On Web, map bfcache load/unload to suspend/resume

CHANGELOG.md

@@ -76,7 +76,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - On Web, use the correct canvas size when calculating the new size during scale factor change,
   instead of using the output bitmap size.
 - On Web, scale factor and dark mode detection are now more robust.
-- On Web, fix the bfcache by not using the `beforeunload` event.
+- On Web, fix the bfcache by not using the `beforeunload` event and map bfcache loading/unloading to `Suspended`/`Resumed` events.
 - On Web, fix scale factor resize suggestion always overwriting the canvas size.
 - On macOS, fix crash when dropping `Window`.
 - On Web, use `Window.requestIdleCallback()` for `ControlFlow::Poll` when available.

Cargo.toml

@@ -148,6 +148,7 @@ features = [
     'KeyboardEvent',
     'MediaQueryList',
     'Node',
+    'PageTransitionEvent',
     'PointerEvent',
     'ResizeObserver',
     'ResizeObserverBoxOptions',

src/event.rs

@@ -125,6 +125,18 @@ pub enum Event<'a, T: 'static> {
     /// [`applicationWillResignActive`]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1622950-applicationwillresignactive
     /// [iOS application lifecycle]: https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle
     ///
+    /// ## Web
+    ///
+    /// On Web, the `Suspended` event is emitted in response to a [`pagehide`] event
+    /// with the property [`persisted`] being true, which means that the page is being
+    /// put in the [´bfcache`] (back/forward cache) - an in-memory cache that stores a
+    /// complete snapshot of a page (including the JavaScript heap) as the user is
+    /// navigating away.
+    ///
+    /// [`pagehide`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/pagehide_event
+    /// [`persisted`]: https://developer.mozilla.org/en-US/docs/Web/API/PageTransitionEvent/persisted
+    /// [`bfcache`]: https://web.dev/bfcache/
+    ///
     /// [`Resumed`]: Self::Resumed
     Suspended,
 
@@ -179,6 +191,18 @@ pub enum Event<'a, T: 'static> {
     /// [`applicationDidBecomeActive`]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1622956-applicationdidbecomeactive
     /// [iOS application lifecycle]: https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle
     ///
+    /// ## Web
+    ///
+    /// On Web, the `Resumed` event is emitted in response to a [`pageshow`] event
+    /// with the property [`persisted`] being true, which means that the page is being
+    /// restored from the [´bfcache`] (back/forward cache) - an in-memory cache that
+    /// stores a complete snapshot of a page (including the JavaScript heap) as the
+    /// user is navigating away.
+    ///
+    /// [`pageshow`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/pageshow_event
+    /// [`persisted`]: https://developer.mozilla.org/en-US/docs/Web/API/PageTransitionEvent/persisted
+    /// [`bfcache`]: https://web.dev/bfcache/
+    ///
     /// [`Suspended`]: Self::Suspended
     Resumed,
 

src/platform_impl/web/event_loop/runner.rs

@@ -18,7 +18,7 @@ use std::{
     rc::{Rc, Weak},
 };
 use wasm_bindgen::prelude::Closure;
-use web_sys::{KeyboardEvent, PointerEvent, WheelEvent};
+use web_sys::{KeyboardEvent, PageTransitionEvent, PointerEvent, WheelEvent};
 use web_time::{Duration, Instant};
 
 pub struct Shared<T: 'static>(Rc<Execution<T>>);
@@ -41,7 +41,7 @@ pub struct Execution<T: 'static> {
     all_canvases: RefCell<Vec<(WindowId, Weak<RefCell<backend::Canvas>>)>>,
     redraw_pending: RefCell<HashSet<WindowId>>,
     destroy_pending: RefCell<VecDeque<WindowId>>,
-    unload_event_handle: RefCell<Option<backend::UnloadEventHandle>>,
+    page_transition_event_handle: RefCell<Option<backend::PageTransitionEventHandle>>,
     device_events: Cell<DeviceEvents>,
     on_mouse_move: OnEventHandle<PointerEvent>,
     on_wheel: OnEventHandle<WheelEvent>,
@@ -146,7 +146,7 @@ impl<T: 'static> Shared<T> {
             all_canvases: RefCell::new(Vec::new()),
             redraw_pending: RefCell::new(HashSet::new()),
             destroy_pending: RefCell::new(VecDeque::new()),
-            unload_event_handle: RefCell::new(None),
+            page_transition_event_handle: RefCell::new(None),
             device_events: Cell::default(),
             on_mouse_move: RefCell::new(None),
             on_wheel: RefCell::new(None),
@@ -183,11 +183,27 @@ impl<T: 'static> Shared<T> {
         }
         self.init();
 
