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>

Cargo.lock

@@ -4303,6 +4303,14 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "test_background_logic"
+version = "0.1.0"
+dependencies = [
+ "eframe",
+ "env_logger",
+]
+
 [[package]]
 name = "test_egui_extras_compilation"
 version = "0.1.0"

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()
+            .or_default();
-            .native_pixels_per_point = Some(super::native_pixels_per_point());
+        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())

tests/test_background_logic/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "test_background_logic"
+version = "0.1.0"
+license = "MIT OR Apache-2.0"
+edition = "2024"
+rust-version = "1.92"
+publish = false
+
+[lints]
+workspace = true
+
+[dependencies]
+eframe = { workspace = true, features = ["default"] }
+env_logger = { workspace = true, features = ["auto-color", "humantime"] }

tests/test_background_logic/src/main.rs

@@ -0,0 +1,64 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+#![expect(rustdoc::missing_crate_level_docs)]
+#![allow(clippy::print_stderr)]
+
+use std::time::Duration;
+
+use eframe::egui::{self, ViewportInfo};
+
+fn main() {
+    env_logger::init();
+
+    let _ = eframe::run_native(
+        "Background Logic Test",
+        eframe::NativeOptions {
+            viewport: egui::ViewportBuilder::default().with_inner_size([400.0, 200.0]),
+            ..Default::default()
+        },
+        Box::new(|_cc| Ok(Box::new(App))),
+    );
+}
+
+struct App;
+
+impl eframe::App for App {
+    fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        eprintln!("App::logic called {}", viewport_info(ctx));
+        ctx.request_repaint_after(Duration::from_secs(1));
+    }
+
+    fn ui(&mut self, ui: &mut egui::Ui, _frame: &mut eframe::Frame) {
+        eprintln!("App::ui called {}", viewport_info(ui.ctx()));
+        ui.centered_and_justified(|ui| {
+            ui.heading("Minimize this window");
+        });
+    }
+}
+
+fn viewport_info(ctx: &egui::Context) -> String {
+    ctx.input(|i| {
+        let ViewportInfo {
+            minimized,
+            focused,
+            occluded,
+            ..
+        } = i.viewport();
+
+        let visible = i.viewport().visible();
+
+        let mut s = String::new();
+
+        let flags = [
+            ("focused", focused),
+            ("occluded", occluded),
+            ("minimized", minimized),
+            ("visible", &visible),
+        ];
+        for (name, value) in flags {
+            if let Some(value) = value {
+                s += &format!(" {name}={value}");
+            }
+        }
+        s
+    })
+}