#gui #bindings #graphics

sys fltk-sys

Rust bindings for the FLTK GUI library

149 releases (12 breaking)

new 0.13.9 Jan 22, 2021
0.12.10 Jan 7, 2021
0.12.2 Dec 30, 2020
0.11.4 Nov 30, 2020
0.1.22 Mar 31, 2020

#56 in GUI

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Used in 3 crates (via fltk)

MIT license

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Documentation Crates.io License Build

Rust bindings for the FLTK Graphical User Interface library.

The FLTK crate is a crossplatform lightweight gui library which can be statically linked to produce small, self-contained and fast gui applications.


  • Video
  • Written
  • Erco's FLTK cheat page, which is an excellent FLTK C++ reference.

Why choose FLTK?

  • Lightweight. Small binary, around 1mb after stripping. Small memory footprint.
  • Speed. Fast to install, fast to build, fast at startup and fast at runtime.
  • Single executable. No DLLs to deploy.
  • Supports old architectures.
  • FLTK's permissive license which allows static linking for closed-source applications.
  • Themability (4 supported themes: Base, GTK, Plastic and Gleam).
  • Provides around 80 customizable widgets.
  • Has inbuilt image support.

Here is a list of software using FLTK.

  • Link to the official FLTK repository.
  • Link to the official documentation.


Just add the following to your project's Cargo.toml file:

fltk = "^0.13"

The library is automatically built and statically linked to your binary.

For faster builds you can enable ninja builds for the C++ source using the "use-ninja" feature.

An example hello world application:

use fltk::{app::*, window::*};

fn main() {
    let app = App::default();
    let mut wind = Window::new(100, 100, 400, 300, "Hello from rust");

Another example showing the basic callback functionality:

use fltk::{app::*, button::*, frame::*, window::*};

fn main() {
    let app = App::default();
    let mut wind = Window::new(100, 100, 400, 300, "Hello from rust");
    let mut frame = Frame::new(0, 0, 400, 200, "");
    let mut but = Button::new(160, 210, 80, 40, "Click me!");
    but.set_callback(move || frame.set_label("Hello World!"));

Please check the examples directory for more examples. You will notice that all widgets are instantiated with a new() method, taking the x and y coordinates, the width and height of the widget, as well as a label which can be left blank if needed. Another way to initialize a widget is using the builder pattern: (The following buttons are equivalent)

let but1 = Button::new(10, 10, 80, 40, "Button 1");

let but2 = Button::default()
    .with_pos(10, 10)
    .with_size(80, 40)
    .with_label("Button 2");

An example of a counter showing use of the builder pattern:

fn main() {
    let app = App::default();
    let mut wind = Window::default()
        .with_size(160, 200)
    let mut frame = Frame::default()
        .with_size(100, 40)
    let mut but_inc = Button::default()
        .above_of(&frame, 0)
    let mut but_dec = Button::default()
        .below_of(&frame, 0)
    /* Event handling */


Event handling must be done after the drawing is done and the main window shown. And must be done in the main thread

Events can be handled using the set_callback method (as above) or the available fltk::app::set_callback() free function, which will handle the default trigger of each widget(like clicks for buttons):

    /* previous hello world code */
    but.set_callback(move || frame.set_label("Hello World!"));

Another way is to use message passing:

    /* previous counter code */
    let (s, r) = app::channel::<Message>();

    but_inc.emit(s, Message::Increment);
    but_dec.emit(s, Message::Decrement);
    while app.wait() {
        let label: i32 = frame.label().parse().unwrap();
        match r.recv() {
            Some(Message::Increment) => frame.set_label(&(label + 1).to_string()),
            Some(Message::Decrement) => frame.set_label(&(label - 1).to_string()),
            None => (),

For the remainder of the code, check the full example here.

For custom event handling, the handle() method can be used:

    some_widget.handle(move |ev: Event| {
        match ev {
            /* handle ev */

Handled or ignored events using the handle method should return true, unhandled events should return false. More examples are available in the fltk/examples directory.


FLTK offers 4 application themes (called schemes):

  • Base
  • Gtk
  • Gleam
  • Plastic

These can be set using the App::with_scheme() method.

let app = App::default().with_scheme(AppScheme::Gleam);

Themes of individual widgets can be optionally modified using the provided methods in the WidgetExt trait, such as set_color(), set_label_font(), set_frame() etc:

    some_button.set_color(Color::Light1); // You can use one of the provided colors in the fltk enums
    some_button.set_color(Color::from_rgb(255, 0, 0)); // Or you can specify a color by rgb or hex/u32 value


The following are the features offered by the crate:

  • use-ninja: If you have ninja build installed, it builds faster than make or VS
  • system-libpng: Uses the system libpng
  • system-libjpeg: Uses the system libjpeg
  • system-zlib: Uses the system zlib
  • fltk-bundled: Support for bundled versions of cfltk and fltk on selected platforms (requires curl and tar)
  • no-pango: Build without pango support on Linux/BSD.
  • enable-glwindow: Support for drawing using OpenGL functions.


