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#13 in Graphics APIs

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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.


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 schemes: Base, GTK, Plastic and Gleam), and additional theming using fltk-theme.
  • Provides around 80 customizable widgets.
  • Has inbuilt image support.

Here is a list of software using FLTK. For software using fltk-rs, check here.

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


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

fltk = "^1.2"

To use the latest changes in the repo:

fltk = { version = "^1.2", git = "https://github.com/fltk-rs/fltk-rs" }

To use the bundled libs (available for x64 windows (msvc & gnu (msys2-mingw)), x64 linux & macos):

fltk = { version = "^1.2", features = ["fltk-bundled"] }

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

An example hello world application:

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

fn main() {
    let app = 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::Button, frame::Frame, prelude::*, window::Window};

fn main() {
    let app = 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!")); // the closure capture is mutable borrow to our button

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)

use fltk::{button::Button, prelude::*};
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:

use fltk::{app, button::Button, frame::Frame, prelude::*, window::Window};
fn main() {
    let app = 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 */

Alternatively, you can use packs, columns, rows to layout your widgets (or the fltk-flex crate for flexbox layouts):

use fltk::{app, button::Button, frame::Frame, group::Pack, prelude::*, window::Window};
fn main() {
    let app = app::App::default();
    let mut wind = Window::default().with_size(160, 200).with_label("Counter");
    // Vertical is default. You can choose horizontal using pack.set_type(PackType::Horizontal);
    let mut pack = Pack::default().with_size(120, 140).center_of(&wind);
    let mut but_inc = Button::default().with_size(0, 40).with_label("+");
    let mut frame = Frame::default().with_size(0, 40).with_label("0");
    let mut but_dec = Button::default().with_size(0, 40).with_label("-");


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_but.set_callback(|this_button| this_button.set_label("Works"));

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();
        if let Some(msg) = r.recv() {
            match msg {
                Message::Increment => frame.set_label(&(label + 1).to_string()),
                Message::Decrement => frame.set_label(&(label - 1).to_string()),

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 |widget, ev: Event| {
        match ev {
            Event::Push => {
            /* other events to be handled */
            _ => false,

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.

For an alternative event handling mechanism using on_<event> methods, check the fltk-evented crate.


FLTK offers 4 application schemes:

  • Base
  • Gtk
  • Gleam
  • Plastic

(Additional theming can be found in the fltk-theme crate)

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

let app = app::App::default().with_scheme(app::Scheme::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

For default application colors, fltk-rs provides app::background(), app::background2() and app::foreground(). You can also specify the default application selection/inactive colors, font, label size, frame type, scrollbar size, menu linespacing. Additionally the fltk-theme crate offers some other predefined color maps (dark theme, tan etc) and widget themes which can be loaded into your application.


Rust (version > 1.45), CMake (version > 3.11), Git and a C++11 compiler need to be installed and in your PATH for a crossplatform build from source. Ninja is recommended, but not required, and will be used if found. This crate also offers a bundled form of fltk on selected x86_64 platforms (Windows (msvc and gnu), MacOS, Linux), this can be enabled using the fltk-bundled feature flag as mentioned in the usage section (this requires curl and tar to download and unpack the bundled libraries).

  • Windows: No external dependencies.
  • MacOS: No external dependencies.
  • Linux/BSD: X11 and OpenGL development headers need to be installed for development. The libraries themselves are normally available on linux/bsd 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 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

For Arch-based GUI distributions, that means running:

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

For Alpine linux:

$ apk add pango-dev fontconfig-dev libxinerama-dev libxfixes-dev libxcursor-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 libcerf pango cairo libGL mesa pkg-config


The following are the features offered by the crate:

  • no-pango: Build without pango support on Linux/BSD, if rtl/cjk font support is not needed.
  • fltk-bundled: Support for bundled versions of cfltk and fltk on selected platforms (requires curl and tar)
  • enable-glwindow: Support for drawing using OpenGL functions.
  • system-libpng: Uses the system libpng
  • system-libjpeg: Uses the system libjpeg
  • system-zlib: Uses the system zlib


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/fltk-rs/fltk-rs
$ cd fltk-rs
$ cargo build


To run the examples:

$ cargo run --example editor
$ cargo run --example calculator
$ cargo run --example calculator2
$ cargo run --example terminal
$ cargo run --example counter
$ cargo run --example hello
$ cargo run --example hello_button
$ cargo run --example fb
$ cargo run --example pong
$ cargo run --example custom_widgets
$ cargo run --example custom_dial

Using custom theming and also FLTK provided default schemes like Gtk:

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

More interesting examples can be found in the fltk-rs-demos repo. Also a nice implementation of the 7guis tasks can be found here. Various advanced examples can also be found here.

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 (single buffered)
    • DoubleWindow (double buffered)
    • MenuWindow
    • OverlayWindow
    • GlWindow (requires the "enable-glwindow" flag)
    • GlutWindow (requires the "enable-glwindow" flag)
  • Groups
    • Group
    • Pack (Horizontal and Vertical)
    • Tabs
    • Scroll
    • Tile
    • Wizard
    • ColorChooser
    • VGrid
    • HGrid
    • Column (vertical pack supporting auto layout)
    • Row (horizontal pack supporting auto layout)
    • Flex
  • 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
  • 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.

No runtime deps