This manual describes the Fast Light Tool Kit ("FLTK") version 1.4.1, a C++ Graphical User Interface ("GUI") toolkit for UNIX, Microsoft Windows, and Apple macOS.
Version 1.4.0 introduced support for a new windowing system under Linux/Unix: Wayland. FLTK applications under Linux/Unix run unchanged as Wayland or X11 clients depending on availability at run-time.
Each of the chapters in this manual is designed as a tutorial for using FLTK, while the appendices provide a convenient reference for all FLTK widgets, functions, and operating system interfaces.
This manual may be printed, modified, and/or used under the terms of the FLTK license provided in: Software License.
Organization
This manual is organized into the following chapters and appendices:
Conventions
This manual was generated using Doxygen (see https://www.doxygen.org/) to process the source code itself, special comments in the code, and additional documentation files. In general, Doxygen recognizes and denotes the following entities as shown:
- classes, such as Fl_Widget,
- methods, such as Fl_Widget::callback(Fl_Callback* cb, void* p),
- functions, such as fl_draw(const char *str, int x, int y),
- internal links, such as Conventions,
- external links, such as https://www.fltk.org/.
Other code samples and commands are shown in regular courier type
.
Abbreviations
The following abbreviations are used in this manual:
- X11
- The X Window System version 11.
- Xlib
- The X Window System interface library.
- Windows, WIN32
- The Microsoft Windows Application Programmer's Interface for Windows 2000, Windows XP, Windows Vista, Windows 7 and later Windows versions. FLTK uses the preprocessor definition
_WIN32
for the 32 bit and 64 bit Windows API.
- macOS (aka Mac OS X), APPLE
- The Apple desktop operating sytem macOS 10.0 and later. MacOS 8 and 9 support was dropped after FLTK 1.0.10. FLTK uses the preprocessor definition
__APPLE__
for macOS.
Copyrights and Trademarks
FLTK is Copyright © 1998 - 2025 by Bill Spitzak and others. Use and distribution of FLTK is governed by the GNU Library General Public License with 4 exceptions, located in Software License.
UNIX is a registered trademark of the X Open Group, Inc. Microsoft and Windows are registered trademarks of Microsoft Corporation. OpenGL is a registered trademark of Silicon Graphics, Inc. Apple, Macintosh, MacOS, macOS, and Mac OS X are registered trademarks of Apple Computer, Inc.