path: root/src/quick/handlers/qquickpointerhandler.cpp

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#include "qquickpointerhandler_p.h"

QT_BEGIN_NAMESPACE

Q_LOGGING_CATEGORY(lcPointerHandlerDispatch, "qt.quick.handler.dispatch")
Q_LOGGING_CATEGORY(lcPointerHandlerGrab, "qt.quick.handler.grab")
Q_LOGGING_CATEGORY(lcPointerHandlerActive, "qt.quick.handler.active")

/*!
    \qmltype PointerHandler
    \qmlabstract
    \since 5.10
    \preliminary
    \instantiates QQuickPointerHandler
    \inqmlmodule Qt.labs.handlers
    \ingroup qtquick-handlers
    \brief Abstract handler for pointer events.

    PointerHandler is the base class handler (not registered as a QML type) for
    pointer events without regard to source (touch, mouse or graphics tablet).
*/

QQuickPointerHandler::QQuickPointerHandler(QObject *parent)
  : QObject(parent)
  , m_currentEvent(nullptr)
  , m_target(nullptr)
  , m_enabled(true)
  , m_active(false)
  , m_targetExplicitlySet(false)
  , m_hadKeepMouseGrab(false)
  , m_hadKeepTouchGrab(false)
  , m_grabPermissions(CanTakeOverFromItems | CanTakeOverFromHandlersOfDifferentType | ApprovesTakeOverByAnything)
{
}

QQuickPointerHandler::~QQuickPointerHandler()
{
    QQuickItem *parItem = parentItem();
    if (parItem) {
        QQuickItemPrivate *p = QQuickItemPrivate::get(parItem);
        p->extra.value().pointerHandlers.removeOne(this);
    }
}

/*!
    Notification that the grab has changed in some way which is relevant to this handler.
    The \a grabber (subject) will be the PointerHandler whose state is changing,
    or null if the state change regards an Item.
    The \a stateChange (verb) tells what happened.
    The \a point (object) is the point that was grabbed or ungrabbed.
    EventPoint has the sole responsibility to call this function.
    The PointerHandler must react in whatever way is appropriate, and must
    emit the relevant signals (for the benefit of QML code).
    A subclass is allowed to override this virtual function, but must always
    call its parent class's implementation in addition to (usually after)
    whatever custom behavior it implements.
*/
void QQuickPointerHandler::onGrabChanged(QQuickPointerHandler *grabber, QQuickEventPoint::GrabState stateChange, QQuickEventPoint *point)
{
    qCDebug(lcPointerHandlerGrab) << point << stateChange << grabber;
    Q_ASSERT(point);
    if (grabber == this) {
        bool wasCanceled = false;
        switch (stateChange) {
        case QQuickEventPoint::GrabPassive:
        case QQuickEventPoint::GrabExclusive:
            break;
        case QQuickEventPoint::CancelGrabPassive:
        case QQuickEventPoint::CancelGrabExclusive:
            wasCanceled = true; // the grab was stolen by something else
            Q_FALLTHROUGH();
        case QQuickEventPoint::UngrabPassive:
        case QQuickEventPoint::UngrabExclusive:
            setActive(false);
            point->setAccepted(false);
            if (auto par = parentItem()) {
                par->setKeepMouseGrab(m_hadKeepMouseGrab);
                par->setKeepTouchGrab(m_hadKeepTouchGrab);
            }
            break;
        case QQuickEventPoint::OverrideGrabPassive:
            // Passive grab is still there, but we won't receive point updates right now.
            // No need to notify about this.
            return;
        }
        if (wasCanceled)
            emit canceled(point);
        else
            emit grabChanged(point);
    }
}

/*!
    \internal
    Acquire or give up a passive grab of the given \a point, according to the \a grab state.

    Unlike the exclusive grab, multiple PointerHandlers can have passive grabs
    simultaneously. This means that each of them will receive further events
    when the \a point moves, and when it is finally released. Typically a
    PointerHandler should acquire a passive grab as soon as a point is pressed,
    if the handler's constraints do not clearly rule out any interest in that
    point. For example, DragHandler needs a passive grab in order to watch the
    movement of a point to see whether it will be dragged past the drag
    threshold. When a handler is actively manipulating its \l target (that is,
    when \l active is true), it may be able to do its work with only a passive
    grab, or it may acquire an exclusive grab if the gesture clearly must not
    be interpreted in another way by another handler.
*/
void QQuickPointerHandler::setPassiveGrab(QQuickEventPoint *point, bool grab)
{
    qCDebug(lcPointerHandlerGrab) << point << grab;
    if (grab) {
        point->setGrabberPointerHandler(this, false);
    } else {
        point->removePassiveGrabber(this);
    }
}

/*!
    Check whether it's OK to take an exclusive grab of the \a point.

