Title bar: a double-click on the macOS app bar zooms the window (fixes #1932)

crates/ui-egui/src/chrome.rs

@@ -22,7 +22,8 @@ const WIDGET_H: f32 = 22.0;
 /// The application bar: brand mark, Home, menus, then Discord, search and the workspace switcher
 /// at the right. With [`VectorcraftApp::custom_titlebar`] it is also the window's title bar
 /// ([`titlebar`]): the caption buttons take the right end and the rest of the bar drags the window.
-/// With the system title bar (Windows and Linux, `system_title_bar`) the OS draws its own icon and
+/// On macOS, under the system's transparent title bar, its empty space drags and zooms the window
+/// too ([`titlebar::drag_area`]). With the system title bar (Windows and Linux, `system_title_bar`) the OS draws its own icon and
 /// title, so the in-app bar shows Home, menus and workspace controls only: no brand mark.
 pub fn app_bar(app: &mut VectorcraftApp, ui: &mut Ui) {
     let t = Tokens::get(ui.ctx());
@@ -31,7 +32,9 @@ pub fn app_bar(app: &mut VectorcraftApp, ui: &mut Ui) {
     let left = app.titlebar_inset.clamp(8.0, f32::from(i8::MAX)) as i8;
     let frame = egui::Frame::NONE.fill(t.app_bar).inner_margin(egui::Margin { left, right: if custom { 0 } else { 14 }, top: 0, bottom: 0 });
     let bar = egui::Panel::top("app_bar").exact_size(APP_BAR_HEIGHT).frame(frame.stroke(Stroke::new(1.0, t.border))).show(ui, |ui| {
-        if custom {
+        // macOS draws the bar under its transparent title bar, so the bar gets the title bar's
+        // clicks: without this a double-click there zooms nothing (#1932).
+        if custom || cfg!(target_os = "macos") {
             titlebar::drag_area(ui, ui.max_rect());
         }
         ui.horizontal_centered(|ui| {

crates/ui-egui/src/titlebar.rs

@@ -1,7 +1,8 @@
 //! The window's own title bar on Windows and Linux, where the window has no OS decorations
 //! ([`VectorcraftApp::custom_titlebar`]): empty space in the app bar drags the window and a
 //! double-click there maximizes it, caption buttons at the far right minimize, maximize/restore and
-//! close, and thin invisible zones along the window's edges resize it.
+//! close, and thin invisible zones along the window's edges resize it. On macOS the app bar sits
+//! under the system's transparent title bar and only its [`drag_area`] is used.
 
 use egui::{CursorIcon, Id, LayerId, Order, PointerButton, Rect, ResizeDirection, Sense, Stroke, Ui, ViewportCommand, pos2, vec2};
 use serde_json::json;
@@ -347,6 +348,21 @@ mod tests {
         assert!(!cmds.iter().any(|c| matches!(c, ViewportCommand::StartDrag)), "{cmds:?}");
     }
 
+    #[test]
+    fn a_double_click_on_the_macos_app_bar_zooms_the_window() {
+        // macOS keeps the system decorations, with the app bar under its transparent title bar
+        // (#1932); Windows and Linux with the system title bar leave it to the OS's bar.
+        let mut w = Win::new(1440.0);
+        w.app.custom_titlebar = false;
+        w.frame(vec![]);
+        let empty = pos2(700.0, 16.0);
+        assert!(w.bar_widgets().iter().all(|r| !r.contains(empty)), "the probe point must be empty bar space");
+        let mut cmds = w.click(empty);
+        cmds.extend(w.click(empty));
+        assert_eq!(cmds.contains(&ViewportCommand::Maximized(true)), cfg!(target_os = "macos"), "{cmds:?}");
+        assert!(!cmds.iter().any(|c| matches!(c, ViewportCommand::Maximized(false))), "{cmds:?}");
+    }
+
     #[test]
     fn edge_zones_resize_unless_maximized() {
         use ResizeDirection::*;