Winit version 0.30.3

This new implementation uses:
- The NSAppearanceCustomization protocol for retrieving the appearance
  of the window, instead of using the application-wide
  `-[NSApplication effectiveAppearance]`.
- Key-Value observing for observing the `effectiveAppearance` to compute
  the `ThemeChanged` event, instead of using the undocumented
  `AppleInterfaceThemeChangedNotification` notification.

This also fixes `WindowBuilder::with_theme` not having any effect, and
the conversion between `Theme` and `NSAppearance` is made a bit more
robust.

.github/workflows/ci.yml

@@ -226,3 +226,19 @@ jobs:
         command: check
         log-level: error
         arguments: --all-features --target ${{ matrix.platform.target }}
+
+  swc:
+    name: Minimize JavaScript
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install SWC
+        run: sudo npm i -g @swc/cli
+      - name: Run SWC
+        run: |
+          swc src/platform_impl/web/web_sys/worker.js -o src/platform_impl/web/web_sys/worker.min.js
+      - name: Check for diff
+        run: |
+          [[ -z $(git status -s) ]]

.gitignore

@@ -3,8 +3,5 @@ target/
 rls/
 .vscode/
 *~
-*.wasm
-*.ts
-*.js
 #*#
 .DS_Store

.swcrc

@@ -0,0 +1,12 @@
+{
+	"minify": true,
+	"jsc": {
+		"target": "es2022",
+		"minify": {
+			"compress": {
+				"unused": true
+			},
+			"mangle": true
+		}
+	}
+}

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "winit"
-version = "0.30.1"
+version = "0.30.3"
 authors = [
     "The winit contributors",
     "Pierre Krieger <pierre.krieger1708@gmail.com>",
@@ -125,6 +125,7 @@ features = [
     "NSDictionary",
     "NSDistributedNotificationCenter",
     "NSEnumerator",
+    "NSKeyValueObserving",
     "NSNotification",
     "NSObjCRuntime",
     "NSPathUtilities",
@@ -142,6 +143,7 @@ features = [
     "NSApplication",
     "NSBitmapImageRep",
     "NSButton",
+    "NSColor",
     "NSControl",
     "NSCursor",
     "NSDragging",
@@ -283,6 +285,7 @@ features = [
     'AbortController',
     'AbortSignal',
     'Blob',
+    'BlobPropertyBag',
     'console',
     'CssStyleDeclaration',
     'Document',
@@ -318,6 +321,7 @@ features = [
     'VisibilityState',
     'Window',
     'WheelEvent',
+    'Worker',
     'Url',
 ]
 

README.md

@@ -8,7 +8,7 @@
 
 ```toml
 [dependencies]
-winit = "0.30.1"
+winit = "0.30.3"
 ```
 
 ## [Documentation](https://docs.rs/winit)

examples/window.rs

@@ -212,6 +212,12 @@ impl Application {
             Action::PrintHelp => self.print_help(),
             #[cfg(macos_platform)]
             Action::CycleOptionAsAlt => window.cycle_option_as_alt(),
+            Action::SetTheme(theme) => {
+                window.window.set_theme(theme);
+                // Get the resulting current theme to draw with
+                let actual_theme = theme.or_else(|| window.window.theme()).unwrap_or(Theme::Dark);
+                window.set_draw_theme(actual_theme);
+            },
             #[cfg(macos_platform)]
             Action::CreateNewTab => {
                 let tab_id = window.window.tabbing_identifier();
@@ -334,7 +340,7 @@ impl ApplicationHandler<UserEvent> for Application {
             },
             WindowEvent::ThemeChanged(theme) => {
                 info!("Theme changed to {theme:?}");
-                window.set_theme(theme);
+                window.set_draw_theme(theme);
             },
             WindowEvent::RedrawRequested => {
                 if let Err(err) = window.draw() {
@@ -733,8 +739,8 @@ impl WindowState {
         self.window.request_redraw();
     }
 
-    /// Change the theme.
-    fn set_theme(&mut self, theme: Theme) {
+    /// Change the theme that things are drawn in.
+    fn set_draw_theme(&mut self, theme: Theme) {
         self.theme = theme;
         self.window.request_redraw();
     }
@@ -884,6 +890,7 @@ enum Action {
     ShowWindowMenu,
     #[cfg(macos_platform)]
     CycleOptionAsAlt,
+    SetTheme(Option<Theme>),
     #[cfg(macos_platform)]
     CreateNewTab,
     RequestResize,
@@ -915,6 +922,9 @@ impl Action {
             Action::ShowWindowMenu => "Show window menu",
             #[cfg(macos_platform)]
             Action::CycleOptionAsAlt => "Cycle option as alt mode",
+            Action::SetTheme(None) => "Change to the system theme",
+            Action::SetTheme(Some(Theme::Light)) => "Change to a light theme",
+            Action::SetTheme(Some(Theme::Dark)) => "Change to a dark theme",
             #[cfg(macos_platform)]
             Action::CreateNewTab => "Create new tab",
             Action::RequestResize => "Request a resize",
@@ -1059,6 +1069,10 @@ const KEY_BINDINGS: &[Binding<&'static str>] = &[
         Action::AnimationCustomCursor,
     ),
     Binding::new("Z", ModifiersState::CONTROL, Action::ToggleCursorVisibility),
+    // K.
+    Binding::new("K", ModifiersState::empty(), Action::SetTheme(None)),
+    Binding::new("K", ModifiersState::SUPER, Action::SetTheme(Some(Theme::Light))),
+    Binding::new("K", ModifiersState::CONTROL, Action::SetTheme(Some(Theme::Dark))),
     #[cfg(macos_platform)]
     Binding::new("T", ModifiersState::SUPER, Action::CreateNewTab),
     #[cfg(macos_platform)]

src/changelog/v0.30.md

@@ -1,3 +1,34 @@
+## 0.30.3
+
+### Added
+
+- On Web, add `EventLoopExtWebSys::(set_)poll_strategy()` to allow setting
+  control flow strategies before starting the event loop.
+- On Web, add `WaitUntilStrategy`, which allows to set different strategies for
+  `ControlFlow::WaitUntil`. By default the Prioritized Task Scheduling API is
+  used, with a fallback to `setTimeout()` with a trick to circumvent throttling
+  to 4ms. But an option to use a Web worker to schedule the timer is available
+  as well, which commonly prevents any throttling when the window is not focused.
+
+### Changed
+
+- On macOS, set the window theme on the `NSWindow` instead of application-wide.
+
+### Fixed
+
+- On X11, build on arm platforms.
+- On macOS, fixed `WindowBuilder::with_theme` not having any effect on the window.
+
+## 0.30.2
+
+### Fixed
+
+- On Web, fix `EventLoopProxy::send_event()` triggering event loop immediately
+  when not called from inside the event loop. Now queues a microtask instead.
+- On Web, stop overwriting default cursor with `CursorIcon::Default`.
+- On Web, prevent crash when using `InnerSizeWriter::request_inner_size()`.
+- On macOS, fix not working opacity for entire window.
+
 ## 0.30.1
 
