Windows QPA: Detect a SetParent into a native window and set isEmbedded

Detecting that a Qt window has been reparented into a native window and
setting isEmbedded automatically. While there is no specific message for
the change in the parent window, a WM_WINDOWPOSCHANGING message
indicating a change in the Z order is sent. We can recognize an
embedding condition by detecting that our QWindow does not have another
QWindow as a parent, but the HWND associated with it has another HWND as
a parent, which is not the desktop window.

This change should cover the use case where a Qt-based plugin must
return a HWND to a host application, where the host application will
then reparent the HWND as it sees fit, outside of Qt control.

Task-number: QTBUG-64116
Change-Id: Iec417c0dd55ad68eff1ea75bb6f5b5495489c31e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 24eab2c662..8702ce7bab 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -2070,9 +2070,17 @@ void QWindowsWindow::propagateSizeHints()
 
 bool QWindowsWindow::handleGeometryChangingMessage(MSG *message, const QWindow *qWindow, const QMargins &margins)
 {
+    WINDOWPOS *windowPos = reinterpret_cast<WINDOWPOS *>(message->lParam);
+    if ((windowPos->flags & SWP_NOZORDER) == 0) {
+        if (QWindowsWindow *platformWindow = QWindowsWindow::windowsWindowOf(qWindow)) {
+            QWindow *parentWindow = qWindow->parent();
+            HWND parentHWND = GetAncestor(windowPos->hwnd, GA_PARENT);
+            HWND desktopHWND = GetDesktopWindow();
+            platformWindow->m_data.embedded = !parentWindow && parentHWND && (parentHWND != desktopHWND);
+        }
+    }
     if (!qWindow->isTopLevel()) // Implement hasHeightForWidth().
         return false;
-    WINDOWPOS *windowPos = reinterpret_cast<WINDOWPOS *>(message->lParam);
     if ((windowPos->flags & (SWP_NOCOPYBITS | SWP_NOSIZE)))
         return false;
     const QRect suggestedFrameGeometry(windowPos->x, windowPos->y,