clarify further exclusive vs. passive grabs

Add documentation to the grab-related event and eventpoint methods.
Rename "grabber" functions which relate only to the exclusive grab,
in cases where it would otherwise be ambiguous.
And a few other documentation changes.

Change-Id: I1a203c8c06a19d4abdb000f08b387c38341ef476
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

6 files changed, 137 insertions, 50 deletions

diff --git a/src/quick/handlers/qquickpointersinglehandler.cpp b/src/quick/handlers/qquickpointersinglehandler.cpp
index 41c9e1f322..c0c88f3852 100644
--- a/src/quick/handlers/qquickpointersinglehandler.cpp
+++ b/src/quick/handlers/qquickpointersinglehandler.cpp
@@ -83,7 +83,7 @@ bool QQuickPointerSingleHandler::wantsPointerEvent(QQuickPointerEvent *event)
         int c = event->pointCount();
         for (int i = 0; i < c && !m_pointId; ++i) {
             QQuickEventPoint *p = event->point(i);
-            if (!p->grabber() && wantsEventPoint(p)) {
+            if (!p->exclusiveGrabber() && wantsEventPoint(p)) {
                 m_pointId = p->pointId();
                 p->setAccepted();
             }
@@ -149,7 +149,7 @@ void QQuickPointerSingleHandler::handleGrabCancel(QQuickEventPoint *point)
 
 void QQuickPointerSingleHandler::onGrabChanged(QQuickEventPoint *point)
 {
-    bool grabbing = (point->grabber() == this);
+    bool grabbing = (point->exclusiveGrabber() == this);
     setActive(grabbing);
     if (grabbing)
         m_sceneGrabPos = point->sceneGrabPos();
diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index 0af19ff750..1843d2b656 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -566,12 +566,26 @@ void QQuickEventPoint::invalidate()
     m_pointId = 0;
 }
 
-QObject *QQuickEventPoint::grabber() const
+/*!
+    If this point has an exclusive grabber, returns a pointer to it; else
+    returns null, if there is no grabber.  The grabber could be either
+    an Item or a PointerHandler.
+*/
+QObject *QQuickEventPoint::exclusiveGrabber() const
 {
     return m_exclusiveGrabber.data();
 }
 
-void QQuickEventPoint::setGrabber(QObject *grabber)
+/*!
+    Set the given Item or PointerHandler as the exclusive grabber of this point.
+    If there was already an exclusive grab, it will be canceled.  If there
+    were passive grabbers, they will continue to lurk, but the exclusive grab
+    is a behavioral override of the passive grab as long as it remains.
+    If you already know whether the grabber is to be an Item or a PointerHandler,
+    you should instead call setGrabberItem() or setGrabberPointerHandler(),
+    because it is slightly more efficient.
+*/
+void QQuickEventPoint::setExclusiveGrabber(QObject *grabber)
 {
     if (QQuickPointerHandler *phGrabber = qmlobject_cast<QQuickPointerHandler *>(grabber))
         setGrabberPointerHandler(phGrabber, true);
@@ -579,11 +593,22 @@ void QQuickEventPoint::setGrabber(QObject *grabber)
         setGrabberItem(static_cast<QQuickItem *>(grabber));
 }
 
+/*!
+    If the exclusive grabber of this point is an Item, returns a
+    pointer to that Item; else returns null, if there is no grabber or if
+    the grabber is a PointerHandler.
+*/
 QQuickItem *QQuickEventPoint::grabberItem() const
 {
     return (m_grabberIsHandler ? nullptr : static_cast<QQuickItem *>(m_exclusiveGrabber.data()));
 }
 
+/*!
+    Set the given Item \a grabber as the exclusive grabber of this point.
+    If there was already an exclusive grab, it will be canceled.  If there
+    were passive grabbers, they will continue to lurk, but the exclusive grab
+    is a behavioral override of the passive grab as long as it remains.
+*/
 void QQuickEventPoint::setGrabberItem(QQuickItem *grabber)
 {
     if (grabber != m_exclusiveGrabber.data()) {
@@ -597,11 +622,21 @@ void QQuickEventPoint::setGrabberItem(QQuickItem *grabber)
     }
 }
 
