Windows: Check for screen changes for each window after adding screen6.10

When a new screen is attached Window might move windows to the new
screen automatically, in which case they will get a WM_DPICHANGED
event. But at that point we have not received WM_DISPLAYCHANGE yet,
so we fail to reflect the new screen's DPI.

To account for this we explicitly check for screen change after adding
a new screen.

Fixes: QTBUG-125319
Change-Id: Ic854fe9f9ae52f53bb34cb8434111a6a1ba032d2
Reviewed-by: Tor Arne Vestbø <[email protected]>
(cherry picked from commit 78a0018c86b98a63ccb13f61d4a33e94c3f053cc)
Reviewed-by: Oliver Wolff <[email protected]>

3 files changed, 26 insertions, 7 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index ddc1114485e..57b833b299b 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -762,6 +762,28 @@ static void moveToVirtualScreen(QWindow *w, const QScreen *newScreen)
     w->setGeometry(geometry);
 }
 
+void QWindowsScreenManager::addScreen(const QWindowsScreenData &screenData)
+{
+    auto *newScreen = new QWindowsScreen(screenData);
+    m_screens.push_back(newScreen);
+    QWindowSystemInterface::handleScreenAdded(newScreen,
+                                              screenData.flags & QWindowsScreenData::PrimaryScreen);
+    qCDebug(lcQpaScreen) << "New Monitor: " << screenData;
+
+    // When a new screen is attached Window might move windows to the new screen
+    // automatically, in which case they will get a WM_DPICHANGED event. But at
+    // that point we have not received WM_DISPLAYCHANGE yet, so we fail to reflect
+    // the new screen's DPI. To account for this we explicitly check for screen
+    // change here, now that we are processing the WM_DISPLAYCHANGE.
+    const auto allWindows = QGuiApplication::allWindows();
+    for (QWindow *w : allWindows) {
+        if (w->isVisible() && w->handle() && w->type() != Qt::Desktop) {
+            if (QWindowsWindow *window = QWindowsWindow::windowsWindowOf(w))
+                window->checkForScreenChanged(QWindowsWindow::ScreenChangeMode::FromScreenAdded);
+        }
+    }
+}
+
 void QWindowsScreenManager::removeScreen(int index)
 {
     qCDebug(lcQpaScreen) << "Removing Monitor:" << m_screens.at(index)->data();
@@ -784,7 +806,7 @@ void QWindowsScreenManager::removeScreen(int index)
                     && (QWindowsWindow::baseWindowOf(w)->exStyle() & WS_EX_TOOLWINDOW)) {
                     moveToVirtualScreen(w, primaryScreen);
                 } else {
-                    QWindowSystemInterface::handleWindowScreenChanged(w, primaryScreen);
+                    QWindowSystemInterface::handleWindowScreenChanged<QWindowSystemInterface::SynchronousDelivery>(w, primaryScreen);
                 }
                 ++movedWindowCount;
             }
@@ -813,11 +835,7 @@ bool QWindowsScreenManager::handleScreenChanges()
             if (existingIndex == 0)
                 primaryScreenChanged = true;
         } else {
-            auto *newScreen = new QWindowsScreen(newData);
-            m_screens.push_back(newScreen);
-            QWindowSystemInterface::handleScreenAdded(newScreen,
-                                                             newData.flags & QWindowsScreenData::PrimaryScreen);
-            qCDebug(lcQpaScreen) << "New Monitor: " << newData;
+            addScreen(newData);
         }    // exists
     }        // for new screens.
     // Remove deleted ones but keep main monitors if we get only the
diff --git a/src/plugins/platforms/windows/qwindowsscreen.h b/src/plugins/platforms/windows/qwindowsscreen.h
index ea6a29efe38..8d555998388 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.h
+++ b/src/plugins/platforms/windows/qwindowsscreen.h
@@ -119,6 +119,7 @@ public:
     static bool isSingleScreen();
 
 private:
+    void addScreen(const QWindowsScreenData &screenData);
     void removeScreen(int index);
 
     HWND m_displayChangeObserver = nullptr;
diff --git a/src/plugins/platforms/windows/qwindowswindow.h b/src/plugins/platforms/windows/qwindowswindow.h
index 424848503be..b67bd2850b3 100644
--- a/src/plugins/platforms/windows/qwindowswindow.h
+++ b/src/plugins/platforms/windows/qwindowswindow.h
@@ -342,7 +342,7 @@ public:
     void alertWindow(int durationMs = 0);
     void stopAlertWindow();
 
-    enum ScreenChangeMode { FromGeometryChange, FromDpiChange };
+    enum ScreenChangeMode { FromGeometryChange, FromDpiChange, FromScreenAdded };
     void checkForScreenChanged(ScreenChangeMode mode = FromGeometryChange);
 
     void registerTouchWindow();