diff --git a/Cargo.toml b/Cargo.toml
index c787c72..c526313 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,9 +5,14 @@ edition = "2021"
 
 [dependencies]
 cascade = "1"
+derivative = "2"
 gdk4 = "0.3.1"
+gdk4-wayland = { version = "0.3", optional = true }
 gdk4-x11 = "0.3.0"
 gio = "0.14.8"
+gobject-sys = "0.14.0"
+wayland-client = { version = "0.28", optional = true }
+wayland-protocols = { version = "0.28", features = [ "client", "unstable_protocols" ], optional = true }
 x11 = { version = "2", features = ["xlib"] }
 
 # examples
@@ -27,10 +32,12 @@ zvariant = "3.0.0"
 zvariant_derive = "3.0.0"
 
 [dependencies.gtk4]
-package = "gtk4"
+version = "0.3"
 features = ["v4_4"]
 
 [profile.release]
 incremental = true
 debug = 1
 
+[features]
+layer-shell = ["gdk4-wayland", "wayland-client", "wayland-protocols"]
diff --git a/src/deref_cell.rs b/src/deref_cell.rs
new file mode 100644
index 0000000..d29cf10
--- /dev/null
+++ b/src/deref_cell.rs
@@ -0,0 +1,33 @@
+#![allow(dead_code)]
+
+use once_cell::unsync::OnceCell;
+
+/// Wrapper around `OnceCell` implementing `Deref`, and thus also panicking
+/// when not set (or set twice).
+///
+/// To be used in place of `gtk::TemplateChild`, but without xml.
+pub struct DerefCell<T>(OnceCell<T>);
+
+impl<T> DerefCell<T> {
+    #[track_caller]
+    pub fn set(&self, value: T) {
+        if self.0.set(value).is_err() {
+            panic!("Initialized twice");
+        }
+    }
+}
+
+impl<T> Default for DerefCell<T> {
+    fn default() -> Self {
+        Self(OnceCell::default())
+    }
+}
+
+impl<T> std::ops::Deref for DerefCell<T> {
+    type Target = T;
+
+    #[track_caller]
+    fn deref(&self) -> &T {
+        self.0.get().unwrap()
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 7a788f2..70ef094 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1,6 @@
+mod deref_cell;
+#[cfg(feature = "layer-shell")]
+pub mod wayland;
+#[cfg(feature = "layer-shell")]
+mod wayland_custom_surface;
 pub mod x;
diff --git a/src/wayland.rs b/src/wayland.rs
new file mode 100644
index 0000000..065147e
--- /dev/null
+++ b/src/wayland.rs
@@ -0,0 +1,563 @@
+// TODO: scale-factor?
+
+use derivative::Derivative;
+use gdk4_wayland::prelude::*;
+use gtk4::{
+    cairo, gdk,
+    glib::{self, clone, subclass::prelude::*, translate::*},
+    gsk::{self, traits::RendererExt},
+    prelude::*,
+    subclass::prelude::*,
+};
+use std::{
+    cell::{Cell, RefCell},
+    os::raw::c_int,
+    ptr,
+    rc::Rc,
+};
+use wayland_client::{event_enum, sys::client::wl_proxy, Filter, GlobalManager, Main, Proxy};
+use wayland_protocols::{
+    wlr::unstable::layer_shell::v1::client::{zwlr_layer_shell_v1, zwlr_layer_surface_v1},
+    xdg_shell::client::xdg_popup,
+};
+
+use crate::{deref_cell::DerefCell, wayland_custom_surface::WaylandCustomSurface};
+
+pub use wayland_protocols::wlr::unstable::layer_shell::v1::client::{
+    zwlr_layer_shell_v1::Layer,
+    zwlr_layer_surface_v1::{Anchor, KeyboardInteractivity},
+};
+
+event_enum!(
+    Events |
+    LayerSurface => zwlr_layer_surface_v1::ZwlrLayerSurfaceV1
+);
+
+struct CosmicWaylandDisplay {
+    event_queue: RefCell<wayland_client::EventQueue>,
+    wayland_display: wayland_client::Display,
+    wlr_layer_shell: Option<Main<zwlr_layer_shell_v1::ZwlrLayerShellV1>>,
+}
+
+impl CosmicWaylandDisplay {
+    fn for_display(display: &gdk4_wayland::WaylandDisplay) -> Rc<Self> {
+        const DATA_KEY: &str = "cosmic-wayland-display";
+
+        // `GdkWaylandDisplay` already associated with a `CosmicWaylandDisplay`
+        if let Some(data) = unsafe { display.data::<Rc<Self>>(DATA_KEY) } {
+            return unsafe { data.as_ref() }.clone();
+        }
+
+        let wayland_display = unsafe {
+            wayland_client::Display::from_external_display(
+                display.wl_display().as_ref().c_ptr() as *mut _
+            )
+        }; // XXX is this sound?