+/*!
+    If the exclusive grabber of this point is a PointerHandler, returns a
+    pointer to that handler; else returns null, if there is no grabber or if
+    the grabber is an Item.
+*/
 QQuickPointerHandler *QQuickEventPoint::grabberPointerHandler() const
 {
     return (m_grabberIsHandler ? static_cast<QQuickPointerHandler *>(m_exclusiveGrabber.data()) : nullptr);
 }
 
+/*!
+    Set the given PointerHandler \a grabber as grabber of this point. If \a
+    exclusive is true, it will override any other grabs; if false, \a grabber
+    will be added to the list of passive grabbers of this point.
+*/
 void QQuickEventPoint::setGrabberPointerHandler(QQuickPointerHandler *grabber, bool exclusive)
 {
     if (Q_UNLIKELY(lcPointerGrab().isDebugEnabled())) {
@@ -633,6 +668,11 @@ void QQuickEventPoint::setGrabberPointerHandler(QQuickPointerHandler *grabber, b
     }
 }
 
+/*!
+    If this point has an existing exclusive grabber (Item or PointerHandler),
+    inform the grabber that its grab is canceled, and remove it as grabber.
+    This normally happens when the grab is stolen by another Item.
+*/
 void QQuickEventPoint::cancelExclusiveGrab()
 {
     if (m_exclusiveGrabber.isNull()) {
@@ -648,6 +688,11 @@ void QQuickEventPoint::cancelExclusiveGrab()
     m_exclusiveGrabber.clear();
 }
 
+/*!
+    If this point has the given \a handler as a passive grabber,
+    inform the grabber that its grab is canceled, and remove it as grabber.
+    This normally happens when another Item or PointerHandler does an exclusive grab.
+*/
 void QQuickEventPoint::cancelPassiveGrab(QQuickPointerHandler *handler)
 {
     if (m_passiveGrabbers.removeOne(QPointer<QQuickPointerHandler>(handler))) {
@@ -659,6 +704,17 @@ void QQuickEventPoint::cancelPassiveGrab(QQuickPointerHandler *handler)
     }
 }
 
+/*!
+    If the given \a handler is grabbing this point passively, exclusively
+    or both, cancel the grab and remove it as grabber.
+    This normally happens when the handler decides that the behavior of this
+    point can no longer satisfy the handler's behavioral constraints within
+    the remainder of the gesture which the user is performing: for example
+    the handler tries to detect a tap but a drag is occurring instead, or
+    it tries to detect a drag in one direction but the drag is going in
+    another direction.  In such cases the handler no longer needs or wants
+    to be informed of any further movements of this point.
+*/
 void QQuickEventPoint::cancelAllGrabs(QQuickPointerHandler *handler)
 {
     if (m_exclusiveGrabber == handler) {
@@ -668,6 +724,12 @@ void QQuickEventPoint::cancelAllGrabs(QQuickPointerHandler *handler)
     cancelPassiveGrab(handler);
 }
 
+/*!
+    Set this point as \a accepted (true) or rejected (false).
+    Accepting a point is intended to stop event propagation.
+    It does not imply any kind of grab, passive or exclusive.
+    TODO explain further under what conditions propagation really does stop...
+*/
 void QQuickEventPoint::setAccepted(bool accepted)
 {
     if (m_accept != accepted) {
@@ -707,11 +769,10 @@ Q_GLOBAL_STATIC(PointDataForPointIdMap, g_previousPointData)
 static const int PointVelocityAgeLimit = 500; // milliseconds
 
 /*!
- * \interal
- * \brief Estimates the velocity based on a weighted average of all previous velocities.
- *        The older the velocity is, the less significant it becomes for the estimate.
- * \return
- */
+    \internal
+    Estimates the velocity based on a weighted average of all previous velocities.
+    The older the velocity is, the less significant it becomes for the estimate.
+*/
 QVector2D QQuickEventPoint::estimatedVelocity() const
 {
     PointVelocityData *prevPoint = g_previousPointData->value(m_pointId);
@@ -838,7 +899,7 @@ QQuickPointerEvent *QQuickPointerTouchEvent::reset(QEvent *event)
         QObject *grabber = nullptr;
         QVector <QPointer <QQuickPointerHandler> > passiveGrabbers;
         if (auto point = pointById(tps.at(i).id())) {
-            grabber = point->grabber();
+            grabber = point->exclusiveGrabber();
             passiveGrabbers = point->passiveGrabbers();
         }
         grabbers.append(grabber);
@@ -854,7 +915,7 @@ QQuickPointerEvent *QQuickPointerTouchEvent::reset(QEvent *event)
             point->setGrabberItem(nullptr);
             point->clearPassiveGrabbers();
         } else {
-            point->setGrabber(grabbers.at(i));
+            point->setExclusiveGrabber(grabbers.at(i));
             point->setPassiveGrabbers(passiveGrabberses.at(i));
         }
     }
@@ -902,7 +963,7 @@ bool QQuickPointerMouseEvent::allUpdatedPointsAccepted() const {
 