 ### Added

src/event.rs

@@ -389,6 +389,8 @@ pub enum WindowEvent {
     /// Applications might wish to react to this to change the theme of the content of the window
     /// when the system changes the window theme.
     ///
+    /// This only reports a change if the window theme was not overridden by [`Window::set_theme`].
+    ///
     /// ## Platform-specific
     ///
     /// - **iOS / Android / X11 / Wayland / Orbital:** Unsupported.

src/platform/android.rs

@@ -62,7 +62,7 @@
 //! If your application is currently based on `NativeActivity` via the `ndk-glue` crate and building
 //! with `cargo apk`, then the minimal changes would be:
 //! 1. Remove `ndk-glue` from your `Cargo.toml`
-//! 2. Enable the `"android-native-activity"` feature for Winit: `winit = { version = "0.30.1",
+//! 2. Enable the `"android-native-activity"` feature for Winit: `winit = { version = "0.30.3",
 //!    features = [ "android-native-activity" ] }`
 //! 3. Add an `android_main` entrypoint (as above), instead of using the '`[ndk_glue::main]` proc
 //!    macro from `ndk-macros` (optionally add a dependency on `android_logger` and initialize

src/platform/web.rs

@@ -190,6 +190,34 @@ pub trait EventLoopExtWebSys {
     fn spawn<F>(self, event_handler: F)
     where
         F: 'static + FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
+
+    /// Sets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn set_poll_strategy(&self, strategy: PollStrategy);
+
+    /// Gets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn poll_strategy(&self) -> PollStrategy;
+
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
 }
 
 impl<T> EventLoopExtWebSys for EventLoop<T> {
@@ -207,6 +235,22 @@ impl<T> EventLoopExtWebSys for EventLoop<T> {
     {
         self.event_loop.spawn(event_handler)
     }
+
+    fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.event_loop.set_poll_strategy(strategy);
+    }
+
+    fn poll_strategy(&self) -> PollStrategy {
+        self.event_loop.poll_strategy()
+    }
+
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.event_loop.set_wait_until_strategy(strategy);
+    }
+
+    fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.event_loop.wait_until_strategy()
+    }
 }
 
 pub trait ActiveEventLoopExtWebSys {
@@ -224,6 +268,20 @@ pub trait ActiveEventLoopExtWebSys {
     /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
     fn poll_strategy(&self) -> PollStrategy;
 
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
+
     /// Async version of [`ActiveEventLoop::create_custom_cursor()`] which waits until the
     /// cursor has completely finished loading.
     fn create_custom_cursor_async(&self, source: CustomCursorSource) -> CustomCursorFuture;
@@ -244,6 +302,16 @@ impl ActiveEventLoopExtWebSys for ActiveEventLoop {
     fn poll_strategy(&self) -> PollStrategy {
         self.p.poll_strategy()
     }
+
+    #[inline]
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.p.set_wait_until_strategy(strategy);
+    }
+
+    #[inline]
+    fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.p.wait_until_strategy()
+    }
 }
 
 /// Strategy used for [`ControlFlow::Poll`][crate::event_loop::ControlFlow::Poll].
@@ -272,6 +340,29 @@ pub enum PollStrategy {
     Scheduler,
 }
 
+/// Strategy used for [`ControlFlow::WaitUntil`][crate::event_loop::ControlFlow::WaitUntil].
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub enum WaitUntilStrategy {
+    /// Uses the [Prioritized Task Scheduling API] to queue the next event loop. If not available
+    /// this will fallback to [`setTimeout()`].
+    ///
+    /// This strategy is commonly not affected by browser throttling unless the window is not
+    /// focused.
+    ///
+    /// This is the default strategy.
+    ///
+    /// [Prioritized Task Scheduling API]: https://developer.mozilla.org/en-US/docs/Web/API/Prioritized_Task_Scheduling_API
+    /// [`setTimeout()`]: https://developer.mozilla.org/en-US/docs/Web/API/setTimeout
+    #[default]
+    Scheduler,
+    /// Equal to [`Scheduler`][Self::Scheduler] but wakes up the event loop from a [worker].
+    ///
+    /// This strategy is commonly not affected by browser throttling regardless of window focus.
+    ///
+    /// [worker]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
+    Worker,
+}
+
 pub trait CustomCursorExtWebSys {
     /// Returns if this cursor is an animation.
     fn is_animation(&self) -> bool;

src/platform_impl/android/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(android_platform)]
-
 use std::cell::Cell;
 use std::collections::VecDeque;
 use std::hash::Hash;

src/platform_impl/ios/app_state.rs

@@ -798,7 +798,7 @@ impl EventLoopWaker {
             // future, but that gets changed to fire immediately in did_finish_launching
             let timer = CFRunLoopTimerCreate(
                 ptr::null_mut(),
-                std::f64::MAX,
+                f64::MAX,
                 0.000_000_1,
                 0,
                 0,
@@ -812,11 +812,11 @@ impl EventLoopWaker {
     }
 
     fn stop(&mut self) {
-        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MAX) }
+        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
     }
 
     fn start(&mut self) {
-        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MIN) }
+        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
     }
 
     fn start_at(&mut self, instant: Instant) {

src/platform_impl/ios/event_loop.rs

@@ -274,8 +274,7 @@ impl<T> EventLoopProxy<T> {
                 cancel: None,
                 perform: event_loop_proxy_handler,
             };
-            let source =
-                CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::max_value() - 1, &mut context);
+            let source = CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::MAX - 1, &mut context);
             CFRunLoopAddSource(rl, source, kCFRunLoopCommonModes);
             CFRunLoopWakeUp(rl);
 
@@ -358,7 +357,7 @@ fn setup_control_flow_observers() {
             ptr::null_mut(),
             kCFRunLoopAfterWaiting,
             1, // repeat = true
-            CFIndex::min_value(),
+            CFIndex::MIN,
             control_flow_begin_handler,
             ptr::null_mut(),
         );
@@ -378,7 +377,7 @@ fn setup_control_flow_observers() {
             ptr::null_mut(),
             kCFRunLoopExit | kCFRunLoopBeforeWaiting,
             1, // repeat = true
-            CFIndex::max_value(),
+            CFIndex::MAX,
             control_flow_end_handler,
             ptr::null_mut(),
         );

src/platform_impl/ios/mod.rs

@@ -1,4 +1,3 @@
-#![cfg(ios_platform)]
 #![allow(clippy::let_unit_value)]
 
 mod app_delegate;

src/platform_impl/linux/wayland/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(wayland_platform)]
-
 //! Winit's Wayland backend.
 
