MultiPointHandler: add a centroid property

One of the reasons we were so fond of using SinglePointHandler for the
"simple" handlers like TapHandler and DragHandler is that it has the
point property, which is easy to bind to in QML.  But multi-point
handlers tend to use the centroid as the focal point or fulcrum of
the transformation, so exposing the centroid as a QQuickHandlerPoint
gadget rather than just a QPointF has all the same advantages as the
point property in SinglePointHandler, including letting the
QQuickHandlerPoint instance store state between events (press
position, grab position, last known position etc.)

Change-Id: I4a955fa21b54b7ebb50b0ee2c942fb98eeccb560
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 14 insertions, 21 deletions

diff --git a/src/quick/handlers/qquickmultipointhandler.cpp b/src/quick/handlers/qquickmultipointhandler.cpp
index d595b4c9b4..89733a4260 100644
--- a/src/quick/handlers/qquickmultipointhandler.cpp
+++ b/src/quick/handlers/qquickmultipointhandler.cpp
@@ -91,6 +91,20 @@ bool QQuickMultiPointHandler::wantsPointerEvent(QQuickPointerEvent *event)
     return ret;
 }
 
+void QQuickMultiPointHandler::handlePointerEventImpl(QQuickPointerEvent *event)
+{
+    QQuickPointerHandler::handlePointerEventImpl(event);
+    m_centroid.reset(m_currentPoints);
+    emit centroidChanged();
+}
+
+void QQuickMultiPointHandler::onActiveChanged()
+{
+    if (active()) {
+        m_centroid.m_sceneGrabPosition = m_centroid.m_scenePosition;
+    }
+}
+
 QVector<QQuickEventPoint *> QQuickMultiPointHandler::eligiblePoints(QQuickPointerEvent *event)
 {
     QVector<QQuickEventPoint *> ret;
@@ -207,27 +221,6 @@ bool QQuickMultiPointHandler::sameAsCurrentPoints(QQuickPointerEvent *event)
     return ret;
 }
 
-// TODO make templates for these functions somehow?
-QPointF QQuickMultiPointHandler::touchPointCentroid()
-{
-    QPointF ret;
-    if (Q_UNLIKELY(m_currentPoints.size() == 0))
-        return ret;
-    for (QQuickEventPoint *point : qAsConst(m_currentPoints))
-        ret += point->scenePosition();
-    return ret / m_currentPoints.size();
-}
-
-QVector2D QQuickMultiPointHandler::touchPointCentroidVelocity()
-{
-    QVector2D ret;
-    if (Q_UNLIKELY(m_currentPoints.size() == 0))
-        return ret;
-    for (QQuickEventPoint *point : qAsConst(m_currentPoints))
-        ret += point->velocity();
-    return ret / m_currentPoints.size();
-}
-
 qreal QQuickMultiPointHandler::averageTouchPointDistance(const QPointF &ref)
 {
     qreal ret = 0;