Track the global focus state of the UI (#1859)

* Track the global focus state of the UI

* Fix changelog entries

* Document the new difference between `Response::has_focus` and `Memory::has_focus`

egui/src/data/input.rs

@@ -62,6 +62,9 @@ pub struct RawInput {
     /// Note: when using `eframe` on Windows you need to enable
     /// drag-and-drop support using `eframe::NativeOptions`.
     pub dropped_files: Vec<DroppedFile>,
+
+    /// The window has the keyboard focus (i.e. is receiving key presses).
+    pub has_focus: bool,
 }
 
 impl Default for RawInput {
@@ -76,6 +79,7 @@ impl Default for RawInput {
             events: vec![],
             hovered_files: Default::default(),
             dropped_files: Default::default(),
+            has_focus: true, // integrations opt into global focus tracking
         }
     }
 }
@@ -96,6 +100,7 @@ impl RawInput {
             events: std::mem::take(&mut self.events),
             hovered_files: self.hovered_files.clone(),
             dropped_files: std::mem::take(&mut self.dropped_files),
+            has_focus: self.has_focus,
         }
     }
 
@@ -111,6 +116,7 @@ impl RawInput {
             mut events,
             mut hovered_files,
             mut dropped_files,
+            has_focus,
         } = newer;
 
         self.screen_rect = screen_rect.or(self.screen_rect);
@@ -122,6 +128,7 @@ impl RawInput {
         self.events.append(&mut events);
         self.hovered_files.append(&mut hovered_files);
         self.dropped_files.append(&mut dropped_files);
+        self.has_focus = has_focus;
     }
 }
 
@@ -541,6 +548,7 @@ impl RawInput {
             events,
             hovered_files,
             dropped_files,
+            has_focus,
         } = self;
 
         ui.label(format!("screen_rect: {:?} points", screen_rect));
@@ -558,6 +566,7 @@ impl RawInput {
         ui.label(format!("modifiers: {:#?}", modifiers));
         ui.label(format!("hovered_files: {}", hovered_files.len()));
         ui.label(format!("dropped_files: {}", dropped_files.len()));
+        ui.label(format!("has_focus: {}", has_focus));
         ui.scope(|ui| {
             ui.set_min_height(150.0);
             ui.label(format!("events: {:#?}", events))

egui/src/memory.rs

@@ -350,6 +350,11 @@ impl Memory {
     }
 
     /// Does this widget have keyboard focus?
+    ///
+    /// This function does not consider whether the UI as a whole (e.g. window)
+    /// has the keyboard focus. That makes this function suitable for deciding
+    /// widget state that should not be disrupted if the user moves away
+    /// from the window and back.
     #[inline(always)]
     pub fn has_focus(&self, id: Id) -> bool {
         self.interaction.focus.id == Some(id)

egui/src/response.rs

@@ -212,8 +212,14 @@ impl Response {
     }
 
     /// This widget has the keyboard focus (i.e. is receiving key presses).
+    ///
+    /// This function only returns true if the UI as a whole (e.g. window)
+    /// also has the keyboard focus. That makes this function suitable
+    /// for style choices, e.g. a thicker border around focused widgets.
     pub fn has_focus(&self) -> bool {
-        self.ctx.memory().has_focus(self.id)
+        // Access input and memory in separate statements to prevent deadlock.
+        let has_global_focus = self.ctx.input().raw.has_focus;
+        has_global_focus && self.ctx.memory().has_focus(self.id)
     }
 
     /// True if this widget has keyboard focus this frame, but didn't last frame.