web: Emit WindowEvent::Resized on Window::set_inner_size (#1717)

* web: Allow event to be queued from inside the EventLoop handler

The Runner is behind a RefCell, which is mutably borrowed when the event
handler is being called. To queue events, `send_events` needs to check
`is_closed()` and the `is_busy` flag, but it cannot be done since the
RefCell is already locked. This commit changes the conditions to work
without needing a successful borrow.

* web: Emit WindowEvent::Resized on Window::set_inner_size

* Update changelog

CHANGELOG.md

@@ -40,6 +40,7 @@
 - On Web (web-sys only), the event listeners are now removed when a `Window` is dropped or when the event loop is destroyed.
 - On Web, the event handler closure passed to `EventLoop::run` now gets dropped after the event loop is destroyed.
 - **Breaking:** On Web, the canvas element associated to a `Window` is no longer removed from the DOM when the `Window` is dropped.
+- On Web, `WindowEvent::Resized` is now emitted when `Window::set_inner_size` is called.
 
 # 0.22.2 (2020-05-16)
 

src/platform_impl/web/event_loop/runner.rs

@@ -9,6 +9,7 @@ use std::{
     clone::Clone,
     collections::{HashSet, VecDeque},
     iter,
+    ops::Deref,
     rc::{Rc, Weak},
 };
 
@@ -53,7 +54,6 @@ impl<T: 'static> RunnerEnum<T> {
 
 struct Runner<T: 'static> {
     state: State,
-    is_busy: bool,
     event_handler: Box<dyn FnMut(Event<'_, T>, &mut root::ControlFlow)>,
 }
 
@@ -61,7 +61,6 @@ impl<T: 'static> Runner<T> {
     pub fn new(event_handler: Box<dyn FnMut(Event<'_, T>, &mut root::ControlFlow)>) -> Self {
         Runner {
             state: State::Init,
-            is_busy: false,
             event_handler,
         }
     }
@@ -87,18 +86,12 @@ impl<T: 'static> Runner<T> {
     fn handle_single_event(&mut self, event: Event<'_, T>, control: &mut root::ControlFlow) {
         let is_closed = *control == root::ControlFlow::Exit;
 
-        // An event is being processed, so the runner should be marked busy
-        self.is_busy = true;
-
         (self.event_handler)(event, control);
 
         // Maintain closed state, even if the callback changes it
         if is_closed {
             *control = root::ControlFlow::Exit;
         }
-
-        // An event is no longer being processed
-        self.is_busy = false;
     }
 }
 
@@ -205,23 +198,25 @@ impl<T: 'static> Shared<T> {
         }
         // If we can run the event processing right now, or need to queue this and wait for later
         let mut process_immediately = true;
-        match &*self.0.runner.borrow() {
+        match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
-            RunnerEnum::Running(ref runner) => {
+            Ok(RunnerEnum::Running(ref runner)) => {
                 // If we're currently polling, queue this and wait for the poll() method to be called
                 if let State::Poll { .. } = runner.state {
                     process_immediately = false;
                 }
-                // If the runner is busy, queue this and wait for it to process it later
-                if runner.is_busy {
-                    process_immediately = false;
-                }
             }
-            RunnerEnum::Pending => {
+            Ok(RunnerEnum::Pending) => {
                 // The runner still hasn't been attached: queue this event and wait for it to be
                 process_immediately = false;
             }
+            // Some other code is mutating the runner, which most likely means
+            // the event loop is running and busy. So we queue this event for
+            // it to be processed later.
+            Err(_) => {
+                process_immediately = false;
+            }
             // This is unreachable since `self.is_closed() == true`.
-            RunnerEnum::Destroyed => unreachable!(),
+            Ok(RunnerEnum::Destroyed) => unreachable!(),
         }
         if !process_immediately {
             // Queue these events to look at later
@@ -502,12 +497,15 @@ impl<T: 'static> Shared<T> {
 
     // Check if the event loop is currently closed
     fn is_closed(&self) -> bool {
-        match *self.0.runner.borrow() {
+        match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
-            RunnerEnum::Running(ref runner) => runner.state.is_exit(),
+            Ok(RunnerEnum::Running(runner)) => runner.state.is_exit(),
             // The event loop is not closed since it is not initialized.
-            RunnerEnum::Pending => false,
+            Ok(RunnerEnum::Pending) => false,
             // The event loop is closed since it has been destroyed.
-            RunnerEnum::Destroyed => true,
+            Ok(RunnerEnum::Destroyed) => true,
+            // Some other code is mutating the runner, which most likely means
+            // the event loop is running and busy.
+            Err(_) => false,
         }
     }
 

src/platform_impl/web/window.rs

@@ -1,5 +1,6 @@
 use crate::dpi::{LogicalSize, PhysicalPosition, PhysicalSize, Position, Size};
 use crate::error::{ExternalError, NotSupportedError, OsError as RootOE};
+use crate::event;
 use crate::icon::Icon;
 use crate::monitor::MonitorHandle as RootMH;
 use crate::window::{CursorIcon, Fullscreen, WindowAttributes, WindowId as RootWI};
@@ -18,6 +19,7 @@ pub struct Window {
     previous_pointer: RefCell<&'static str>,
     id: Id,
     register_redraw_request: Box<dyn Fn()>,
+    resize_notify_fn: Box<dyn Fn(PhysicalSize<u32>)>,
     destroy_fn: Option<Box<dyn FnOnce()>>,
 }
 
@@ -38,6 +40,14 @@ impl Window {
 
         target.register(&mut canvas, id);
 
+        let runner = target.runner.clone();
+        let resize_notify_fn = Box::new(move |new_size| {
+            runner.send_event(event::Event::WindowEvent {
+                window_id: RootWI(id),
+                event: event::WindowEvent::Resized(new_size),
+            });
+        });
+
         let runner = target.runner.clone();
         let destroy_fn = Box::new(move || runner.notify_destroy_window(RootWI(id)));
 
@@ -46,13 +56,17 @@ impl Window {
             previous_pointer: RefCell::new("auto"),
             id,
             register_redraw_request,
+            resize_notify_fn,
             destroy_fn: Some(destroy_fn),
         };
 
-        window.set_inner_size(attr.inner_size.unwrap_or(Size::Logical(LogicalSize {
+        backend::set_canvas_size(
-            width: 1024.0,
+            window.canvas.borrow().raw(),
-            height: 768.0,
+            attr.inner_size.unwrap_or(Size::Logical(LogicalSize {
-        })));
+                width: 1024.0,
+                height: 768.0,
+            })),
+        );
         window.set_title(&attr.title);
         window.set_maximized(attr.maximized);
         window.set_visible(attr.visible);
@@ -112,7 +126,12 @@ impl Window {
 
     #[inline]
     pub fn set_inner_size(&self, size: Size) {
+        let old_size = self.inner_size();
         backend::set_canvas_size(self.canvas.borrow().raw(), size);
+        let new_size = self.inner_size();
+        if old_size != new_size {
+            (self.resize_notify_fn)(new_size);
+        }
     }
 
     #[inline]