The Fast Light Tool Kit ("FLTK", pronounced "fulltick") is a LGPL'd
C++ graphical user interface toolkit for X (UNIX®), OpenGL®, and
Microsoft® Windows® NT 4.0, 95, or 98. 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 FL) 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 the 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
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
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
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.
FLTK was designed to be statically linked. This was done by splitting
it into many small objects and desigining 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 has started being included on Linux distributions.
Here are some of the core features unique to FLTK:
- sizeof(Fl_Widget) == 40 to 48.
- The "core" (the "hello" program compiled & linked with a static
FLTK library using gcc on a 486 and then stripped) is 110K.
- The FLUID program (which includes every widget) is 372k.
- Written directly atop Xlib (or WIN32) for maximum speed, and
carefully optimized for code size and performance.
- Precise low-level compatability between the X11 and WIN32 version
(only about 10% of the code is different).
- Interactive user interface builder program. Output is
human-readable and editable C++ source code.
- Support for X11 overlay hardware (emulation if none and under
- Very small & fast portable 2-D drawing library to hide Xlib and
- OpenGL/Mesa drawing area widget.
- Support for OpenGL overlay hardware on both X11 and WIN32.
Emulation if none.
- Text input fields with Emacs key bindings, X cut & paste, and
foreign letter compose!
- Compatibility header file for the GLUT library.
- Compatibility header file for the XForms library.
- Much too much to list here...
FLTK comes with complete free source code. FLTK is available under the
terms of the GNU Library General Public License.
Contrary to popular belief, it can be used in commercial software!
(Even Bill Gates could use it.)
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", and even a bogus excuse that it stands for "The Fast Light Tool
Building and Installing FLTK Under UNIX
In most cases you can just type "make". This will run configure with
the default of no options and then compile everything.
FLTK uses GNU autoconf to configure itself for your UNIX platform.
The main things that the configure script will look for are the X11 and
OpenGL (or Mesa) header and library files. If these cannot be
found in the standard include/library locations you'll need to define the
CFLAGS, CXXFLAGS, and LDFLAGS environment
variables. For the Bourne and Korn shells you'd use:
CFLAGS=-Iincludedir; export CFLAGS
CXXFLAGS=-Iincludedir; export CXXFLAGS
LDFLAGS=-Llibdir; export LDFLAGS
For C shell and tcsh, use:
setenv CFLAGS "-Iincludedir"
setenv CXXFLAGS "-Iincludedir"
setenv LDFLAGS "-Llibdir"
By default configure will look for a C++ compiler named CC, c++,
g++, or gcc in that order. To use another compiler you need
to set the CXX environment variable:
CXX=xlC; export xlC
setenv CXX "xlC"
The CC environment variable can also be used to override the
default C compiler (cc or gcc), which is used for a
few FLTK source files.
You can run configure yourself to get the exact setup you need. Type
"./configure <options>", where options are:
When the configure script is done you can just run the "make" command.
This will build the library, FLUID tool, and all of the test programs.
- Enable debugging code & symbols
- Enable generation of shared libraries
- Set the location for executables [default = /usr/local/bin]
- Set the location for libraries [default = /usr/local/lib]
- Set the location for include files. [default = /usr/local/include]
- Set the directory prefix for files [default = /usr/local]
To install the library, become root and type "make install". This
will copy the "fluid" executable to "bindir", the header files to
"includedir", and the library files to "libdir".
Building FLTK Under Microsoft Windows
There are two ways to build FLTK under Microsoft Windows. The first
is to use the Visual C++ 5.0 project files under the "visualc"
directory. Just open (or double-click on) the "fltk.dsw" file to get
the whole shebang.
The second method is to use a GNU-based development tool with the
files in the "makefiles" directory. To build using one of these tools
simply copy the appropriate makeinclude and config files to the main
directory and do a make:
copy makefiles\Makefile.<env> Makefile
Using the Visual C++ DLL Library
The "fltkdll.dsp" project file builds a DLL-version of the FLTK
library. Because of name mangling differences between PC compilers (even
between different versions of Visual C++!) you can only use the DLL that
is generated with the same version compiler that you built it with.
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.
Building FLTK Under OS/2
The current OS/2 build requires XFree86 for OS/2 to work. A native
Presentation Manager version has not been implemented yet (volunteers
The current set of Makefiles/configuration failes assumes that
EMX 0.9d and libExt
To build the XFree86 version of FLTK for OS/2, copy the appropriate
makeinclude and config files to the main directory and do a make:
copy makefiles\Makefile.os2x Makefile
FLTK is available on the 'net in a bunch of locations:
To send a message to the FLTK mailing list ("email@example.com") you
must first join the list. Non-member submissions are blocked to avoid
problems with unsolicited email.
- California, USA (ftp.fltk.org)
- Maryland, USA (ftp2.fltk.org)
- Espoo, Finland (ftp.funet.fi)
- Germany (linux.mathematik.tu-darmstadt.de)
- Austria (gd.tuwien.ac.at)
- firstname.lastname@example.org [see
- email@example.com [for
To join the FLTK mailing list, send a message to
"firstname.lastname@example.org" with "subscribe fltk" in the message body. A
digest of this list is available by subscribing to the "fltk-digest"
To report a bug in FLTK, send an email to "email@example.com".
Please include the FLTK version, operating system & version, and
compiler that you are using when describing the bug or problem.
For general support and questions, please use the FLTK mailing list