X11: Fix events not being reported when using run_return (#1245)

* X11: Fix events not being reported using `run_return`

* Adapt examples to be more practical

* Add CHANGELOG entry

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 - On macOS, fix application termination on `ControlFlow::Exit`
+- On X11, fix events not being reported when using `run_return`.
 - On X11, fix key modifiers being incorrectly reported.
 
 # 0.20.0 Alpha 4 (2019-10-18)

examples/timer.rs

@@ -17,7 +17,10 @@ fn main() {
     let timer_length = Duration::new(1, 0);
 
     event_loop.run(move |event, _, control_flow| {
-        println!("{:?}", event);
+        if let Event::WindowEvent { event, .. } = &event {
+            // Print only Window events to reduce noise
+            println!("{:?}", event);
+        }
 
         match event {
             Event::NewEvents(StartCause::Init) => {

examples/window_run_return.rs

@@ -9,6 +9,7 @@
     target_os = "openbsd"
 ))]
 fn main() {
+    use std::{thread::sleep, time::Duration};
     use winit::{
         event::{Event, WindowEvent},
         event_loop::{ControlFlow, EventLoop},
@@ -17,36 +18,38 @@ fn main() {
     };
     let mut event_loop = EventLoop::new();
 
-    let window = WindowBuilder::new()
+    let _window = WindowBuilder::new()
         .with_title("A fantastic window!")
         .build(&event_loop)
         .unwrap();
 
-    println!("Close the window to continue.");
-    event_loop.run_return(|event, _, control_flow| match event {
-        Event::WindowEvent {
-            event: WindowEvent::CloseRequested,
-            ..
-        } => *control_flow = ControlFlow::Exit,
-        _ => *control_flow = ControlFlow::Wait,
-    });
-    drop(window);
+    let mut quit = false;
 
-    let _window_2 = WindowBuilder::new()
-        .with_title("A second, fantasticer window!")
-        .build(&event_loop)
-        .unwrap();
+    while !quit {
+        event_loop.run_return(|event, _, control_flow| {
+            if let Event::WindowEvent { event, .. } = &event {
+                // Print only Window events to reduce noise
+                println!("{:?}", event);
+            }
 
-    println!("Wa ha ha! You thought that closing the window would finish this?!");
-    event_loop.run_return(|event, _, control_flow| match event {
-        Event::WindowEvent {
-            event: WindowEvent::CloseRequested,
-            ..
-        } => *control_flow = ControlFlow::Exit,
-        _ => *control_flow = ControlFlow::Wait,
-    });
+            match event {
+                Event::WindowEvent {
+                    event: WindowEvent::CloseRequested,
+                    ..
+                } => {
+                    quit = true;
+                    *control_flow = ControlFlow::Exit;
+                }
+                Event::EventsCleared => {
+                    *control_flow = ControlFlow::Exit;
+                }
+                _ => *control_flow = ControlFlow::Wait,
+            }
+        });
 
-    println!("Okay we're done now for real.");
+        // Sleep for 1/60 second to simulate rendering
+        sleep(Duration::from_millis(16));
+    }
 }
 
 #[cfg(any(target_os = "ios", target_os = "android", target_arch = "wasm32"))]

src/platform_impl/linux/x11/event_processor.rs

@@ -66,6 +66,13 @@ impl<T: 'static> EventProcessor<T> {
         self.with_window(window_id, |_| ()).is_some()
     }
 
+    pub(super) fn poll(&self) -> bool {
+        let wt = get_xtarget(&self.target);
+        let result = unsafe { (wt.xconn.xlib.XPending)(wt.xconn.display) };
+
+        result != 0
+    }
+
     pub(super) unsafe fn poll_one_event(&mut self, event_ptr: *mut ffi::XEvent) -> bool {
         let wt = get_xtarget(&self.target);
         // This function is used to poll and remove a single event

src/platform_impl/linux/x11/mod.rs

@@ -26,6 +26,7 @@ use std::{
     rc::Rc,
     slice,
     sync::{mpsc, Arc, Mutex, Weak},
+    time::{Duration, Instant},
 };
 
