FLTK 1.4.0

This manual describes the Fast Light Tool Kit ("FLTK") version 1.4.0, a C++ Graphical User Interface ("GUI") toolkit for UNIX, Microsoft Windows and Apple macOS.

Version 1.4.0 introduces 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.


This manual is organized into the following chapters and appendices:


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:

Other code samples and commands are shown in regular courier type.


The following abbreviations are used in this manual:

The X Window System version 11.
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 - 2024 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.

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