Boxes; function Hello_World return Integer is My_Win : FLTK.Widgets.Groups.Windows.Window := FLTK.Widgets.Groups.Windows.Forge.Create (100, 100, 200, 200, "Untitled"); My_Box : FLTK.Widgets.Boxes.Box := FLTK.Widgets.Boxes.Forge.Create (50, 50, 100, 100, "Hello, World!"); begin My_Win.Add (My_Box); My_Win.Show; return FLTK.Run; end Hello_World;

Aside from reworking the types to better fit the strongly typed philosophy of Ada, the entire library has been structured to avoid explicit heap usage. As you can see from the above example, the intended use is to declare FLTK objects on the stack. Allocation and deallocation of the C++ internals is handled automatically.

A few other minor changes were involved, such as requiring widgets to be explicitly added to a group rather than implicitly being added to the last group not yet ended. At the moment the package specifications should provide sufficient information to allow programmers to work with the library.