UI/Qt: Add optional rounded window corners on macOS

Add an advanced setting for rounded browser window corners. On macOS,
Qt browser windows now use a layer-backed corner radius, and clear it
when maximized, fullscreen, or the setting is disabled.

Hide the setting from about:settings on other platforms for now since Qt
does not expose a native antialiased window corner API there.

Libraries/LibWebView/Settings.cpp

@@ -89,6 +89,14 @@ static Array<ConfigVariableDefinition, static_cast<size_t>(ConfigVariableID::Cou
         .default_value = JsonArray {},
         .array_element_type = JsonValue::Type::String,
     },
+    {
+        .id = ConfigVariableID::UseRoundedWindowCorners,
+        .name = "ui.window.use_rounded_corners"sv,
+        .title = "Use rounded window corners"sv,
+        .description = "Clip browser windows to rounded corners."sv,
+        .default_value = true,
+        .array_element_type = {},
+    },
 } };
 
 ReadonlySpan<ConfigVariableDefinition const> config_variable_definitions()

Libraries/LibWebView/Settings.h

@@ -52,6 +52,7 @@ enum class ConfigVariableID : u8 {
     ShowWebContentProcessIDInTabTitle,
     ShowAdvancedDebugMenu,
     ContentBlockerListPaths,
+    UseRoundedWindowCorners,
 
     Count,
 };

Libraries/LibWebView/WebUI/SettingsUI.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <AK/JsonArray.h>
+#include <AK/Platform.h>
 #include <LibURL/Parser.h>
 #include <LibWebView/Application.h>
 #include <LibWebView/SearchEngine.h>
@@ -32,6 +33,16 @@ static StringView config_variable_type_to_string(JsonValue::Type type)
     VERIFY_NOT_REACHED();
 }
 
+static bool should_show_config_variable([[maybe_unused]] ConfigVariableID id)
+{
+#if !defined(AK_OS_MACOS)
+    if (id == ConfigVariableID::UseRoundedWindowCorners)
+        return false;
+#endif
+
+    return true;
+}
+
 void SettingsUI::register_interfaces()
 {
     register_interface("loadFeatures"sv, [this](auto const&) {
@@ -127,6 +138,9 @@ void SettingsUI::load_current_settings()
 
     JsonArray config_variables;
     for (auto const& variable : config_variable_definitions()) {
+        if (!should_show_config_variable(variable.id))
+            continue;
+
         JsonObject variable_object;
         variable_object.set("name"sv, variable.name);
         variable_object.set("title"sv, variable.title);

UI/Qt/BrowserWindow.cpp

@@ -10,6 +10,7 @@
  */
 
 #include <AK/HashMap.h>
+#include <AK/Platform.h>
 #include <AK/RefPtr.h>
 #include <AK/StdLibExtras.h>
 #include <AK/TypeCasts.h>
@@ -19,6 +20,9 @@
 #include <UI/Qt/BrowserWindow.h>
 #include <UI/Qt/ChromeStyle.h>
 #include <UI/Qt/Icon.h>
+#if defined(AK_OS_MACOS)
+#    include <UI/Qt/MacWindow.h>
+#endif
 #include <UI/Qt/Menu.h>
 #include <UI/Qt/Settings.h>
 #include <UI/Qt/StringUtils.h>
@@ -55,6 +59,9 @@ namespace Ladybird {
 static constexpr auto AUDIO_STATE_BUTTON_POSITION = QTabBar::LeftSide;
 static constexpr auto TAB_CLOSE_BUTTON_POSITION = QTabBar::RightSide;
 static constexpr auto WINDOW_DRAG_REGION_PROPERTY = "LadybirdWindowDragRegion";
+#if defined(AK_OS_MACOS)
+static constexpr qreal WINDOW_CORNER_RADIUS = 12.0;
+#endif
 
 static bool should_use_screen_signal_for_dpi_changes()
 {
@@ -227,6 +234,7 @@ BrowserWindow::BrowserWindow(Vector<URL::URL> const& initial_urls, IsPopupWindow
     setAttribute(Qt::WA_OpaquePaintEvent);
     setWindowIcon(app_icon());
     qApp->installEventFilter(this);
+    update_window_corners();
 
     update_tabs_display();
 
@@ -1229,6 +1237,7 @@ void BrowserWindow::clear_resize_cursor()
 void BrowserWindow::resizeEvent(QResizeEvent* event)
 {
     QWidget::resizeEvent(event);
+    update_window_corners();
 
     for_each_tab([&](auto& tab) {
         tab.view().set_window_size({ width(), height() });
@@ -1244,6 +1253,7 @@ void BrowserWindow::changeEvent(QEvent* event)
     } else if (event->type() == QEvent::WindowStateChange) {
         update_menu_bar_window_control_icons();
         m_tabs_container->update_window_button_icons();
+        update_window_corners();
 