    The default implementation will call approveGrabTransition() to check this
    handler's \l grabPermissions. If grabbing can be done only by taking over
    the exclusive grab from an Item, approveGrabTransition() checks the Item's
    \l keepMouseGrab or \l keepTouchGrab flags appropriately. If grabbing can
    be done only by taking over another handler's exclusive grab, canGrab()
    also calls approveGrabTransition() on the handler which is about to lose
    its grab. Either one can deny the takeover.
*/
bool QQuickPointerHandler::canGrab(QQuickEventPoint *point)
{
    QQuickPointerHandler *existingPhGrabber = point->grabberPointerHandler();
    return approveGrabTransition(point, this) &&
        (existingPhGrabber ? existingPhGrabber->approveGrabTransition(point, this) : true);
}

/*!
    Check this handler's rules to see if \l proposedGrabber will be allowed to take
    the exclusive grab.  This function may be called twice: once on the instance which
    will take the grab, and once on the instance which would thereby lose its grab,
    in case of a takeover scenario.
*/
bool QQuickPointerHandler::approveGrabTransition(QQuickEventPoint *point, QObject *proposedGrabber)
{
    bool allowed = false;
    if (proposedGrabber == this) {
        QObject* existingGrabber = point->exclusiveGrabber();
        allowed = (existingGrabber == nullptr) || ((m_grabPermissions & CanTakeOverFromAnything) == CanTakeOverFromAnything);
        if (existingGrabber) {
            if (QQuickPointerHandler *existingPhGrabber = point->grabberPointerHandler()) {
                if (!allowed && (m_grabPermissions & CanTakeOverFromHandlersOfDifferentType) &&
                        existingPhGrabber->metaObject()->className() != metaObject()->className())
                    allowed = true;
                if (!allowed && (m_grabPermissions & CanTakeOverFromHandlersOfSameType) &&
                        existingPhGrabber->metaObject()->className() == metaObject()->className())
                    allowed = true;
            } else if ((m_grabPermissions & CanTakeOverFromItems)) {
                QQuickItem * existingItemGrabber = point->grabberItem();
                if (existingItemGrabber && !((existingItemGrabber->keepMouseGrab() && point->pointerEvent()->asPointerMouseEvent()) ||
                                             (existingItemGrabber->keepTouchGrab() && point->pointerEvent()->asPointerTouchEvent())))
                    allowed = true;
            }
        }
    } else {
        // proposedGrabber is different: that means this instance will lose its grab
        if (proposedGrabber) {
            if ((m_grabPermissions & ApprovesTakeOverByAnything) == ApprovesTakeOverByAnything)
                allowed = true;
            if (!allowed && (m_grabPermissions & ApprovesTakeOverByHandlersOfDifferentType) &&
                    proposedGrabber->metaObject()->className() != metaObject()->className())
                allowed = true;
            if (!allowed && (m_grabPermissions & ApprovesTakeOverByHandlersOfSameType) &&
                    proposedGrabber->metaObject()->className() == metaObject()->className())
                allowed = true;
            if (!allowed && (m_grabPermissions & ApprovesTakeOverByItems) && proposedGrabber->inherits("QQuickItem"))
                allowed = true;
        } else {
            if (!allowed && (m_grabPermissions & ApprovesCancellation))
                allowed = true;
        }
    }
    qCDebug(lcPointerHandlerGrab) << "point" << hex << point->pointId() << "permission" <<
            QMetaEnum::fromType<GrabPermissions>().valueToKeys(grabPermissions()) <<
            ':' << this << (allowed ? "approved to" : "denied to") << proposedGrabber;
    return allowed;
}

/*!
    \qmlproperty bool QtQuick::PointerHandler::grabPermission

    This property specifies the permissions when this handler's logic decides
    to take over the exclusive grab, or when it is asked to approve grab
    takeover or cancellation by another handler.

    The default is
    \c {CanTakeOverFromItems | CanTakeOverFromHandlersOfDifferentType | ApprovesTakeOverByAnything}
    which allows most takeover scenarios but avoids e.g. two PinchHandlers fighting
    over the same touchpoints.
*/
void QQuickPointerHandler::setGrabPermissions(GrabPermissions grabPermission)
{
    if (m_grabPermissions == grabPermission)
        return;

    m_grabPermissions = grabPermission;
    emit grabPermissionChanged();
}

/*!
    \internal
    Acquire or give up the exclusive grab of the given \a point, according to
    the \a grab state, and subject to the rules: canGrab(), and the rule not to
    relinquish another handler's grab. Returns true if permission is granted,
    or if the exclusive grab has already been acquired or relinquished as
    specified. Returns false if permission is denied either by this handler or
    by the handler or item from which this handler would take over
*/
bool QQuickPointerHandler::setExclusiveGrab(QQuickEventPoint *point, bool grab)
{
    if ((grab && point->exclusiveGrabber() == this) || (!grab && point->exclusiveGrabber() != this))
        return true;
    // TODO m_hadKeepMouseGrab m_hadKeepTouchGrab
    bool allowed = true;
    if (grab) {
        allowed = canGrab(point);
    } else {
        QQuickPointerHandler *existingPhGrabber = point->grabberPointerHandler();
        // Ask before allowing one handler to cancel another's grab
        if (existingPhGrabber && existingPhGrabber != this && !existingPhGrabber->approveGrabTransition(point, nullptr))
            allowed = false;
    }
    qCDebug(lcPointerHandlerGrab) << point << (grab ? "grab" : "ungrab") << (allowed ? "allowed" : "forbidden") <<
        point->exclusiveGrabber() << "->" << (grab ? this : nullptr);
    if (allowed)
        point->setGrabberPointerHandler(grab ? this : nullptr, true);
    return allowed;
}