 bool QQuickPointerMouseEvent::allPointsGrabbed() const
 {
-    return m_mousePoint->grabber() != nullptr;
+    return m_mousePoint->exclusiveGrabber() != nullptr;
 }
 
 QMouseEvent *QQuickPointerMouseEvent::asMouseEvent(const QPointF &localPos) const
@@ -912,22 +973,31 @@ QMouseEvent *QQuickPointerMouseEvent::asMouseEvent(const QPointF &localPos) cons
     return event;
 }
 
-QVector<QObject *> QQuickPointerMouseEvent::grabbers() const
+/*!
+    Returns the exclusive grabber of this event, if any, in a vector.
+*/
+QVector<QObject *> QQuickPointerMouseEvent::exclusiveGrabbers() const
 {
     QVector<QObject *> result;
-    if (QObject *grabber = m_mousePoint->grabber())
+    if (QObject *grabber = m_mousePoint->exclusiveGrabber())
         result << grabber;
     return result;
 }
 
+/*!
+    Remove all passive and exclusive grabbers of this event, without notifying.
+*/
 void QQuickPointerMouseEvent::clearGrabbers() const {
     m_mousePoint->setGrabberItem(nullptr);
     m_mousePoint->clearPassiveGrabbers();
 }
 
-bool QQuickPointerMouseEvent::hasGrabber(const QQuickPointerHandler *handler) const
+/*!
+    Returns whether the given \a handler is the exclusive grabber of this event.
+*/
+bool QQuickPointerMouseEvent::hasExclusiveGrabber(const QQuickPointerHandler *handler) const
 {
-    return m_mousePoint->grabber() == handler;
+    return m_mousePoint->exclusiveGrabber() == handler;
 }
 
 bool QQuickPointerMouseEvent::isPressEvent() const
@@ -957,18 +1027,20 @@ bool QQuickPointerTouchEvent::allUpdatedPointsAccepted() const {
 bool QQuickPointerTouchEvent::allPointsGrabbed() const
 {
     for (int i = 0; i < m_pointCount; ++i) {
-        if (!m_touchPoints.at(i)->grabber())
+        if (!m_touchPoints.at(i)->exclusiveGrabber())
             return false;
     }
     return true;
 }
 
-QVector<QObject *> QQuickPointerTouchEvent::grabbers() const
+/*!
+    Returns the exclusive grabbers of all points in this event, if any, in a vector.
+*/
+QVector<QObject *> QQuickPointerTouchEvent::exclusiveGrabbers() const
 {
     QVector<QObject *> result;
     for (int i = 0; i < m_pointCount; ++i) {
-        auto point = m_touchPoints.at(i);
-        if (QObject *grabber = point->grabber()) {
+        if (QObject *grabber = m_touchPoints.at(i)->exclusiveGrabber()) {
             if (!result.contains(grabber))
                 result << grabber;
         }
@@ -976,17 +1048,25 @@ QVector<QObject *> QQuickPointerTouchEvent::grabbers() const
     return result;
 }
 
+/*!
+    Remove all passive and exclusive grabbers of all touchpoints in this event,
+    without notifying.
+*/
 void QQuickPointerTouchEvent::clearGrabbers() const {
     for (auto point: m_touchPoints) {
-        point->setGrabber(nullptr);
+        point->setGrabberItem(nullptr);
         point->clearPassiveGrabbers();
     }
 }
 