-        let close_instance = self.clone();
-        *self.0.unload_event_handle.borrow_mut() =
-            Some(backend::on_unload(self.window(), move || {
-                close_instance.handle_unload()
-            }));
+        *self.0.page_transition_event_handle.borrow_mut() = Some(backend::on_page_transition(
+            self.window(),
+            {
+                let runner = self.clone();
+                move |event: PageTransitionEvent| {
+                    if event.persisted() {
+                        runner.send_event(Event::Resumed);
+                    }
+                }
+            },
+            {
+                let runner = self.clone();
+                move |event: PageTransitionEvent| {
+                    if event.persisted() {
+                        runner.send_event(Event::Suspended);
+                    } else {
+                        runner.handle_unload();
+                    }
+                }
+            },
+        ));
 
         let runner = self.clone();
         let window = self.window().clone();
@@ -605,7 +621,7 @@ impl<T: 'static> Shared<T> {
     fn handle_loop_destroyed(&self, control: &mut ControlFlow) {
         self.handle_event(Event::LoopDestroyed, control);
         let all_canvases = std::mem::take(&mut *self.0.all_canvases.borrow_mut());
-        *self.0.unload_event_handle.borrow_mut() = None;
+        *self.0.page_transition_event_handle.borrow_mut() = None;
         *self.0.on_mouse_move.borrow_mut() = None;
         *self.0.on_wheel.borrow_mut() = None;
         *self.0.on_mouse_press.borrow_mut() = None;

src/platform_impl/web/web_sys/mod.rs

@@ -16,7 +16,7 @@ use crate::dpi::LogicalSize;
 use crate::platform::web::WindowExtWebSys;
 use crate::window::Window;
 use wasm_bindgen::closure::Closure;
-use web_sys::{CssStyleDeclaration, Element, HtmlCanvasElement};
+use web_sys::{CssStyleDeclaration, Element, HtmlCanvasElement, PageTransitionEvent};
 
 pub fn throw(msg: &str) {
     wasm_bindgen::throw_str(msg);
@@ -28,16 +28,24 @@ pub fn exit_fullscreen(window: &web_sys::Window) {
     document.exit_fullscreen();
 }
 
-pub struct UnloadEventHandle {
-    _listener: event_handle::EventListenerHandle<dyn FnMut()>,
+pub struct PageTransitionEventHandle {
+    _show_listener: event_handle::EventListenerHandle<dyn FnMut(PageTransitionEvent)>,
+    _hide_listener: event_handle::EventListenerHandle<dyn FnMut(PageTransitionEvent)>,
 }
 
-pub fn on_unload(window: &web_sys::Window, handler: impl FnMut() + 'static) -> UnloadEventHandle {
-    let closure = Closure::new(handler);
+pub fn on_page_transition(
+    window: &web_sys::Window,
+    show_handler: impl FnMut(PageTransitionEvent) + 'static,
+    hide_handler: impl FnMut(PageTransitionEvent) + 'static,
+) -> PageTransitionEventHandle {
+    let show_closure = Closure::new(show_handler);
+    let hide_closure = Closure::new(hide_handler);
 
-    let listener = event_handle::EventListenerHandle::new(window, "pagehide", closure);
-    UnloadEventHandle {
-        _listener: listener,
+    let show_listener = event_handle::EventListenerHandle::new(window, "pageshow", show_closure);
+    let hide_listener = event_handle::EventListenerHandle::new(window, "pagehide", hide_closure);
+    PageTransitionEventHandle {
+        _show_listener: show_listener,
+        _hide_listener: hide_listener,
     }
 }