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Detach event points when cloning pointer events

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Input events that originate from actual device interaction should reflect the
device's state, and device and events need to be kept in sync so that event
sequences (such as multi-touch events, where we have begin/update/end cycles
spanning multiple events) are working correctly.

For that reason, the event point data in pointer events is explicitly shared,
and we only detach in exceptional situations. This saves us memory allocations,
and makes sure that the event point data carried by events, and the event point
data stored persistently in the device, are kept in sync.

Cloned pointer events do not originate from device interactions, and should
therefore not sync back to the device. E.g. accepting a clone should not modify
the original event data stored in the device. There are exceptions here as
well, e.g. when cloning an event in Qt in order to deliver a translated version
of it to a different scene. Different points might even get delivered to
different scenes or windows, or at least different items in the same scene. For
that reason, we explicitly detach, and then explicitly write back the relevant
states after the cloned event has been delivered.

But in general, we should assume that cloned events do not write back to the
device. Since QEventPoint is an explicitly shared data type that never detaches
itself, we have to explicitly detach it when making copies that should not be
shared.

The ideal implementation of this would be to do the detach in the copy
constructor of QPointerEvent, which is called when cloning. However, Qt itself
makes copies of QPointerEvent without using clone, e.g. when assembling lists
of touch events for the different subscenes or windows in
QGuiApplicationPrivate::processTouchEvent, where event objects are added to a
QVarLengthArray<QMutableTouchEvent>. This makes copies, and those copies must
not detach.

So we have to implement the special cloning behavior in each override of
QPointerEvent::clone(). For this, introduce a dedicated macro for the common
member functions. This macro must be used for QPointerEvent subclasses.

Fixes: QTBUG-107560
Change-Id: I4b56f9e71c7d067ba9054a2a631e8ba5bc7b1ab9
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
This commit is contained in:
Volker Hilsheimer 2022-10-14 10:15:01 +02:00
parent 585f2a31c6
commit 12b7eab4d2
2 changed files with 45 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
src/gui/kernel/qevent.cpp
View File

@ -28,6 +28,22 @@
#include <private/qdebug_p.h>
#define Q_IMPL_POINTER_EVENT(Class) \
Class::Class(const Class &) = default; \
Class::~Class() = default; \
Class* Class::clone() const \
{ \
auto c = new Class(*this); \
for (auto &point : c->m_points) \
QMutableEventPoint::detach(point); \
QEvent *e = c; \
/* check that covariant return is safe to add */ \
Q_ASSERT(reinterpret_cast<quintptr>(c) == reinterpret_cast<quintptr>(e)); \
return c; \
}
QT_BEGIN_NAMESPACE
static_assert(sizeof(QMutableTouchEvent) == sizeof(QTouchEvent));
@ -59,7 +75,7 @@ QEnterEvent::QEnterEvent(const QPointF &localPos, const QPointF &scenePos, const
{
}
Q_IMPL_EVENT_COMMON(QEnterEvent)
Q_IMPL_POINTER_EVENT(QEnterEvent)
/*!
\fn QPoint QEnterEvent::globalPos() const
@ -252,7 +268,7 @@ QPointerEvent::QPointerEvent(QEvent::Type type, QEvent::SinglePointEventTag, con
{
}
Q_IMPL_EVENT_COMMON(QPointerEvent)
Q_IMPL_POINTER_EVENT(QPointerEvent);
/*!
Returns the point whose \l {QEventPoint::id()}{id} matches the given \a id,
@ -555,7 +571,7 @@ QSinglePointEvent::QSinglePointEvent(QEvent::Type type, const QPointingDevice *d
m_points << point;
}
Q_IMPL_EVENT_COMMON(QSinglePointEvent)
Q_IMPL_POINTER_EVENT(QSinglePointEvent)
/*!
Returns \c true if this event represents a \l {button()}{button} being pressed.
@ -744,7 +760,7 @@ QMouseEvent::QMouseEvent(QEvent::Type type, const QPointF &localPos, const QPoin
{
}
Q_IMPL_EVENT_COMMON(QMouseEvent)
Q_IMPL_POINTER_EVENT(QMouseEvent)
/*!
\fn Qt::MouseEventSource QMouseEvent::source() const
@ -1062,7 +1078,7 @@ QHoverEvent::QHoverEvent(Type type, const QPointF &pos, const QPointF &oldPos,
}
#endif
Q_IMPL_EVENT_COMMON(QHoverEvent)
Q_IMPL_POINTER_EVENT(QHoverEvent)
#if QT_CONFIG(wheelevent)
/*!
@ -1187,7 +1203,7 @@ QWheelEvent::QWheelEvent(const QPointF &pos, const QPointF &globalPos, QPoint pi
m_invertedScrolling = inverted;
}
Q_IMPL_EVENT_COMMON(QWheelEvent)
Q_IMPL_POINTER_EVENT(QWheelEvent)
/*!
Returns \c true if this event's phase() is Qt::ScrollBegin.
@ -2494,7 +2510,7 @@ QTabletEvent::QTabletEvent(Type type, const QPointingDevice *dev, const QPointF
QMutableEventPoint::setRotation(p, rotation);
}
Q_IMPL_EVENT_COMMON(QTabletEvent)
Q_IMPL_POINTER_EVENT(QTabletEvent)
/*!
\fn qreal QTabletEvent::tangentialPressure() const
@ -2818,7 +2834,7 @@ QNativeGestureEvent::QNativeGestureEvent(Qt::NativeGestureType type, const QPoin
Q_ASSERT(fingerCount < 16); // we store it in 4 bits unsigned
}
Q_IMPL_EVENT_COMMON(QNativeGestureEvent)
Q_IMPL_POINTER_EVENT(QNativeGestureEvent)
/*!
\fn QNativeGestureEvent::gestureType() const
@ -4481,7 +4497,7 @@ QTouchEvent::QTouchEvent(QEvent::Type eventType,
}
#endif // QT_DEPRECATED_SINCE(6, 0)
Q_IMPL_EVENT_COMMON(QTouchEvent)
Q_IMPL_POINTER_EVENT(QTouchEvent)
/*!
Returns true if this event includes at least one newly-pressed touchpoint.

20
tests/auto/gui/kernel/qmouseevent/tst_qmouseevent.cpp
View File

@ -97,6 +97,7 @@ private slots:
void grabbers_data();
void grabbers();
void velocity();
void clone();
private:
MouseEventWidget* testMouseWidget;
@ -309,5 +310,24 @@ void tst_QMouseEvent::velocity()
QVERIFY(testMouseWidget->velocity.y() > 0);
}
void tst_QMouseEvent::clone()
{
const QPointF pos(10.0f, 10.0f);
QMouseEvent originalMe(QEvent::MouseButtonPress, pos, pos, pos, Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);
QVERIFY(!originalMe.allPointsAccepted());
QVERIFY(!originalMe.points().first().isAccepted());
// create a clone of the original
std::unique_ptr<QMouseEvent> clonedMe(originalMe.clone());
QVERIFY(!clonedMe->allPointsAccepted());
QVERIFY(!clonedMe->points().first().isAccepted());
// now we alter originalMe, which should *not* change clonedMe
originalMe.setAccepted(true);
QVERIFY(!clonedMe->allPointsAccepted());
QVERIFY(!clonedMe->points().first().isAccepted());
}
QTEST_MAIN(tst_QMouseEvent)
#include "tst_qmouseevent.moc"