On Wayland, use frame callbacks to throttle RedrawRequested

Throttle RedrawRequested events by the frame callbacks, so the users
could render at the display refresh rate.

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On Wayland, use frame callbacks to throttle `RedrawRequested` events so redraws will align with compositor.
 - Add `Window::pre_present_notify` to notify winit before presenting to the windowing system.
 - On Windows, added `WindowBuilderExtWindows::with_class_name` to customize the internal class name.
 - **Breaking:** Remove lifetime parameter from `Event` and `WindowEvent`.

src/platform_impl/linux/wayland/event_loop/mod.rs

@@ -32,6 +32,7 @@ pub use proxy::EventLoopProxy;
 use sink::EventSink;
 
 use super::state::{WindowCompositorUpdate, WinitState};
+use super::window::state::FrameCallbackState;
 use super::{DeviceId, WindowId};
 
 type WaylandDispatcher = calloop::Dispatcher<'static, WaylandSource<WinitState>, WinitState>;
@@ -494,22 +495,29 @@ impl<T: 'static> EventLoop<T> {
                     mem::drop(state.windows.get_mut().remove(&window_id));
                     false
                 } else {
-                    let mut redraw_requested = window_requests
-                        .get(&window_id)
-                        .unwrap()
-                        .take_redraw_requested();
-
-                    // Redraw the frames while at it.
-                    redraw_requested |= state
+                    let mut window = state
                         .windows
                         .get_mut()
                         .get_mut(&window_id)
                         .unwrap()
                         .lock()
-                        .unwrap()
-                        .refresh_frame();
+                        .unwrap();
 
-                    redraw_requested
+                    if window.frame_callback_state() == FrameCallbackState::Requested {
+                        false
+                    } else {
+                        // Reset the frame callbacks state.
+                        window.frame_callback_reset();
+                        let mut redraw_requested = window_requests
+                            .get(&window_id)
+                            .unwrap()
+                            .take_redraw_requested();
+
+                        // Redraw the frame while at it.
+                        redraw_requested |= window.refresh_frame();
+
+                        redraw_requested
+                    }
                 }
             });
 

src/platform_impl/linux/wayland/state.rs

@@ -321,7 +321,15 @@ impl CompositorHandler for WinitState {
         self.scale_factor_changed(surface, scale_factor as f64, true)
     }
 
-    fn frame(&mut self, _: &Connection, _: &QueueHandle<Self>, _: &WlSurface, _: u32) {}
+    fn frame(&mut self, _: &Connection, _: &QueueHandle<Self>, surface: &WlSurface, _: u32) {
+        let window_id = super::make_wid(surface);
+        let window = match self.windows.get_mut().get(&window_id) {
+            Some(window) => window,
+            None => return,
+        };
+
+        window.lock().unwrap().frame_callback_received();
+    }
 }
 
 impl ProvidesRegistryState for WinitState {

src/platform_impl/linux/wayland/window/mod.rs

@@ -38,7 +38,7 @@ use super::state::WinitState;
 use super::types::xdg_activation::XdgActivationTokenData;
 use super::{EventLoopWindowTarget, WindowId};
 
-mod state;
+pub(crate) mod state;
 
 pub use state::WindowState;
 
@@ -295,7 +295,7 @@ impl Window {
 
     #[inline]
     pub fn pre_present_notify(&self) {
-        // TODO
+        self.window_state.lock().unwrap().request_frame_callback();
     }
 
     #[inline]

src/platform_impl/linux/wayland/window/state.rs

@@ -125,6 +125,9 @@ pub struct WindowState {
     /// sends `None` for the new size in the configure.
     stateless_size: LogicalSize<u32>,
 
+    /// The state of the frame callback.
+    frame_callback_state: FrameCallbackState,
+
     viewport: Option<WpViewport>,
     fractional_scale: Option<WpFractionalScaleV1>,
 
@@ -134,26 +137,62 @@ pub struct WindowState {
     has_pending_move: Option<u32>,
 }
 
