Windows QPA: Use the native algorithm to find out the window's screen

QPlatformWindow::screenForGeometry uses the screen where the center
of the window is, but native application use the one which intersects
with the bigger area. It might not be the same.

Change-Id: I831a5fcaea0e293e9f0f93ef5e562cce57fae2f4
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

3 files changed, 12 insertions, 4 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index bd598630ba..24fb12d27a 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -82,6 +82,7 @@ static bool monitorData(HMONITOR hMonitor, QWindowsScreenData *data)
     if (GetMonitorInfo(hMonitor, &info) == FALSE)
         return false;
 
+    data->hMonitor = hMonitor;
     data->geometry = QRect(QPoint(info.rcMonitor.left, info.rcMonitor.top), QPoint(info.rcMonitor.right - 1, info.rcMonitor.bottom - 1));
     data->availableGeometry = QRect(QPoint(info.rcWork.left, info.rcWork.top), QPoint(info.rcWork.right - 1, info.rcWork.bottom - 1));
     data->name = QString::fromWCharArray(info.szDevice);
diff --git a/src/plugins/platforms/windows/qwindowsscreen.h b/src/plugins/platforms/windows/qwindowsscreen.h
index 00722e2fa4..9a8997326b 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.h
+++ b/src/plugins/platforms/windows/qwindowsscreen.h
@@ -69,6 +69,7 @@ struct QWindowsScreenData
     QString name;
     Qt::ScreenOrientation orientation = Qt::LandscapeOrientation;
     qreal refreshRateHz = 60;
+    HMONITOR hMonitor = nullptr;
 };
 
 class QWindowsScreen : public QPlatformScreen
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 3024e15eca..42eb6d4ca7 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1533,10 +1533,16 @@ void QWindowsWindow::handleGeometryChange()
         && !(m_data.geometry.width() > previousGeometry.width() || m_data.geometry.height() > previousGeometry.height())) {
         fireExpose(QRect(QPoint(0, 0), m_data.geometry.size()), true);
     }
-    if (previousGeometry.topLeft() != m_data.geometry.topLeft()) {
-        QPlatformScreen *newScreen = screenForGeometry(m_data.geometry);
-        if (newScreen != screen())
-            QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
+    if (!parent() && previousGeometry.topLeft() != m_data.geometry.topLeft()) {
+        HMONITOR hMonitor = MonitorFromWindow(m_data.hwnd, MONITOR_DEFAULTTONULL);
+        QPlatformScreen *currentScreen = screen();
+        const auto screens = QWindowsContext::instance()->screenManager().screens();
+        auto newScreenIt = std::find_if(screens.begin(), screens.end(), [&](QWindowsScreen *s) {
+            return s->data().hMonitor == hMonitor
+                && s->data().flags & QWindowsScreenData::VirtualDesktop;
+        });
+        if (newScreenIt != screens.end() && *newScreenIt != currentScreen)
+            QWindowSystemInterface::handleWindowScreenChanged(window(), (*newScreenIt)->screen());
     }
     if (testFlag(SynchronousGeometryChangeEvent))
         QWindowSystemInterface::flushWindowSystemEvents(QEventLoop::ExcludeUserInputEvents);