 use std::fmt::Display;

src/platform_impl/linux/x11/event_processor.rs

@@ -434,7 +434,7 @@ impl EventProcessor {
             let flags = xev.data.get_long(1);
             let version = flags >> 24;
             self.dnd.version = Some(version);
-            let has_more_types = flags - (flags & (c_long::max_value() - 1)) == 1;
+            let has_more_types = flags - (flags & (c_long::MAX - 1)) == 1;
             if !has_more_types {
                 let type_list = vec![
                     xev.data.get_long(2) as xproto::Atom,

src/platform_impl/linux/x11/ime/context.rs

@@ -158,7 +158,9 @@ struct PreeditCallbacks {
 impl PreeditCallbacks {
     pub fn new(client_data: ffi::XPointer) -> PreeditCallbacks {
         let start_callback = create_xim_callback(client_data, unsafe {
-            mem::transmute(preedit_start_callback as usize)
+            mem::transmute::<usize, unsafe extern "C" fn(ffi::XIM, ffi::XPointer, ffi::XPointer)>(
+                preedit_start_callback as usize,
+            )
         });
         let done_callback = create_xim_callback(client_data, preedit_done_callback);
         let caret_callback = create_xim_callback(client_data, preedit_caret_callback);

src/platform_impl/linux/x11/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(x11_platform)]
-
 use std::cell::{Cell, RefCell};
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::ffi::CStr;

src/platform_impl/macos/event_loop.rs

@@ -482,8 +482,7 @@ impl<T> EventLoopProxy<T> {
                 cancel: None,
                 perform: event_loop_proxy_handler,
             };
-            let source =
-                CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::max_value() - 1, &mut context);
+            let source = CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::MAX - 1, &mut context);
             CFRunLoopAddSource(rl, source, kCFRunLoopCommonModes);
             CFRunLoopWakeUp(rl);
 

src/platform_impl/macos/observer.rs

@@ -214,13 +214,13 @@ pub fn setup_control_flow_observers(mtm: MainThreadMarker, panic_info: Weak<Pani
         };
         run_loop.add_observer(
             kCFRunLoopAfterWaiting,
-            CFIndex::min_value(),
+            CFIndex::MIN,
             control_flow_begin_handler,
             &mut context as *mut _,
         );
         run_loop.add_observer(
             kCFRunLoopExit | kCFRunLoopBeforeWaiting,
-            CFIndex::max_value(),
+            CFIndex::MAX,
             control_flow_end_handler,
             &mut context as *mut _,
         );
@@ -260,7 +260,7 @@ impl EventLoopWaker {
             // future, but that gets changed to fire immediately in did_finish_launching
             let timer = CFRunLoopTimerCreate(
                 ptr::null_mut(),
-                std::f64::MAX,
+                f64::MAX,
                 0.000_000_1,
                 0,
                 0,
@@ -275,14 +275,14 @@ impl EventLoopWaker {
     pub fn stop(&mut self) {
         if self.next_fire_date.is_some() {
             self.next_fire_date = None;
-            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MAX) }
+            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
         }
     }
 
     pub fn start(&mut self) {
         if self.next_fire_date != Some(self.start_instant) {
             self.next_fire_date = Some(self.start_instant);
-            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MIN) }
+            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
         }
     }
 

src/platform_impl/macos/window_delegate.rs

@@ -1,6 +1,8 @@
 #![allow(clippy::unnecessary_cast)]
 use std::cell::{Cell, RefCell};
 use std::collections::VecDeque;
+use std::ffi::c_void;
+use std::ptr;
 use std::sync::{Arc, Mutex};
 
 use core_graphics::display::{CGDisplay, CGPoint};
@@ -9,18 +11,20 @@ use objc2::rc::{autoreleasepool, Retained};
 use objc2::runtime::{AnyObject, ProtocolObject};
 use objc2::{declare_class, msg_send_id, mutability, sel, ClassType, DeclaredClass};
 use objc2_app_kit::{
-    NSAppKitVersionNumber, NSAppKitVersionNumber10_12, NSAppearance, NSApplication,
-    NSApplicationPresentationOptions, NSBackingStoreType, NSDraggingDestination,
-    NSFilenamesPboardType, NSPasteboard, NSRequestUserAttentionType, NSScreen, NSView,
-    NSWindowButton, NSWindowDelegate, NSWindowFullScreenButton, NSWindowLevel,
-    NSWindowOcclusionState, NSWindowOrderingMode, NSWindowSharingType, NSWindowStyleMask,
-    NSWindowTabbingMode, NSWindowTitleVisibility,
+    NSAppKitVersionNumber, NSAppKitVersionNumber10_12, NSAppearance, NSAppearanceCustomization,
+    NSAppearanceNameAqua, NSApplication, NSApplicationPresentationOptions, NSBackingStoreType,
+    NSColor, NSDraggingDestination, NSFilenamesPboardType, NSPasteboard,
+    NSRequestUserAttentionType, NSScreen, NSView, NSWindowButton, NSWindowDelegate,
+    NSWindowFullScreenButton, NSWindowLevel, NSWindowOcclusionState, NSWindowOrderingMode,
+    NSWindowSharingType, NSWindowStyleMask, NSWindowTabbingMode, NSWindowTitleVisibility,
 };
 use objc2_foundation::{
-    ns_string, CGFloat, MainThreadMarker, NSArray, NSCopying, NSDistributedNotificationCenter,
-    NSObject, NSObjectNSDelayedPerforming, NSObjectNSThreadPerformAdditions, NSObjectProtocol,
-    NSPoint, NSRect, NSSize, NSString,
+    ns_string, CGFloat, MainThreadMarker, NSArray, NSCopying, NSDictionary, NSKeyValueChangeKey,
+    NSKeyValueChangeNewKey, NSKeyValueChangeOldKey, NSKeyValueObservingOptions, NSObject,
+    NSObjectNSDelayedPerforming, NSObjectNSKeyValueObserverRegistration, NSObjectProtocol, NSPoint,
+    NSRect, NSSize, NSString,
 };
+use tracing::{trace, warn};
 
 use super::app_state::ApplicationDelegate;
 use super::cursor::cursor_from_icon;
@@ -79,8 +83,6 @@ pub(crate) struct State {
 
     window: Retained<WinitWindow>,
 
-    current_theme: Cell<Option<Theme>>,
-
     // During `windowDidResize`, we use this to only send Moved if the position changed.
     //
     // This is expressed in native screen coordinates.
@@ -419,32 +421,66 @@ declare_class!(
         }
     }
 
+    // Key-Value Observing
     unsafe impl WindowDelegate {
-        // Observe theme change
-        #[method(effectiveAppearanceDidChange:)]
-        fn effective_appearance_did_change(&self, sender: Option<&AnyObject>) {
-            trace_scope!("effectiveAppearanceDidChange:");
-            unsafe {
-                self.performSelectorOnMainThread_withObject_waitUntilDone(
-                    sel!(effectiveAppearanceDidChangedOnMainThread:),
-                    sender,
-                    false,
-                )
-            };
-        }
+        #[method(observeValueForKeyPath:ofObject:change:context:)]
+        fn observe_value(
+            &self,
+            key_path: Option<&NSString>,
+            _object: Option<&AnyObject>,
+            change: Option<&NSDictionary<NSKeyValueChangeKey, AnyObject>>,
+            _context: *mut c_void,
+        ) {
+            trace_scope!("observeValueForKeyPath:ofObject:change:context:");
+            // NOTE: We don't _really_ need to check the key path, as there should only be one, but
+            // in the future we might want to observe other key paths.
+            if key_path == Some(ns_string!("effectiveAppearance")) {
+                let change = change.expect("requested a change dictionary in `addObserver`, but none was provided");
+                let old = change.get(unsafe { NSKeyValueChangeOldKey }).expect("requested change dictionary did not contain `NSKeyValueChangeOldKey`");
+                let new = change.get(unsafe { NSKeyValueChangeNewKey }).expect("requested change dictionary did not contain `NSKeyValueChangeNewKey`");
 