/*!
    \internal
    Cancel any existing grab of the given \a point.
*/
void QQuickPointerHandler::cancelAllGrabs(QQuickEventPoint *point)
{
    qCDebug(lcPointerHandlerGrab) << point;
    point->cancelAllGrabs(this);
}

QPointF QQuickPointerHandler::eventPos(const QQuickEventPoint *point) const
{
    return (target() ? target()->mapFromScene(point->scenePosition()) : point->scenePosition());
}

bool QQuickPointerHandler::parentContains(const QQuickEventPoint *point) const
{
    if (point) {
        if (QQuickItem *par = parentItem())
            return par->contains(par->mapFromScene(point->scenePosition()));
    }
    return false;
}

/*!
     \qmlproperty bool QtQuick::PointerHandler::enabled

     If a PointerHandler is disabled, it will reject all events
     and no signals will be emitted.
*/
void QQuickPointerHandler::setEnabled(bool enabled)
{
    if (m_enabled == enabled)
        return;

    m_enabled = enabled;
    emit enabledChanged();
}

/*!
    \qmlproperty Item QtQuick::PointerHandler::target

    The Item which this handler will manipulate.

    By default, it is the same as the \l [QML] {parent}, the Item within which
    the handler is declared. However, it can sometimes be useful to set the
    target to a different Item, in order to handle events within one item
    but manipulate another; or to \c null, to disable the default behavior
    and do something else instead.
*/
void QQuickPointerHandler::setTarget(QQuickItem *target)
{
    m_targetExplicitlySet = true;
    if (m_target == target)
        return;

    QQuickItem *oldTarget = m_target;
    m_target = target;
    onTargetChanged(oldTarget);
    emit targetChanged();
}

QQuickItem *QQuickPointerHandler::target() const
{
    if (!m_targetExplicitlySet)
        return parentItem();
    return m_target;
}

void QQuickPointerHandler::handlePointerEvent(QQuickPointerEvent *event)
{
    bool wants = wantsPointerEvent(event);
    qCDebug(lcPointerHandlerDispatch) << metaObject()->className() << objectName()
                                      << "on" << parentItem()->metaObject()->className() << parentItem()->objectName()
                                      << (wants ? "WANTS" : "DECLINES") << event;
    if (wants) {
        handlePointerEventImpl(event);
    } else {
        setActive(false);
        int pCount = event->pointCount();
        for (int i = 0; i < pCount; ++i) {
            QQuickEventPoint *pt = event->point(i);
            if (pt->grabberPointerHandler() == this && pt->state() != QQuickEventPoint::Stationary)
                pt->cancelExclusiveGrab();
        }
    }
    event->device()->eventDeliveryTargets().append(this);
}

bool QQuickPointerHandler::wantsPointerEvent(QQuickPointerEvent *event)
{
    Q_UNUSED(event)
    return m_enabled;
}

/*!
    \readonly
    \qmlproperty bool QtQuick::PointerHandler::active

    This holds true whenever this PointerHandler has taken sole responsibility
    for handing one or more EventPoints, by successfully taking an exclusive
    grab of those points. This means that it is keeping its properties
    up-to-date according to the movements of those Event Points and actively
    manipulating its \l target (if any).
*/
void QQuickPointerHandler::setActive(bool active)
{
    if (m_active != active) {
        qCDebug(lcPointerHandlerActive) << this << m_active << "->" << active;
        m_active = active;
        onActiveChanged();
        emit activeChanged();
    }
}

void QQuickPointerHandler::handlePointerEventImpl(QQuickPointerEvent *event)
{
    m_currentEvent = event;
}

/*!
    \readonly
    \qmlproperty Item QtQuick::PointerHandler::parent

    The \l Item which is the scope of the handler; the Item in which it was declared.
    The handler will handle events on behalf of this Item, which means a
    pointer event is relevant if at least one of its event points occurs within
    the Item's interior.  Initially \l [QML] {target} {target()} is the same, but it
    can be reassigned.

    \sa {target}, QObject::parent()
*/

/*!
    \qmlsignal QtQuick::PointerHandler::grabChanged(EventPoint point)

    This signal is emitted when this handler has acquired or relinquished a
    passive or exclusive grab of the given \a point.
*/

/*!
    \qmlsignal QtQuick::PointerHandler::canceled(EventPoint point)

    If this handler has already grabbed the given \a point, this signal is
    emitted when the grab is stolen by a different Pointer Handler or Item.
*/

QT_END_NAMESPACE