4 files changed, 79 insertions, 4 deletions

diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index d05dc8cbdc..82e0e44ac7 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -89,6 +89,26 @@ void QWindowSystemInterface::handleLeaveEvent(QWindow *tlw)
     QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
 }
 
+/*!
+    This method can be used to ensure leave and enter events are both in queue when moving from
+    one QWindow to another. This allows QWindow subclasses to check for a queued enter event
+    when handling the leave event (\c QWindowSystemInterfacePrivate::peekWindowSystemEvent) to
+    determine where mouse went and act accordingly. E.g. QWidgetWindow needs to know if mouse
+    cursor moves between windows in same window hierarchy.
+*/
+void QWindowSystemInterface::handleEnterLeaveEvent(QWindow *enter, QWindow *leave)
+{
+    bool wasSynchronous = QWindowSystemInterfacePrivate::synchronousWindowsSystemEvents;
+    if (wasSynchronous)
+        setSynchronousWindowsSystemEvents(false);
+    handleLeaveEvent(leave);
+    handleEnterEvent(enter);
+    if (wasSynchronous) {
+        flushWindowSystemEvents();
+        setSynchronousWindowsSystemEvents(true);
+    }
+}
+
 void QWindowSystemInterface::handleWindowActivated(QWindow *tlw)
 {
     QWindowSystemInterfacePrivate::ActivatedWindowEvent *e = new QWindowSystemInterfacePrivate::ActivatedWindowEvent(tlw);
@@ -324,6 +344,16 @@ QWindowSystemInterfacePrivate::WindowSystemEvent * QWindowSystemInterfacePrivate
     return windowSystemEventQueue.takeFirstOrReturnNull();
 }
 
+QWindowSystemInterfacePrivate::WindowSystemEvent *QWindowSystemInterfacePrivate::peekWindowSystemEvent(EventType t)
+{
+    return windowSystemEventQueue.peekAtFirstOfType(t);
+}
+
+void QWindowSystemInterfacePrivate::removeWindowSystemEvent(WindowSystemEvent *event)
+{
+    windowSystemEventQueue.remove(event);
+}
+
 void QWindowSystemInterfacePrivate::handleWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent *ev)
 {
     if (synchronousWindowsSystemEvents) {
diff --git a/src/gui/kernel/qwindowsysteminterface.h b/src/gui/kernel/qwindowsysteminterface.h
index cf5d22edbd..74b5a136f4 100644
--- a/src/gui/kernel/qwindowsysteminterface.h
+++ b/src/gui/kernel/qwindowsysteminterface.h
@@ -136,6 +136,7 @@ public:
     static void handleCloseEvent(QWindow *w);
     static void handleEnterEvent(QWindow *w);
     static void handleLeaveEvent(QWindow *w);
+    static void handleEnterLeaveEvent(QWindow *enter, QWindow *leave);
     static void handleWindowActivated(QWindow *w);
     static void handleWindowStateChanged(QWindow *w, Qt::WindowState newState);
 
diff --git a/src/gui/kernel/qwindowsysteminterface_p.h b/src/gui/kernel/qwindowsysteminterface_p.h
index e9d2fadc84..4e907f3f51 100644
--- a/src/gui/kernel/qwindowsysteminterface_p.h
+++ b/src/gui/kernel/qwindowsysteminterface_p.h
@@ -52,7 +52,7 @@ QT_BEGIN_HEADER
 
 QT_BEGIN_NAMESPACE
 
-class QWindowSystemInterfacePrivate {
+class Q_GUI_EXPORT QWindowSystemInterfacePrivate {
 public:
     enum EventType {
         Close,
@@ -349,6 +349,25 @@ public:
         { const QMutexLocker locker(&mutex); impl.append(e); }
         int count() const
         { const QMutexLocker locker(&mutex); return impl.count(); }
+        WindowSystemEvent *peekAtFirstOfType(EventType t) const
+        {
+            const QMutexLocker locker(&mutex);
+            for (int i = 0; i < impl.size(); ++i) {
+                if (impl.at(i)->type == t)
+                    return impl.at(i);
+            }
+            return 0;
+        }
+        void remove(const WindowSystemEvent *e)
+        {
+            const QMutexLocker locker(&mutex);
+            for (int i = 0; i < impl.size(); ++i) {
+                if (impl.at(i) == e) {
+                    impl.removeAt(i);
+                    break;
+                }
+            }
+        }
     private:
         Q_DISABLE_COPY(WindowSystemEventList);
     };
@@ -356,7 +375,9 @@ public:
     static WindowSystemEventList windowSystemEventQueue;
 
     static int windowSystemEventsQueued();
-    static WindowSystemEvent * getWindowSystemEvent();
+    static WindowSystemEvent *getWindowSystemEvent();
+    static WindowSystemEvent *peekWindowSystemEvent(EventType t);
+    static void removeWindowSystemEvent(WindowSystemEvent *event);
     static void handleWindowSystemEvent(WindowSystemEvent *ev);
 
     static QElapsedTimer eventTime;
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 10ec4d3745..5f25e1274e 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -47,6 +47,7 @@
 #include <QtGui/qaccessible.h>
 #endif
 #include <private/qwidgetbackingstore_p.h>
+#include <qpa/qwindowsysteminterface_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -212,9 +213,31 @@ QPointer<QWidget> qt_last_mouse_receiver = 0;
 void QWidgetWindow::handleEnterLeaveEvent(QEvent *event)
 {
     if (event->type() == QEvent::Leave) {
+        QWidget *enter = 0;
+        // Check from window system event queue if the next queued enter targets a window
+        // in the same window hierarchy (e.g. enter a child of this window). If so,
+        // remove the enter event from queue and handle both in single dispatch.
+        QWindowSystemInterfacePrivate::EnterEvent *systemEvent =
+            static_cast<QWindowSystemInterfacePrivate::EnterEvent *>
+            (QWindowSystemInterfacePrivate::peekWindowSystemEvent(QWindowSystemInterfacePrivate::Enter));
+        if (systemEvent) {
+            if (QWidgetWindow *enterWindow = qobject_cast<QWidgetWindow *>(systemEvent->enter))
+            {
+                QWindow *thisParent = this;
+                QWindow *enterParent = enterWindow;
+                while (thisParent->parent())
+                    thisParent = thisParent->parent();
+                while (enterParent->parent())
+                    enterParent = enterParent->parent();
+                if (thisParent == enterParent) {
+                    enter = enterWindow->widget();
+                    QWindowSystemInterfacePrivate::removeWindowSystemEvent(systemEvent);
+                }
+            }
+        }
         QWidget *leave = qt_last_mouse_receiver ? qt_last_mouse_receiver.data() : m_widget;
-        QApplicationPrivate::dispatchEnterLeave(0, leave);
-        qt_last_mouse_receiver = 0;
+        QApplicationPrivate::dispatchEnterLeave(enter, leave);
+        qt_last_mouse_receiver = enter;
     } else {
         QApplicationPrivate::dispatchEnterLeave(m_widget, 0);
         qt_last_mouse_receiver = m_widget;