-        #[method(effectiveAppearanceDidChangedOnMainThread:)]
-        fn effective_appearance_did_changed_on_main_thread(&self, _: Option<&AnyObject>) {
-            let mtm = MainThreadMarker::from(self);
-            let theme = get_ns_theme(mtm);
-            let old_theme = self.ivars().current_theme.replace(Some(theme));
-            if old_theme != Some(theme) {
-                self.queue_event(WindowEvent::ThemeChanged(theme));
+                // SAFETY: The value of `effectiveAppearance` is `NSAppearance`
+                let old: *const AnyObject = old;
+                let old: *const NSAppearance = old.cast();
+                let old: &NSAppearance = unsafe { &*old };
+                let new: *const AnyObject = new;
+                let new: *const NSAppearance = new.cast();
+                let new: &NSAppearance = unsafe { &*new };
+
+                trace!(old = %unsafe { old.name() }, new = %unsafe { new.name() }, "effectiveAppearance changed");
+
+                // Ignore the change if the window's theme is customized by the user (since in that
+                // case the `effectiveAppearance` is only emitted upon said customization, and then
+                // it's triggered directly by a user action, and we don't want to emit the event).
+                if unsafe { self.window().appearance() }.is_some() {
+                    return;
+                }
+
+                let old = appearance_to_theme(old);
+                let new = appearance_to_theme(new);
+                // Check that the theme changed in Winit's terms (the theme might have changed on
+                // other parameters, such as level of contrast, but the event should not be emitted
+                // in those cases).
+                if old == new {
+                    return;
+                }
+
+                self.queue_event(WindowEvent::ThemeChanged(new));
+            } else {
+                panic!("unknown observed keypath {key_path:?}");
             }
         }
     }
 );
 
+impl Drop for WindowDelegate {
+    fn drop(&mut self) {
+        unsafe {
+            self.window().removeObserver_forKeyPath(self, ns_string!("effectiveAppearance"));
+        }
+    }
+}
+
 fn new_window(
     app_delegate: &ApplicationDelegate,
     attrs: &WindowAttributes,
@@ -613,6 +649,8 @@ fn new_window(
 
         if attrs.transparent {
             window.setOpaque(false);
+            // See `set_transparent` for details on why we do this.
+            window.setBackgroundColor(unsafe { Some(&NSColor::clearColor()) });
         }
 
         // register for drag and drop operations.
@@ -666,15 +704,13 @@ impl WindowDelegate {
 
         let scale_factor = window.backingScaleFactor() as _;
 
-        let current_theme = match attrs.preferred_theme {
-            Some(theme) => Some(theme),
-            None => Some(get_ns_theme(mtm)),
-        };
+        if let Some(appearance) = theme_to_appearance(attrs.preferred_theme) {
+            unsafe { window.setAppearance(Some(&appearance)) };
+        }
 
         let delegate = mtm.alloc().set_ivars(State {
             app_delegate: app_delegate.retain(),
             window: window.retain(),
-            current_theme: Cell::new(current_theme),
             previous_position: Cell::new(None),
             previous_scale_factor: Cell::new(scale_factor),
             resize_increments: Cell::new(resize_increments),
@@ -700,14 +736,16 @@ impl WindowDelegate {
         }
         window.setDelegate(Some(ProtocolObject::from_ref(&*delegate)));
 
-        // Enable theme change event
-        let notification_center = unsafe { NSDistributedNotificationCenter::defaultCenter() };
+        // Listen for theme change event.
+        //
+        // SAFETY: The observer is un-registered in the `Drop` of the delegate.
         unsafe {
-            notification_center.addObserver_selector_name_object(
+            window.addObserver_forKeyPath_options_context(
                 &delegate,
-                sel!(effectiveAppearanceDidChange:),
-                Some(ns_string!("AppleInterfaceThemeChangedNotification")),
-                None,
+                ns_string!("effectiveAppearance"),
+                NSKeyValueObservingOptions::NSKeyValueObservingOptionNew
+                    | NSKeyValueObservingOptions::NSKeyValueObservingOptionOld,
+                ptr::null_mut(),
             )
         };
 
@@ -821,7 +859,23 @@ impl WindowDelegate {
     }
 
     pub fn set_transparent(&self, transparent: bool) {
-        self.window().setOpaque(!transparent)
+        // This is just a hint for Quartz, it doesn't actually speculate with window alpha.
+        // Providing a wrong value here could result in visual artifacts, when the window is
+        // transparent.
+        self.window().setOpaque(!transparent);
+
+        // AppKit draws the window with a background color by default, which is usually really
+        // nice, but gets in the way when we want to allow the contents of the window to be
+        // transparent, as in that case, the transparent contents will just be drawn on top of
+        // the background color. As such, to allow the window to be transparent, we must also set
+        // the background color to one with an empty alpha channel.
+        let color = if transparent {
+            unsafe { NSColor::clearColor() }
+        } else {
+            unsafe { NSColor::windowBackgroundColor() }
+        };
+
+        self.window().setBackgroundColor(Some(&color));
     }
 
     pub fn set_blur(&self, blur: bool) {
@@ -920,8 +974,8 @@ impl WindowDelegate {
 
     pub fn set_max_inner_size(&self, dimensions: Option<Size>) {
         let dimensions = dimensions.unwrap_or(Size::Logical(LogicalSize {
-            width: std::f32::MAX as f64,
-            height: std::f32::MAX as f64,
+            width: f32::MAX as f64,
+            height: f32::MAX as f64,
         }));
         let scale_factor = self.scale_factor();
         let max_size = dimensions.to_logical::<CGFloat>(scale_factor);
@@ -1597,20 +1651,24 @@ impl WindowDelegate {
         }
     }
 
-    #[inline]
-    pub fn theme(&self) -> Option<Theme> {
-        self.ivars().current_theme.get()
-    }
-
     #[inline]
     pub fn has_focus(&self) -> bool {
         self.window().isKeyWindow()
     }
 
+    pub fn theme(&self) -> Option<Theme> {
+        // Note: We could choose between returning the value of `effectiveAppearance` or
+        // `appearance`, depending on what the user is asking about:
+        // - "how should I render on this particular frame".
+        // - "what is the configuration for this window".
+        //
+        // We choose the latter for consistency with the `set_theme` call, though it might also be
+        // useful to expose the former.
+        Some(appearance_to_theme(unsafe { &*self.window().appearance()? }))
+    }
+
     pub fn set_theme(&self, theme: Option<Theme>) {
-        let mtm = MainThreadMarker::from(self);
-        set_ns_theme(theme, mtm);
-        self.ivars().current_theme.set(theme.or_else(|| Some(get_ns_theme(mtm))));
+        unsafe { self.window().setAppearance(theme_to_appearance(theme).as_deref()) };
     }
 
