Add and use QQuickPointerSingleHandler::moveTarget()

Until now, DragHandler::pos() was not staying constant during a drag,
because we update m_pos from the EventPoint, then move the Item.
scenePos() also returns mapToScene(m_pos).  If the Item is being dragged
to follow the finger or the mouse cursor exactly, unconstrained, then
pos() should always be the same as the parent-relative position where
the press occurred.

Change-Id: Ia02738c0cf458e039cf90371f9c8a7becb75a035
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

3 files changed, 9 insertions, 1 deletions

diff --git a/src/quick/handlers/qquickdraghandler.cpp b/src/quick/handlers/qquickdraghandler.cpp
index b4006ab5c7..27edffd65a 100644
--- a/src/quick/handlers/qquickdraghandler.cpp
+++ b/src/quick/handlers/qquickdraghandler.cpp
@@ -107,7 +107,7 @@ void QQuickDragHandler::handleEventPoint(QQuickEventPoint *point)
             if (target() && target()->parentItem()) {
                 QPointF pos = target()->parentItem()->mapFromScene(m_targetStartPos + delta);
                 enforceAxisConstraints(&pos);
-                target()->setPosition(pos);
+                moveTarget(pos, point);
             }
         } else if (!point->exclusiveGrabber() &&
                    ((m_xAxis.enabled() && QQuickWindowPrivate::dragOverThreshold(delta.x(), Qt::XAxis, point)) ||
diff --git a/src/quick/handlers/qquickpointersinglehandler.cpp b/src/quick/handlers/qquickpointersinglehandler.cpp
index 4e89d71eab..80632303f1 100644
--- a/src/quick/handlers/qquickpointersinglehandler.cpp
+++ b/src/quick/handlers/qquickpointersinglehandler.cpp
@@ -199,6 +199,12 @@ void QQuickPointerSingleHandler::setIgnoreAdditionalPoints(bool v)
     m_ignoreAdditionalPoints = v;
 }
 
+void QQuickPointerSingleHandler::moveTarget(QPointF pos, QQuickEventPoint *point)
+{
+    target()->setPosition(pos);
+    m_pos = target()->mapFromScene(point->scenePos());
+}
+
 void QQuickPointerSingleHandler::setPressedButtons(Qt::MouseButtons buttons)
 {
     if (buttons != m_pressedButtons) {
diff --git a/src/quick/handlers/qquickpointersinglehandler_p.h b/src/quick/handlers/qquickpointersinglehandler_p.h
index 70aa26801f..06b8ec45dc 100644
--- a/src/quick/handlers/qquickpointersinglehandler_p.h
+++ b/src/quick/handlers/qquickpointersinglehandler_p.h
@@ -108,6 +108,8 @@ protected:
 
     void setIgnoreAdditionalPoints(bool v = true);
 
+    void moveTarget(QPointF pos, QQuickEventPoint *point);
+
 private:
     void setPressedButtons(Qt::MouseButtons buttons);
     void reset();