add new event WindowOccluded from winit (#10735)

forward for bevy user to consume

# Objective

- since winit 0.27 an event WindowOccluded will be produced:
https://docs.rs/winit/latest/winit/event/enum.WindowEvent.html#variant.Occluded
- on ios this is currently the only way to know if an app comes back
from the background which is an important time to to things (like
resetting the badge)

## Solution

- pick up the winit event and forward it to a new `EventWriter`

---

## Changelog

### Added
- new Event `WindowOccluded` added allowing to hook into
`WindowEvent::Occluded` of winit

crates/bevy_window/src/event.rs

@@ -57,7 +57,7 @@ pub struct WindowCreated {
 /// be closed. This will be sent when the close button of the window is pressed.
 ///
 /// If the default [`WindowPlugin`] is used, these events are handled
-/// by closing the corresponding [`Window`].  
+/// by closing the corresponding [`Window`].
 /// To disable this behavior, set `close_when_requested` on the [`WindowPlugin`]
 /// to `false`.
 ///
@@ -236,6 +236,29 @@ pub struct WindowFocused {
     pub focused: bool,
 }
 
+/// The window has been occluded (completely hidden from view).
+///
+/// This is different to window visibility as it depends on
+/// whether the window is closed, minimised, set invisible,
+/// or fully occluded by another window.
+///
+/// It is the translated version of [`WindowEvent::Occluded`] from the `winit` crate.
+///
+/// [`WindowEvent::Occluded`]: https://docs.rs/winit/latest/winit/event/enum.WindowEvent.html#variant.Occluded
+#[derive(Event, Debug, Clone, PartialEq, Eq, Reflect)]
+#[reflect(Debug, PartialEq)]
+#[cfg_attr(
+    feature = "serialize",
+    derive(serde::Serialize, serde::Deserialize),
+    reflect(Serialize, Deserialize)
+)]
+pub struct WindowOccluded {
+    /// Window that changed occluded state.
+    pub window: Entity,
+    /// Whether it was occluded (true) or not occluded (false).
+    pub occluded: bool,
+}
+
 /// An event that indicates a window's scale factor has changed.
 #[derive(Event, Debug, Clone, PartialEq, Reflect)]
 #[reflect(Debug, PartialEq)]

crates/bevy_window/src/lib.rs

@@ -93,6 +93,7 @@ impl Plugin for WindowPlugin {
             .add_event::<ReceivedCharacter>()
             .add_event::<Ime>()
             .add_event::<WindowFocused>()
+            .add_event::<WindowOccluded>()
             .add_event::<WindowScaleFactorChanged>()
             .add_event::<WindowBackendScaleFactorChanged>()
             .add_event::<FileDragAndDrop>()
@@ -137,6 +138,7 @@ impl Plugin for WindowPlugin {
             .register_type::<CursorLeft>()
             .register_type::<ReceivedCharacter>()
             .register_type::<WindowFocused>()
+            .register_type::<WindowOccluded>()
             .register_type::<WindowScaleFactorChanged>()
             .register_type::<WindowBackendScaleFactorChanged>()
             .register_type::<FileDragAndDrop>()

crates/bevy_winit/src/lib.rs

@@ -40,7 +40,8 @@ use bevy_window::{
     exit_on_all_closed, ApplicationLifetime, CursorEntered, CursorLeft, CursorMoved,
     FileDragAndDrop, Ime, ReceivedCharacter, RequestRedraw, Window,
     WindowBackendScaleFactorChanged, WindowCloseRequested, WindowCreated, WindowDestroyed,
-    WindowFocused, WindowMoved, WindowResized, WindowScaleFactorChanged, WindowThemeChanged,
+    WindowFocused, WindowMoved, WindowOccluded, WindowResized, WindowScaleFactorChanged,
+    WindowThemeChanged,
 };
 #[cfg(target_os = "android")]
 use bevy_window::{PrimaryWindow, RawHandleWrapper};
@@ -275,6 +276,7 @@ struct WindowAndInputEventWriters<'w> {
     window_scale_factor_changed: EventWriter<'w, WindowScaleFactorChanged>,
     window_backend_scale_factor_changed: EventWriter<'w, WindowBackendScaleFactorChanged>,
     window_focused: EventWriter<'w, WindowFocused>,
+    window_occluded: EventWriter<'w, WindowOccluded>,
     window_moved: EventWriter<'w, WindowMoved>,
     window_theme_changed: EventWriter<'w, WindowThemeChanged>,
     window_destroyed: EventWriter<'w, WindowDestroyed>,
@@ -658,6 +660,12 @@ pub fn winit_runner(mut app: App) {
                             focused,
                         });
                     }
+                    WindowEvent::Occluded(occluded) => {
+                        event_writers.window_occluded.send(WindowOccluded {
+                            window: window_entity,
+                            occluded,
+                        });
+                    }
                     WindowEvent::DroppedFile(path_buf) => {
                         event_writers
                             .file_drag_and_drop