Avoid segfault in QWindow::mapFromGlobal when platformWindow is null

If the window hasn't been shown yet (as is the case when running
./tst_qquickmaterialstyle Material::test_background:drawer in
qtdeclarative), platformWindow can be null. Check for that and use
the pre-67fa2585ac48e64972d1c0a20b3add5c3ef72e51 code path instead.

Fixes: QTBUG-119517
Change-Id: I8333578b94f91b5a2994875da6dc568a360d2edf
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 13bcc56f95..178b1f51e5 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -2888,7 +2888,12 @@ QPointF QWindow::mapFromGlobal(const QPointF &pos) const
     // Calculate local position in the native coordinate system. (See comment for the
     // corresponding mapToGlobal() code above).
     QPointF nativeGlobalPos = QHighDpi::toNativeGlobalPosition(pos, this);
-    QPointF nativeWindowGlobalPos = d->platformWindow->mapToGlobal(QPoint(0,0)).toPointF();
+    // Get the native window position directly from the platform window
+    // if available (it can be null if the window hasn't been shown yet),
+    // or fall back to scaling the QWindow position.
+    QPointF nativeWindowGlobalPos = d->platformWindow
+        ? d->platformWindow->mapToGlobal(QPoint(0,0)).toPointF()
+        : QHighDpi::toNativeGlobalPosition(QPointF(d->globalPosition()), this);
     QPointF nativeLocalPos = nativeGlobalPos - nativeWindowGlobalPos;
     QPointF deviceIndependentLocalPos = QHighDpi::fromNativeLocalPosition(nativeLocalPos, this);
     return deviceIndependentLocalPos;