Implement changes to RedrawRequested event (#1062)

* Implement changes to `RedrawRequested` event

Implements the changes described in #1041 for the X11 platform and for
platform-independent public-facing code.

* Fix `request_redraw` example

* Fix examples in lib docs

* Only issue `RedrawRequested` on final `Expose` event

CHANGELOG.md

@@ -100,6 +100,11 @@
 - On iOS, fix DPI sent out by views on creation was `0.0` - now it gives a reasonable number.
 - On iOS, RedrawRequested now works for gl/metal backed views.
 - On iOS, RedrawRequested is generally ordered after EventsCleared.
+- Changes to the `RedrawRequested` event (#1041):
+  - `RedrawRequested` has been moved from `WindowEvent` to `Event`.
+  - `EventsCleared` has been renamed to `MainEventsCleared`.
+  - `RedrawRequested` is now issued only after `MainEventsCleared`.
+  - `RedrawEventsCleared` is issued after each set of `RedrawRequested` events.
 
 # 0.20.0 Alpha 2 (2019-07-09)
 

examples/request_redraw.rs

@@ -20,14 +20,11 @@ fn main() {
             event: WindowEvent::CloseRequested,
             ..
         } => *control_flow = ControlFlow::Exit,
-        Event::EventsCleared => {
+        Event::MainEventsCleared => {
             window.request_redraw();
             *control_flow = ControlFlow::WaitUntil(Instant::now() + Duration::new(1, 0))
         }
-        Event::WindowEvent {
+        Event::RedrawRequested(_) => {
-            event: WindowEvent::RedrawRequested,
-            ..
-        } => {
             println!("{:?}", event);
         }
         _ => (),

src/event.rs

@@ -30,9 +30,22 @@ pub enum Event<T> {
     UserEvent(T),
     /// Emitted when new events arrive from the OS to be processed.
     NewEvents(StartCause),
-    /// Emitted when all of the event loop's events have been processed and control flow is about
+    /// Emitted when all events (except for `RedrawRequested`) have been reported.
-    /// to be taken away from the program.
+    ///
-    EventsCleared,
+    /// This event is followed by zero or more instances of `RedrawRequested`
+    /// and, finally, `RedrawEventsCleared`.
+    MainEventsCleared,
+
+    /// The OS or application has requested that a window be redrawn.
+    ///
+    /// Emitted only after `MainEventsCleared`.
+    RedrawRequested(WindowId),
+
+    /// Emitted after any `RedrawRequested` events.
+    ///
+    /// If there are no `RedrawRequested` events, it is reported immediately after
+    /// `MainEventsCleared`.
+    RedrawEventsCleared,
 
     /// Emitted when the event loop is being shut down. This is irreversable - if this event is
     /// emitted, it is guaranteed to be the last event emitted.
@@ -53,7 +66,9 @@ impl<T> Event<T> {
             WindowEvent { window_id, event } => Ok(WindowEvent { window_id, event }),
             DeviceEvent { device_id, event } => Ok(DeviceEvent { device_id, event }),
             NewEvents(cause) => Ok(NewEvents(cause)),
-            EventsCleared => Ok(EventsCleared),
+            MainEventsCleared => Ok(MainEventsCleared),
+            RedrawRequested(wid) => Ok(RedrawRequested(wid)),
+            RedrawEventsCleared => Ok(RedrawEventsCleared),
             LoopDestroyed => Ok(LoopDestroyed),
             Suspended => Ok(Suspended),
             Resumed => Ok(Resumed),
@@ -194,9 +209,6 @@ pub enum WindowEvent {
         value: f64,
     },
 
-    /// The OS or application has requested that the window be redrawn.
-    RedrawRequested,
-
     /// Touch event has been received
     Touch(Touch),
 

src/lib.rs

@@ -48,19 +48,16 @@
 //!
 //! event_loop.run(move |event, _, control_flow| {
 //!     match event {
-//!         Event::EventsCleared => {
+//!         Event::MainEventsCleared => {
 //!             // Application update code.
 //!
 //!             // Queue a RedrawRequested event.
 //!             window.request_redraw();
 //!         },
-//!         Event::WindowEvent {
+//!         Event::RedrawRequested(_) => {
-//!             event: WindowEvent::RedrawRequested,
-//!             ..
-//!         } => {
 //!             // Redraw the application.
 //!             //
-//!             // It's preferrable to render in this event rather than in EventsCleared, since
+//!             // It's preferrable to render in this event rather than in MainEventsCleared, since
 //!             // rendering in here allows the program to gracefully handle redraws requested
 //!             // by the OS.
 //!         },

src/platform_impl/linux/wayland/event_loop.rs

@@ -526,7 +526,7 @@ impl<T: 'static> EventLoop<T> {
             // send Events cleared
             {
                 sticky_exit_callback(
-                    crate::event::Event::EventsCleared,
+                    crate::event::Event::MainEventsCleared,
                     &self.window_target,
                     &mut control_flow,
                     &mut callback,
@@ -704,7 +704,8 @@ impl<T> EventLoop<T> {
                 );
             }
             if window.refresh {
-                sink.send_window_event(crate::event::WindowEvent::RedrawRequested, window.wid);
+                unimplemented!()
+                //sink.send_window_event(crate::event::WindowEvent::RedrawRequested, window.wid);
             }
             if window.closed {
                 sink.send_window_event(crate::event::WindowEvent::CloseRequested, window.wid);

src/platform_impl/linux/x11/event_processor.rs

@@ -534,13 +534,14 @@ impl<T: 'static> EventProcessor<T> {
             ffi::Expose => {
                 let xev: &ffi::XExposeEvent = xev.as_ref();
 