+
+        let mut event_queue = wayland_display.create_event_queue();
+        let attached_display = wayland_display.attach(event_queue.token());
+        let globals = GlobalManager::new(&attached_display);
+
+        event_queue.sync_roundtrip(&mut (), |_, _, _| {}).unwrap();
+
+        let wlr_layer_shell = globals
+            .instantiate_exact::<zwlr_layer_shell_v1::ZwlrLayerShellV1>(1)
+            .ok();
+
+        let cosmic_wayland_display = Rc::new(Self {
+            event_queue: RefCell::new(event_queue),
+            wayland_display,
+            wlr_layer_shell,
+        });
+
+        unsafe { display.set_data(DATA_KEY, cosmic_wayland_display.clone()) };
+
+        // XXX Efficient way to poll?
+        // XXX unwrap?
+        glib::idle_add_local(
+            clone!(@weak cosmic_wayland_display => @default-return Continue(false), move || {
+                cosmic_wayland_display.wayland_display.flush().unwrap();
+                let mut event_queue = cosmic_wayland_display.event_queue.borrow_mut();
+                if let Some(guard) = event_queue.prepare_read() {
+                    guard.read_events().unwrap();
+                }
+                event_queue.dispatch_pending(&mut (), |_, _, _| {}).unwrap();
+                Continue(true)
+            }),
+        );
+
+        cosmic_wayland_display
+    }
+}
+
+#[derive(Derivative)]
+#[derivative(Default)]
+pub struct LayerShellWindowInner {
+    display: DerefCell<gdk4_wayland::WaylandDisplay>,
+    surface: RefCell<Option<WaylandCustomSurface>>,
+    renderer: RefCell<Option<gsk::Renderer>>,
+    wlr_layer_surface: RefCell<Option<Main<zwlr_layer_surface_v1::ZwlrLayerSurfaceV1>>>,
+    constraint_solver: DerefCell<ConstraintSolver>,
+    child: RefCell<Option<gtk4::Widget>>,
+    monitor: DerefCell<Option<gdk4_wayland::WaylandMonitor>>,
+    #[derivative(Default(value = "Cell::new(Layer::Background)"))]
+    layer: Cell<Layer>,
+    #[derivative(Default(value = "Cell::new(Anchor::empty())"))]
+    anchor: Cell<Anchor>,
+    exclusive_zone: Cell<i32>,
+    margin: Cell<(i32, i32, i32, i32)>,
+    #[derivative(Default(value = "Cell::new(KeyboardInteractivity::None)"))]
+    keyboard_interactivity: Cell<KeyboardInteractivity>,
+    namespace: DerefCell<String>,
+    focus_widget: RefCell<Option<gtk4::Widget>>,
+}
+
+#[glib::object_subclass]
+impl ObjectSubclass for LayerShellWindowInner {
+    const NAME: &'static str = "S76CosmicLayerShellWindow";
+    type ParentType = gtk4::Widget;
+    type Interfaces = (gtk4::Native, gtk4::Root);
+    type Type = LayerShellWindow;
+}
+
+impl ObjectImpl for LayerShellWindowInner {
+    fn constructed(&self, obj: &Self::Type) {
+        self.display
+            .set(gdk::Display::default().unwrap().downcast().unwrap()); // XXX any issue unwrapping?
