QQuickWindow touch event compression: retain previous positions

The previous positions in the delayed touch event should be from
the first touchpoint which is being delayed, not updated based on
subsequent updates that are being merged into it.  Clarified
naming and comments in this section.

Task-number: QTBUG-40167
Change-Id: Ie419267e4a33277f9154bd80f5bce104e52d773e
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 35f4a84980..696f8f9080 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -1868,19 +1868,23 @@ void QQuickWindowPrivate::deliverTouchEvent(QTouchEvent *event)
                 Qt::TouchPointStates states;
                 for (int i = 0; i < event->touchPoints().count(); ++i) {
                     const QTouchEvent::TouchPoint &tp = tpts.at(i);
-                    const QTouchEvent::TouchPoint &tp2 = delayedTouch->touchPoints().at(i);
-                    if (tp.id() != tp2.id()) {
+                    const QTouchEvent::TouchPoint &tpDelayed = delayedTouch->touchPoints().at(i);
+                    if (tp.id() != tpDelayed.id()) {
                         mismatch = true;
                         break;
                     }
 
-                    if (tp2.state() == Qt::TouchPointMoved && tp.state() == Qt::TouchPointStationary)
+                    if (tpDelayed.state() == Qt::TouchPointMoved && tp.state() == Qt::TouchPointStationary)
                         tpts[i].setState(Qt::TouchPointMoved);
+                    tpts[i].setLastPos(tpDelayed.lastPos());
+                    tpts[i].setLastScenePos(tpDelayed.lastScenePos());
+                    tpts[i].setLastScreenPos(tpDelayed.lastScreenPos());
+                    tpts[i].setLastNormalizedPos(tpDelayed.lastNormalizedPos());
 
                     states |= tpts.at(i).state();
                 }
 
-                // same touch event? then merge if so
+                // matching touch event? then merge the new event into the old one
                 if (!mismatch) {
                     delayedTouch->setTouchPoints(tpts);
                     delayedTouch->setTimestamp(event->timestamp());
@@ -1888,8 +1892,7 @@ void QQuickWindowPrivate::deliverTouchEvent(QTouchEvent *event)
                 }
             }
 
-            // otherwise; we need to deliver the delayed event first, and
-            // then delay this one..
+            // merging wasn't possible, so deliver the delayed event first, and then delay this one
             reallyDeliverTouchEvent(delayedTouch);
             delete delayedTouch;
             delayedTouch = new QTouchEvent(event->type(), event->device(), event->modifiers(), event->touchPointStates(), event->touchPoints());