+                // Multiple Expose events may be received for subareas of a window.
+                // We issue `RedrawRequested` only for the last event of such a series.
+                if xev.count == 0 {
                     let window = xev.window;
                     let window_id = mkwid(window);
 
-                callback(Event::WindowEvent {
+                    callback(Event::RedrawRequested(window_id));
-                    window_id,
+                }
-                    event: WindowEvent::RedrawRequested,
-                });
             }
 
             ffi::KeyPress | ffi::KeyRelease => {

src/platform_impl/linux/x11/mod.rs

@@ -45,7 +45,7 @@ use self::{
 };
 use crate::{
     error::OsError as RootOsError,
-    event::{Event, StartCause, WindowEvent},
+    event::{Event, StartCause},
     event_loop::{ControlFlow, EventLoopClosed, EventLoopWindowTarget as RootELW},
     platform_impl::{platform::sticky_exit_callback, PlatformSpecificWindowBuilderAttributes},
     window::WindowAttributes,
@@ -151,6 +151,8 @@ impl<T: 'static> EventLoop<T> {
 
         xconn.update_cached_wm_info(root);
 
+        let pending_redraws: Arc<Mutex<HashSet<WindowId>>> = Default::default();
+
         let mut mod_keymap = ModifierKeymap::new();
         mod_keymap.reset_from_x_connection(&xconn);
 
@@ -164,7 +166,7 @@ impl<T: 'static> EventLoop<T> {
                 xconn,
                 wm_delete_window,
                 net_wm_ping,
-                pending_redraws: Default::default(),
+                pending_redraws: pending_redraws.clone(),
             }),
             _marker: ::std::marker::PhantomData,
         });
@@ -227,7 +229,9 @@ impl<T: 'static> EventLoop<T> {
                     if evt.readiness.is_readable() {
                         let mut processor = processor.borrow_mut();
                         let mut pending_events = pending_events.borrow_mut();
-                        drain_events(&mut processor, &mut pending_events);
+                        let mut pending_redraws = pending_redraws.lock().unwrap();
+
+                        drain_events(&mut processor, &mut pending_events, &mut pending_redraws);
                     }
                 }
             })
@@ -293,6 +297,15 @@ impl<T: 'static> EventLoop<T> {
                     );
                 }
             }
+            // send MainEventsCleared
+            {
+                sticky_exit_callback(
+                    crate::event::Event::MainEventsCleared,
+                    &self.target,
+                    &mut control_flow,
+                    &mut callback,
+                );
+            }
             // Empty the redraw requests
             {
                 // Release the lock to prevent deadlock
@@ -300,20 +313,17 @@ impl<T: 'static> EventLoop<T> {
 
                 for wid in windows {
                     sticky_exit_callback(
-                        Event::WindowEvent {
+                        Event::RedrawRequested(crate::window::WindowId(super::WindowId::X(wid))),
-                            window_id: crate::window::WindowId(super::WindowId::X(wid)),
-                            event: WindowEvent::RedrawRequested,
-                        },
                         &self.target,
                         &mut control_flow,
                         &mut callback,
                     );
                 }
             }
-            // send Events cleared
+            // send RedrawEventsCleared
             {
                 sticky_exit_callback(
-                    crate::event::Event::EventsCleared,
+                    crate::event::Event::RedrawEventsCleared,
                     &self.target,
                     &mut control_flow,
                     &mut callback,
@@ -392,8 +402,10 @@ impl<T: 'static> EventLoop<T> {
     fn drain_events(&self) {
         let mut processor = self.event_processor.borrow_mut();
         let mut pending_events = self.pending_events.borrow_mut();
+        let wt = get_xtarget(&self.target);
+        let mut pending_redraws = wt.pending_redraws.lock().unwrap();
 
-        drain_events(&mut processor, &mut pending_events);
+        drain_events(&mut processor, &mut pending_events, &mut pending_redraws);
     }
 
     fn events_waiting(&self) -> bool {
@@ -404,9 +416,14 @@ impl<T: 'static> EventLoop<T> {
 fn drain_events<T: 'static>(
     processor: &mut EventProcessor<T>,
     pending_events: &mut VecDeque<Event<T>>,
+    pending_redraws: &mut HashSet<WindowId>,
 ) {
     let mut callback = |event| {
+        if let Event::RedrawRequested(crate::window::WindowId(super::WindowId::X(wid))) = event {
+            pending_redraws.insert(wid);
+        } else {
             pending_events.push_back(event);
+        }
     };
 
     // process all pending events