Add QSinglePointEvent::exclusivePointGrabber convenience property

Since a single-point event (such as a QMouseEvent) only carries one
point, it only has one grabber, so we can have a normal Q_PROPERTY.

It's named exclusivePointGrabber to avoid shadowing the
QPointerEvent::[set]exclusiveGrabber functions that take QEventPoint&.

Change-Id: Ie18f1c1849ed057b98f229de7b17b7fc3f3eea36
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/kernel/qevent.cpp

@@ -963,6 +963,21 @@ bool QSinglePointEvent::isEndEvent() const
     return m_button != Qt::NoButton && !m_mouseState.testFlag(m_button);
 }
 
+/*!
+    \property QSinglePointEvent::exclusivePointGrabber
+    \brief the object that will receive future updates
+
+    The exclusive grabber is an object that has chosen to receive all future
+    update events and the release event containing the same point that this
+    event carries.
+
+    Setting the exclusivePointGrabber property is a convenience equivalent to:
+    \code
+    setExclusiveGrabber(points().first(), exclusiveGrabber);
+    \endcode
+*/
+
+
 /*!
     \class QMouseEvent
     \ingroup events

src/gui/kernel/qevent.h

@@ -233,6 +233,9 @@ protected:
 
 class Q_GUI_EXPORT QSinglePointEvent : public QPointerEvent
 {
+    Q_GADGET
+    Q_PROPERTY(QObject *exclusivePointGrabber READ exclusivePointGrabber WRITE setExclusivePointGrabber)
+
 public:
     QSinglePointEvent(Type type, const QPointingDevice *dev, const QPointF &localPos,
                       const QPointF &scenePos, const QPointF &globalPos,
@@ -253,6 +256,11 @@ public:
     bool isUpdateEvent() const override;
     bool isEndEvent() const override;
 
+    QObject *exclusivePointGrabber() const
+    { return QPointerEvent::exclusiveGrabber(points().first()); }
+    void setExclusivePointGrabber(QObject *exclusiveGrabber)
+    { QPointerEvent::setExclusiveGrabber(points().first(), exclusiveGrabber); }
+
 protected:
     QSinglePointEvent(Type type, const QPointingDevice *dev, const QEventPoint &point,
                       Qt::MouseButton button, Qt::MouseButtons buttons,