+        self.constraint_solver.set(glib::Object::new(&[]).unwrap());
+
+        obj.add_css_class("background");
+    }
+}
+
+impl WidgetImpl for LayerShellWindowInner {
+    fn realize(&self, widget: &Self::Type) {
+        let surface = WaylandCustomSurface::new(&*self.display);
+        surface.set_get_popup_func(Some(Box::new(clone!(@strong widget => move |_surface, popup| {
+            if let Some(wlr_layer_surface) = widget.inner().wlr_layer_surface.borrow().as_ref() {
+                let xdg_popup: xdg_popup::XdgPopup =
+                    unsafe { Proxy::from_c_ptr(gdk_wayland_popup_get_xdg_popup(popup.to_glib_none().0)).into() };
+                wlr_layer_surface.get_popup(&xdg_popup);
+            }
+            true
+        }))));
+        widget.layer_shell_init(&surface);
+
+        let widget_ptr: *mut _ = widget.to_glib_none().0;
+        let surface_ptr: *mut _ = surface.to_glib_none().0;
+        unsafe { gdk_surface_set_widget(surface_ptr as *mut _, widget_ptr as *mut _) };
+        *self.surface.borrow_mut() = Some(surface.clone());
+        surface.connect_render(move |_surface, region| {
+            unsafe {
+                gtk_widget_render(
+                    widget_ptr as *mut _,
+                    surface_ptr as *mut _,
+                    region.to_glib_none().0,
+                )
+            };
+            true
+        });
+        surface.connect_event(|_, event| {
+            unsafe { gtk_main_do_event(event.to_glib_none().0) };
+            true
+        });
+
+        self.parent_realize(widget);
+
+        *self.renderer.borrow_mut() =
+            Some(gsk::Renderer::for_surface(surface.upcast_ref()).unwrap()); // XXX unwrap?
+
+        unsafe { gtk4::ffi::gtk_native_realize(widget_ptr as *mut _) };
+    }
+
+    fn unrealize(&self, widget: &Self::Type) {
+        let widget_ptr: *mut Self::Instance = widget.to_glib_none().0;
+
+        unsafe { gtk4::ffi::gtk_native_unrealize(widget_ptr as *mut _) };
+
+        self.parent_unrealize(widget);
+
+        if let Some(renderer) = self.renderer.borrow_mut().take() {
+            renderer.unrealize();
+        }
+
+        if let Some(surface) = self.surface.borrow().as_ref() {
+            let surface_ptr: *mut _ = surface.to_glib_none().0;
+            unsafe { gdk_surface_set_widget(surface_ptr as *mut _, ptr::null_mut()) };
+        }
+    }
+
+    fn map(&self, widget: &Self::Type) {
+        if let Some(surface) = self.surface.borrow().as_ref() {
+            let width = widget.measure(gtk4::Orientation::Horizontal, -1).1;
+            let height = widget.measure(gtk4::Orientation::Vertical, width).1;
+            widget.set_size(width as u32, height as u32);
+            surface.present(width, height);
+        }
+
+        self.parent_map(widget);
+
+        if let Some(child) = self.child.borrow().as_ref() {
+            child.map();
+        }
+    }
+
+    fn unmap(&self, widget: &Self::Type) {
+        self.parent_unmap(widget);
+
+        if let Some(surface) = self.surface.borrow().as_ref() {
+            surface.hide();
+        }
+
+        if let Some(child) = self.child.borrow().as_ref() {
+            child.unmap();
+        }
+    }
+
+    fn measure(
+        &self,
+        _widget: &Self::Type,
+        orientation: gtk4::Orientation,
+        for_size: i32,
+    ) -> (i32, i32, i32, i32) {
+        if let Some(child) = self.child.borrow().as_ref() {
+            child.measure(orientation, for_size)
+        } else {
+            (0, 0, 0, 0)
+        }
+    }
+
+    fn size_allocate(&self, _widget: &Self::Type, width: i32, height: i32, baseline: i32) {
+        if let Some(child) = self.child.borrow().as_ref() {
+            child.allocate(width, height, baseline, None)
+        }
+    }
+
+    fn show(&self, widget: &Self::Type) {
+        widget.realize();
+        self.parent_show(widget);
+        widget.map();
+    }
+
+    fn hide(&self, widget: &Self::Type) {
+        self.parent_hide(widget);
+        widget.unmap();
+    }
+}
+
+// TODO: Move into gtk4-rs when support merged/released in gtk
+unsafe impl IsImplementable<LayerShellWindowInner> for gtk4::Native {
+    fn interface_init(iface: &mut glib::Interface<Self>) {
+        let iface = unsafe { &mut *(iface as *mut _ as *mut GtkNativeInterface) };
+        iface.get_surface = Some(get_surface);
+        iface.get_renderer = Some(get_renderer);
+        iface.get_surface_transform = Some(get_surface_transform);
+        iface.layout = Some(layout);
+    }
+
+    fn instance_init(_instance: &mut glib::subclass::InitializingObject<LayerShellWindowInner>) {}
+}
+
+// TODO: Move into gtk4-rs when support merged/released in gtk
+unsafe impl IsImplementable<LayerShellWindowInner> for gtk4::Root {
+    fn interface_init(iface: &mut glib::Interface<Self>) {
+        let iface = unsafe { &mut *(iface as *mut _ as *mut GtkRootInterface) };
+        iface.get_display = Some(get_display);
+        iface.get_constraint_solver = Some(get_constraint_solver);
+        iface.get_focus = Some(get_focus);
+        iface.set_focus = Some(set_focus);
+    }
+
+    fn instance_init(_instance: &mut glib::subclass::InitializingObject<LayerShellWindowInner>) {}
+}
+
+glib::wrapper! {
+    pub struct LayerShellWindow(ObjectSubclass<LayerShellWindowInner>)
+        @extends gtk4::Widget, @implements gtk4::Accessible, gtk4::Buildable, gtk4::ConstraintTarget, gtk4::Native, gtk4::Root;
+}
+// TODO handle configure/destroy
+// TODO presumably call destroy() when appropriate?