-bool QQuickPointerTouchEvent::hasGrabber(const QQuickPointerHandler *handler) const
+/*!
+    Returns whether the given \a handler is the exclusive grabber of any
+    touchpoint within this event.
+*/
+bool QQuickPointerTouchEvent::hasExclusiveGrabber(const QQuickPointerHandler *handler) const
 {
     for (auto point: m_touchPoints)
-        if (point->grabber() == handler)
+        if (point->exclusiveGrabber() == handler)
             return true;
     return false;
 }
@@ -1111,7 +1191,7 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
         auto p = m_touchPoints.at(i);
         if (p->isAccepted())
             continue;
-        bool isGrabber = p->grabber() == item;
+        bool isGrabber = p->exclusiveGrabber() == item;
         bool isPressInside = p->state() == QQuickEventPoint::Pressed && item->contains(item->mapFromScene(p->scenePos()));
         if (!(isGrabber || isPressInside || isFiltering))
             continue;
diff --git a/src/quick/items/qquickevents_p_p.h b/src/quick/items/qquickevents_p_p.h
index d042f318e9..00da53eb48 100644
--- a/src/quick/items/qquickevents_p_p.h
+++ b/src/quick/items/qquickevents_p_p.h
@@ -263,7 +263,7 @@ class Q_QUICK_PRIVATE_EXPORT QQuickEventPoint : public QObject
     Q_PROPERTY(qreal timeHeld READ timeHeld)
     Q_PROPERTY(QVector2D velocity READ velocity)
     Q_PROPERTY(bool accepted READ isAccepted WRITE setAccepted)
-    Q_PROPERTY(QObject *grabber READ grabber WRITE setGrabber)
+    Q_PROPERTY(QObject *exclusiveGrabber READ exclusiveGrabber WRITE setExclusiveGrabber)
 
 public:
     enum State {
@@ -295,14 +295,14 @@ public:
     bool isAccepted() const { return m_accept; }
     void setAccepted(bool accepted = true);
     bool isDraggedOverThreshold() const;
-    QObject *grabber() const;
-    void setGrabber(QObject *grabber);
+    QObject *exclusiveGrabber() const;
+    void setExclusiveGrabber(QObject *exclusiveGrabber);
 
     QQuickItem *grabberItem() const;
-    void setGrabberItem(QQuickItem *grabber);
+    void setGrabberItem(QQuickItem *exclusiveGrabber);
 
     QQuickPointerHandler *grabberPointerHandler() const;
-    void setGrabberPointerHandler(QQuickPointerHandler *grabber, bool exclusive = false);
+    void setGrabberPointerHandler(QQuickPointerHandler *exclusiveGrabber, bool exclusive = false);
 
     Q_INVOKABLE void cancelExclusiveGrab();
     Q_INVOKABLE void cancelPassiveGrab(QQuickPointerHandler *handler);
@@ -409,9 +409,9 @@ public: // helpers for C++ only (during event delivery)
     virtual int pointCount() const = 0;
     virtual QQuickEventPoint *point(int i) const = 0;
     virtual QQuickEventPoint *pointById(quint64 pointId) const = 0;
-    virtual QVector<QObject *> grabbers() const = 0;
+    virtual QVector<QObject *> exclusiveGrabbers() const = 0;
     virtual void clearGrabbers() const = 0;
-    virtual bool hasGrabber(const QQuickPointerHandler *handler) const = 0;
+    virtual bool hasExclusiveGrabber(const QQuickPointerHandler *handler) const = 0;
 
     ulong timestamp() const { return m_event->timestamp(); }
 
@@ -442,9 +442,9 @@ public:
     bool allPointsAccepted() const override;
     bool allUpdatedPointsAccepted() const override;
     bool allPointsGrabbed() const override;
-    QVector<QObject *> grabbers() const override;
+    QVector<QObject *> exclusiveGrabbers() const override;
     void clearGrabbers() const override;
-    bool hasGrabber(const QQuickPointerHandler *handler) const override;
+    bool hasExclusiveGrabber(const QQuickPointerHandler *handler) const override;
 
     QMouseEvent *asMouseEvent(const QPointF& localPos) const;
 
@@ -476,9 +476,9 @@ public:
     bool allPointsAccepted() const override;
     bool allUpdatedPointsAccepted() const override;
     bool allPointsGrabbed() const override;
-    QVector<QObject *> grabbers() const override;
+    QVector<QObject *> exclusiveGrabbers() const override;
     void clearGrabbers() const override;
-    bool hasGrabber(const QQuickPointerHandler *handler) const override;
+    bool hasExclusiveGrabber(const QQuickPointerHandler *handler) const override;
 
