Velocities reported by Flickable in onFlickStarted can be 0

Ensure the smoothed velocity is set at the start of the flick.  Ensure
that the smoothed velocity animation isn't restarted unless there is
new valid data.

Change-Id: I00f8bbf1fe91faeea752b093c4658ad0f53ad06d
Task-number: QTBUG-19676
Reviewed-by: Bea Lam
(cherry picked from commit a2d97672bfaace677a4308db93f5802ba53af46e)

2 files changed, 90 insertions, 9 deletions

diff --git a/src/declarative/graphicsitems/qdeclarativeflickable.cpp b/src/declarative/graphicsitems/qdeclarativeflickable.cpp
index 4a465cc408..b8577e9ff1 100644
--- a/src/declarative/graphicsitems/qdeclarativeflickable.cpp
+++ b/src/declarative/graphicsitems/qdeclarativeflickable.cpp
@@ -910,18 +910,24 @@ void QDeclarativeFlickablePrivate::handleMouseReleaseEvent(QGraphicsSceneMouseEv
     qreal velocity = vData.velocity;
     if (vData.atBeginning || vData.atEnd)
         velocity /= 2;
-    if (qAbs(velocity) > MinimumFlickVelocity && qAbs(event->pos().y() - pressPos.y()) > FlickThreshold)
+    if (q->yflick() && qAbs(velocity) > MinimumFlickVelocity && qAbs(event->pos().y() - pressPos.y()) > FlickThreshold) {
+        velocityTimeline.reset(vData.smoothVelocity);
+        vData.smoothVelocity.setValue(-velocity);
         flickY(velocity);
-    else
+    } else {
         fixupY();
+    }
 
     velocity = hData.velocity;
     if (hData.atBeginning || hData.atEnd)
         velocity /= 2;
-    if (qAbs(velocity) > MinimumFlickVelocity && qAbs(event->pos().x() - pressPos.x()) > FlickThreshold)
+    if (q->xflick() && qAbs(velocity) > MinimumFlickVelocity && qAbs(event->pos().x() - pressPos.x()) > FlickThreshold) {
+        velocityTimeline.reset(hData.smoothVelocity);
+        hData.smoothVelocity.setValue(-velocity);
         flickX(velocity);
-    else
+    } else {
         fixupX();
+    }
 
     if (!timeline.isActive())
         q->movementEnding();
@@ -1121,19 +1127,25 @@ void QDeclarativeFlickable::viewportMoved()
 
     qreal prevX = d->lastFlickablePosition.x();
     qreal prevY = d->lastFlickablePosition.y();
-    d->velocityTimeline.clear();
     if (d->pressed || d->calcVelocity) {
         int elapsed = QDeclarativeItemPrivate::restart(d->velocityTime);
         if (elapsed > 0) {
             qreal horizontalVelocity = (prevX - d->hData.move.value()) * 1000 / elapsed;
+            if (qAbs(horizontalVelocity) > 0) {
+                d->velocityTimeline.reset(d->hData.smoothVelocity);
+                d->velocityTimeline.move(d->hData.smoothVelocity, horizontalVelocity, d->reportedVelocitySmoothing);
+                d->velocityTimeline.move(d->hData.smoothVelocity, 0, d->reportedVelocitySmoothing);
+            }
             qreal verticalVelocity = (prevY - d->vData.move.value()) * 1000 / elapsed;
-            d->velocityTimeline.move(d->hData.smoothVelocity, horizontalVelocity, d->reportedVelocitySmoothing);
-            d->velocityTimeline.move(d->hData.smoothVelocity, 0, d->reportedVelocitySmoothing);
-            d->velocityTimeline.move(d->vData.smoothVelocity, verticalVelocity, d->reportedVelocitySmoothing);
-            d->velocityTimeline.move(d->vData.smoothVelocity, 0, d->reportedVelocitySmoothing);
+            if (qAbs(verticalVelocity) > 0) {
+                d->velocityTimeline.reset(d->vData.smoothVelocity);
+                d->velocityTimeline.move(d->vData.smoothVelocity, verticalVelocity, d->reportedVelocitySmoothing);
+                d->velocityTimeline.move(d->vData.smoothVelocity, 0, d->reportedVelocitySmoothing);
+            }
         }
     } else {
         if (d->timeline.time() > d->vTime) {
+            d->velocityTimeline.clear();
             qreal horizontalVelocity = (prevX - d->hData.move.value()) * 1000 / (d->timeline.time() - d->vTime);
             qreal verticalVelocity = (prevY - d->vData.move.value()) * 1000 / (d->timeline.time() - d->vTime);
             d->hData.smoothVelocity.setValue(horizontalVelocity);
diff --git a/tests/auto/declarative/qdeclarativeflickable/tst_qdeclarativeflickable.cpp b/tests/auto/declarative/qdeclarativeflickable/tst_qdeclarativeflickable.cpp
index b077fdc7ab..31a6b107ac 100644
--- a/tests/auto/declarative/qdeclarativeflickable/tst_qdeclarativeflickable.cpp
+++ b/tests/auto/declarative/qdeclarativeflickable/tst_qdeclarativeflickable.cpp
@@ -78,6 +78,7 @@ private slots:
     void testQtQuick11Attributes();
     void testQtQuick11Attributes_data();
     void wheel();
+    void flickVelocity();
 
 private:
     QDeclarativeEngine engine;
@@ -480,6 +481,74 @@ void tst_qdeclarativeflickable::wheel()
     delete canvas;
 }
 
+void tst_qdeclarativeflickable::flickVelocity()
+{
+    QDeclarativeView *canvas = new QDeclarativeView;
+    canvas->setSource(QUrl::fromLocalFile(SRCDIR "/data/flickable03.qml"));
+    canvas->show();
+    canvas->setFocus();
+    QVERIFY(canvas->rootObject() != 0);
+
+    QDeclarativeFlickable *flickable = qobject_cast<QDeclarativeFlickable*>(canvas->rootObject());
+    QVERIFY(flickable != 0);
+
+    QTest::mousePress(canvas->viewport(), Qt::LeftButton, 0, canvas->mapFromScene(QPoint(20, 90)));
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,80)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,70)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,60)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,50)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+
+    QTest::mouseRelease(canvas->viewport(), Qt::LeftButton, 0, canvas->mapFromScene(QPoint(20, 50)));
+
+    QVERIFY(flickable->verticalVelocity() > 0.0);
+    QTRY_VERIFY(flickable->verticalVelocity() == 0.0);
+
+    QTest::mousePress(canvas->viewport(), Qt::LeftButton, 0, canvas->mapFromScene(QPoint(20, 10)));
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,20)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,30)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,40)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+    {
+        QMouseEvent mv(QEvent::MouseMove, canvas->mapFromScene(QPoint(20,50)), Qt::LeftButton, Qt::LeftButton,Qt::NoModifier);
+        QApplication::sendEvent(canvas->viewport(), &mv);
+    }
+    QTest::qWait(10);
+
+    QTest::mouseRelease(canvas->viewport(), Qt::LeftButton, 0, canvas->mapFromScene(QPoint(20, 50)));
+
+    QVERIFY(flickable->verticalVelocity() < 0.0);
+    QTRY_VERIFY(flickable->verticalVelocity() == 0.0);
+
+    delete canvas;
+}
+
 
 template<typename T>
 T *tst_qdeclarativeflickable::findItem(QGraphicsObject *parent, const QString &objectName)