     #[inline]
@@ -1769,34 +1827,39 @@ impl WindowExtMacOS for WindowDelegate {
 const DEFAULT_STANDARD_FRAME: NSRect =
     NSRect::new(NSPoint::new(50.0, 50.0), NSSize::new(800.0, 600.0));
 
-pub(super) fn get_ns_theme(mtm: MainThreadMarker) -> Theme {
-    let app = NSApplication::sharedApplication(mtm);
-    if !app.respondsToSelector(sel!(effectiveAppearance)) {
-        return Theme::Light;
-    }
-    let appearance = app.effectiveAppearance();
-    let name = appearance
-        .bestMatchFromAppearancesWithNames(&NSArray::from_id_slice(&[
-            NSString::from_str("NSAppearanceNameAqua"),
-            NSString::from_str("NSAppearanceNameDarkAqua"),
-        ]))
-        .unwrap();
-    match &*name.to_string() {
-        "NSAppearanceNameDarkAqua" => Theme::Dark,
-        _ => Theme::Light,
+fn dark_appearance_name() -> &'static NSString {
+    // Don't use the static `NSAppearanceNameDarkAqua` to allow linking on macOS < 10.14
+    ns_string!("NSAppearanceNameDarkAqua")
+}
+
+fn appearance_to_theme(appearance: &NSAppearance) -> Theme {
+    let best_match = appearance.bestMatchFromAppearancesWithNames(&NSArray::from_id_slice(&[
+        unsafe { NSAppearanceNameAqua.copy() },
+        dark_appearance_name().copy(),
+    ]));
+    if let Some(best_match) = best_match {
+        if *best_match == *dark_appearance_name() {
+            Theme::Dark
+        } else {
+            Theme::Light
+        }
+    } else {
+        warn!(?appearance, "failed to determine the theme of the appearance");
+        // Default to light in this case
+        Theme::Light
     }
 }
 
-fn set_ns_theme(theme: Option<Theme>, mtm: MainThreadMarker) {
-    let app = NSApplication::sharedApplication(mtm);
-    if app.respondsToSelector(sel!(effectiveAppearance)) {
-        let appearance = theme.map(|t| {
-            let name = match t {
-                Theme::Dark => NSString::from_str("NSAppearanceNameDarkAqua"),
-                Theme::Light => NSString::from_str("NSAppearanceNameAqua"),
-            };
-            NSAppearance::appearanceNamed(&name).unwrap()
-        });
-        app.setAppearance(appearance.as_ref().map(|a| a.as_ref()));
+fn theme_to_appearance(theme: Option<Theme>) -> Option<Retained<NSAppearance>> {
+    let appearance = match theme? {
+        Theme::Light => unsafe { NSAppearance::appearanceNamed(NSAppearanceNameAqua) },
+        Theme::Dark => NSAppearance::appearanceNamed(dark_appearance_name()),
+    };
+    if let Some(appearance) = appearance {
+        Some(appearance)
+    } else {
+        warn!(?theme, "could not find appearance for theme");
+        // Assume system appearance in this case
+        None
     }
 }

src/platform_impl/orbital/mod.rs

@@ -103,7 +103,7 @@ pub struct WindowId {
 
 impl WindowId {
     pub const fn dummy() -> Self {
-        WindowId { fd: u64::max_value() }
+        WindowId { fd: u64::MAX }
     }
 }
 

src/platform_impl/web/async/dispatcher.rs

@@ -68,7 +68,12 @@ impl<T> Dispatcher<T> {
             // SAFETY: The `transmute` is necessary because `Closure` requires `'static`. This is
             // safe because this function won't return until `f` has finished executing. See
             // `Self::new()`.
-            let closure = Closure(unsafe { std::mem::transmute(closure) });
+            let closure = Closure(unsafe {
+                std::mem::transmute::<
+                    Box<dyn FnOnce(&T) + Send>,
+                    Box<dyn FnOnce(&T) + Send + 'static>,
+                >(closure)
+            });
 
             self.0.send(closure);
 

src/platform_impl/web/async/waker.rs

@@ -1,4 +1,5 @@
 use std::future;
+use std::num::NonZeroUsize;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::task::Poll;
@@ -6,13 +7,13 @@ use std::task::Poll;
 use super::super::main_thread::MainThreadMarker;
 use super::{AtomicWaker, Wrapper};
 
-pub struct WakerSpawner<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
+pub struct WakerSpawner<T: 'static>(Wrapper<Handler<T>, Sender, NonZeroUsize>);
 
-pub struct Waker<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
+pub struct Waker<T: 'static>(Wrapper<Handler<T>, Sender, NonZeroUsize>);
 
 struct Handler<T> {
     value: T,
-    handler: fn(&T, usize),
+    handler: fn(&T, NonZeroUsize, bool),
 }
 
 #[derive(Clone)]
@@ -20,7 +21,11 @@ struct Sender(Arc<Inner>);
 
 impl<T> WakerSpawner<T> {
     #[track_caller]
-    pub fn new(main_thread: MainThreadMarker, value: T, handler: fn(&T, usize)) -> Option<Self> {
+    pub fn new(
+        main_thread: MainThreadMarker,
+        value: T,
+        handler: fn(&T, NonZeroUsize, bool),
+    ) -> Option<Self> {
         let inner = Arc::new(Inner {
             counter: AtomicUsize::new(0),
             waker: AtomicWaker::new(),
@@ -37,7 +42,7 @@ impl<T> WakerSpawner<T> {
             |handler, count| {
                 let handler = handler.borrow();
                 let handler = handler.as_ref().unwrap();
-                (handler.handler)(&handler.value, count);
+                (handler.handler)(&handler.value, count, true);
             },
             {
                 let inner = Arc::clone(&inner);
@@ -46,29 +51,31 @@ impl<T> WakerSpawner<T> {
                     while let Some(count) = future::poll_fn(|cx| {
                         let count = inner.counter.swap(0, Ordering::Relaxed);
 
-                        if count > 0 {
-                            Poll::Ready(Some(count))
-                        } else {
-                            inner.waker.register(cx.waker());
+                        match NonZeroUsize::new(count) {
+                            Some(count) => Poll::Ready(Some(count)),
+                            None => {
+                                inner.waker.register(cx.waker());
 
-                            let count = inner.counter.swap(0, Ordering::Relaxed);
+                                let count = inner.counter.swap(0, Ordering::Relaxed);
 