     QMouseEvent *syntheticMouseEvent(int pointID, QQuickItem *relativeTo) const;
     QTouchEvent *touchEventForItem(QQuickItem *item, bool isFiltering = false) const;
diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index 9b91b4bda4..7adf455ac6 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -5091,7 +5091,14 @@ void QQuickItemPrivate::deliverShortcutOverrideEvent(QKeyEvent *event)
     }
 }
 
-bool QQuickItemPrivate::handlePointerEvent(QQuickPointerEvent *event, bool avoidGrabber)
+/*!
+    \internal
+    Deliver the \a event to all PointerHandlers which are in the pre-determined
+    eventDeliveryTargets() vector.  If \a avoidExclusiveGrabber is true, it skips
+    delivery to any handler which is the exclusive grabber of any point within this event
+    (because delivery to exclusive grabbers is handled separately).
+*/
+bool QQuickItemPrivate::handlePointerEvent(QQuickPointerEvent *event, bool avoidExclusiveGrabber)
 {
     Q_Q(QQuickItem);
     bool delivered = false;
@@ -5099,7 +5106,7 @@ bool QQuickItemPrivate::handlePointerEvent(QQuickPointerEvent *event, bool avoid
     if (extra.isAllocated()) {
         for (QQuickPointerHandler *handler : extra->pointerHandlers) {
             qCDebug(lcPointerHandlerDispatch) << "   delivering" << event << "to" << handler << "on" << q;
-            if ((!avoidGrabber || !event->hasGrabber(handler)) && !eventDeliveryTargets.contains(handler)) {
+            if ((!avoidExclusiveGrabber || !event->hasExclusiveGrabber(handler)) && !eventDeliveryTargets.contains(handler)) {
                 handler->handlePointerEvent(event);
                 delivered = true;
                 eventDeliveryTargets.append(handler);
diff --git a/src/quick/items/qquickitem_p.h b/src/quick/items/qquickitem_p.h
index b39c437da5..6ce6a233d6 100644
--- a/src/quick/items/qquickitem_p.h
+++ b/src/quick/items/qquickitem_p.h
@@ -563,7 +563,7 @@ public:
 #endif
     void deliverShortcutOverrideEvent(QKeyEvent *);
 
-    virtual bool handlePointerEvent(QQuickPointerEvent *, bool avoidGrabber = false);
+    virtual bool handlePointerEvent(QQuickPointerEvent *, bool avoidExclusiveGrabber = false);
 
     bool isTransparentForPositioner() const;
     void setTransparentForPositioner(bool trans);
diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 669e521b7f..0cd9357b9a 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -790,7 +790,7 @@ void QQuickWindowPrivate::grabTouchPoints(QObject *grabber, const QVector<int> &
             auto point = touchMouseDevice->pointerEvent()->pointById(id);
             auto touchMouseGrabber = point->grabberItem();
             if (touchMouseGrabber) {
-                point->setGrabber(nullptr);
+                point->setExclusiveGrabber(nullptr);
                 touchMouseGrabber->mouseUngrabEvent();
                 ungrab.insert(touchMouseGrabber);
                 touchMouseDevice = nullptr;
@@ -804,11 +804,11 @@ void QQuickWindowPrivate::grabTouchPoints(QObject *grabber, const QVector<int> &
             auto point = device->pointerEvent()->pointById(id);
             if (!point)
                 continue;
-            QObject *oldGrabber = point->grabber();
+            QObject *oldGrabber = point->exclusiveGrabber();
             if (oldGrabber == grabber)
                 continue;
 
-            point->setGrabber(grabber);
+            point->setExclusiveGrabber(grabber);
             if (oldGrabber)
                 ungrab.insert(oldGrabber);
         }
@@ -827,7 +827,7 @@ void QQuickWindowPrivate::removeGrabber(QQuickItem *grabber, bool mouse, bool to
         for (auto device : touchDevices) {
             auto pointerEvent = device->pointerEvent();
             for (int i = 0; i < pointerEvent->pointCount(); ++i) {
-                if (pointerEvent->point(i)->grabber() == grabber) {
+                if (pointerEvent->point(i)->exclusiveGrabber() == grabber) {
                     pointerEvent->point(i)->setGrabberItem(nullptr);
                     // FIXME send ungrab event only once
                     grabber->touchUngrabEvent();
@@ -1658,7 +1658,7 @@ void QQuickWindowPrivate::deliverMouseEvent(QQuickPointerMouseEvent *pointerEven
     auto point = pointerEvent->point(0);
     lastMousePosition = point->scenePos();
 
