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Type: Bug
Resolution: Fixed
Priority: P2: Important
Fix Version/s: 6.5.4, 6.6.1, 6.7.0 FF
Affects Version/s: 6.2, 6.5, 6.6
Component/s: Quick: Core Declarative QML, Quick: Mouse Touch and Tablet input
Labels:
- reported_by_support_standard

Platform/s:

All
Commits:
5093e4c24 (dev), 3544aae72 (6.6), c6f88a807 (tqtc/lts-6.5)

Short description:

In situations where QWindowSystemInterface::handleTouchCancelEvent is triggered for various reasons (such as losing focus), the interaction of qquickflickable is not canceled.

Simple test case:

void tst_qquickflickable::touchCancel()
{
    QQuickView *window = new QQuickView;
    QScopedPointer<QQuickView> windowPtr(window);
    windowPtr->setSource(testFileUrl("flickable03.qml"));
    QTRY_COMPARE(window->status(), QQuickView::Ready);
    QQuickVisualTestUtils::centerOnScreen(window);
    QQuickVisualTestUtils::moveMouseAway(window);
    window->show();
    QVERIFY(QTest::qWaitForWindowActive(window));
    QVERIFY(window->rootObject() != nullptr);

    QQuickFlickable *flickable = qobject_cast<QQuickFlickable*>(window->rootObject());
    QVERIFY(flickable != nullptr);

    QSignalSpy movementStartedSpy(flickable, SIGNAL(movementStarted()));
    QSignalSpy movementEndedSpy(flickable, SIGNAL(movementEnded()));

    int dragDistance = qApp->styleHints()->startDragDistance();
    int newY = dragDistance;
    QTest::touchEvent(window, touchDevice).press(0, {10, newY}).commit();
    QQuickTouchUtils::flush(window);

    newY += dragDistance;
    QTest::touchEvent(window, touchDevice).move(0, {10, newY}).commit();
    QQuickTouchUtils::flush(window);

    newY += dragDistance;
    QTest::touchEvent(window, touchDevice).move(0, {10, newY}).commit();
    QQuickTouchUtils::flush(window);

    newY += dragDistance;
    QTest::touchEvent(window, touchDevice).move(0, {10, newY}).commit();
    QQuickTouchUtils::flush(window);

    QWindowSystemInterface::handleTouchCancelEvent(nullptr, touchDevice);
    QCoreApplication::processEvents();

    QTRY_COMPARE(movementStartedSpy.size(), 1);
    QTRY_COMPARE(movementEndedSpy.size(), 1);
}

In this test case, movementEnded signal is not occured.

Case 1. quicktemplates2_multitouch disabled

We should not call setAcceptTouchEvents(true) for flickable.

So below fix could be enough.

void QQuickFlickablePrivate::init()
{
................
#if QT_CONFIG(quicktemplates2_multitouch)
    q->setAcceptTouchEvents(true);
#endif
................
}

it's just a example because we cannot use quicktemplates2_multitouch define here.

: quicktemplates2_multitouch is a config for Quick Template 2, so it can't be applied to QQuickFlickable. It was just an example for illustration. In Quick Templates 2, if multi-touch is disabled, is there a need for setAcceptTouchEvents(true) in Flickable? It seems somewhat inconsistent. If setAcceptTouchEvents(false) is used, then "grabberItem->mouseUngrabEvent()" will be called in QQuickDeliveryAgentPrivate::onGrabChanged(), triggering qquickflickable's cancelInteraction().

Case 1. quicktemplates2_multitouch enabled

First, we have to override touchUngrabEvent() like

void QQuickFlickable::touchUngrabEvent()
{
    Q_D(QQuickFlickable);
    if (!d->replayingPressEvent) {
        d->cancelInteraction();
    }
}

but it's not enough because

when we call QWindowSystemInterface::handleTouchCancelEvent(nullptr, touchDevice);

void QPointingDevicePrivate::sendTouchCancelEvent(QTouchEvent *cancelEvent)
{
    ...
    for (auto &epd : activePoints.values()) {                 
        if (epd.exclusiveGrabber)
            QCoreApplication::sendEvent(epd.exclusiveGrabber, cancelEvent);
        // The next touch event can only be a TouchBegin, so clean up.         
        cancelEvent->setExclusiveGrabber(epd.eventPoint, nullptr);
        cancelEvent->clearPassiveGrabbers(epd.eventPoint);
    }
}

cancelEvent->setExclusiveGrabber() will be called with "nullptr" exclusiveGrabber

then,

void QPointingDevicePrivate::setExclusiveGrabber(const QPointerEvent *event, const QEventPoint &point, QObject *exclusiveGrabber)
{
....
    if (oldGrabber)
        emit q->grabChanged(oldGrabber, exclusiveGrabber ? QPointingDevice::CancelGrabExclusive : QPointingDevice::UngrabExclusive,
                            event, persistentPoint->eventPoint);
....
}

grabChanged signal will be emitted with QPointingDevice::UngrabExclusive (not CancelGrabExclusive)

This is the part that becomes problematic.

Because

void QQuickDeliveryAgentPrivate::onGrabChanged(QObject *grabber, QPointingDevice::GrabTransition transition,
                                               const QPointerEvent *event, const QEventPoint &point)
.........
        switch (transition) {
        case QPointingDevice::CancelGrabExclusive:
        case QPointingDevice::UngrabExclusive:
            if (isDeliveringTouchAsMouse()
                || point.device()->type() == QInputDevice::DeviceType::Mouse
                || point.device()->type() == QInputDevice::DeviceType::TouchPad) {
                QMutableSinglePointEvent e(QEvent::UngrabMouse, point.device(), point);
                hasFiltered.clear();
                if (!sendFilteredMouseEvent(&e, grabberItem, grabberItem->parentItem())) {
                    lastUngrabbed = grabberItem;
                    grabberItem->mouseUngrabEvent();
                }
            }
            if (point.device()->type() == QInputDevice::DeviceType::TouchScreen) {
                bool allReleasedOrCancelled = true;
                if (transition == QPointingDevice::UngrabExclusive && event) {
                    for (const auto &pt : event->points()) {
                        if (pt.state() != QEventPoint::State::Released) {
                            allReleasedOrCancelled = false;
                            break;
                        }
                    }
                }
                if (allReleasedOrCancelled)
                    grabberItem->touchUngrabEvent();
            }
            break;
......

When "point.device()>type() == QInputDevice::DeviceType::TouchScreen" and "transition == QPointingDevice::UngrabExclusive", "grabberItem>touchUngrabEvent()" will not be called if any of the event->points() is not in the State::Released.

So, further review is needed for QPointingDevicePrivate::sendTouchCancelEvent(), QPointingDevicePrivate::setExclusiveGrabber(), and QQuickDeliveryAgentPrivate::onGrabChanged().