Start over with event delivery when touchpoint releases occur

The new rule is that when the number of touchpoints changes, we start
over with event delivery as if the touch had just begun, to give more
opportunities to hand off processing from one item or handler to
another.  And MultiPointTouchArea can now handle the handoff:
for example in tests/manual/pointer/pinchDragFlingMPTA.qml when the
user is pressing three fingers, the PinchHandler is active; when the
user then lifts one finger, the MPTA can resume handling the two
remaining touchpoints as if they were just pressed.

The change in QQuickMultiPointerHandler::wantsPointerEvent is both
a behavior change and an optimization: released points aren't eligible;
but if some points are released, then pressed, updated and stationary
points are all eligible. And, figure this out without looping over the
points twice.

Change-Id: I26b7593de8e72b471adfec4a4482dd87a8288442
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 29 insertions, 7 deletions

diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index 0f613d300b..bde271882c 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -1055,6 +1055,18 @@ bool QQuickPointerMouseEvent::isPressEvent() const
             (me->buttons() & me->button()) == me->buttons());
 }
 
+bool QQuickPointerMouseEvent::isUpdateEvent() const
+{
+    auto me = static_cast<QMouseEvent*>(m_event);
+    return me->type() == QEvent::MouseMove;
+}
+
+bool QQuickPointerMouseEvent::isReleaseEvent() const
+{
+    auto me = static_cast<QMouseEvent*>(m_event);
+    return me->type() == QEvent::MouseButtonRelease;
+}
+
 bool QQuickPointerTouchEvent::allPointsAccepted() const {
     for (int i = 0; i < m_pointCount; ++i) {
         if (!m_touchPoints.at(i)->isAccepted())
@@ -1124,6 +1136,16 @@ bool QQuickPointerTouchEvent::isPressEvent() const
     return static_cast<QTouchEvent*>(m_event)->touchPointStates() & Qt::TouchPointPressed;
 }
 
+bool QQuickPointerTouchEvent::isUpdateEvent() const
+{
+    return static_cast<QTouchEvent*>(m_event)->touchPointStates() & (Qt::TouchPointMoved | Qt::TouchPointStationary);
+}
+
+bool QQuickPointerTouchEvent::isReleaseEvent() const
+{
+    return static_cast<QTouchEvent*>(m_event)->touchPointStates() & Qt::TouchPointReleased;
+}
+
 QVector<QPointF> QQuickPointerEvent::unacceptedPressedPointScenePositions() const
 {
     QVector<QPointF> points;
@@ -1239,7 +1261,7 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
     // Or else just document that velocity is always scene-relative and is not scaled and rotated with the item
     // but that would require changing tst_qquickwindow::touchEvent_velocity(): it expects transformed velocity
 
-    bool anyPressInside = false;
+    bool anyPressOrReleaseInside = false;
     bool anyGrabber = false;
     QMatrix4x4 transformMatrix(QQuickItemPrivate::get(item)->windowToItemTransform());
     for (int i = 0; i < m_pointCount; ++i) {
@@ -1250,8 +1272,9 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
         bool isGrabber = p->exclusiveGrabber() == item;
         if (isGrabber)
             anyGrabber = true;
-        // include points inside the bounds
+        // include points inside the bounds if no other item is the grabber or if the item is filtering
         bool isInside = item->contains(item->mapFromScene(p->scenePos()));
+        bool hasAnotherGrabber = p->exclusiveGrabber() && p->exclusiveGrabber() != item;
 
         // filtering: (childMouseEventFilter) include points that are grabbed by children of the target item
         bool grabberIsChild = false;
@@ -1265,11 +1288,10 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
         }
         bool filterRelevant = isFiltering && grabberIsChild;
 
-        if (!(isGrabber || isInside || filterRelevant))
+        if (!(isGrabber || (isInside && (!hasAnotherGrabber || isFiltering)) || filterRelevant))
             continue;
-        bool isPress = p->state() == QQuickEventPoint::Pressed;
-        if (isPress && isInside)
-            anyPressInside = true;
+        if ((p->state() == QQuickEventPoint::Pressed || p->state() == QQuickEventPoint::Released) && isInside)
+            anyPressOrReleaseInside = true;
         const QTouchEvent::TouchPoint *tp = touchPointById(p->pointId());
         if (tp) {
             eventStates |= tp->state();
@@ -1285,7 +1307,7 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
 
     // Now touchPoints will have only points which are inside the item.
     // But if none of them were just pressed inside, and the item has no other reason to care, ignore them anyway.
-    if (eventStates == Qt::TouchPointStationary || touchPoints.isEmpty() || (!anyPressInside && !anyGrabber && !isFiltering))
+    if (eventStates == Qt::TouchPointStationary || touchPoints.isEmpty() || (!anyPressOrReleaseInside && !anyGrabber && !isFiltering))
         return nullptr;
 
     // if all points have the same state, set the event type accordingly