UI/Qt: Add an advanced setting to enable server-side decorations

This adds a setting to disable our custom window decorations and let the
system's window server paint the window instead.

Libraries/LibWebView/Application.h

@@ -73,6 +73,7 @@ public:
     static ImageDecoderClient::Client& image_decoder_client() { return *the().m_image_decoder_client; }
 
     virtual bool supports_vertical_tabs() const { return false; }
+    virtual bool supports_server_side_window_decorations() const { return false; }
     void tab_settings_changed(Badge<ApplicationSettingsObserver>);
 
     static BookmarkStore& bookmark_store() { return the().m_bookmark_store; }

Libraries/LibWebView/Settings.cpp

@@ -98,6 +98,14 @@ static Array<ConfigVariableDefinition, static_cast<size_t>(ConfigVariableID::Cou
         .default_value = true,
         .array_element_type = {},
     },
+    {
+        .id = ConfigVariableID::UseServerSideWindowDecorations,
+        .name = "ui.window.use_server_side_decorations"sv,
+        .title = "Use server-side window decorations"sv,
+        .description = "Use the system window frame instead of the custom title bar and window controls."sv,
+        .default_value = false,
+        .array_element_type = {},
+    },
 } };
 
 ReadonlySpan<ConfigVariableDefinition const> config_variable_definitions()

Libraries/LibWebView/Settings.h

@@ -54,6 +54,7 @@ enum class ConfigVariableID : u8 {
     ShowAdvancedDebugMenu,
     ContentBlockerListPaths,
     UseRoundedWindowCorners,
+    UseServerSideWindowDecorations,
 
     Count,
 };

Libraries/LibWebView/WebUI/SettingsUI.cpp

@@ -39,6 +39,8 @@ static bool should_show_config_variable([[maybe_unused]] ConfigVariableID id)
     if (id == ConfigVariableID::UseRoundedWindowCorners)
         return false;
 #endif
+    if (id == ConfigVariableID::UseServerSideWindowDecorations)
+        return Application::the().supports_server_side_window_decorations();
 
     return true;
 }

UI/Qt/Application.h

@@ -60,6 +60,7 @@ private:
     virtual void insert_clipboard_entry(Web::Clipboard::SystemClipboardRepresentation) override;
 
     virtual bool supports_vertical_tabs() const override { return true; }
+    virtual bool supports_server_side_window_decorations() const override { return true; }
     virtual void update_tabs_display() const override;
 
     virtual void rebuild_bookmarks_menu() const override;

UI/Qt/BrowserWindow.cpp

@@ -231,7 +231,7 @@ BrowserWindow::BrowserWindow(Vector<URL::URL> const& initial_urls, IsPopupWindow
 {
     auto const& browser_options = WebView::Application::browser_options();
 
-    setWindowFlag(Qt::FramelessWindowHint);
+    setWindowFlag(Qt::FramelessWindowHint, uses_client_side_decorations());
     setAttribute(Qt::WA_OpaquePaintEvent);
     setWindowIcon(app_icon());
     qApp->installEventFilter(this);
@@ -573,6 +573,11 @@ FullscreenMode& BrowserWindow::fullscreen_mode()
     return *m_fullscreen_mode;
 }
 
+bool BrowserWindow::uses_client_side_decorations()
+{
+    return !WebView::Application::settings().config_variable_as_bool(WebView::ConfigVariableID::UseServerSideWindowDecorations);
+}
+
 Tab& BrowserWindow::create_new_tab(Web::HTML::ActivateTab activate_tab)
 {
     auto* tab = new Tab(this);
@@ -931,8 +936,8 @@ void BrowserWindow::update_menu_bar_visibility(bool show_menubar)
 {
     menuBar()->setVisible(show_menubar);
     if (m_menu_bar_window_controls)
-        m_menu_bar_window_controls->setVisible(show_menubar);
-    m_tabs_container->set_window_controls_visible(!show_menubar);
+        m_menu_bar_window_controls->setVisible(show_menubar && uses_client_side_decorations());
+    m_tabs_container->set_window_controls_visible(!show_menubar && uses_client_side_decorations());
 }
 
 void BrowserWindow::update_menu_bar_window_control_icons()
@@ -947,6 +952,33 @@ void BrowserWindow::update_menu_bar_window_control_icons()
     m_menu_bar_close_window_button->setIcon(create_chrome_icon(ChromeIcon::WindowClose, palette()));
 }
 
