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, 11 insertions, 26 deletions

diff --git a/src/quick/handlers/qquickpinchhandler.cpp b/src/quick/handlers/qquickpinchhandler.cpp
index fc69accffc..7dafb16d3f 100644
--- a/src/quick/handlers/qquickpinchhandler.cpp
+++ b/src/quick/handlers/qquickpinchhandler.cpp
@@ -287,11 +287,11 @@ bool QQuickPinchHandler::wantsPointerEvent(QQuickPointerEvent *event)
 
 void QQuickPinchHandler::onActiveChanged()
 {
+    QQuickMultiPointHandler::onActiveChanged();
     if (active()) {
         m_startMatrix = QMatrix4x4();
-        m_startCentroid = touchPointCentroid();
-        m_startAngles = angles(m_startCentroid);
-        m_startDistance = averageTouchPointDistance(m_startCentroid);
+        m_startAngles = angles(m_centroid.sceneGrabPosition());
+        m_startDistance = averageTouchPointDistance(m_centroid.sceneGrabPosition());
         m_activeRotation = 0;
         m_activeTranslation = QVector2D();
         if (const QQuickItem *t = target()) {
@@ -319,6 +319,7 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
         for (QQuickEventPoint *point : qAsConst(m_currentPoints))
             qCDebug(lcPinchHandler) << point->state() << point->sceneGrabPosition() << "->" << point->scenePosition();
     }
+    QQuickMultiPointHandler::handlePointerEventImpl(event);
 
     qreal dist = 0;
 #if QT_CONFIG(gestures)
@@ -328,8 +329,7 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
             m_activeScale = 1;
             m_activeRotation = 0;
             m_activeTranslation = QVector2D();
-            m_centroid = QPointF();
-            m_centroidVelocity = QVector2D();
+            m_centroid.reset();
             setActive(false);
             emit updated();
             return;
@@ -344,12 +344,9 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
             return;
         }
         if (!active()) {
-            m_centroid = gesture->point(0)->scenePosition();
             setActive(true);
-            m_startCentroid = m_centroid;
             // Native gestures for 2-finger pinch do not allow dragging, so
             // the centroid won't move during the gesture, and translation stays at zero
-            m_centroidVelocity = QVector2D();
             m_activeTranslation = QVector2D();
         }
     } else
@@ -374,17 +371,15 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
                 return;
         }
         // TODO check m_pinchOrigin: right now it acts like it's set to PinchCenter
-        m_centroid = touchPointCentroid();
-        m_centroidVelocity = touchPointCentroidVelocity();
         // avoid mapping the minima and maxima, as they might have unmappable values
         // such as -inf/+inf. Because of this we perform the bounding to min/max in local coords.
         // 1. scale
-        dist = averageTouchPointDistance(m_centroid);
+        dist = averageTouchPointDistance(m_centroid.scenePosition());
         m_activeScale = dist / m_startDistance;
         m_activeScale = qBound(m_minimumScale/m_startScale, m_activeScale, m_maximumScale/m_startScale);
 
         // 2. rotate
-        QVector<PointData> newAngles = angles(m_centroid);
+        QVector<PointData> newAngles = angles(m_centroid.scenePosition());
         const qreal angleDelta = averageAngleDelta(m_startAngles, newAngles);
         m_activeRotation += angleDelta;
         m_startAngles = std::move(newAngles);
@@ -396,7 +391,7 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
     QPointF centroidParentPos;
     QRectF bounds(m_minimumX, m_minimumY, m_maximumX - m_minimumX, m_maximumY - m_minimumY);
     if (target() && target()->parentItem()) {
-        centroidParentPos = target()->parentItem()->mapFromScene(m_centroid);
+        centroidParentPos = target()->parentItem()->mapFromScene(m_centroid.scenePosition());
         centroidParentPos = QPointF(qBound(bounds.left(), centroidParentPos.x(), bounds.right()),
                                    qBound(bounds.top(), centroidParentPos.y(), bounds.bottom()));
     }
@@ -407,9 +402,8 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
 
     if (target() && target()->parentItem()) {
         // 3. Drag/translate
-        const QPointF centroidStartParentPos = target()->parentItem()->mapFromScene(m_startCentroid);
+        const QPointF centroidStartParentPos = target()->parentItem()->mapFromScene(m_centroid.sceneGrabPosition());
         m_activeTranslation = QVector2D(centroidParentPos - centroidStartParentPos);
-
         // apply rotation + scaling around the centroid - then apply translation.
         QMatrix4x4 mat;
 
@@ -432,10 +426,10 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
 
         // TODO some translation inadvertently happens; try to hold the chosen pinch origin in place
     } else {
-        m_activeTranslation = QVector2D(m_centroid - m_startCentroid);
+        m_activeTranslation = QVector2D(m_centroid.scenePosition() - m_centroid.scenePressPosition());
     }
 
-    qCDebug(lcPinchHandler) << "centroid" << m_startCentroid << "->"  << m_centroid
+    qCDebug(lcPinchHandler) << "centroid" << m_centroid.scenePressPosition() << "->"  << m_centroid.scenePosition()
                             << ", distance" << m_startDistance << "->" << dist
                             << ", startScale" << m_startScale << "->" << scale
                             << ", activeRotation" << m_activeRotation
@@ -456,15 +450,6 @@ void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
 
 /*!
     \readonly
-    \qmlproperty QVector2D QtQuick::PinchHandler::centroidVelocity
-
-    The average velocity of the \l centroid: a vector representing the speed
-    and direction of movement of the whole group of touchpoints, in logical
-    pixels per second.
-*/
-
-/*!
-    \readonly
     \qmlproperty real QtQuick::PinchHandler::scale
 
     The scale factor. It is 1.0 when the gesture begins, increases as the