Windows: Keep monitors when system is locked.

Prevent windows from being recreated due to screen changes which
can cause GL widgets to stop updating among other things.

EnumMonitors returns only one temporary monitor named "WinDisc"
when locked. Do not remove monitors when that happens.

Task-number: QTBUG-33062
Change-Id: Ia2247bb04b3e10f99f594245f84238b5f9044f70
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/plugins/platforms/windows/qwindowsscreen.cpp

@@ -98,6 +98,10 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
     WindowsScreenDataList *result = reinterpret_cast<WindowsScreenDataList *>(p);
     QWindowsScreenData data;
     data.geometry = QRect(QPoint(info.rcMonitor.left, info.rcMonitor.top), QPoint(info.rcMonitor.right - 1, info.rcMonitor.bottom - 1));
+    data.name = QString::fromWCharArray(info.szDevice);
+    if (data.name == QLatin1String("WinDisc")) {
+        data.flags |= QWindowsScreenData::LockScreen;
+    } else {
 #ifdef Q_OS_WINCE
         //Windows CE, just supports one Display and expects to get only DISPLAY,
         //instead of DISPLAY0 and so on, which are passed by info.szDevice
@@ -111,22 +115,22 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
             data.format = data.depth == 16 ? QImage::Format_RGB16 : QImage::Format_RGB32;
             data.physicalSizeMM = QSizeF(GetDeviceCaps(hdc, HORZSIZE), GetDeviceCaps(hdc, VERTSIZE));
             const int refreshRate = GetDeviceCaps(hdc, VREFRESH);
-        if (refreshRate > 1) // 0,1 means heardware default.
+            if (refreshRate > 1) // 0,1 means hardware default.
                 data.refreshRateHz = refreshRate;
             DeleteDC(hdc);
         } else {
             qWarning("%s: Unable to obtain handle for monitor '%s', defaulting to %g DPI.",
                      __FUNCTION__, qPrintable(QString::fromWCharArray(info.szDevice)),
                      data.dpi.first);
-    }
+        } // CreateDC() failed
+    } // not lock screen
     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.orientation = data.geometry.height() > data.geometry.width() ?
                        Qt::PortraitOrientation : Qt::LandscapeOrientation;
     // EnumDisplayMonitors (as opposed to EnumDisplayDevices) enumerates only
     // virtual desktop screens.
-    data.name = QString::fromWCharArray(info.szDevice);
+    data.flags |= QWindowsScreenData::VirtualDesktop;
-    data.flags = QWindowsScreenData::VirtualDesktop;
     if (info.dwFlags & MONITORINFOF_PRIMARY) {
         data.flags |= QWindowsScreenData::PrimaryScreen;
         // QPlatformIntegration::screenAdded() documentation specifies that first
@@ -162,6 +166,8 @@ static QDebug operator<<(QDebug dbg, const QWindowsScreenData &d)
         nospace << " primary";
     if (d.flags & QWindowsScreenData::VirtualDesktop)
         nospace << " virtual desktop";
+    if (d.flags & QWindowsScreenData::LockScreen)
+        nospace << " lock screen";
     return dbg;
 }
 
@@ -392,7 +398,8 @@ static inline int indexOfMonitor(const QList<QWindowsScreenData> &screenData,
 bool QWindowsScreenManager::handleScreenChanges()
 {
     // Look for changed monitors, add new ones
-    const WindowsScreenDataList newDataList = monitorData();
+    WindowsScreenDataList newDataList = monitorData();
+    const bool lockScreen = newDataList.size() == 1 && (newDataList.front().flags & QWindowsScreenData::LockScreen);
     foreach (const QWindowsScreenData &newData, newDataList) {
         const int existingIndex = indexOfMonitor(m_screens, newData.name);
         if (existingIndex != -1) {
@@ -405,7 +412,9 @@ bool QWindowsScreenManager::handleScreenChanges()
                 qDebug() << "New Monitor: " << newData;
         }    // exists
     }        // for new screens.
-    // Remove deleted ones.
+    // Remove deleted ones but keep main monitors if we get only the
+    // temporary lock screen to avoid window recreation (QTBUG-33062).
+    if (!lockScreen) {
         for (int i = m_screens.size() - 1; i >= 0; --i) {
             if (indexOfMonitor(newDataList, m_screens.at(i)->data().name) == -1) {
                 if (QWindowsContext::verboseWindows)
@@ -413,6 +422,7 @@ bool QWindowsScreenManager::handleScreenChanges()
                 delete m_screens.takeAt(i);
             } // not found
         }     // for existing screens
+    }     // not lock screen
     return true;
 }
 

src/plugins/platforms/windows/qwindowsscreen.h

@@ -59,7 +59,8 @@ struct QWindowsScreenData
     enum Flags
     {
         PrimaryScreen = 0x1,
-        VirtualDesktop = 0x2
+        VirtualDesktop = 0x2,
+        LockScreen = 0x4 // Temporary screen existing during user change, etc.
     };
 
     QWindowsScreenData();