Attempt to make resizes repaint in time

This introduces a RedrawGuard concept, which allows the event loop to
block until the window has been repainted. This hopefully will resolve
khonsulabs/cushy#114.

CHANGELOG.md

@@ -27,6 +27,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - All `&Appplication` bounds now are `?Sized`, enabling `&dyn Application`
   parameters.
+- Redraw requests from `winit` now block the event loop thread until the window
+  has been repainted.
 
 ### Added
 

src/lib.rs

@@ -10,9 +10,10 @@ mod window;
 use std::collections::HashMap;
 use std::process::exit;
 use std::sync::{mpsc, Arc, Mutex, PoisonError};
+use std::time::Duration;
 
 use private::{OpenedWindow, WindowSpawner};
-pub use window::{RunningWindow, Window, WindowAttributes, WindowBehavior, WindowBuilder};
+pub use window::{Run, RunningWindow, Window, WindowAttributes, WindowBehavior, WindowBuilder};
 pub use winit;
 use winit::application::ApplicationHandler;
 use winit::error::{EventLoopError, OsError};
@@ -149,10 +150,13 @@ where
         window_id: WindowId,
         event: winit::event::WindowEvent,
     ) {
-        let event = WindowEvent::from(event);
+        let (event, waiter) = WindowEvent::from_winit(event);
         self.running
             .windows
             .send(window_id, WindowMessage::Event(event));
+        if let Some(waiter) = waiter {
+            waiter.wait(Duration::from_millis(16));
+        }
     }
 
     fn user_event(&mut self, event_loop: &ActiveEventLoop, message: EventLoopMessage<AppMessage>) {
@@ -379,7 +383,7 @@ impl<Message> Windows<Message> {
     /// Gets an instance of the winit window for the given window id, if it has
     /// been opened and is still open.
     pub fn get(&self, id: WindowId) -> Option<Arc<winit::window::Window>> {
-        let windows = self.data.lock().map_or_else(PoisonError::into_inner, |g| g);
+        let windows = self.data.lock().unwrap_or_else(PoisonError::into_inner);
         windows.get(&id).and_then(|w| w.winit.winit())
     }
 
@@ -441,7 +445,7 @@ impl<Message> Windows<Message> {
         let winit = Arc::new(target.create_window(builder)?);
         let id = winit.id();
         let winit = OpenedWindow(Arc::new(Mutex::new(Some(winit))));
-        let mut windows = self.data.lock().map_or_else(PoisonError::into_inner, |g| g);
+        let mut windows = self.data.lock().unwrap_or_else(PoisonError::into_inner);
         windows.insert(
             id,
             OpenWindow {
@@ -453,7 +457,7 @@ impl<Message> Windows<Message> {
     }
 
     fn send(&self, window: WindowId, message: WindowMessage<Message>) {
-        let mut data = self.data.lock().map_or_else(PoisonError::into_inner, |g| g);
+        let mut data = self.data.lock().unwrap_or_else(PoisonError::into_inner);
         if let Some(open_window) = data.get(&window) {
             match open_window.sender.try_send(message) {
                 Ok(()) => {}
@@ -469,7 +473,7 @@ impl<Message> Windows<Message> {
     }
 
     fn close(&self, window: WindowId) -> bool {
-        let mut data = self.data.lock().map_or_else(PoisonError::into_inner, |g| g);
+        let mut data = self.data.lock().unwrap_or_else(PoisonError::into_inner);
         data.remove(&window);
         data.is_empty()
     }

src/private.rs

@@ -1,5 +1,6 @@
 use std::path::PathBuf;
 use std::sync::{mpsc, Arc, Mutex, PoisonError};
+use std::time::Duration;
 
 use winit::dpi::{PhysicalPosition, PhysicalSize};
 use winit::error::OsError;
@@ -34,7 +35,7 @@ impl OpenedWindow {
     pub fn winit(&self) -> Option<Arc<winit::window::Window>> {
         self.0
             .lock()
-            .map_or_else(PoisonError::into_inner, |g| g)
+            .unwrap_or_else(PoisonError::into_inner)
             .clone()
     }
 }
@@ -63,9 +64,33 @@ pub enum WindowMessage<User> {
     Event(WindowEvent),
 }
 