+// What do wayland-client types do when associated connection is gone? Panic? UB?
+impl LayerShellWindow {
+    pub fn new(
+        monitor: Option<&gdk4_wayland::WaylandMonitor>,
+        layer: Layer,
+        namespace: &str,
+    ) -> Self {
+        let obj: Self = glib::Object::new(&[]).unwrap();
+        obj.inner().monitor.set(monitor.cloned());
+        obj.inner().layer.set(layer);
+        obj.inner().namespace.set(namespace.to_string());
+        obj
+    }
+
+    fn inner(&self) -> &LayerShellWindowInner {
+        LayerShellWindowInner::from_instance(self)
+    }
+
+    pub fn set_child<T: IsA<gtk4::Widget>>(&self, w: Option<&T>) {
+        let mut child = self.inner().child.borrow_mut();
+        if let Some(child) = child.take() {
+            child.unparent();
+        }
+        if let Some(w) = w {
+            w.set_parent(self);
+        }
+        *child = w.map(|x| x.clone().upcast());
+    }
+
+    fn layer_shell_init(&self, surface: &WaylandCustomSurface) {
+        let width = self.measure(gtk4::Orientation::Horizontal, -1).1;
+        let height = self.measure(gtk4::Orientation::Vertical, width).1;
+        // XXX needed for wl_surface to exist
+        surface.present(width, height);
+
+        let wl_surface = surface.wl_surface();
+
+        let cosmic_wayland_display = CosmicWaylandDisplay::for_display(&*self.inner().display);
+        let wlr_layer_shell = match cosmic_wayland_display.wlr_layer_shell.as_ref() {
+            Some(wlr_layer_shell) => wlr_layer_shell,
+            None => {
+                eprintln!("Error: Layer shell not supported by compositor");
+                return;
+            }
+        };
+
+        let output = self.inner().monitor.as_ref().map(|x| x.wl_output());
+        let layer = self.layer();
+        let namespace = self.namespace().to_string();
+        let wlr_layer_surface =
+            wlr_layer_shell.get_layer_surface(&wl_surface, output.as_ref(), layer, namespace);
+
+        wlr_layer_surface.set_anchor(self.anchor());
+        wlr_layer_surface.set_exclusive_zone(self.exclusive_zone());
+        let margin = self.margin();
+        wlr_layer_surface.set_margin(margin.0, margin.1, margin.2, margin.3);
+        wlr_layer_surface.set_keyboard_interactivity(self.keyboard_interactivity());
+        wlr_layer_surface.set_size(width as u32, height as u32);
+
+        let filter = Filter::new(
+            clone!(@strong self as self_ => move |event, _, _| match event {
+                Events::LayerSurface { event, object } => match event {
+                    zwlr_layer_surface_v1::Event::Configure {
+                        serial,
+                        width: _,
+                        height: _,
+                    } => {
+                        // TODO: should size window to match `width`/`height`
+                        object.ack_configure(serial);
+                    }
+                    zwlr_layer_surface_v1::Event::Closed => {}
+                    _ => {}
+                },
+            }),
+        );
+        wlr_layer_surface.assign(filter);
+
+        wl_surface.commit();
+
+        cosmic_wayland_display
+            .event_queue
+            .borrow_mut()
+            .sync_roundtrip(&mut (), |_, _, _| {})
+            .unwrap();
+
+        *self.inner().wlr_layer_surface.borrow_mut() = Some(wlr_layer_surface);
+    }
+
+    fn set_size(&self, width: u32, height: u32) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_size(width, height);
+        };
+    }
+
+    pub fn anchor(&self) -> Anchor {
+        self.inner().anchor.get()
+    }
+
+    pub fn set_anchor(&self, anchor: Anchor) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_anchor(anchor);
