Fix web redraw requested (#1181)

* Keep track of what windows have requested redraw

Instead of using request_animation_frame and sending redraw request
events, just keep track of all windows that have asked for a redraw.
This doesn't handle dispatching the events

* Issue redraw events to windows that request it

* Cargo fmt

src/platform_impl/web/event_loop/runner.rs

@@ -1,9 +1,15 @@
 use super::{backend, state::State};
-use crate::event::{Event, StartCause};
+use crate::event::{Event, StartCause, WindowEvent};
 use crate::event_loop as root;
+use crate::window::WindowId;
 
 use instant::{Duration, Instant};
-use std::{cell::RefCell, clone::Clone, collections::VecDeque, rc::Rc};
+use std::{
+    cell::RefCell,
+    clone::Clone,
+    collections::{HashSet, VecDeque},
+    rc::Rc,
+};
 
 pub struct Shared<T>(Rc<Execution<T>>);
 
@@ -17,6 +23,7 @@ pub struct Execution<T> {
     runner: RefCell<Option<Runner<T>>>,
     events: RefCell<VecDeque<Event<T>>>,
     id: RefCell<u32>,
+    redraw_pending: RefCell<HashSet<WindowId>>,
 }
 
 struct Runner<T> {
@@ -41,6 +48,7 @@ impl<T: 'static> Shared<T> {
             runner: RefCell::new(None),
             events: RefCell::new(VecDeque::new()),
             id: RefCell::new(0),
+            redraw_pending: RefCell::new(HashSet::new()),
         }))
     }
 
@@ -64,6 +72,10 @@ impl<T: 'static> Shared<T> {
         *id
     }
 
+    pub fn request_redraw(&self, id: WindowId) {
+        self.0.redraw_pending.borrow_mut().insert(id);
+    }
+
     // Add an event to the event loop runner
     //
     // It will determine if the event should be immediately sent to the user or buffered for later
@@ -115,6 +127,17 @@ impl<T: 'static> Shared<T> {
         if !event_is_start {
             self.handle_event(event, &mut control);
         }
+        // Collect all of the redraw events to avoid double-locking the RefCell
+        let redraw_events: Vec<WindowId> = self.0.redraw_pending.borrow_mut().drain().collect();
+        for window_id in redraw_events {
+            self.handle_event(
+                Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::RedrawRequested,
+                },
+                &mut control,
+            );
+        }
         self.handle_event(Event::EventsCleared, &mut control);
         self.apply_control_flow(control);
         // If the event loop is closed, it has been closed this iteration and now the closing