Allow parent to filter out-of-bounds synth-mouse for grabbing handler

Consider

Flickable {
	Text {
		TapHandler { gesturePolicy: TapHandler.ReleaseWithinBounds }
	}
}

On press, TapHandler gets the exclusive grab.  Now drag vertically.
The Text is short in stature, so your finger soon strays out of bounds
of the Text, likely before you have dragged past the drag threshold.
In this case, we want Flickable to continue to filter the move events
because of the fact that TapHandler is the grabber.  If it was a
MouseArea instead of a TapHandler, it already worked that way; so this
makes behavior of handlers more consistent with that.

More specifically: QQuickPointerTouchEvent::touchEventForItem() now
generates a touch event even if the touchpoint is not within the bounds
of the given item, but is grabbed by one of that item's handlers.  Until
now, we had that exception only if it was grabbed by the item itself.

tst_FlickableInterop::touchAndDragHandlerOnFlickable now always drags
the delegate at index 2 (the third one) from its upper-right corner,
upwards and to the left.  The first drag goes outside the delegate's
bounds, but the Flickable/ListView/TableView filters and takes over
anyway (on the next drag), to prove that it is correctly depending
on the grab that the TapHandler (or DragHandler) took on press.

Pick-to: 5.15
Pick-to: 6.0
Fixes: QTBUG-75223
Change-Id: Ie4e22c87be0af9aa3ff0146067b7705949b15c40
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index a8cb45a891..ccd1168278 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -8377,9 +8377,9 @@ QQuickItemLayer *QQuickItemPrivate::layer() const
     coordinate system.
 
     Returns an invalid event with type \l QEvent::None if all points are
-    stationary, or there are no points inside the item, or none of the points
-    were pressed inside and the item was not grabbing any of them and
-    \a isFiltering is false.
+    stationary; or there are no points inside the item; or none of the points
+    were pressed inside, neither the item nor any of its handlers is grabbing
+    any of them, and \a isFiltering is false.
 
     When \a isFiltering is true, it is assumed that the item cares about all
     points which are inside its bounds, because most filtering items need to
@@ -8397,11 +8397,18 @@ void QQuickItemPrivate::localizedTouchEvent(const QTouchEvent *event, bool isFil
     for (auto &p : event->points()) {
         if (p.isAccepted())
             continue;
-        // include points where item is the grabber
+
+        // include points where item is the grabber, or if any of its handlers is the grabber while some parent is filtering
         auto pointGrabber = event->exclusiveGrabber(p);
         bool isGrabber = (pointGrabber == q);
+        if (!isGrabber && pointGrabber && isFiltering) {
+            auto handlerGrabber = qmlobject_cast<QQuickPointerHandler *>(pointGrabber);
+            if (handlerGrabber && handlerGrabber->parentItem() == q)
+                isGrabber = true;
+        }
         if (isGrabber)
             anyGrabber = true;
+
         // include points inside the bounds if no other item is the grabber or if the item is filtering
         const auto localPos = q->mapFromScene(p.scenePosition());
         bool isInside = q->contains(localPos);