Add QGuiApplication::sync() function

This will allow applications to make sure Qt has the same state as the
window system at any given point. The use of this function is
discouraged but it is very useful for auto tests.

Change-Id: I691bff365fc391e9d7213f2607008983505bb774
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

src/gui/kernel/qguiapplication.cpp

@@ -2801,6 +2801,27 @@ bool QGuiApplication::isSavingSession() const
     return d->is_saving_session;
 }
 
+/*!
+    \since 5.2
+
+    Function that can be used to sync Qt state with the Window Systems state.
+
+    This function will first empty Qts events by calling QCoreApplication::processEvents(),
+    then the platform plugin will sync up with the windowsystem, and finally Qts events
+    will be delived by another call to QCoreApplication::processEvents();
+
+    This function is timeconsuming and its use is discouraged.
+*/
+void QGuiApplication::sync()
+{
+    QCoreApplication::processEvents();
+    if (QGuiApplicationPrivate::platform_integration
+            && QGuiApplicationPrivate::platform_integration->hasCapability(QPlatformIntegration::SyncState)) {
+        QGuiApplicationPrivate::platform_integration->sync();
+        QCoreApplication::processEvents();
+    }
+}
+
 void QGuiApplicationPrivate::commitData()
 {
     Q_Q(QGuiApplication);

src/gui/kernel/qguiapplication.h

@@ -155,6 +155,7 @@ public:
     bool isSavingSession() const;
 #endif
 
+    static void sync();
 Q_SIGNALS:
     void fontDatabaseChanged();
     void screenAdded(QScreen *screen);

src/gui/kernel/qplatformintegration.cpp

@@ -435,4 +435,19 @@ QPlatformSessionManager *QPlatformIntegration::createPlatformSessionManager(cons
 }
 #endif
 
+/*!
+   \since 5.2
+
+   Function to sync the platform integrations state with the window system.
+
+   This is often implemented as a roundtrip from the platformintegration to the window system.
+
+   This function should not call QWindowSystemInterface::flushWindowSystemEvents() or
+   QCoreApplication::processEvents()
+*/
+void QPlatformIntegration::sync()
+{
+
+}
+
 QT_END_NAMESPACE

src/gui/kernel/qplatformintegration.h

@@ -94,7 +94,8 @@ public:
         ForeignWindows,
         NonFullScreenWindows,
         NativeWidgets,
-        WindowManagement
+        WindowManagement,
+        SyncState
     };
 
     virtual ~QPlatformIntegration() { }
@@ -162,6 +163,8 @@ public:
 #ifndef QT_NO_SESSIONMANAGER
     virtual QPlatformSessionManager *createPlatformSessionManager(const QString &id, const QString &key) const;
 #endif
+
+    virtual void sync();
 protected:
     void screenAdded(QPlatformScreen *screen);
 };

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -282,6 +282,7 @@ bool QXcbIntegration::hasCapability(QPlatformIntegration::Capability cap) const
     case WindowMasks: return true;
     case MultipleWindows: return true;
     case ForeignWindows: return true;
+    case SyncState: return true;
     default: return QPlatformIntegration::hasCapability(cap);
     }
 }
@@ -458,4 +459,11 @@ QPlatformSessionManager *QXcbIntegration::createPlatformSessionManager(const QSt
 }
 #endif
 
+void QXcbIntegration::sync()
+{
+    for (int i = 0; i < m_connections.size(); i++) {
+        m_connections.at(i)->sync();
+    }
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/xcb/qxcbintegration.h

@@ -106,6 +106,7 @@ public:
     QPlatformSessionManager *createPlatformSessionManager(const QString &id, const QString &key) const Q_DECL_OVERRIDE;
 #endif
 
+    void sync();
 private:
     QList<QXcbConnection *> m_connections;