Articles & FAQs

FLTK is a LGPL'd C++ graphical user interface toolkit for X (UNIX®), Linux® (X11 and Wayland), macOS (aka OS X), OpenGL, and Windows (Microsoft® Windows® XP, 2000, and later). ...

There is a lot of confusion, especially for people who are new to FLTK, about the different versions that are available, what they offer, and when they will be released. This article attempts to clarify matters.

Our FLTK code repository is on GitHub since Dec 01, 2018.
Subversion access has been closed at the same time.

This article is an attempt to summarize third-party widgets that are available as add-ons for FLTK. I think these only apply to FLTK-1. The toolkits provide additional support classes, but only the major widgets are included here.

FLTK comes with complete free source code.  FLTK is available under the terms of the GNU Library General Public License.

1. FLTK has a "global event handler" that makes Escape try to close the window, the same as clicking the close box.  To disable this everywhere you can install your own that pretends it wants the escape key and thus stops the default one from seeing...

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 t...

Yes, you can. The LGPL allows you to do this, and you do not need to release the source code to your program. You do need to release the source code for any modifications you make to FLTK itself, but we would hope you would send any improvements l...

FLTK uses the underlying UNIX or Microsoft Windows time and date support for timeouts and the Fl_Clock widget.  As long as the operating system and libraries are compliant, then FLTK is year 2000 compliant.

In most cases you can just type "make". This will run configure with  the default of no options and then compile everything.

There are two ways to build FLTK under Microsoft Windows. The first is to use the Visual C++ 6.0 project files under the "visualc" directory. Just open (or double-click on) the "fltk.dsw" file to get the whole shebang, and buil...

Microsoft's fundamental problem with its three different styles (actually six) of linking libraries is exactly that: a Microsoft problem.

When compiling an application or DLL that uses the FLTK DLL, you will need to define the FL_DLL preprocessor symbol to get the correct linkage commands embedded within the FLTK header files.

The most common link error involves a missing select() function, which is located in the WSOCK32.LIB or WS2_32.LIB libraries.  You'll also need to link against the FLTK library (obviously), which is the F...

Configure FLTK with the --enable-xft option, e.g.:

FLTK supports modal windows, which force all input to the currently visible modal window.  You can make a window modal by using the Fl_Window::set_modal() method.

The easiest way to wait for a window to close is to use the Fl_Window::shown() and Fl::wait() methods in a while loop:

You can make the menubar shortcuts apply to all windows by using the Fl_Menu_Bar::global() method.

To get the this pointer for the class you can pass the pointer as the user_data argument for your callback. Typically this is then used to call a non-static method:

class MyClass {
  static...