Flickable: avoid infinite velocity during release after drag

It sometimes happens on touchscreens that mouse events occur too close
together.  We cannot calculate velocity based on zero elapsed time,
so just ignore the event.

Task-number: QTBUG-45527
Change-Id: I120e73cfa60e2fcc594cb1f3b69f530e746abddd
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/quick/items/qquickflickable.cpp b/src/quick/items/qquickflickable.cpp
index b0980cd2c1..760eeed452 100644
--- a/src/quick/items/qquickflickable.cpp
+++ b/src/quick/items/qquickflickable.cpp
@@ -1224,13 +1224,17 @@ void QQuickFlickablePrivate::handleMouseMoveEvent(QMouseEvent *event)
         return;
 
     qint64 currentTimestamp = computeCurrentTime(event);
-    qreal elapsed = qreal(currentTimestamp - (lastPos.isNull() ? lastPressTime : lastPosTime)) / 1000.;
     QVector2D deltas = QVector2D(event->localPos() - pressPos);
     bool overThreshold = false;
     QVector2D velocity = QGuiApplicationPrivate::mouseEventVelocity(event);
     // TODO guarantee that events always have velocity so that it never needs to be computed here
-    if (!(QGuiApplicationPrivate::mouseEventCaps(event) & QTouchDevice::Velocity))
+    if (!(QGuiApplicationPrivate::mouseEventCaps(event) & QTouchDevice::Velocity)) {
+        qint64 lastTimestamp = (lastPos.isNull() ? lastPressTime : lastPosTime);
+        if (currentTimestamp == lastTimestamp)
+            return; // events are too close together: velocity would be infinite
+        qreal elapsed = qreal(currentTimestamp - lastTimestamp) / 1000.;
         velocity = QVector2D(event->localPos() - (lastPos.isNull() ? pressPos : lastPos)) / elapsed;
+    }
 
     if (q->yflick())
         overThreshold |= QQuickWindowPrivate::dragOverThreshold(deltas.y(), Qt::YAxis, event);