notify a PointerHandler when it loses grab due to Item::grabTouchPoints

and move more notification responsibility into QQuickEventPoint,
thus simplifying QQuickWindowPrivate::grabTouchPoints() which is the
implementation behind QQuickItem::grabTouchPoints.
It's important for QQuickEventPoint::setGrabberItem to
change local state first and then notify, to prevent recursive
notify/ungrab loops.  MPTA for example does an ungrab
when it receives touchUngrabEvent, which then notifies again
if the first ungrab was not already fully completed.

Change-Id: I6f7b939c8cd76ac5f2d1ddda8b210fa3d31d619a
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

3 files changed, 33 insertions, 16 deletions

diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index bbea32f905..97183c55bc 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -609,13 +609,20 @@ void QQuickEventPoint::setGrabberItem(QQuickItem *grabber)
             qCDebug(lcPointerGrab) << pointDeviceName(this) << "point" << hex << m_pointId << pointStateString(this)
                                    << ": grab" << m_exclusiveGrabber << "->" << grabber;
         }
-        if (auto handler = grabberPointerHandler())
-            handler->onGrabChanged(handler, CancelGrabExclusive, this);
-        for (QPointer<QQuickPointerHandler> passiveGrabber : m_passiveGrabbers)
-            passiveGrabber->onGrabChanged(passiveGrabber, OverrideGrabPassive, this);
+        QQuickPointerHandler *oldGrabberHandler = grabberPointerHandler();
+        QQuickItem *oldGrabberItem = grabberItem();
         m_exclusiveGrabber = QPointer<QObject>(grabber);
         m_grabberIsHandler = false;
         m_sceneGrabPos = m_scenePos;
+        if (oldGrabberHandler)
+            oldGrabberHandler->onGrabChanged(oldGrabberHandler, CancelGrabExclusive, this);
+        else if (oldGrabberItem && oldGrabberItem != grabber) {
+            auto pte = pointerEvent()->asPointerTouchEvent();
+            if (pte && pte->asTouchEvent() && pte->asTouchEvent()->touchPointStates() == Qt::TouchPointReleased)
+                oldGrabberItem->touchUngrabEvent();
+        }
+        for (QPointer<QQuickPointerHandler> passiveGrabber : m_passiveGrabbers)
+            passiveGrabber->onGrabChanged(passiveGrabber, OverrideGrabPassive, this);
     }
 }
 
@@ -656,7 +663,14 @@ void QQuickEventPoint::setGrabberPointerHandler(QQuickPointerHandler *grabber, b
                 }
             } else if (QQuickPointerHandler *oldGrabberPointerHandler = qmlobject_cast<QQuickPointerHandler *>(m_exclusiveGrabber.data())) {
                 oldGrabberPointerHandler->onGrabChanged(oldGrabberPointerHandler, UngrabExclusive, this);
+            } else if (!m_exclusiveGrabber.isNull()) {
+                // If there is a previous grabber and it's not a PointerHandler, it must be an Item.
+                QQuickItem *oldGrabberItem = static_cast<QQuickItem *>(m_exclusiveGrabber.data());
+                // If this point came from a touchscreen, notify that previous grabber Item that it's losing its touch grab.
+                if (pointerEvent()->asPointerTouchEvent())
+                    oldGrabberItem->touchUngrabEvent();
             }
+
             m_exclusiveGrabber = QPointer<QObject>(grabber);
             m_grabberIsHandler = true;
             m_sceneGrabPos = m_scenePos;
diff --git a/src/quick/items/qquickitem.h b/src/quick/items/qquickitem.h
index c9494d91bd..279d052db9 100644
--- a/src/quick/items/qquickitem.h
+++ b/src/quick/items/qquickitem.h
@@ -447,6 +447,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_resourceObjectDeleted(QObject *))
     Q_PRIVATE_SLOT(d_func(), quint64 _q_createJSWrapper(QV4::ExecutionEngine *))
 
+    friend class QQuickEventPoint;
     friend class QQuickWindow;
     friend class QQuickWindowPrivate;
     friend class QSGRenderer;
diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 57d9ac4ad2..0105e84cd6 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -778,9 +778,7 @@ void QQuickWindowPrivate::setMouseGrabber(QQuickItem *grabber)
 
 void QQuickWindowPrivate::grabTouchPoints(QObject *grabber, const QVector<int> &ids)
 {
-    QSet<QObject*> ungrab;
     for (int i = 0; i < ids.count(); ++i) {
-        // FIXME: deprecate this function, we need a device
         int id = ids.at(i);
         if (Q_UNLIKELY(id < 0)) {
             qWarning("ignoring grab of touchpoint %d", id);
@@ -792,7 +790,7 @@ void QQuickWindowPrivate::grabTouchPoints(QObject *grabber, const QVector<int> &
             if (touchMouseGrabber) {
                 point->setExclusiveGrabber(nullptr);
                 touchMouseGrabber->mouseUngrabEvent();
-                ungrab.insert(touchMouseGrabber);
+                touchMouseGrabber->touchUngrabEvent();
                 touchMouseDevice = nullptr;
                 touchMouseId = -1;
             }
@@ -807,18 +805,20 @@ void QQuickWindowPrivate::grabTouchPoints(QObject *grabber, const QVector<int> &
             QObject *oldGrabber = point->exclusiveGrabber();
             if (oldGrabber == grabber)
                 continue;
-
             point->setExclusiveGrabber(grabber);
-            if (oldGrabber)
-                ungrab.insert(oldGrabber);
         }
     }
-    for (QObject *oldGrabber : qAsConst(ungrab))
-        if (QQuickItem *item = qmlobject_cast<QQuickItem *>(oldGrabber))
-            item->touchUngrabEvent();
-        // TODO else if the old grabber was a PointerHandler, notify it somehow?
 }
 
+/*!
+    Ungrabs all touchpoint grabs and/or the mouse grab from the given item \a grabber.
+    This should not be called when processing a release event - that's redundant.
+    It is called in other cases, when the points may not be released, but the item
+    nevertheless must lose its grab due to becoming disabled, invisible, etc.
+    QQuickEventPoint::setGrabberItem() calls touchUngrabEvent() when all points are released,
+    but if not all points are released, it cannot be sure whether to call touchUngrabEvent()
+    or not; so we have to do it here.
+*/
 void QQuickWindowPrivate::removeGrabber(QQuickItem *grabber, bool mouse, bool touch)
 {
     Q_Q(QQuickWindow);
@@ -827,17 +827,19 @@ void QQuickWindowPrivate::removeGrabber(QQuickItem *grabber, bool mouse, bool to
         setMouseGrabber(nullptr);
     }
     if (Q_LIKELY(touch)) {
+        bool ungrab = false;
         const auto touchDevices = QQuickPointerDevice::touchDevices();
         for (auto device : touchDevices) {
             auto pointerEvent = device->pointerEvent();
             for (int i = 0; i < pointerEvent->pointCount(); ++i) {
                 if (pointerEvent->point(i)->exclusiveGrabber() == grabber) {
                     pointerEvent->point(i)->setGrabberItem(nullptr);
-                    // FIXME send ungrab event only once
-                    grabber->touchUngrabEvent();
+                    ungrab = true;
                 }
             }
         }
+        if (ungrab)
+            grabber->touchUngrabEvent();
     }
 }