Windows QPA: Update theme fonts when the primary screen changes

Call into the theme to update the fonts on a change. This
at least helps in the case of disabled High DPI scaling.

Task-number: QTBUG-77144
Change-Id: I2c8fd85259403eaaeea56cd096f99116fc6bba9a
Reviewed-by: André de la Rocha <andre.rocha@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

src/plugins/platforms/windows/qwindowsscreen.cpp

@@ -42,6 +42,7 @@
 #include "qwindowswindow.h"
 #include "qwindowsintegration.h"
 #include "qwindowscursor.h"
+#include "qwindowstheme.h"
 
 #include <QtCore/qt_windows.h>
 
@@ -547,10 +548,13 @@ bool QWindowsScreenManager::handleScreenChanges()
     // Look for changed monitors, add new ones
     const WindowsScreenDataList newDataList = monitorData();
     const bool lockScreen = newDataList.size() == 1 && (newDataList.front().flags & QWindowsScreenData::LockScreen);
+    bool primaryScreenChanged = false;
     for (const QWindowsScreenData &newData : newDataList) {
         const int existingIndex = indexOfMonitor(m_screens, newData.name);
         if (existingIndex != -1) {
             m_screens.at(existingIndex)->handleChanges(newData);
+            if (existingIndex == 0)
+                primaryScreenChanged = true;
         } else {
             QWindowsScreen *newScreen = new QWindowsScreen(newData);
             m_screens.push_back(newScreen);
@@ -567,6 +571,8 @@ bool QWindowsScreenManager::handleScreenChanges()
                 removeScreen(i);
         }     // for existing screens
     }     // not lock screen
+    if (primaryScreenChanged)
+        QWindowsTheme::instance()->refreshFonts();
     return true;
 }
 

src/plugins/platforms/windows/qwindowstheme.h

@@ -85,6 +85,8 @@ public:
 
     static bool useNativeMenus();
 
+    void refreshFonts();
+
     static const char *name;
 
 private:
@@ -92,7 +94,6 @@ private:
     void clearPalettes();
     void refreshPalettes();
     void clearFonts();
-    void refreshFonts();
     void refreshIconPixmapSizes();
 
     static QWindowsTheme *m_instance;