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, 3 insertions, 1 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index 46e381db7d..9b91b4bda4 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -5095,12 +5095,14 @@ bool QQuickItemPrivate::handlePointerEvent(QQuickPointerEvent *event, bool avoid
 {
     Q_Q(QQuickItem);
     bool delivered = false;
+    QVector<QQuickPointerHandler *> &eventDeliveryTargets = event->device()->eventDeliveryTargets();
     if (extra.isAllocated()) {
         for (QQuickPointerHandler *handler : extra->pointerHandlers) {
             qCDebug(lcPointerHandlerDispatch) << "   delivering" << event << "to" << handler << "on" << q;
-            if (!avoidGrabber || !event->hasGrabber(handler)) {
+            if ((!avoidGrabber || !event->hasGrabber(handler)) && !eventDeliveryTargets.contains(handler)) {
                 handler->handlePointerEvent(event);
                 delivered = true;
+                eventDeliveryTargets.append(handler);
             }
         }
     }