FLTK fork

X11-only C++ widget toolkit with a hand-written Makefile

Warning: experimental software

This project has not been properly tested yet. Use at your own risk.

What is this?

This is a fork of FLTK (Fast Light Toolkit), a cross-platform C++ GUI library originally written by Bill Spitzak. The original FLTK started as a clean, lightweight toolkit, but recent versions (1.4 and especially 1.5) moved to CMake and adopted so-called “modern C++” features, making the project unsuitable for our use.

This fork is based on the FLTK 1.4 tree and aims to strip away the unnecessary complexity: CMake is replaced with a hand-written Makefile, platform support is narrowed to X11 only, and the required subset of X11 headers is bundled directly in the source tree so that no external dependencies beyond a C/C++ compiler and make are needed.

How it was made

The refactoring was done with the help of Claude Code, an AI coding assistant by Anthropic. The following changes were made:

Removed CMake build system entirely — replaced with a single hand-written Makefile
Dropped all platforms except X11 (removed Windows, macOS, Wayland code paths)
Bundled X11 headers in xlibs/ so the build is self-contained
Added optional Cairo/Pango rendering support (on by default, can be disabled)
Removed autoconf, configure scripts, and all external build tool dependencies
Kept the bundled jpeg, png, and zlib libraries

The result is a project that builds with nothing more than g++ and make.

Source code

Browse or clone the repository:

Browse source (cgit)
git clone https://git.mlibren.com/fltk.git

Building

Requirements: a C/C++ compiler (g++ or clang++), make, and X11 development libraries. Cairo and Pango are optional (enabled by default).

make
make install

To build without Cairo/Pango (pure Xlib+Xft rendering):

make USE_CAIRO=0