-/// The state of the cursor grabs.
-#[derive(Clone, Copy)]
-struct GrabState {
-    /// The grab mode requested by the user.
-    user_grab_mode: CursorGrabMode,
+impl WindowState {
+    /// Create new window state.
+    pub fn new(
+        connection: Connection,
+        queue_handle: &QueueHandle<WinitState>,
+        winit_state: &WinitState,
+        size: LogicalSize<u32>,
+        window: Window,
+        theme: Option<Theme>,
+    ) -> Self {
+        let compositor = winit_state.compositor_state.clone();
+        let pointer_constraints = winit_state.pointer_constraints.clone();
+        let viewport = winit_state
+            .viewporter_state
+            .as_ref()
+            .map(|state| state.get_viewport(window.wl_surface(), queue_handle));
+        let fractional_scale = winit_state
+            .fractional_scaling_manager
+            .as_ref()
+            .map(|fsm| fsm.fractional_scaling(window.wl_surface(), queue_handle));
 
-    /// The current grab mode.
-    current_grab_mode: CursorGrabMode,
-}
-
-impl GrabState {
-    fn new() -> Self {
         Self {
-            user_grab_mode: CursorGrabMode::None,
-            current_grab_mode: CursorGrabMode::None,
+            compositor,
+            connection,
+            csd_fails: false,
+            cursor_grab_mode: GrabState::new(),
+            cursor_icon: CursorIcon::Default,
+            cursor_visible: true,
+            decorate: true,
+            fractional_scale,
+            frame: None,
+            frame_callback_state: FrameCallbackState::None,
+            has_focus: false,
+            has_pending_move: None,
+            ime_allowed: false,
+            ime_purpose: ImePurpose::Normal,
+            last_configure: None,
+            max_inner_size: None,
+            min_inner_size: MIN_WINDOW_SIZE,
+            pointer_constraints,
+            pointers: Default::default(),
+            queue_handle: queue_handle.clone(),
+            resizable: true,
+            scale_factor: 1.,
+            shm: winit_state.shm.wl_shm().clone(),
+            size,
+            stateless_size: size,
+            text_inputs: Vec::new(),
+            theme,
+            title: String::default(),
+            transparent: false,
+            viewport,
+            window: ManuallyDrop::new(window),
         }
     }
-}
 
-impl WindowState {
     /// Apply closure on the given pointer.
     fn apply_on_poiner<F: Fn(&ThemedPointer<WinitPointerData>, &WinitPointerData)>(
         &self,
@@ -168,6 +207,33 @@ impl WindowState {
             })
     }
 
+    /// Get the current state of the frame callback.
+    pub fn frame_callback_state(&self) -> FrameCallbackState {
+        self.frame_callback_state
+    }
+
+    /// The frame callback was received, but not yet sent to the user.
+    pub fn frame_callback_received(&mut self) {
+        self.frame_callback_state = FrameCallbackState::Received;
+    }
+
+    /// Reset the frame callbacks state.
+    pub fn frame_callback_reset(&mut self) {
+        self.frame_callback_state = FrameCallbackState::None;
+    }
+
+    /// Request a frame callback if we don't have one for this window in flight.
+    pub fn request_frame_callback(&mut self) {
+        let surface = self.window.wl_surface();
+        match self.frame_callback_state {
+            FrameCallbackState::None | FrameCallbackState::Received => {
+                self.frame_callback_state = FrameCallbackState::Requested;
+                surface.frame(&self.queue_handle, surface.clone());
+            }
+            FrameCallbackState::Requested => (),
+        }
+    }
+
     pub fn configure(
         &mut self,
         configure: WindowConfigure,
@@ -391,60 +457,6 @@ impl WindowState {
         }
     }
 
