Fix restoring maximized window corner case

For issue #553

On Windows it's possible to have normal geometry
in a different screen than the maximized window if
you drag a window across monitors and touch an
aerosnap edge.

While restoring, we need a fake setGeometry()
call to set the normal geometry, since Qt doesn't
provide QWindow::setNormalGeometry(), that resulted
in the window being maximized on the wrong window.

The solution is to patch the normal geometry to be
in the first screen.

Changelog

@@ -10,6 +10,7 @@
   - Fix case where persistent central widget would detach when dragged
   - Allow to build against external KDBindings
   - Fix restore layout of nested main windows (#508)
+  - Fix restore maximized window corner case (#553)
 
 * v2.1.0 (08 May 2024)
   - Added standalone layouting example using Slint

src/LayoutSaver.cpp

@@ -642,6 +642,18 @@ void LayoutSaver::Private::deserializeWindowGeometry(const T &saved, Window::Ptr
         // The window will be maximized. We first set its geometry to normal
         // Later it's maximized and will remember this value
         geometry = saved.normalGeometry;
+
+        if (saved.screenIndex != Platform::instance()->screenNumberForPoint(geometry.topLeft())) {
+            // Workaround bug #553. Window is maximized on screen 2 but its normal
+            // geometry is on screen 1. Restoring normal geometry would move it to screen 2
+            // To avoid that, we move its normal geometry to screen 2. Could be fixed
+            // without workarounds if Qt supported QWindow::setNormalGeometry()
+            window->setScreen(saved.screenIndex);
+            if (auto screen = window->screen()) {
+                // center is as good as any
+                geometry.moveCenter(screen->geometry().center());
+            }
+        }
     }
 
     Core::FloatingWindow::ensureRectIsOnScreen(geometry);

src/core/Platform.h

@@ -83,6 +83,10 @@ class DOCKS_EXPORT Platform
     /// @brief Returns the size of the screen where this view is in
     virtual Size screenSizeFor(View *) const = 0;
 
+    /// @brief Returns which screen the point is in
+    /// -1 if not found
+    virtual int screenNumberForPoint(Point) const = 0;
+
     /// @brief Create an empty view
     /// For Qt this would just returns a empty QWidget or QQuickItem
     /// other frontends can return something as basic.

src/core/Window_p.h

@@ -96,6 +96,11 @@ class DOCKS_EXPORT Window
     /// @brief Returns the screen this window is on
     virtual Screen::Ptr screen() const = 0;
 
+    /// @brief Sets the screen this window belongs to
+    /// Does not move it
+    virtual void setScreen(int) = 0;
+    virtual int screenIndex() const = 0;
+
     /// Deletes the underlying window. Only used during tests.
     virtual void destroy() = 0;
 

src/qtcommon/Platform.cpp

@@ -216,6 +216,17 @@ int Platform_qt::screenNumberForWindow(std::shared_ptr<Core::Window> window) con
     return screenNumberForQWindow(static_cast<Window *>(window.get())->qtWindow());
 }
 
+int Platform_qt::screenNumberForPoint(Point pt) const
+{
+    const auto screens = qApp->screens();
+    for (int i = 0; i < screens.size(); ++i) {
+        if (screens[i]->geometry().contains(pt))
+            return i;
+    }
+
+    return -1;
+}
+
 int Platform_qt::screenNumberForQWindow(QWindow *window) const
 {
     if (QScreen *screen = window->screen()) {

src/qtcommon/Platform.h

@@ -39,6 +39,7 @@ class DOCKS_EXPORT Platform_qt : public Core::Platform
     QVector<std::shared_ptr<Core::Window>> windows() const override;
     virtual std::shared_ptr<Core::Window> windowFromQWindow(QWindow *) const = 0;
     int screenNumberForWindow(std::shared_ptr<Core::Window>) const override;
+    int screenNumberForPoint(Point) const override;
 
     void sendEvent(Core::View *, QEvent *) const override;
 

src/qtcommon/Window.cpp

@@ -17,6 +17,7 @@
 #include <QWindow>
 #include <QScreen>
 #include <QVariant>
+#include <QGuiApplication>
 
 #include <QtGui/private/qhighdpiscaling_p.h>
 
@@ -178,3 +179,29 @@ bool Window::isFullScreen() const
 {
     return m_window->windowStates() & Qt::WindowFullScreen;
 }
+
+void Window::setScreen(int index)
+{
+    const auto screens = qApp->screens();
+    const int numScreens = screens.size();
+    if (index >= numScreens || index < 0) {
+        qWarning() << Q_FUNC_INFO << "index out of bounds" << index << numScreens;
+        return;
+    }
+
+    if (m_window) {
+        m_window->setScreen(screens[index]);
+    } else {
+        qWarning() << Q_FUNC_INFO << "window is nullptr";
+    }
+}
+
+int Window::screenIndex() const
+{
+    if (!m_window) {
+        qWarning() << Q_FUNC_INFO << "window is nullptr";
+        return -1;
+    }
+
+    return qApp->screens().indexOf(m_window->screen());
+}

src/qtcommon/Window_p.h

@@ -54,6 +54,9 @@ class DOCKS_EXPORT Window : public Core::Window
     QPoint mapFromGlobal(QPoint globalPos) const override;
     QPoint mapToGlobal(QPoint localPos) const override;
     Screen_qt::Ptr screen() const override;
+    void setScreen(int) override;
+    int screenIndex() const override;
+
     void destroy() override;
     QSize minSize() const override;
     QSize maxSize() const override;