+#[derive(Debug)]
+pub struct RedrawGuard(mpsc::SyncSender<()>);
+
+impl Drop for RedrawGuard {
+    fn drop(&mut self) {
+        let _ignored = self.0.send(());
+    }
+}
+
+pub struct WaitForRedraw(mpsc::Receiver<()>);
+
+impl WaitForRedraw {
+    pub fn wait(self, timeout: Duration) {
+        let _result = self.0.recv_timeout(timeout);
+    }
+}
+
+impl RedrawGuard {
+    pub fn new() -> (Self, WaitForRedraw) {
+        let (sender, receiver) = mpsc::sync_channel(1);
+        (Self(sender), WaitForRedraw(receiver))
+    }
+}
+
 #[derive(Debug)]
 pub enum WindowEvent {
-    RedrawRequested,
+    RedrawRequested(RedrawGuard),
 
     /// The size of the window has changed. Contains the client area's new dimensions.
     Resized(PhysicalSize<u32>),
@@ -262,11 +287,15 @@ pub enum WindowEvent {
     },
 }
 
-impl From<winit::event::WindowEvent> for WindowEvent {
+impl WindowEvent {
     #[allow(clippy::too_many_lines)] // it's a match statement
-    fn from(event: winit::event::WindowEvent) -> Self {
-        match event {
-            winit::event::WindowEvent::RedrawRequested => Self::RedrawRequested,
+    pub fn from_winit(event: winit::event::WindowEvent) -> (Self, Option<WaitForRedraw>) {
+        (
+            match event {
+            winit::event::WindowEvent::RedrawRequested => {
+                let (guard, wait) = RedrawGuard::new();
+                return (Self::RedrawRequested(guard), Some(wait))
+            },
             winit::event::WindowEvent::Resized(size) => Self::Resized(size),
             winit::event::WindowEvent::Moved(pos) => Self::Moved(pos),
             winit::event::WindowEvent::CloseRequested => Self::CloseRequested,
@@ -381,6 +410,8 @@ impl From<winit::event::WindowEvent> for WindowEvent {
             winit::event::WindowEvent::ActivationTokenDone { serial, token } => {
                 Self::ActivationTokenDone { serial, token }
             }
-        }
+        },
+            None,
+        )
     }
 }

src/window.rs

@@ -15,7 +15,7 @@ use winit::event::{
 use winit::keyboard::PhysicalKey;
 use winit::window::{Fullscreen, Icon, Theme, WindowButtons, WindowId, WindowLevel};
 
-use crate::private::{self, OpenedWindow, WindowEvent, WindowSpawner};
+use crate::private::{self, OpenedWindow, RedrawGuard, WindowEvent, WindowSpawner};
 use crate::{
     App, Application, AsApplication, EventLoopMessage, Message, PendingApp, WindowMessage, Windows,
 };
@@ -34,7 +34,7 @@ impl<Message> Window<Message> {
         self.opened
             .0
             .lock()
-            .map_or_else(PoisonError::into_inner, |g| g)
+            .unwrap_or_else(PoisonError::into_inner)
             .as_ref()
             .map(|w| w.id())
     }
@@ -264,6 +264,12 @@ where
 type SyncArcChannel<T> = (Arc<mpsc::SyncSender<T>>, mpsc::Receiver<T>);
 type SyncChannel<T> = (mpsc::SyncSender<T>, mpsc::Receiver<T>);
 
+enum HandleMessageResult {
+    Ok,
+    RedrawRequired(RedrawGuard),
+    Destroyed,
+}
+
 /// A window that is running in its own thread.
 pub struct RunningWindow<AppMessage>
 where
@@ -442,9 +448,15 @@ where
         // the entire app panics or not.
         let possible_panic = std::panic::catch_unwind(AssertUnwindSafe(move || {
             let mut behavior = Behavior::initialize(&mut self, context);
-            while !self.close && self.process_messages_until_redraw(&mut behavior) {
-                self.next_redraw_target = None;
-                behavior.redraw(&mut self);
+            while !self.close {
+                match self.process_messages_until_redraw(&mut behavior) {
+                    Ok(guard) => {
+                        self.next_redraw_target = None;
+                        behavior.redraw(&mut self);
+                        drop(guard);
+                    }
+                    Err(()) => break,
+                }
             }
             // Do not notify the main thread to close the window until after the
             // behavior is dropped. This upholds the requirement for RawWindowHandle
@@ -460,7 +472,10 @@ where
         }
     }
 
