Add 'WindowEvent::Occluded(bool)'

This commits and an event to track window occlusion state,
which could help optimize rendering downstream.

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- Added `WindowEvent::Occluded(bool)`, currently implemented on macOS and X11.
 - On X11, fix events for caps lock key not being sent
 - Build docs on `docs.rs` for iOS and Android as well.
 - **Breaking:** Removed the `WindowAttributes` struct, since all its functionality is accessible from `WindowBuilder`.

src/event.rs

@@ -372,6 +372,15 @@ pub enum WindowEvent<'a> {
     ///
     /// At the moment this is only supported on Windows.
     ThemeChanged(Theme),
+
+    /// 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.
+    ///
+    /// Platform-specific behavior:
+    /// - **iOS / Android / Web / Wayland / Windows :** Unsupported.
+    Occluded(bool),
 }
 
 impl Clone for WindowEvent<'static> {
@@ -461,6 +470,7 @@ impl Clone for WindowEvent<'static> {
             ScaleFactorChanged { .. } => {
                 unreachable!("Static event can't be about scale factor changing")
             }
+            Occluded(occluded) => Occluded(*occluded),
         };
     }
 }
@@ -546,6 +556,7 @@ impl<'a> WindowEvent<'a> {
             Touch(touch) => Some(Touch(touch)),
             ThemeChanged(theme) => Some(ThemeChanged(theme)),
             ScaleFactorChanged { .. } => None,
+            Occluded(occluded) => Some(Occluded(occluded)),
         }
     }
 }

src/platform_impl/linux/x11/event_processor.rs

@@ -531,8 +531,13 @@ impl<T: 'static> EventProcessor<T> {
             ffi::VisibilityNotify => {
                 let xev: &ffi::XVisibilityEvent = xev.as_ref();
                 let xwindow = xev.window;
-
-                self.with_window(xwindow, |window| window.visibility_notify());
+                callback(Event::WindowEvent {
+                    window_id: mkwid(xwindow),
+                    event: WindowEvent::Occluded(xev.state == ffi::VisibilityFullyObscured),
+                });
+                self.with_window(xwindow, |window| {
+                    window.visibility_notify();
+                });
             }
 
             ffi::Expose => {

src/platform_impl/macos/window_delegate.rs

@@ -5,7 +5,7 @@ use std::{
 };
 
 use cocoa::{
-    appkit::{self, NSApplicationPresentationOptions, NSView, NSWindow},
+    appkit::{self, NSApplicationPresentationOptions, NSView, NSWindow, NSWindowOcclusionState},
     base::{id, nil},
     foundation::NSUInteger,
 };
@@ -220,6 +220,10 @@ static WINDOW_DELEGATE_CLASS: Lazy<WindowDelegateClass> = Lazy::new(|| unsafe {
         sel!(windowDidFailToEnterFullScreen:),
         window_did_fail_to_enter_fullscreen as extern "C" fn(&Object, Sel, id),
     );
+    decl.add_method(
+        sel!(windowDidChangeOcclusionState:),
+        window_did_change_occlusion_state as extern "C" fn(&Object, Sel, id),
+    );
 
     decl.add_ivar::<*mut c_void>("winitState");
     WindowDelegateClass(decl.register())
@@ -554,3 +558,18 @@ extern "C" fn window_did_fail_to_enter_fullscreen(this: &Object, _: Sel, _: id)
         }
     });
 }
+
+// Invoked when the occlusion state of the window changes
+extern "C" fn window_did_change_occlusion_state(this: &Object, _: Sel, _: id) {
+    trace_scope!("windowDidChangeOcclusionState:");
+    unsafe {
+        with_state(this, |state| {
+            state.emit_event(WindowEvent::Occluded(
+                !state
+                    .ns_window
+                    .occlusionState()
+                    .contains(NSWindowOcclusionState::NSWindowOcclusionStateVisible),
+            ))
+        });
+    }
+}