Fix QApplication::primaryScreen() in Windows

QPlatformInterface::screenAdded() documentation specifies that first
added screen will be the primary screen, so we need to ensure that
the screen Windows reports as the main display gets added first.

Task-number: QTBUG-27988
Change-Id: Ibc17b05a6c37007ff749fb54ab62d47ffa40f8ac
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index 0717a8ec60..a09ab583c8 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -125,11 +125,19 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
                        Qt::PortraitOrientation : Qt::LandscapeOrientation;
     // EnumDisplayMonitors (as opposed to EnumDisplayDevices) enumerates only
     // virtual desktop screens.
+    data.name = QString::fromWCharArray(info.szDevice);
     data.flags = QWindowsScreenData::VirtualDesktop;
-    if (info.dwFlags & MONITORINFOF_PRIMARY)
+    if (info.dwFlags & MONITORINFOF_PRIMARY) {
         data.flags |= QWindowsScreenData::PrimaryScreen;
-    data.name = QString::fromWCharArray(info.szDevice);
-    result->append(data);
+        // QPlatformIntegration::screenAdded() documentation specifies that first
+        // added screen will be the primary screen, so order accordingly.
+        // Note that the side effect of this policy is that there is no way to change primary
+        // screen reported by Qt, unless we want to delete all existing screens and add them
+        // again whenever primary screen changes.
+        result->prepend(data);
+    } else {
+        result->append(data);
+    }
     return TRUE;
 }