 use libc::{self, setlocale, LC_CTYPE};
@@ -38,7 +39,7 @@ use self::{
 };
 use crate::{
     error::OsError as RootOsError,
-    event::{Event, WindowEvent},
+    event::{Event, StartCause, WindowEvent},
     event_loop::{ControlFlow, EventLoopClosed, EventLoopWindowTarget as RootELW},
     platform_impl::{platform::sticky_exit_callback, PlatformSpecificWindowBuilderAttributes},
     window::WindowAttributes,
@@ -262,6 +263,8 @@ impl<T: 'static> EventLoop<T> {
         );
 
         loop {
+            self.drain_events();
+
             // Empty the event buffer
             {
                 let mut guard = self.pending_events.borrow_mut();
@@ -309,69 +312,58 @@ impl<T: 'static> EventLoop<T> {
                 );
             }
 
+            let start = Instant::now();
+            let (mut cause, deadline, mut timeout);
+
             match control_flow {
                 ControlFlow::Exit => break,
                 ControlFlow::Poll => {
-                    // non-blocking dispatch
-                    self.inner_loop
-                        .dispatch(Some(::std::time::Duration::from_millis(0)), &mut ())
-                        .unwrap();
-                    callback(
-                        crate::event::Event::NewEvents(crate::event::StartCause::Poll),
-                        &self.target,
-                        &mut control_flow,
-                    );
+                    cause = StartCause::Poll;
+                    deadline = None;
+                    timeout = Some(Duration::from_millis(0));
                 }
                 ControlFlow::Wait => {
-                    self.inner_loop.dispatch(None, &mut ()).unwrap();
-                    callback(
-                        crate::event::Event::NewEvents(crate::event::StartCause::WaitCancelled {
-                            start: ::std::time::Instant::now(),
-                            requested_resume: None,
-                        }),
-                        &self.target,
-                        &mut control_flow,
-                    );
-                }
-                ControlFlow::WaitUntil(deadline) => {
-                    let start = ::std::time::Instant::now();
-                    // compute the blocking duration
-                    let duration = if deadline > start {
-                        deadline - start
-                    } else {
-                        ::std::time::Duration::from_millis(0)
+                    cause = StartCause::WaitCancelled {
+                        start,
+                        requested_resume: None,
                     };
-                    self.inner_loop.dispatch(Some(duration), &mut ()).unwrap();
-                    let now = std::time::Instant::now();
-                    if now < deadline {
-                        callback(
-                            crate::event::Event::NewEvents(
-                                crate::event::StartCause::WaitCancelled {
-                                    start,
-                                    requested_resume: Some(deadline),
-                                },
-                            ),
-                            &self.target,
-                            &mut control_flow,
-                        );
+                    deadline = None;
+                    timeout = None;
+                }
+                ControlFlow::WaitUntil(wait_deadline) => {
+                    cause = StartCause::ResumeTimeReached {
+                        start,
+                        requested_resume: wait_deadline,
+                    };
+                    timeout = if wait_deadline > start {
+                        Some(wait_deadline - start)
                     } else {
-                        callback(
-                            crate::event::Event::NewEvents(
-                                crate::event::StartCause::ResumeTimeReached {
-                                    start,
-                                    requested_resume: deadline,
-                                },
-                            ),
-                            &self.target,
-                            &mut control_flow,
-                        );
-                    }
+                        Some(Duration::from_millis(0))
+                    };
+                    deadline = Some(wait_deadline);
                 }
             }
 
-            // If the user callback had any interaction with the X server,
-            // it may have received and buffered some user input events.
-            self.drain_events();
+            if self.events_waiting() {
+                timeout = Some(Duration::from_millis(0));
+            }
+
+            self.inner_loop.dispatch(timeout, &mut ()).unwrap();
+
+            if let Some(deadline) = deadline {
+                if deadline > Instant::now() {
+                    cause = StartCause::WaitCancelled {
+                        start,
+                        requested_resume: Some(deadline),
+                    };
+                }
+            }
+
+            callback(
+                crate::event::Event::NewEvents(cause),
+                &self.target,
+                &mut control_flow,
+            );
         }
 
         callback(
@@ -395,6 +387,10 @@ impl<T: 'static> EventLoop<T> {
 
         drain_events(&mut processor, &mut pending_events);
     }
+
+    fn events_waiting(&self) -> bool {
+        !self.pending_events.borrow().is_empty() || self.event_processor.borrow().poll()
+    }
 }
 
 fn drain_events<T: 'static>(