-    fn process_messages_until_redraw<Behavior>(&mut self, behavior: &mut Behavior) -> bool
+    fn process_messages_until_redraw<Behavior>(
+        &mut self,
+        behavior: &mut Behavior,
+    ) -> Result<Option<RedrawGuard>, ()>
     where
         Behavior: self::WindowBehavior<AppMessage>,
     {
@@ -471,27 +486,29 @@ where
                 // block.
                 TimeUntilRedraw::None => match self.messages.1.try_recv() {
                     Ok(message) => message,
-                    Err(mpsc::TryRecvError::Disconnected) => return false,
-                    Err(mpsc::TryRecvError::Empty) => return true,
+                    Err(mpsc::TryRecvError::Disconnected) => return Err(()),
+                    Err(mpsc::TryRecvError::Empty) => return Ok(None),
                 },
                 // We have a scheduled time for the next frame, and it hasn't
                 // elapsed yet.
                 TimeUntilRedraw::Some(duration_remaining) => {
                     match self.messages.1.recv_timeout(duration_remaining) {
                         Ok(message) => message,
-                        Err(mpsc::RecvTimeoutError::Timeout) => return true,
-                        Err(mpsc::RecvTimeoutError::Disconnected) => return false,
+                        Err(mpsc::RecvTimeoutError::Timeout) => return Ok(None),
+                        Err(mpsc::RecvTimeoutError::Disconnected) => return Err(()),
                     }
                 }
                 // No scheduled redraw time, sleep until the next message.
                 TimeUntilRedraw::Indefinite => match self.messages.1.recv() {
                     Ok(message) => message,
-                    Err(_) => return false,
+                    Err(_) => return Err(()),
                 },
             };
 
-            if !self.handle_message(message, behavior) {
-                break false;
+            match self.handle_message(message, behavior) {
+                HandleMessageResult::Ok => {}
+                HandleMessageResult::RedrawRequired(guard) => return Ok(Some(guard)),
+                HandleMessageResult::Destroyed => return Err(()),
             }
         }
     }
@@ -501,15 +518,16 @@ where
         &mut self,
         message: WindowMessage<AppMessage::Window>,
         behavior: &mut Behavior,
-    ) -> bool
+    ) -> HandleMessageResult
     where
         Behavior: self::WindowBehavior<AppMessage>,
     {
         match message {
             WindowMessage::User(user) => behavior.event(self, user),
             WindowMessage::Event(evt) => match evt {
-                WindowEvent::RedrawRequested => {
+                WindowEvent::RedrawRequested(guard) => {
                     self.set_needs_redraw();
+                    return HandleMessageResult::RedrawRequired(guard);
                 }
                 WindowEvent::CloseRequested => {
                     if behavior.close_requested(self) {
@@ -546,7 +564,7 @@ where
                     self.position = position;
                 }
                 WindowEvent::Destroyed => {
-                    return false;
+                    return HandleMessageResult::Destroyed;
                 }
                 WindowEvent::ThemeChanged(theme) => {
                     self.theme = theme;
@@ -667,7 +685,7 @@ where
             },
         }
 
-        true
+        HandleMessageResult::Ok
     }
 
     /// Sets this window to close as soon as possible.
@@ -1090,12 +1108,18 @@ where
     fn event(&mut self, window: &mut RunningWindow<AppMessage>, event: AppMessage::Window) {}
 }
 
+/// A runnable window.
 pub trait Run: WindowBehavior<()> {
     /// Runs a window with a default instance of this behavior's
     /// [`Context`](Self::Context).
     ///
     /// This function is shorthand for creating a [`PendingApp`], opening this
     /// window inside of it, and running the pending app.
+    ///
+    /// # Errors
+    ///
+    /// Returns an [`EventLoopError`] upon the loop exiting due to an error. See
+    /// [`EventLoop::run`] for more information.
     fn run() -> Result<(), EventLoopError>
     where
         Self::Context: Default,
@@ -1109,6 +1133,11 @@ pub trait Run: WindowBehavior<()> {
     ///
     /// This function is shorthand for creating a [`PendingApp`], opening this
     /// window inside of it, and running the pending app.
+    ///
+    /// # Errors
+    ///
+    /// Returns an [`EventLoopError`] upon the loop exiting due to an error. See
+    /// [`EventLoop::run`] for more information.
     fn run_with(context: Self::Context) -> Result<(), EventLoopError> {
         let mut app = PendingApp::new();
         Self::open_with(&mut app, context).expect("error opening initial window");