QQuickWindow: use QVector eventDeliveryTargets to avoid repeated delivery

If no handler or item accepts a newly-pressed point, the event will be
re-delivered in deliverTouchEvent().  It doesn't make sense to
re-deliver to the same handlers though.

A temporary QSet isn't cheap to create, whereas it seems we will need
to keep track of handlers which have already been visited, in order to
avoid visiting passively-grabbing handlers multiple times.  Since both
a QVector and a QSet are heap-allocated, and we expect to have a limited
quantity of handlers grabbing at one time, a retained QVector (cleared
between events) seems to be the cheapest data structure.

Change-Id: I831e9a2576b2fcb9095e065795f2baff58115a49
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index a68e72b0b7..d7b5fe79de 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -731,6 +731,7 @@ QQuickPointerEvent *QQuickPointerMouseEvent::reset(QEvent *event)
         return this;
 
     m_device = QQuickPointerDevice::genericMouseDevice();
+    m_device->eventDeliveryTargets().clear();
     m_button = ev->button();
     m_pressedButtons = ev->buttons();
     Qt::TouchPointState state = Qt::TouchPointStationary;
@@ -765,6 +766,7 @@ QQuickPointerEvent *QQuickPointerTouchEvent::reset(QEvent *event)
         return this;
 
     m_device = QQuickPointerDevice::touchDevice(ev->device());
+    m_device->eventDeliveryTargets().clear();
     m_button = Qt::NoButton;
     m_pressedButtons = Qt::NoButton;