Add ViewportInfo::occluded and visible (#7948)

* Part of https://github.com/emilk/egui/issues/5112
* Part of https://github.com/emilk/egui/issues/5113
* Part of https://github.com/emilk/egui/issues/5136

Once we support calling `App::logic` when an app is occluded or
minimized, it is useful to know that it is, in fact, occluded or
minimized.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

crates/eframe/src/native/glow_integration.rs

@@ -822,6 +822,14 @@ impl GlowWinitRunning<'_> {
                 }
             }
 
+            winit::event::WindowEvent::Occluded(is_occluded) => {
+                if let Some(viewport_id) = viewport_id
+                    && let Some(viewport) = glutin.viewports.get_mut(&viewport_id)
+                {
+                    viewport.info.occluded = Some(*is_occluded);
+                }
+            }
+
             winit::event::WindowEvent::CloseRequested => {
                 if viewport_id == Some(ViewportId::ROOT) && self.integration.should_close() {
                     log::debug!(

crates/eframe/src/native/wgpu_integration.rs

@@ -852,6 +852,14 @@ impl WgpuWinitRunning<'_> {
                 }
             }
 
+            winit::event::WindowEvent::Occluded(is_occluded) => {
+                if let Some(viewport_id) = viewport_id
+                    && let Some(viewport) = shared.viewports.get_mut(&viewport_id)
+                {
+                    viewport.info.occluded = Some(*is_occluded);
+                }
+            }
+
             winit::event::WindowEvent::CloseRequested => {
                 if viewport_id == Some(ViewportId::ROOT) && integration.should_close() {
                     log::debug!(

crates/eframe/src/web/backend.rs

@@ -31,11 +31,18 @@ impl WebInput {
             time: Some(super::now_sec()),
             ..self.raw.take()
         };
-        raw_input
+        let viewport = raw_input
             .viewports
             .entry(egui::ViewportId::ROOT)
-            .or_default()
-            .native_pixels_per_point = Some(super::native_pixels_per_point());
+            .or_default();
+        viewport.native_pixels_per_point = Some(super::native_pixels_per_point());
+
+        // A hidden browser tab is effectively occluded.
+        let hidden = web_sys::window()
+            .and_then(|w| w.document())
+            .is_some_and(|doc| doc.hidden());
+        viewport.occluded = Some(hidden);
+
         raw_input
     }
 

crates/egui/src/data/input.rs

@@ -253,9 +253,28 @@ pub struct ViewportInfo {
     ///
     /// This should be the same as [`RawInput::focused`].
     pub focused: Option<bool>,
+
+    /// Is the window fully occluded (completely covered) by another window?
+    ///
+    /// Not all platforms support this.
+    /// On platforms that don't, this will be `None` or `Some(false)`.
+    pub occluded: Option<bool>,
 }
 
 impl ViewportInfo {
+    /// Is the window considered visible for rendering purposes?
+    ///
+    /// A window is not visible if it is minimized or occluded.
+    /// When not visible, the UI is not painted and rendering is skipped,
+    /// but application logic may still be executed by some integrations.
+    pub fn visible(&self) -> Option<bool> {
+        match (self.minimized, self.occluded) {
+            (Some(true), _) | (_, Some(true)) => Some(false),
+            (Some(false), Some(false)) => Some(true),
+            (_, None) | (None, _) => None,
+        }
+    }
+
     /// This viewport has been told to close.
     ///
     /// If this is the root viewport, the application will exit
@@ -282,6 +301,7 @@ impl ViewportInfo {
             maximized: self.maximized,
             fullscreen: self.fullscreen,
             focused: self.focused,
+            occluded: self.occluded,
         }
     }
 
@@ -298,6 +318,7 @@ impl ViewportInfo {
             maximized,
             fullscreen,
             focused,
+            occluded,
         } = self;
 
         crate::Grid::new("viewport_info").show(ui, |ui| {
@@ -345,6 +366,16 @@ impl ViewportInfo {
             ui.label(opt_as_str(focused));
             ui.end_row();
 
+            ui.label("Occluded:");
+            ui.label(opt_as_str(occluded));
+            ui.end_row();
+
+            let visible = self.visible();
+
+            ui.label("Visible:");
+            ui.label(opt_as_str(&visible));
+            ui.end_row();
+
             fn opt_rect_as_string(v: &Option<Rect>) -> String {
                 v.as_ref().map_or(String::new(), |r| {
                     format!("Pos: {:?}, size: {:?}", r.min, r.size())