         QWindowStateChangeEvent* stateChangeEvent = static_cast<QWindowStateChangeEvent*>(event);
         bool was_fullscreen = stateChangeEvent->oldState() & Qt::WindowFullScreen;
@@ -1260,6 +1270,26 @@ void BrowserWindow::changeEvent(QEvent* event)
     QWidget::changeEvent(event);
 }
 
+void BrowserWindow::config_variable_changed(WebView::ConfigVariableID variable)
+{
+    if (variable == WebView::ConfigVariableID::UseRoundedWindowCorners)
+        update_window_corners();
+}
+
+void BrowserWindow::update_window_corners()
+{
+    auto should_use_rounded_corners = WebView::Application::settings().config_variable_as_bool(WebView::ConfigVariableID::UseRoundedWindowCorners);
+    auto should_round_window = should_use_rounded_corners && !isMaximized() && !isFullScreen();
+
+#if defined(AK_OS_MACOS)
+    clearMask();
+    set_rounded_window_corners(*this, should_round_window, WINDOW_CORNER_RADIUS);
+#else
+    clearMask();
+    (void)should_round_window;
+#endif
+}
+
 void BrowserWindow::moveEvent(QMoveEvent* event)
 {
     QWidget::moveEvent(event);

UI/Qt/BrowserWindow.h

@@ -11,6 +11,7 @@
 #include <LibWeb/HTML/ActivateTab.h>
 #include <LibWeb/HTML/AudioPlayState.h>
 #include <LibWebView/Forward.h>
+#include <LibWebView/Settings.h>
 #include <UI/Qt/Tab.h>
 #include <UI/Qt/TabBar.h>
 
@@ -80,7 +81,9 @@ private:
     bool m_debounce { false };
 };
 
-class BrowserWindow : public QMainWindow {
+class BrowserWindow
+    : public QMainWindow
+    , public WebView::SettingsObserver {
     Q_OBJECT
 
 public:
@@ -151,6 +154,7 @@ private:
     virtual void moveEvent(QMoveEvent*) override;
     virtual void wheelEvent(QWheelEvent*) override;
     virtual void closeEvent(QCloseEvent*) override;
+    virtual void config_variable_changed(WebView::ConfigVariableID) override;
 
     Tab& create_new_tab(Web::HTML::ActivateTab, Tab& parent, Optional<u64> page_index);
     void initialize_tab(Tab*);
@@ -161,6 +165,7 @@ private:
     Optional<Qt::CursorShape> resize_cursor_for_edges(Qt::Edges) const;
     void update_resize_cursor(QPoint const&);
     void clear_resize_cursor();
+    void update_window_corners();
 
     template<typename Callback>
     void for_each_tab(Callback&& callback)

UI/Qt/CMakeLists.txt

@@ -25,6 +25,12 @@ target_sources(ladybird PRIVATE
     ladybird.qrc
 )
 target_link_libraries(ladybird PRIVATE Qt::Core Qt::Gui Qt::Widgets)
+
+if (APPLE)
+    target_sources(ladybird PRIVATE MacWindow.mm)
+    target_link_libraries(ladybird PRIVATE "-framework Cocoa" "-framework QuartzCore")
+endif()
+
 create_ladybird_bundle(ladybird)
 
 if (WIN32)

UI/Qt/MacWindow.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2026-present, the Ladybird developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+class QWidget;
+
+namespace Ladybird {
+
+void set_rounded_window_corners(QWidget&, bool enabled, double radius);
+
+}

UI/Qt/MacWindow.mm

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2026-present, the Ladybird developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <UI/Qt/MacWindow.h>
+
+#include <QWidget>
+
+#import <Cocoa/Cocoa.h>
+#import <QuartzCore/QuartzCore.h>
+
+namespace Ladybird {
+
+void set_rounded_window_corners(QWidget& widget, bool enabled, double radius)
+{
+    auto* view = reinterpret_cast<NSView*>(widget.winId());
+    if (!view)
+        return;
+
+    auto* window = view.window;
+    if (!window)
+        return;
+
+    auto* content_view = window.contentView;
+    if (!content_view)
+        return;
+
+    content_view.wantsLayer = YES;
+    content_view.layer.cornerRadius = enabled ? radius : 0.0;
+    content_view.layer.masksToBounds = enabled ? YES : NO;
+}
+
+}