new file mode 100644
--- /dev/null
+++ b/src/gtk.rs
@@ -0,0 +1,190 @@
+// Tablet emulator, for people who don’t own one
+// Copyright © 2020 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+use gio::prelude::*;
+use glib::clone;
+use gtk::prelude::*;
+
+use std::env::args;
+use std::io::ErrorKind;
+use std::sync::Arc;
+use input_linux::Key;
+
+use crate::{
+    state::State,
+    DEFAULT_WIDTH, DEFAULT_HEIGHT,
+};
+
+fn build_main_menu(application: &gtk::Application) {
+    let quit = gio::SimpleAction::new("quit", None);
+    application.set_accels_for_action("app.quit", &["<Control>q"]);
+    application.add_action(&quit);
+    quit.connect_activate(clone!(@weak application => move |_, _| application.quit()));
+
+    let about = gio::SimpleAction::new("about", None);
+    application.add_action(&about);
+    about.connect_activate(|_, _| {
+        let about = gtk::AboutDialog::new();
+        about.set_program_name("TabletEmu");
+        about.set_logo_icon_name(Some("input-tablet"));
+        about.set_website(Some("https://hg.linkmauve.fr/tablet-emu"));
+        about.set_version(Some("0.1"));
+        about.set_license_type(gtk::License::Agpl30);
+        about.set_copyright(Some("© 2020 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>"));
+        about.run();
+        unsafe {
+            about.destroy();
+        }
+    });
+
+    let menu = gio::Menu::new();
+    {
+        let file = gio::Menu::new();
+        file.append(Some("_Quit"), Some("app.quit"));
+        menu.append_submenu(Some("_File"), &file);
+    }
+    {
+        let help = gio::Menu::new();
+        help.append(Some("_About"), Some("app.about"));
+        menu.append_submenu(Some("_Help"), &help);
+    }
+    application.set_menubar(Some(&menu));
+}
+
+fn build_ui(application: &gtk::Application) {
+    build_main_menu(application);
+
+    let state = match State::new() {
+        Ok(state) => state,
+        Err(err) => {
+            match err.kind() {
+                ErrorKind::NotFound => {
+                    eprintln!("Couldn’t find /dev/uinput: {}", err);
+                    eprintln!("Maybe you forgot to `modprobe uinput`?");
+                }
+                ErrorKind::PermissionDenied => {
+                    eprintln!("Couldn’t open /dev/uinput for writing: {}", err);
+                    eprintln!("Maybe you aren’t allowed to create input devices?");
+                }
+                _ => eprintln!("Couldn’t open /dev/uinput for writing: {}", err),
+            }
+            std::process::exit(1);
+        }
+    };
+
+    let window = gtk::ApplicationWindow::new(application);
+    window.set_title("tablet-emu");
+    window.set_position(gtk::WindowPosition::Center);
+
+    let hbox = gtk::Box::new(gtk::Orientation::Horizontal, 0);
+    let tools_box = gtk::Box::new(gtk::Orientation::Vertical, 0);
+
+    macro_rules! impl_tool {
+        ($tool:tt) => {
+            let tool = gtk::Button::with_mnemonic($tool);
+            let state_weak = Arc::downgrade(&state);
+            tool.connect_clicked(move |b| {
+                let state = state_weak.upgrade().unwrap();
+                let mut state = state.lock().unwrap();
+                let tool = match b.get_label().unwrap().as_str() {
+                    "_Pen" => Key::ButtonToolPen,
+                    "_Rubber" => Key::ButtonToolRubber,
+                    "_Brush" => Key::ButtonToolBrush,
+                    "P_encil" => Key::ButtonToolPencil,
+                    "_Airbrush" => Key::ButtonToolAirbrush,
+                    _ => unreachable!(),
+                };
+                state.select_tool(tool);
+            });
+            tools_box.add(&tool);
+        };
+    };
+    impl_tool!("_Pen");
+    impl_tool!("_Rubber");
+    impl_tool!("_Brush");
+    impl_tool!("P_encil");
+    impl_tool!("_Airbrush");
+
+    let drawing_area = gtk::DrawingArea::new();
+    drawing_area.set_size_request(DEFAULT_WIDTH, DEFAULT_HEIGHT);
+    drawing_area.set_hexpand(true);
+    drawing_area.set_events(
+        gdk::EventMask::BUTTON_PRESS_MASK
+            | gdk::EventMask::BUTTON_RELEASE_MASK
+            | gdk::EventMask::POINTER_MOTION_MASK,
+    );
+    let state_weak = Arc::downgrade(&state);
+    drawing_area.connect_configure_event(move |_, event| {
+        let state = state_weak.upgrade().unwrap();
+        let mut state = state.lock().unwrap();
+        state.set_size(event.get_size());
+        true
+    });
+    let state_weak = Arc::downgrade(&state);
+    drawing_area.connect_button_press_event(move |_, event| {
+        if event.get_button() != 1 {
+            return Inhibit(false);
+        }
+
+        let state = state_weak.upgrade().unwrap();
+        let mut state = state.lock().unwrap();
+        let (x, y) = event.get_position();
+        state.press(x, y).unwrap();
+        Inhibit(false)
+    });
+    let state_weak = Arc::downgrade(&state);
+    drawing_area.connect_button_release_event(move |_, event| {
+        if event.get_button() != 1 {
+            return Inhibit(false);
+        }
+
+        let state = state_weak.upgrade().unwrap();
+        let mut state = state.lock().unwrap();
+        let (x, y) = event.get_position();
+        state.release(x, y).unwrap();
+        Inhibit(false)
+    });
+    drawing_area.connect_motion_notify_event(move |_, event| {
+        let mut state = state.lock().unwrap();
+        let (x, y) = event.get_position();
+        state.motion(x, y).unwrap();
+        Inhibit(false)
+    });
+    drawing_area.connect_draw(move |_, ctx| {
+        //println!("drawing {}", drawing_area);
+        ctx.set_source_rgb(1., 0., 0.);
+        ctx.set_operator(cairo::Operator::Screen);
+        ctx.paint();
+        Inhibit(false)
+    });
+
+    hbox.add(&tools_box);
+    hbox.add(&drawing_area);
+
+    window.add(&hbox);
+
+    window.show_all();
+}
+
+pub fn main() {
+    let application = gtk::Application::new(
+        Some("fr.linkmauve.TabletEmu"),
+        gio::ApplicationFlags::empty(),
+    )
+    .expect("Initialisation failed…");
+    application.connect_activate(build_ui);
+    application.run(&args().collect::<Vec<_>>());
+}