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, 0 deletions

diff --git a/src/quick/items/qquickevents_p_p.h b/src/quick/items/qquickevents_p_p.h
index bbfc34dacf..1751e366b2 100644
--- a/src/quick/items/qquickevents_p_p.h
+++ b/src/quick/items/qquickevents_p_p.h
@@ -553,6 +553,8 @@ public:
     static QQuickPointerDevice *genericMouseDevice();
     static QQuickPointerDevice *tabletDevice(qint64);
 
+    QVector<QQuickPointerHandler *> &eventDeliveryTargets() { return m_eventDeliveryTargets; }
+
 private:
     QQuickPointerDevice(DeviceType devType, PointerType pType, Capabilities caps, int maxPoints, int buttonCount, const QString &name, qint64 uniqueId = 0)
       : m_deviceType(devType), m_pointerType(pType), m_capabilities(caps)
@@ -579,6 +581,7 @@ private:
     QPointingDeviceUniqueId m_uniqueId;
     // the device-specific event instance which is reused during event delivery
     QQuickPointerEvent *m_event;
+    QVector<QQuickPointerHandler *> m_eventDeliveryTargets; // during delivery, handlers which have already seen the event
 
     Q_DISABLE_COPY(QQuickPointerDevice)
     friend struct ConstructableQQuickPointerDevice;