+        };
+        self.inner().anchor.set(anchor);
+    }
+
+    pub fn exclusive_zone(&self) -> i32 {
+        self.inner().exclusive_zone.get()
+    }
+
+    pub fn set_exclusive_zone(&self, zone: i32) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_exclusive_zone(zone);
+        };
+        self.inner().exclusive_zone.set(zone);
+    }
+
+    pub fn margin(&self) -> (i32, i32, i32, i32) {
+        self.inner().margin.get()
+    }
+
+    pub fn set_margin(&self, top: i32, right: i32, bottom: i32, left: i32) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_margin(top, right, bottom, left);
+        };
+        self.inner().margin.set((top, right, bottom, left));
+    }
+
+    pub fn keyboard_interactivity(&self) -> KeyboardInteractivity {
+        self.inner().keyboard_interactivity.get()
+    }
+
+    pub fn set_keyboard_interactivity(&self, interactivity: KeyboardInteractivity) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_keyboard_interactivity(interactivity);
+        };
+        self.inner().keyboard_interactivity.set(interactivity);
+    }
+
+    pub fn layer(&self) -> Layer {
+        self.inner().layer.get()
+    }
+
+    pub fn set_layer(&self, layer: Layer) {
+        if let Some(wlr_layer_surface) = self.inner().wlr_layer_surface.borrow().as_ref() {
+            wlr_layer_surface.set_layer(layer);
+        };
+        self.inner().layer.set(layer);
+    }
+
+    pub fn namespace(&self) -> &str {
+        self.inner().namespace.as_str()
+    }
+}
+
+pub struct GtkConstraintSolver {
+    _private: [u8; 0],
+}
+
+// XXX needs to be public in gtk
+#[link(name = "gtk-4")]
+extern "C" {
+    pub fn gtk_constraint_solver_get_type() -> glib::ffi::GType;
+
+    pub fn gdk_surface_set_widget(surface: *mut gdk::ffi::GdkSurface, widget: glib::ffi::gpointer);
+
+    pub fn _gtk_widget_set_visible_flag(
+        widget: *mut gtk4::ffi::GtkWidget,
+        visible: glib::ffi::gboolean,
+    );
+
+    pub fn gtk_widget_render(
+        widget: *mut gtk4::ffi::GtkWidget,
+        surface: *mut gdk::ffi::GdkSurface,
+        region: *const cairo::ffi::cairo_region_t,
+    );
+
+    pub fn gtk_main_do_event(event: *mut gdk::ffi::GdkEvent);
+
+    // Added API
+    pub fn gdk_wayland_popup_get_xdg_popup(
+        popup: *mut gdk4_wayland::ffi::GdkWaylandPopup,
+    ) -> *mut wl_proxy;
+}
+
+glib::wrapper! {
+    pub struct ConstraintSolver(Object<GtkConstraintSolver>);
+
+    match fn {
+        type_ => || gtk_constraint_solver_get_type(),
+    }
+}
+
+pub struct GtkNativeInterface {
+    pub g_iface: gobject_sys::GTypeInterface,
+    pub get_surface:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkNative) -> *mut gdk::ffi::GdkSurface>,
+    pub get_renderer: Option<
+        unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkNative) -> *mut gsk::ffi::GskRenderer,
+    >,
+    pub get_surface_transform:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkNative, x: *mut f64, y: *mut f64)>,
+    pub layout:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkNative, width: c_int, height: c_int)>,
+}
+
+pub struct GtkRootInterface {
+    pub g_iface: gobject_sys::GTypeInterface,
+    pub get_display:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkRoot) -> *mut gdk::ffi::GdkDisplay>,
+    pub get_constraint_solver:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkRoot) -> *mut GtkConstraintSolver>,
+    pub get_focus:
+        Option<unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkRoot) -> *mut gtk4::ffi::GtkWidget>,
+    pub set_focus: Option<
+        unsafe extern "C" fn(self_: *mut gtk4::ffi::GtkRoot, focus: *mut gtk4::ffi::GtkWidget),
