Keep the window on screen after screen changes

Re-fits on a resolution change or a move to another screen, without
overwriting the saved geometry.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/window/FloatingWindow.cpp

@@ -36,6 +36,20 @@ FloatingWindow::FloatingWindow(QWindow *window, QObject *parent)
     }
     m_position = defaultPosition();
     apply();
+    followScreen(window->screen());
+    connect(window, &QWindow::screenChanged, this, &FloatingWindow::followScreen);
+}
+
+// Re-fits the window (not saved: the stored geometry is the user's choice).
+void FloatingWindow::followScreen(QScreen *screen)
+{
+    if (m_screen)
+        disconnect(m_screen, nullptr, this, nullptr);
+    m_screen = screen;
+    if (!m_screen)
+        return;
+    connect(m_screen, &QScreen::geometryChanged, this, [this] { setGeometry(geometry()); });
+    setGeometry(geometry());
 }
 
 QRect FloatingWindow::geometry() const

src/window/FloatingWindow.h

@@ -4,13 +4,15 @@
 #include <QRect>
 #include <QRectF>
 
+class QScreen;
 class QWindow;
 namespace LayerShellQt { class Window; }
 
 // Places a keyboard window as a free-floating overlay that never takes focus.
 // On Wayland: a layer-shell surface anchored top-left, positioned via margins.
 // On X11: a frameless, non-focusable, always-on-top tool window.
-// Geometry is relative to the window's screen and always kept on it.
+// Geometry is relative to the window's screen and always kept on it, also
+// when the screen's resolution changes or the window moves to another one.
 class FloatingWindow : public QObject
 {
     Q_OBJECT
@@ -42,8 +44,10 @@ private:
     QPoint clamped(QPoint position, QSize size) const;
     QPoint defaultPosition() const;
     void apply();
+    void followScreen(QScreen *screen);
 
     QWindow *m_window;
     LayerShellQt::Window *m_layerSurface = nullptr;
     QPoint m_position;
+    QScreen *m_screen = nullptr;
 };