Allow for requesting the user's attention to the window (#2905)

* add method for requesting attention to the main window

* use another enum member for user attention type instead of nested `Option`s

(also, document the enum members now that they don't mirror `winit`)

* update the docstring

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* add an example app for testing window attention requests

* Apply suggestions from code review

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* remove `chrono` dependency and improve the attention example's readability

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/eframe/src/epi.rs

@@ -802,6 +802,20 @@ impl Frame {
         self.output.focus = Some(true);
     }
 
+    /// If the window is unfocused, attract the user's attention (native only).
+    ///
+    /// Typically, this means that the window will flash on the taskbar, or bounce, until it is interacted with.
+    ///
+    /// When the window comes into focus, or if `None` is passed, the attention request will be automatically reset.
+    ///
+    /// See [winit's documentation][user_attention_details] for platform-specific effect details.
+    ///
+    /// [user_attention_details]: https://docs.rs/winit/latest/winit/window/enum.UserAttentionType.html
+    #[cfg(not(target_arch = "wasm32"))]
+    pub fn request_user_attention(&mut self, kind: egui::UserAttentionType) {
+        self.output.attention = Some(kind);
+    }
+
     /// Maximize or unmaximize window. (native only)
     #[cfg(not(target_arch = "wasm32"))]
     pub fn set_maximized(&mut self, maximized: bool) {
@@ -1126,6 +1140,10 @@ pub(crate) mod backend {
         #[cfg(not(target_arch = "wasm32"))]
         pub focus: Option<bool>,
 
+        /// Set to request a user's attention to the native window.
+        #[cfg(not(target_arch = "wasm32"))]
+        pub attention: Option<egui::UserAttentionType>,
+
         #[cfg(not(target_arch = "wasm32"))]
         pub screenshot_requested: bool,
     }

crates/eframe/src/native/epi_integration.rs

@@ -235,6 +235,7 @@ pub fn handle_app_output(
         minimized,
         maximized,
         focus,
+        attention,
     } = app_output;
 
     if let Some(decorated) = decorated {
@@ -289,8 +290,17 @@ pub fn handle_app_output(
         window_state.maximized = maximized;
     }
 
-    if focus == Some(true) {
-        window.focus_window();
+    if !window.has_focus() {
+        if focus == Some(true) {
+            window.focus_window();
+        } else if let Some(attention) = attention {
+            use winit::window::UserAttentionType;
+            window.request_user_attention(match attention {
+                egui::UserAttentionType::Reset => None,
+                egui::UserAttentionType::Critical => Some(UserAttentionType::Critical),
+                egui::UserAttentionType::Informational => Some(UserAttentionType::Informational),
+            });
+        }
     }
 }
 
@@ -487,6 +497,9 @@ impl EpiIntegration {
             }
             self.frame.output.visible = app_output.visible; // this is handled by post_present
             self.frame.output.screenshot_requested = app_output.screenshot_requested;
+            if self.frame.output.attention.is_some() {
+                self.frame.output.attention = None;
+            }
             handle_app_output(
                 window,
                 self.egui_ctx.pixels_per_point(),

crates/egui/src/data/output.rs

@@ -185,6 +185,23 @@ impl OpenUrl {
     }
 }
 
+/// Types of attention to request from a user when a native window is not in focus.
+///
+/// See [winit's documentation][user_attention_type] for platform-specific meaning of the attention types.
+///
+/// [user_attention_type]: https://docs.rs/winit/latest/winit/window/enum.UserAttentionType.html
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum UserAttentionType {
+    /// Request an elevated amount of animations and flair for the window and the task bar or dock icon.
+    Critical,
+
+    /// Request a standard amount of attention-grabbing actions.
+    Informational,
+
+    /// Reset the attention request and interrupt related animations and flashes.
+    Reset,
+}
+
 /// A mouse cursor icon.
 ///
 /// egui emits a [`CursorIcon`] in [`PlatformOutput`] each frame as a request to the integration.

crates/egui/src/lib.rs

@@ -357,7 +357,7 @@ pub use {
     context::Context,
     data::{
         input::*,
-        output::{self, CursorIcon, FullOutput, PlatformOutput, WidgetInfo},
+        output::{self, CursorIcon, FullOutput, PlatformOutput, UserAttentionType, WidgetInfo},
     },
     grid::Grid,
     id::{Id, IdMap},