+    >,
+}
+
+unsafe extern "C" fn get_surface(native: *mut gtk4::ffi::GtkNative) -> *mut gdk::ffi::GdkSurface {
+    let instance = &*(native as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    imp.surface.borrow().as_ref().map_or(ptr::null_mut(), |x| {
+        x.upcast_ref::<gdk::Surface>().to_glib_none().0
+    })
+}
+
+unsafe extern "C" fn get_renderer(native: *mut gtk4::ffi::GtkNative) -> *mut gsk::ffi::GskRenderer {
+    let instance = &*(native as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    imp.renderer
+        .borrow()
+        .as_ref()
+        .map_or(ptr::null_mut(), |x| x.to_glib_none().0)
+}
+
+unsafe extern "C" fn get_surface_transform(
+    _native: *mut gtk4::ffi::GtkNative,
+    x: *mut f64,
+    y: *mut f64,
+) {
+    // TODO: add css logic like `GtkWindow` has
+
+    *x = 0.;
+    *y = 0.;
+}
+
+unsafe extern "C" fn layout(native: *mut gtk4::ffi::GtkNative, width: c_int, height: c_int) {
+    // TODO: `GtkWindow` has more here
+    gtk4::ffi::gtk_widget_allocate(native as *mut _, width, height, -1, ptr::null_mut());
+}
+
+unsafe extern "C" fn get_display(root: *mut gtk4::ffi::GtkRoot) -> *mut gdk::ffi::GdkDisplay {
+    let instance = &*(root as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    imp.display.upcast_ref::<gdk::Display>().to_glib_none().0
+}
+
+unsafe extern "C" fn get_constraint_solver(
+    root: *mut gtk4::ffi::GtkRoot,
+) -> *mut GtkConstraintSolver {
+    let instance = &*(root as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    imp.constraint_solver.to_glib_none().0
+}
+
+unsafe extern "C" fn get_focus(root: *mut gtk4::ffi::GtkRoot) -> *mut gtk4::ffi::GtkWidget {
+    let instance = &*(root as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    imp.focus_widget
+        .borrow()
+        .as_ref()
+        .map_or(ptr::null_mut(), |x| x.to_glib_none().0)
+}
+
+unsafe extern "C" fn set_focus(root: *mut gtk4::ffi::GtkRoot, focus: *mut gtk4::ffi::GtkWidget) {
+    // TODO: `GtkWindow` does more here
+    let instance = &*(root as *mut <LayerShellWindowInner as ObjectSubclass>::Instance);
+    let imp = instance.impl_();
+    *imp.focus_widget.borrow_mut() = if focus.is_null() {
+        None
+    } else {
+        Some(gtk4::Widget::from_glib_none(focus))
+    };
+}
diff --git a/src/wayland_custom_surface.rs b/src/wayland_custom_surface.rs
new file mode 100644
index 0000000..fceb4cb
--- /dev/null
+++ b/src/wayland_custom_surface.rs
@@ -0,0 +1,144 @@
+use gdk4_wayland::{WaylandDisplay, WaylandPopup};
+use gtk4::{
+    gdk,
+    glib::{self, translate::*},
+};
+use std::boxed::Box as Box_;
+use std::fmt;
+
+mod ffi {
+    use gdk4_wayland::ffi::{GdkWaylandDisplay, GdkWaylandPopup};
+    use gtk4::{
+        gdk::ffi::GdkFrameClock,
+        glib::ffi::{gboolean, gpointer, GDestroyNotify, GType},
+    };
+    use std::os::raw::c_int;
+
+    pub type GdkWaylandCustomSurfaceGetPopupFunc = Option<
+        unsafe extern "C" fn(
+            *mut GdkWaylandCustomSurface,
+            *mut GdkWaylandPopup,
+            gpointer,
+        ) -> gboolean,
+    >;
+
+    #[repr(C)]
+    pub struct GdkWaylandCustomSurface {
+        _data: [u8; 0],
+        _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
+    }
+
+    impl ::std::fmt::Debug for GdkWaylandCustomSurface {
+        fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            f.debug_struct(&format!("GdkWaylandCustomSurface @ {:p}", self))
+                .finish()
+        }
+    }
+
+    extern "C" {
+        pub fn gdk_wayland_custom_surface_get_type() -> GType;
+
+        pub fn gdk_wayland_custom_surface_new(
+            display: *mut GdkWaylandDisplay,