-                            if count > 0 {
-                                Poll::Ready(Some(count))
-                            } else {
-                                if inner.closed.load(Ordering::Relaxed) {
-                                    return Poll::Ready(None);
+                                match NonZeroUsize::new(count) {
+                                    Some(count) => Poll::Ready(Some(count)),
+                                    None => {
+                                        if inner.closed.load(Ordering::Relaxed) {
+                                            return Poll::Ready(None);
+                                        }
+
+                                        Poll::Pending
+                                    },
                                 }
-
-                                Poll::Pending
-                            }
+                            },
                         }
                     })
                     .await
                     {
                         let handler = handler.borrow();
                         let handler = handler.as_ref().unwrap();
-                        (handler.handler)(&handler.value, count);
+                        (handler.handler)(&handler.value, count, false);
                     }
                 }
             },
@@ -107,7 +114,7 @@ impl<T> Drop for WakerSpawner<T> {
 
 impl<T> Waker<T> {
     pub fn wake(&self) {
-        self.0.send(1)
+        self.0.send(NonZeroUsize::MIN)
     }
 }
 

src/platform_impl/web/cursor.rs

@@ -324,7 +324,11 @@ impl Inner {
             match &self.cursor {
                 SelectedCursor::Icon(icon)
                 | SelectedCursor::Loading { previous: Previous::Icon(icon), .. } => {
-                    self.style.set("cursor", icon.name())
+                    if let CursorIcon::Default = icon {
+                        self.style.remove("cursor")
+                    } else {
+                        self.style.set("cursor", icon.name())
+                    }
                 },
                 SelectedCursor::Loading { previous: Previous::Image(cursor), .. }
                 | SelectedCursor::Image(cursor) => {

src/platform_impl/web/event_loop/mod.rs

@@ -4,6 +4,7 @@ use std::sync::mpsc::{self, Receiver, Sender};
 use crate::error::EventLoopError;
 use crate::event::Event;
 use crate::event_loop::ActiveEventLoop as RootActiveEventLoop;
+use crate::platform::web::{ActiveEventLoopExtWebSys, PollStrategy, WaitUntilStrategy};
 
 use super::{backend, device, window};
 
@@ -53,7 +54,11 @@ impl<T> EventLoop<T> {
         // SAFETY: The `transmute` is necessary because `run()` requires `'static`. This is safe
         // because this function will never return and all resources not cleaned up by the point we
         // `throw` will leak, making this actually `'static`.
-        let handler = unsafe { std::mem::transmute(handler) };
+        let handler = unsafe {
+            std::mem::transmute::<Box<dyn FnMut(Event<()>)>, Box<dyn FnMut(Event<()>) + 'static>>(
+                handler,
+            )
+        };
         self.elw.p.run(handler, false);
 
         // Throw an exception to break out of Rust execution and use unreachable to tell the
@@ -95,4 +100,20 @@ impl<T> EventLoop<T> {
     pub fn window_target(&self) -> &RootActiveEventLoop {
         &self.elw
     }
+
+    pub fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.elw.set_poll_strategy(strategy);
+    }
+
+    pub fn poll_strategy(&self) -> PollStrategy {
+        self.elw.poll_strategy()
+    }
+
+    pub fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.elw.set_wait_until_strategy(strategy);
+    }
+
+    pub fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.elw.wait_until_strategy()
+    }
 }

src/platform_impl/web/event_loop/runner.rs

@@ -8,18 +8,21 @@ use crate::event::{
     WindowEvent,
 };
 use crate::event_loop::{ControlFlow, DeviceEvents};
-use crate::platform::web::PollStrategy;
+use crate::platform::web::{PollStrategy, WaitUntilStrategy};
 use crate::platform_impl::platform::backend::EventListenerHandle;
 use crate::platform_impl::platform::r#async::{DispatchRunner, Waker, WakerSpawner};
 use crate::platform_impl::platform::window::Inner;
 use crate::window::WindowId;
 
+use js_sys::Function;
 use std::cell::{Cell, RefCell};
 use std::collections::{HashSet, VecDeque};
 use std::iter;
+use std::num::NonZeroUsize;
 use std::ops::Deref;
 use std::rc::{Rc, Weak};
-use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::prelude::{wasm_bindgen, Closure};
+use wasm_bindgen::JsCast;
 use web_sys::{Document, KeyboardEvent, PageTransitionEvent, PointerEvent, WheelEvent};
 use web_time::{Duration, Instant};
 
@@ -40,6 +43,7 @@ pub struct Execution {
     proxy_spawner: WakerSpawner<Weak<Self>>,
     control_flow: Cell<ControlFlow>,
     poll_strategy: Cell<PollStrategy>,
+    wait_until_strategy: Cell<WaitUntilStrategy>,
     exit: Cell<bool>,
     runner: RefCell<RunnerEnum>,
     suspended: Cell<bool>,
@@ -133,18 +137,20 @@ impl Shared {
         let document = window.document().expect("Failed to obtain document");
 
         Shared(Rc::<Execution>::new_cyclic(|weak| {
-            let proxy_spawner = WakerSpawner::new(main_thread, weak.clone(), |runner, count| {
-                if let Some(runner) = runner.upgrade() {
-                    Shared(runner).send_events(iter::repeat(Event::UserEvent(())).take(count))
-                }
-            })
-            .expect("`EventLoop` has to be created in the main thread");
+            let proxy_spawner =
+                WakerSpawner::new(main_thread, weak.clone(), |runner, count, local| {
+                    if let Some(runner) = runner.upgrade() {
+                        Shared(runner).send_user_events(count, local)
+                    }
+                })
+                .expect("`EventLoop` has to be created in the main thread");
 
             Execution {
                 main_thread,
                 proxy_spawner,
                 control_flow: Cell::new(ControlFlow::default()),
                 poll_strategy: Cell::new(PollStrategy::default()),
+                wait_until_strategy: Cell::new(WaitUntilStrategy::default()),
                 exit: Cell::new(false),
                 runner: RefCell::new(RunnerEnum::Pending),
                 suspended: Cell::new(false),
@@ -460,6 +466,51 @@ impl Shared {
         self.send_events(iter::once(event));
     }
 
+    // Add a series of user events to the event loop runner
+    //
+    // This will schedule the event loop to wake up instead of waking it up immediately if its not
+    // running.
+    pub(crate) fn send_user_events(&self, count: NonZeroUsize, local: bool) {
+        // If the event loop is closed, it should discard any new events
+        if self.is_closed() {
+            return;
+        }
+
+        if local {
+            // If the loop is not running and triggered locally, queue on next microtick.
+            if let Ok(RunnerEnum::Running(ref runner)) =
+                self.0.runner.try_borrow().as_ref().map(Deref::deref)
+            {
+                // If we're currently polling let `send_events` do its job.
+                if !matches!(runner.state, State::Poll { .. }) {
+                    #[wasm_bindgen]
+                    extern "C" {
+                        #[wasm_bindgen(js_name = queueMicrotask)]
+                        fn queue_microtask(task: Function);
+                    }
+
+                    queue_microtask(
+                        Closure::once_into_js({
+                            let this = Rc::downgrade(&self.0);
+                            move || {
+                                if let Some(shared) = this.upgrade() {
+                                    Shared(shared).send_events(
+                                        iter::repeat(Event::UserEvent(())).take(count.get()),
+                                    )
+                                }
+                            }
+                        })
+                        .unchecked_into(),
+                    );
+
+                    return;
+                }
+            }
+        }
+
+        self.send_events(iter::repeat(Event::UserEvent(())).take(count.get()))
+    }
+
     // Add a series of events to the event loop runner
     //
     // It will determine if the event should be immediately sent to the user or buffered for later
@@ -473,7 +524,7 @@ impl Shared {
         match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
             Ok(RunnerEnum::Running(ref runner)) => {
                 // If we're currently polling, queue this and wait for the poll() method to be
-                // called
+                // called.
                 if let State::Poll { .. } = runner.state {
                     process_immediately = false;
                 }
@@ -647,6 +698,7 @@ impl Shared {
                         start,
                         end,
                         _timeout: backend::Schedule::new_with_duration(
+                            self.wait_until_strategy(),
                             self.window(),
                             move || cloned.resume_time_reached(start, end),
                             delay,
@@ -759,6 +811,14 @@ impl Shared {
         self.0.poll_strategy.get()
     }
 
