Add catch-all DPR update to expose event handling

The platform plugin should already DPR (or DPI) change
events, however if that does not happen we update in
the expose event as well as a last resort to make sure
the window's DPR value is in sync.

Also print a warning and ask for a bug report.

Pick-to: 6.6 6.0
Change-Id: Ibb144f163281a28216c2fa3353ed50237e91ce25
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 00d66913e1..691bc5c269 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -1358,8 +1358,9 @@ qreal QWindow::devicePixelRatio() const
 /*
     Updates the cached devicePixelRatio value by polling for a new value.
     Sends QEvent::DevicePixelRatioChange to the window if the DPR has changed.
+    Returns true if the DPR was changed.
 */
-void QWindowPrivate::updateDevicePixelRatio()
+bool QWindowPrivate::updateDevicePixelRatio()
 {
     Q_Q(QWindow);
 
@@ -1370,11 +1371,12 @@ void QWindowPrivate::updateDevicePixelRatio()
         platformWindow->devicePixelRatio() * QHighDpiScaling::factor(q) : q->screen()->devicePixelRatio();
 
     if (newDevicePixelRatio == devicePixelRatio)
-        return;
+        return false;
 
     devicePixelRatio = newDevicePixelRatio;
     QEvent dprChangeEvent(QEvent::DevicePixelRatioChange);
     QGuiApplication::sendEvent(q, &dprChangeEvent);
+    return true;
 }
 
 Qt::WindowState QWindowPrivate::effectiveState(Qt::WindowStates state)