Rust (version > 1.38), CMake (version > 3.0), Git and a C++11 compiler need to be installed and in your PATH for a crossplatform build from source. This crate also offers a bundled form of fltk on selected platforms, this can be enabled using the fltk-bundled feature flag (which requires curl and tar to download and unpack the bundled libraries). If you have ninja-build installed, you can enable it using the "use-ninja" feature. This should accelerate build times significantly.

  • Windows: No dependencies.
  • MacOS: No dependencies.
  • Linux: X11 and OpenGL development headers need to be installed for development. The libraries themselves are available on linux distros with a graphical user interface.

For Debian-based GUI distributions, that means running:

$ sudo apt-get install libx11-dev libxext-dev libxft-dev libxinerama-dev libxcursor-dev libxrender-dev libxfixes-dev libpango1.0-dev libpng-dev libgl1-mesa-dev libglu1-mesa-dev

For RHEL-based GUI distributions, that means running:

$ sudo yum groupinstall "X Software Development" && yum install pango-devel libXinerama-devel libpng-devel

For Arch-based GUI distributions, that means running:

$ sudo pacman -S libx11 libxext libxft libxinerama libxcursor libxrender libxfixes libpng pango cairo libgl mesa --needed

For Alpine linux:

$ apk add pango-dev fontconfig-dev libxinerama-dev libxfixes-dev libxcursor-dev libpng-dev mesa-gl

For NixOS (Linux distribution) this nix-shell environment can be used:

$ nix-shell --packages rustc cmake git gcc xorg.libXext xorg.libXft xorg.libXinerama xorg.libXcursor xorg.libXrender xorg.libXfixes libpng libcerf pango cairo libGL mesa pkg-config
  • Android: Android Studio, Android Sdk, Android Ndk.


please check the FAQ page for frequently asked questions, encountered issues, guides on deployment, and contribution.


To build, just run:

$ git clone https://github.com/MoAlyousef/fltk-rs
$ cd fltk-rs
$ cargo build


To run the examples:

$ cargo run --example editor
$ cargo run --example calculator
$ cargo run --example gallery
$ cargo run --example terminal_colored
$ cargo run --example counter
$ cargo run --example hello
$ cargo run --example hello_button


Setting the scheme to Gtk:




Check the full code for the custom theming.

Setting the scheme to Gtk:







Different frame types which can be used with many different widgets such as Frame, Button widgets, In/Output widgets...etc.

Currently implemented types:

Image types:

  • SharedImage
  • BmpImage
  • JpegImage
  • GifImage
  • PngImage
  • SvgImage
  • Pixmap
  • RgbImage
  • XpmImage
  • XbmImage
  • PnmImage
  • TiledImage


  • Buttons
    • Button
    • RadioButton
    • ToggleButton
    • RoundButton
    • CheckButton
    • LightButton
    • RepeatButton
    • RadioLightButton
    • RadioRoundButton
  • Dialogs
    • Native FileDialog
    • FileChooser
    • HelpDialog
    • Message dialog
    • Alert dialog
    • Password dialog
    • Choice dialog
    • Input dialog
    • ColorChooser dialog
  • Frame (Fl_Box)
  • Windows
    • Window
    • SingleWindow
    • DoubleWindow
    • MenuWindow
    • GlWindow (requires the "enable-glwindow" flag)
  • Groups
    • Group
    • Pack
    • Tabs
    • Scroll
    • Tile
    • Wizard
    • ColorChooser
    • VGrind
    • HGrid
  • Text display widgets
    • TextDisplay
    • TextEditor
    • SimpleTerminal
  • Input widgets
    • Input
    • IntInput
    • FloatInput
    • MultilineInput
    • SecretInput
    • FileInput
  • Output widgets
    • Output
    • MultilineOutput
  • Menu widgets
    • MenuBar
    • MenuItem
    • Choice (dropdown list)
    • SysMenuBar (MacOS menu bar which appears at the top of the screen)
  • Valuator widgets
    • Slider
    • NiceSlider
    • ValueSlider
    • Dial
    • LineDial
    • Counter
    • Scrollbar
    • Roller
    • Adjuster
    • ValueInput
    • ValueOutput
    • FillSlider
    • FillDial
    • HorSlider (Horizontal slider)
    • HorFillSlider
    • HorNiceSlider
    • HorValueSlider
  • Browsing widgets
    • Browser
    • SelectBrowser
    • HoldBrowser
    • MultiBrowser
    • FileBrowser
    • CheckBrowser
  • Miscelaneous widgets
    • Spinner
    • Clock (Round and Square)
    • Chart (several chart types are available)
    • Progress (progress bar)
    • Tooltip
    • InputChoice
    • HelpView
  • Table widgets
    • Table
    • TableRow
  • Trees
    • Tree
    • TreeItem

Drawing primitives

(In the draw module)

Surface types:

  • Printer.
  • ImageSurface.
  • SvgFileSurface.


More videos in the playlist here. Some of the demo projects can be found here.