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.0.wait_until_strategy.set(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.0.wait_until_strategy.get()
+    }
+
     pub(crate) fn waker(&self) -> Waker<Weak<Execution>> {
         self.0.proxy_spawner.waker()
     }

src/platform_impl/web/event_loop/window_target.rs

@@ -18,7 +18,7 @@ use crate::event::{
 };
 use crate::event_loop::{ControlFlow, DeviceEvents};
 use crate::keyboard::ModifiersState;
-use crate::platform::web::{CustomCursorFuture, PollStrategy};
+use crate::platform::web::{CustomCursorFuture, PollStrategy, WaitUntilStrategy};
 use crate::platform_impl::platform::cursor::CustomCursor;
 use crate::platform_impl::platform::r#async::Waker;
 use crate::window::{
@@ -682,6 +682,14 @@ impl ActiveEventLoop {
         self.runner.poll_strategy()
     }
 
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.runner.set_wait_until_strategy(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.runner.wait_until_strategy()
+    }
+
     pub(crate) fn waker(&self) -> Waker<Weak<Execution>> {
         self.runner.waker()
     }

src/platform_impl/web/web_sys/canvas.rs

@@ -427,8 +427,8 @@ impl Canvas {
 
     pub(crate) fn on_resize_scale<S, R>(&mut self, scale_handler: S, size_handler: R)
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
         self.on_resize_scale = Some(ResizeScaleHandle::new(
             self.window().clone(),

src/platform_impl/web/web_sys/resize_scaling.rs

@@ -16,7 +16,7 @@ use super::media_query_handle::MediaQueryListHandle;
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 
-pub struct ResizeScaleHandle(Rc<RefCell<ResizeScaleInternal>>);
+pub struct ResizeScaleHandle(Rc<ResizeScaleInternal>);
 
 impl ResizeScaleHandle {
     pub(crate) fn new<S, R>(
@@ -28,8 +28,8 @@ impl ResizeScaleHandle {
         resize_handler: R,
     ) -> Self
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
         Self(ResizeScaleInternal::new(
             window,
@@ -42,7 +42,7 @@ impl ResizeScaleHandle {
     }
 
     pub(crate) fn notify_resize(&self) {
-        self.0.borrow_mut().notify()
+        self.0.notify()
     }
 }
 
@@ -53,11 +53,11 @@ struct ResizeScaleInternal {
     document: Document,
     canvas: HtmlCanvasElement,
     style: Style,
-    mql: MediaQueryListHandle,
+    mql: RefCell<MediaQueryListHandle>,
     observer: ResizeObserver,
     _observer_closure: Closure<dyn FnMut(Array, ResizeObserver)>,
-    scale_handler: Box<dyn FnMut(PhysicalSize<u32>, f64)>,
-    resize_handler: Box<dyn FnMut(PhysicalSize<u32>)>,
+    scale_handler: Box<dyn Fn(PhysicalSize<u32>, f64)>,
+    resize_handler: Box<dyn Fn(PhysicalSize<u32>)>,
     notify_scale: Cell<bool>,
 }
 
@@ -69,12 +69,12 @@ impl ResizeScaleInternal {
         style: Style,
         scale_handler: S,
         resize_handler: R,
-    ) -> Rc<RefCell<Self>>
+    ) -> Rc<Self>
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
-        Rc::<RefCell<ResizeScaleInternal>>::new_cyclic(|weak_self| {
+        Rc::<ResizeScaleInternal>::new_cyclic(|weak_self| {
             let mql = Self::create_mql(&window, {
                 let weak_self = weak_self.clone();
                 move |mql| {
@@ -86,9 +86,7 @@ impl ResizeScaleInternal {
 
             let weak_self = weak_self.clone();
             let observer_closure = Closure::new(move |entries: Array, _| {
-                if let Some(rc_self) = weak_self.upgrade() {
-                    let mut this = rc_self.borrow_mut();
-
+                if let Some(this) = weak_self.upgrade() {
                     let size = this.process_entry(entries);
 
                     if this.notify_scale.replace(false) {
@@ -101,18 +99,18 @@ impl ResizeScaleInternal {
             });
             let observer = Self::create_observer(&canvas, observer_closure.as_ref());
 
-            RefCell::new(Self {
+            Self {
                 window,
                 document,
                 canvas,
                 style,
-                mql,
+                mql: RefCell::new(mql),
                 observer,
                 _observer_closure: observer_closure,
                 scale_handler: Box::new(scale_handler),
                 resize_handler: Box::new(resize_handler),
                 notify_scale: Cell::new(false),
-            })
+            }
         })
     }
 
@@ -152,7 +150,7 @@ impl ResizeScaleInternal {
         observer
     }
 
-    fn notify(&mut self) {
+    fn notify(&self) {
         if !self.document.contains(Some(&self.canvas)) || self.style.get("display") == "none" {
             let size = PhysicalSize::new(0, 0);
 
@@ -200,10 +198,9 @@ impl ResizeScaleInternal {
         }
     }
 
-    fn handle_scale(this: Rc<RefCell<Self>>, mql: &MediaQueryList) {
-        let weak_self = Rc::downgrade(&this);
-        let mut this = this.borrow_mut();
-        let scale = super::scale_factor(&this.window);
+    fn handle_scale(self: Rc<Self>, mql: &MediaQueryList) {
+        let weak_self = Rc::downgrade(&self);
+        let scale = super::scale_factor(&self.window);
 
         // TODO: confirm/reproduce this problem, see:
         // <https://github.com/rust-windowing/winit/issues/2597>.
@@ -217,15 +214,15 @@ impl ResizeScaleInternal {
             return;
         }
 
-        let new_mql = Self::create_mql(&this.window, move |mql| {
+        let new_mql = Self::create_mql(&self.window, move |mql| {
             if let Some(rc_self) = weak_self.upgrade() {
                 Self::handle_scale(rc_self, mql);
             }
         });
-        this.mql = new_mql;
+        self.mql.replace(new_mql);
 
-        this.notify_scale.set(true);
-        this.notify();
+        self.notify_scale.set(true);
+        self.notify();
     }
 
     fn process_entry(&self, entries: Array) -> PhysicalSize<u32> {

src/platform_impl/web/web_sys/schedule.rs

@@ -1,12 +1,14 @@
-use js_sys::{Function, Object, Promise, Reflect};
+use js_sys::{Array, Function, Object, Promise, Reflect};
 use std::cell::OnceCell;
 use std::time::Duration;
 use wasm_bindgen::closure::Closure;
 use wasm_bindgen::prelude::wasm_bindgen;
 use wasm_bindgen::{JsCast, JsValue};
-use web_sys::{AbortController, AbortSignal, MessageChannel, MessagePort};
+use web_sys::{
+    AbortController, AbortSignal, Blob, BlobPropertyBag, MessageChannel, MessagePort, Url, Worker,
+};
 