-    if (point->grabber()) {
+    if (point->exclusiveGrabber()) {
         bool mouseIsReleased = (point->state() == QQuickEventPoint::Released && pointerEvent->buttons() == Qt::NoButton);
         if (auto grabber = point->grabberItem()) {
             if (sendFilteredPointerEvent(pointerEvent, grabber))
@@ -1721,7 +1721,7 @@ void QQuickWindowPrivate::deliverMouseEvent(QQuickPointerMouseEvent *pointerEven
                         if (itemPrivate->handlePointerEvent(pointerEvent, true)) // avoid re-delivering to grabbers
                             delivered = true;
                     }
-                    if (point->grabber())
+                    if (point->exclusiveGrabber())
                         break;
                 }
             }
@@ -1929,7 +1929,7 @@ bool QQuickWindowPrivate::deliverTouchCancelEvent(QTouchEvent *event)
     // A TouchCancel event will typically not contain any points.
     // Deliver it to all items that have active touches.
     QQuickPointerEvent *pointerEvent = QQuickPointerDevice::touchDevice(event->device())->pointerEvent();
-    QVector<QObject *> grabbers = pointerEvent->grabbers();
+    QVector<QObject *> grabbers = pointerEvent->exclusiveGrabbers();
 
     for (QObject *grabber: qAsConst(grabbers)) {
         if (QQuickItem *grabberItem = qmlobject_cast<QQuickItem *>(grabber))
@@ -2106,7 +2106,7 @@ void QQuickWindowPrivate::handleMouseEvent(QMouseEvent *event)
         updateCursor(event->windowPos());
     #endif
 
-        if (!QQuickPointerDevice::genericMouseDevice()->pointerEvent()->point(0)->grabber()) {
+        if (!QQuickPointerDevice::genericMouseDevice()->pointerEvent()->point(0)->exclusiveGrabber()) {
             QPointF last = lastMousePosition.isNull() ? event->windowPos() : lastMousePosition;
             lastMousePosition = event->windowPos();
 
@@ -2283,8 +2283,8 @@ void QQuickWindowPrivate::deliverTouchEvent(QQuickPointerTouchEvent *event)
         }
     }
 
-    if (allReleased && !event->grabbers().isEmpty()) {
-        qWarning() << "No release received for some grabbers" << event->grabbers();
+    if (allReleased && !event->exclusiveGrabbers().isEmpty()) {
+        qWarning() << "No release received for some grabbers" << event->exclusiveGrabbers();
         event->clearGrabbers();
     }
 }
@@ -2292,7 +2292,7 @@ void QQuickWindowPrivate::deliverTouchEvent(QQuickPointerTouchEvent *event)
 // Deliver touch points to existing grabbers
 void QQuickWindowPrivate::deliverUpdatedTouchPoints(QQuickPointerTouchEvent *event)
 {
-    const auto grabbers = event->grabbers();
+    const auto grabbers = event->exclusiveGrabbers();
     for (auto grabber : grabbers) {
         // The grabber is guaranteed to be either an item or a handler.
         QQuickItem *receiver = qmlobject_cast<QQuickItem *>(grabber);
@@ -2467,7 +2467,7 @@ void QQuickWindowPrivate::deliverMatchingPointsToItem(QQuickItem *item, QQuickPo
         // will not be interested in further updates for those touchpoint IDs either.
         for (auto point: qAsConst(touchEvent->touchPoints())) {
             if (point.state() == Qt::TouchPointPressed) {
-                if (ptEvent->pointById(point.id())->grabber() == item) {
+                if (ptEvent->pointById(point.id())->exclusiveGrabber() == item) {
                     qCDebug(DBG_TOUCH_TARGET) << "TP" << hex << point.id() << "disassociated";
                     ptEvent->pointById(point.id())->setGrabberItem(nullptr);
                 }