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#15 in Graphics APIs

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Used in 23 crates (via fltk)

MIT license

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C++ 117K SLoC // 0.2% comments C 55K SLoC // 0.2% comments Rust 36K SLoC // 0.0% comments Objective-C++ 5K SLoC // 0.1% comments Shell 277 SLoC // 0.2% comments Objective-C 19 SLoC


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 = "^1.1"

To use the latest changes in the repo:

fltk = { version = "^1.1", 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 = "^1.1", features = ["fltk-bundled"] }

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, 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.


FLTK offers 4 application schemes:

  • Base
  • Gtk
  • Gleam
  • Plastic

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.


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.
  • 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


Rust (version > 1.45), 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 (win 10 x64, macos 10.15 x64, linux x64), this can be enabled using the fltk-bundled feature-flag (which 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 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 (experimental): 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/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 (Supports flexbox layouts, provided by the fltk-flex crate)
  • 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.

No runtime deps