-use crate::platform::web::PollStrategy;
+use crate::platform::web::{PollStrategy, WaitUntilStrategy};
 
 #[derive(Debug)]
 pub struct Schedule {
@@ -29,6 +31,7 @@ enum Inner {
         port: MessagePort,
         _timeout_closure: Closure<dyn FnMut()>,
     },
+    Worker(MessagePort),
 }
 
 impl Schedule {
@@ -45,14 +48,24 @@ impl Schedule {
         }
     }
 
-    pub fn new_with_duration<F>(window: &web_sys::Window, f: F, duration: Duration) -> Schedule
+    pub fn new_with_duration<F>(
+        strategy: WaitUntilStrategy,
+        window: &web_sys::Window,
+        f: F,
+        duration: Duration,
+    ) -> Schedule
     where
         F: 'static + FnMut(),
     {
-        if has_scheduler_support(window) {
-            Self::new_scheduler(window, f, Some(duration))
-        } else {
-            Self::new_timeout(window.clone(), f, Some(duration))
+        match strategy {
+            WaitUntilStrategy::Scheduler => {
+                if has_scheduler_support(window) {
+                    Self::new_scheduler(window, f, Some(duration))
+                } else {
+                    Self::new_timeout(window.clone(), f, Some(duration))
+                }
+            },
+            WaitUntilStrategy::Worker => Self::new_worker(f, duration),
         }
     }
 
@@ -153,6 +166,44 @@ impl Schedule {
             },
         }
     }
+
+    fn new_worker<F>(f: F, duration: Duration) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        thread_local! {
+            static URL: ScriptUrl = ScriptUrl::new(include_str!("worker.min.js"));
+            static WORKER: Worker = URL.with(|url| Worker::new(&url.0)).expect("`new Worker()` is not expected to fail with a local script");
+        }
+
+        let channel = MessageChannel::new().unwrap();
+        let closure = Closure::new(f);
+        let port_1 = channel.port1();
+        port_1.set_onmessage(Some(closure.as_ref().unchecked_ref()));
+        port_1.start();
+
+        // `Duration::as_millis()` always rounds down (because of truncation), we want to round
+        // up instead. This makes sure that the we never wake up **before** the given time.
+        let duration = duration
+            .as_secs()
+            .try_into()
+            .ok()
+            .and_then(|secs: u32| secs.checked_mul(1000))
+            .and_then(|secs| secs.checked_add(duration_millis_ceil(duration)))
+            .unwrap_or(u32::MAX);
+
+        WORKER
+            .with(|worker| {
+                let port_2 = channel.port2();
+                worker.post_message_with_transfer(
+                    &Array::of2(&port_2, &duration.into()),
+                    &Array::of1(&port_2).into(),
+                )
+            })
+            .expect("`Worker.postMessage()` is not expected to fail");
+
+        Schedule { _closure: closure, inner: Inner::Worker(port_1) }
+    }
 }
 
 impl Drop for Schedule {
@@ -165,6 +216,10 @@ impl Drop for Schedule {
                 port.close();
                 port.set_onmessage(None);
             },
+            Inner::Worker(port) => {
+                port.close();
+                port.set_onmessage(None);
+            },
         }
     }
 }
@@ -226,6 +281,29 @@ fn has_idle_callback_support(window: &web_sys::Window) -> bool {
     })
 }
 
+struct ScriptUrl(String);
+
+impl ScriptUrl {
+    fn new(script: &str) -> Self {
+        let sequence = Array::of1(&script.into());
+        let mut property = BlobPropertyBag::new();
+        property.type_("text/javascript");
+        let blob = Blob::new_with_str_sequence_and_options(&sequence, &property)
+            .expect("`new Blob()` should never throw");
+
+        let url = Url::create_object_url_with_blob(&blob)
+            .expect("`URL.createObjectURL()` should never throw");
+
+        Self(url)
+    }
+}
+
+impl Drop for ScriptUrl {
+    fn drop(&mut self) {
+        Url::revoke_object_url(&self.0).expect("`URL.revokeObjectURL()` should never throw");
+    }
+}
+
 #[wasm_bindgen]
 extern "C" {
     type WindowSupportExt;

src/platform_impl/web/web_sys/worker.js

@@ -0,0 +1,10 @@
+onmessage = event => {
+    const [port, timeout] = event.data
+    const f = () => port.postMessage(undefined)
+
+    if ('scheduler' in this) {
+        scheduler.postTask(f, { delay: timeout })
+    } else {
+        setTimeout(f, timeout)
+    }
+}

src/platform_impl/web/web_sys/worker.min.js

@@ -0,0 +1 @@
+onmessage=e=>{let[s,t]=e.data,a=()=>s.postMessage(void 0);"scheduler"in this?scheduler.postTask(a,{delay:t}):setTimeout(a,t)};

src/platform_impl/windows/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(windows_platform)]
-
 use smol_str::SmolStr;
 use windows_sys::Win32::Foundation::{HANDLE, HWND};
 use windows_sys::Win32::UI::WindowsAndMessaging::{HMENU, WINDOW_LONG_PTR_INDEX};

src/window.rs

@@ -393,7 +393,6 @@ impl WindowAttributes {
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
     /// - **Wayland:** This controls only CSD. When using `None` it'll try to use dbus to get the
     ///   system preference. When explicit theme is used, this will avoid dbus all together.
     /// - **x11:** Build window with `_GTK_THEME_VARIANT` hint set to `dark` or `light`.
@@ -942,8 +941,7 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** If you're not drawing to the window yourself, you might have to set the
-    ///   background color of the window to enable transparency.
+    /// - **macOS:** This will reset the window's background color.
     /// - **Web / iOS / Android:** Unsupported.
     /// - **X11:** Can only be set while building the window, with
     ///   [`WindowAttributes::with_transparent`].
@@ -1355,11 +1353,12 @@ impl Window {
         self.window.maybe_queue_on_main(move |w| w.request_user_attention(request_type))
     }
 
-    /// Sets the current window theme. Use `None` to fallback to system default.
+    /// Set or override the window theme.
+    ///
+    /// Specify `None` to reset the theme to the system default.
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
     /// - **Wayland:** Sets the theme for the client side decorations. Using `None` will use dbus to
     ///   get the system preference.
     /// - **X11:** Sets `_GTK_THEME_VARIANT` hint to `dark` or `light` and if `None` is used, it
@@ -1375,12 +1374,14 @@ impl Window {
         self.window.maybe_queue_on_main(move |w| w.set_theme(theme))
     }
 
-    /// Returns the current window theme.
+    /// Returns the current window theme override.
+    ///
+    /// Returns `None` if the current theme is set as the system default, or if it cannot be
+    /// determined on the current platform.
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
-    /// - **iOS / Android / Wayland / x11 / Orbital:** Unsupported.
+    /// - **iOS / Android / Wayland / x11 / Orbital:** Unsupported, returns `None`.
     #[inline]
     pub fn theme(&self) -> Option<Theme> {
         let _span = tracing::debug_span!("winit::Window::theme",).entered();