+        ) -> *mut GdkWaylandCustomSurface;
+
+        pub fn gdk_wayland_custom_surface_present(
+            custom_surface: *mut GdkWaylandCustomSurface,
+            width: c_int,
+            height: c_int,
+        );
+
+        pub fn gdk_wayland_custom_surface_set_get_popup_func(
+            custom_surface: *mut GdkWaylandCustomSurface,
+            get_popup_func: GdkWaylandCustomSurfaceGetPopupFunc,
+            user_data: gpointer,
+            destroy: GDestroyNotify,
+        );
+
+        pub fn _gdk_frame_clock_idle_new() -> *mut GdkFrameClock;
+    }
+}
+
+glib::wrapper! {
+    #[doc(alias = "GdkWaylandCustomSurface")]
+    pub struct WaylandCustomSurface(Object<ffi::GdkWaylandCustomSurface>) @extends gdk4_wayland::WaylandSurface, gdk::Surface;
+
+    match fn {
+        type_ => || ffi::gdk_wayland_custom_surface_get_type(),
+    }
+}
+
+impl WaylandCustomSurface {
+    #[doc(alias = "gdk_wayland_custom_surface_new")]
+    pub fn new(display: &WaylandDisplay) -> WaylandCustomSurface {
+        unsafe {
+            from_glib_full(ffi::gdk_wayland_custom_surface_new(
+                display.to_glib_none().0,
+            ))
+        }
+    }
+
+    #[doc(alias = "gdk_wayland_custom_surface_present")]
+    pub fn present(&self, width: i32, height: i32) {
+        unsafe {
+            ffi::gdk_wayland_custom_surface_present(self.to_glib_none().0, width, height);
+        }
+    }
+
+    #[doc(alias = "gdk_wayland_custom_surface_set_get_popup_func")]
+    pub fn set_get_popup_func(
+        &self,
+        get_popup_func: Option<
+            Box_<dyn Fn(&WaylandCustomSurface, &WaylandPopup) -> bool + 'static>,
+        >,
+    ) {
+        let get_popup_func_data: Box_<
+            Option<Box_<dyn Fn(&WaylandCustomSurface, &WaylandPopup) -> bool + 'static>>,
+        > = Box_::new(get_popup_func);
+        unsafe extern "C" fn get_popup_func_func(
+            custom_surface: *mut ffi::GdkWaylandCustomSurface,
+            popup: *mut gdk4_wayland::ffi::GdkWaylandPopup,
+            user_data: glib::ffi::gpointer,
+        ) -> glib::ffi::gboolean {
+            let custom_surface = from_glib_borrow(custom_surface);
+            let popup = from_glib_borrow(popup);
+            let callback: &Option<
+                Box_<dyn Fn(&WaylandCustomSurface, &WaylandPopup) -> bool + 'static>,
+            > = &*(user_data as *mut _);
+            let res = if let Some(ref callback) = *callback {
+                callback(&custom_surface, &popup)
+            } else {
+                panic!("cannot get closure...")
+            };
+            res.into_glib()
+        }
+        let get_popup_func = if get_popup_func_data.is_some() {
+            Some(get_popup_func_func as _)
+        } else {
+            None
+        };
+        unsafe extern "C" fn destroy_func(data: glib::ffi::gpointer) {
+            let _callback: Box_<
+                Option<Box_<dyn Fn(&WaylandCustomSurface, &WaylandPopup) -> bool + 'static>>,
+            > = Box_::from_raw(data as *mut _);
+        }
+        let destroy_call3 = Some(destroy_func as _);
+        let super_callback0: Box_<
+            Option<Box_<dyn Fn(&WaylandCustomSurface, &WaylandPopup) -> bool + 'static>>,
+        > = get_popup_func_data;
+        unsafe {
+            ffi::gdk_wayland_custom_surface_set_get_popup_func(
+                self.to_glib_none().0,
+                get_popup_func,
+                Box_::into_raw(super_callback0) as *mut _,
+                destroy_call3,
+            );
+        }
+    }
+}
+
+impl fmt::Display for WaylandCustomSurface {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("WaylandCustomSurface")
+    }
+}