+void BrowserWindow::update_window_decoration_state()
+{
+    clear_resize_cursor();
+
+    auto should_be_frameless = uses_client_side_decorations();
+    auto is_frameless = windowFlags().testFlag(Qt::FramelessWindowHint);
+
+    if (is_frameless != should_be_frameless) {
+        auto was_visible = isVisible();
+        auto was_fullscreen = isFullScreen();
+        auto was_maximized = isMaximized();
+
+        setWindowFlag(Qt::FramelessWindowHint, should_be_frameless);
+
+        if (was_visible) {
+            if (was_fullscreen)
+                showFullScreen();
+            else if (was_maximized)
+                showMaximized();
+            else
+                show();
+        }
+    }
+
+    update_menu_bar_visibility(Settings::the()->show_menubar());
+}
+
 void BrowserWindow::toggle_window_maximized()
 {
     if (isMaximized())
@@ -1133,6 +1165,8 @@ bool BrowserWindow::eventFilter(QObject* object, QEvent* event)
     auto* widget = as_if<QWidget>(object);
     if (!widget || widget->window() != this)
         return QMainWindow::eventFilter(object, event);
+    if (!uses_client_side_decorations())
+        return QMainWindow::eventFilter(object, event);
 
     auto const is_button = qobject_cast<QAbstractButton*>(object) != nullptr;
 
@@ -1233,7 +1267,7 @@ Optional<Qt::CursorShape> BrowserWindow::resize_cursor_for_edges(Qt::Edges edges
 
 void BrowserWindow::update_resize_cursor(QPoint const& position)
 {
-    if (isMaximized() || isFullScreen() || !rect().contains(position)) {
+    if (!uses_client_side_decorations() || isMaximized() || isFullScreen() || !rect().contains(position)) {
         clear_resize_cursor();
         return;
     }
@@ -1301,6 +1335,8 @@ void BrowserWindow::config_variable_changed(WebView::ConfigVariableID variable)
 {
     if (variable == WebView::ConfigVariableID::UseRoundedWindowCorners)
         update_window_corners();
+    else if (variable == WebView::ConfigVariableID::UseServerSideWindowDecorations)
+        update_window_decoration_state();
 }
 
 void BrowserWindow::update_window_corners()

UI/Qt/BrowserWindow.h

@@ -106,6 +106,7 @@ public:
     FullscreenMode& fullscreen_mode();
 
     QMenu& hamburger_menu() const { return *m_hamburger_menu; }
+    static bool uses_client_side_decorations();
 
     QAction& new_window_action() const { return *m_new_window_action; }
     QAction& find_action() const { return *m_find_in_page_action; }
@@ -181,6 +182,7 @@ private:
     void update_menu_bar_style();
     void update_menu_bar_visibility(bool);
     void update_menu_bar_window_control_icons();
+    void update_window_decoration_state();
     void toggle_window_maximized();
     bool start_window_move();
     bool connect_window_screen_changed_signal();

UI/Qt/TabBar.cpp

@@ -99,6 +99,12 @@ static QPointer<Tab> s_active_tab_dragged_tab;
 static QPointer<TabWidget> s_pending_tab_drop_target;
 static int s_pending_tab_drop_index { -1 };
 
+static bool window_uses_client_side_decorations(QWidget& widget)
+{
+    auto* top_level_window = qobject_cast<BrowserWindow*>(widget.window());
+    return !top_level_window || top_level_window->uses_client_side_decorations();
+}
+
 static QPainterPath tab_shape_path(QRectF const& rect, qreal top_radius, qreal bottom_radius)
 {
     top_radius = min(top_radius, rect.height() / 2.0);
@@ -735,7 +741,7 @@ void TabBar::mouseReleaseEvent(QMouseEvent* event)
 
 void TabBar::mouseDoubleClickEvent(QMouseEvent* event)
 {
-    if (tab_index_at(event->pos()) < 0 && event->button() == Qt::LeftButton) {
+    if (window_uses_client_side_decorations(*this) && tab_index_at(event->pos()) < 0 && event->button() == Qt::LeftButton) {
         toggle_window_maximized();
         event->accept();
         return;
@@ -1465,7 +1471,7 @@ bool TabWidget::eventFilter(QObject* watched, QEvent* event)
         }
     }
 
-    if (watched == m_tab_bar_row || watched == m_vertical_tab_bar_column) {
+    if ((watched == m_tab_bar_row || watched == m_vertical_tab_bar_column) && window_uses_client_side_decorations(*this)) {
         auto is_empty_chrome_area = [this, watched](QMouseEvent const& mouse_event) {
             if (watched == m_vertical_tab_bar_column) {
                 auto* child = m_vertical_tab_bar_column->childAt(mouse_event.pos());