-    /// Create new window state.
-    pub fn new(
-        connection: Connection,
-        queue_handle: &QueueHandle<WinitState>,
-        winit_state: &WinitState,
-        size: LogicalSize<u32>,
-        window: Window,
-        theme: Option<Theme>,
-    ) -> Self {
-        let compositor = winit_state.compositor_state.clone();
-        let pointer_constraints = winit_state.pointer_constraints.clone();
-        let viewport = winit_state
-            .viewporter_state
-            .as_ref()
-            .map(|state| state.get_viewport(window.wl_surface(), queue_handle));
-        let fractional_scale = winit_state
-            .fractional_scaling_manager
-            .as_ref()
-            .map(|fsm| fsm.fractional_scaling(window.wl_surface(), queue_handle));
-
-        Self {
-            compositor,
-            connection,
-            theme,
-            csd_fails: false,
-            decorate: true,
-            cursor_grab_mode: GrabState::new(),
-            cursor_icon: CursorIcon::Default,
-            cursor_visible: true,
-            fractional_scale,
-            frame: None,
-            has_focus: false,
-            ime_allowed: false,
-            ime_purpose: ImePurpose::Normal,
-            last_configure: None,
-            max_inner_size: None,
-            min_inner_size: MIN_WINDOW_SIZE,
-            pointer_constraints,
-            pointers: Default::default(),
-            queue_handle: queue_handle.clone(),
-            scale_factor: 1.,
-            shm: winit_state.shm.wl_shm().clone(),
-            size,
-            stateless_size: size,
-            text_inputs: Vec::new(),
-            title: String::default(),
-            transparent: false,
-            resizable: true,
-            viewport,
-            window: ManuallyDrop::new(window),
-            has_pending_move: None,
-        }
-    }
-
     /// Get the outer size of the window.
     #[inline]
     pub fn outer_size(&self) -> LogicalSize<u32> {
@@ -892,6 +904,37 @@ impl Drop for WindowState {
     }
 }
 
+/// The state of the cursor grabs.
+#[derive(Clone, Copy)]
+struct GrabState {
+    /// The grab mode requested by the user.
+    user_grab_mode: CursorGrabMode,
+
+    /// The current grab mode.
+    current_grab_mode: CursorGrabMode,
+}
+
+impl GrabState {
+    fn new() -> Self {
+        Self {
+            user_grab_mode: CursorGrabMode::None,
+            current_grab_mode: CursorGrabMode::None,
+        }
+    }
+}
+
+/// The state of the frame callback.
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FrameCallbackState {
+    /// No frame callback was requsted.
+    #[default]
+    None,
+    /// The frame callback was requested, but not yet arrived, the redraw events are throttled.
+    Requested,
+    /// The callback was marked as done, and user could receive redraw requested
+    Received,
+}
+
 impl From<ResizeDirection> for ResizeEdge {
     fn from(value: ResizeDirection) -> Self {
         match value {

src/window.rs

@@ -524,11 +524,12 @@ impl Window {
         self.window.scale_factor()
     }
 
-    /// Requests a future [`Event::RedrawRequested`] event to be emitted in a way that is
-    /// synchronized and / or throttled by the windowing system.
+    /// Queues a [`Event::RedrawRequested`] event to be emitted that aligns with the windowing
+    /// system drawing loop.
     ///
     /// This is the **strongly encouraged** method of redrawing windows, as it can integrate with
-    /// OS-requested redraws (e.g. when a window gets resized).
+    /// OS-requested redraws (e.g. when a window gets resized). To improve the event delivery
+    /// consider using [`Window::pre_present_notify`] as described in docs.
     ///
     /// Applications should always aim to redraw whenever they receive a `RedrawRequested` event.
     ///
@@ -536,11 +537,16 @@ impl Window {
     /// with respect to other events, since the requirements can vary significantly between
     /// windowing systems.
     ///
+    /// However as the event aligns with the windowing system drawing loop, it may not arrive in
+    /// same or even next event loop iteration.
+    ///
     /// ## Platform-specific
     ///
     /// - **Windows** This API uses `RedrawWindow` to request a `WM_PAINT` message and `RedrawRequested`
     ///   is emitted in sync with any `WM_PAINT` messages
     /// - **iOS:** Can only be called on the main thread.
+    /// - **Wayland:** The events are aligned with the frame callbacks when [`Window::pre_present_notify`]
+    ///                is used.
     ///
     /// [`Event::RedrawRequested`]: crate::event::Event::RedrawRequested
     #[inline]