Make QEventPoint an idiomatic value type

Use atomic ref counting and make type movable.

Make a moved-from QEventPoint valid but undefined. Given that the
d pointer is anyway loaded into the register, the additional check
doesn't cost much, and makes the class more compliant with our
guide for value types in Qt.

Add a free swap overload via Q_DECLARED_SHARED, which also declares
the type as movable.

As a drive-by, remove superfluous inline.
This also silences some static analyser warnings.

Change-Id: I7c4a436fce44556aa37026ac26dc2061e1f01de9
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 71 insertions, 72 deletions

diff --git a/src/gui/kernel/qeventpoint.cpp b/src/gui/kernel/qeventpoint.cpp
index 86382a9d15..41f8dd90a2 100644
--- a/src/gui/kernel/qeventpoint.cpp
+++ b/src/gui/kernel/qeventpoint.cpp
@@ -46,6 +46,8 @@ QT_BEGIN_NAMESPACE
 Q_LOGGING_CATEGORY(lcPointerVel, "qt.pointer.velocity")
 Q_LOGGING_CATEGORY(lcEPDetach, "qt.pointer.eventpoint.detach")
 
+QT_DEFINE_QESDP_SPECIALIZATION_DTOR(QEventPointPrivate)
+
 /*! \class QEventPoint
     \brief The QEventPoint class provides information about a point in a QPointerEvent.
     \since 6.0
@@ -94,26 +96,13 @@ QEventPoint::QEventPoint(int pointId, State state, const QPointF &scenePosition,
 /*!
     Constructs an event point by making a shallow copy of \a other.
 */
-QEventPoint::QEventPoint(const QEventPoint &other)
-    : d(other.d)
-{
-    if (d)
-        d->refCount++;
-}
+QEventPoint::QEventPoint(const QEventPoint &other) noexcept = default;
 
 /*!
     Assigns \a other to this event point and returns a reference to this
     event point.
 */
-QEventPoint &QEventPoint::operator=(const QEventPoint &other)
-{
-    if (other.d)
-        other.d->refCount++;
-    if (d && !(--d->refCount))
-        delete d;
-    d = other.d;
-    return *this;
-}
+QEventPoint &QEventPoint::operator=(const QEventPoint &other) noexcept = default;
 
 /*!
     \fn QEventPoint::QEventPoint(QEventPoint &&other) noexcept
@@ -150,11 +139,7 @@ bool QEventPoint::operator==(const QEventPoint &other) const noexcept
 /*!
     Destroys the event point.
 */
-QEventPoint::~QEventPoint()
-{
-    if (d && !(--d->refCount))
-        delete d;
-}
+QEventPoint::~QEventPoint() = default;
 
 /*! \fn QPointF QEventPoint::pos() const
     \obsolete
@@ -171,7 +156,7 @@ QEventPoint::~QEventPoint()
     The position is relative to the widget or item that received the event.
 */
 QPointF QEventPoint::position() const
-{ return d->pos; }
+{ return d ? d->pos : QPointF(); }
 
 /*!
     \property QEventPoint::pressPosition
@@ -182,7 +167,7 @@ QPointF QEventPoint::position() const
     \sa position
 */
 QPointF QEventPoint::pressPosition() const
-{ return d->globalPressPos - d->globalPos + d->pos; }
+{ return d ? d->globalPressPos - d->globalPos + d->pos : QPointF(); }
 
 /*!
     \property QEventPoint::grabPosition
@@ -193,7 +178,7 @@ QPointF QEventPoint::pressPosition() const
     \sa position
 */
 QPointF QEventPoint::grabPosition() const
-{ return d->globalGrabPos - d->globalPos + d->pos; }
+{ return d ? d->globalGrabPos - d->globalPos + d->pos : QPointF(); }
 
 /*!
     \property QEventPoint::lastPosition
@@ -204,7 +189,7 @@ QPointF QEventPoint::grabPosition() const
     \sa position, pressPosition
 */
 QPointF QEventPoint::lastPosition() const
-{ return d->globalLastPos - d->globalPos + d->pos; }
+{ return d ? d->globalLastPos - d->globalPos + d->pos : QPointF(); }
 
 /*!
     \property QEventPoint::scenePosition
@@ -217,7 +202,7 @@ QPointF QEventPoint::lastPosition() const
     \sa scenePressPosition, position, globalPosition
 */
 QPointF QEventPoint::scenePosition() const
-{ return d->scenePos; }
+{ return d ? d->scenePos : QPointF(); }
 
 /*!
     \property QEventPoint::scenePressPosition
@@ -230,7 +215,7 @@ QPointF QEventPoint::scenePosition() const
     \sa scenePosition, pressPosition, globalPressPosition
 */
 QPointF QEventPoint::scenePressPosition() const
-{ return d->globalPressPos - d->globalPos + d->scenePos; }
+{ return d ? d->globalPressPos - d->globalPos + d->scenePos : QPointF(); }
 
 /*!
     \property QEventPoint::sceneGrabPosition
@@ -243,7 +228,7 @@ QPointF QEventPoint::scenePressPosition() const
     \sa scenePosition, grabPosition, globalGrabPosition
 */
 QPointF QEventPoint::sceneGrabPosition() const
-{ return d->globalGrabPos - d->globalPos + d->scenePos; }
+{ return d ? d->globalGrabPos - d->globalPos + d->scenePos : QPointF(); }
 
 /*!
     \property QEventPoint::sceneLastPosition
@@ -256,7 +241,7 @@ QPointF QEventPoint::sceneGrabPosition() const
     \sa scenePosition, scenePressPosition
 */
 QPointF QEventPoint::sceneLastPosition() const
-{ return d->globalLastPos - d->globalPos + d->scenePos; }
+{ return d ? d->globalLastPos - d->globalPos + d->scenePos : QPointF(); }
 
 /*!
     \property QEventPoint::globalPosition
@@ -267,7 +252,7 @@ QPointF QEventPoint::sceneLastPosition() const
     \sa globalPressPosition, position, scenePosition
 */
 QPointF QEventPoint::globalPosition() const
-{ return d->globalPos; }
+{ return d ? d->globalPos : QPointF(); }
 
 /*!
     \property QEventPoint::globalPressPosition
@@ -278,7 +263,7 @@ QPointF QEventPoint::globalPosition() const
     \sa globalPosition, pressPosition, scenePressPosition
 */
 QPointF QEventPoint::globalPressPosition() const
-{ return d->globalPressPos; }
+{ return d ? d->globalPressPos : QPointF(); }
 
 /*!
     \property QEventPoint::globalGrabPosition
@@ -289,7 +274,7 @@ QPointF QEventPoint::globalPressPosition() const
     \sa globalPosition, grabPosition, sceneGrabPosition
 */
 QPointF QEventPoint::globalGrabPosition() const
-{ return d->globalGrabPos; }
+{ return d ? d->globalGrabPos : QPointF(); }
 
 /*!
     \property QEventPoint::globalLastPosition
@@ -300,7 +285,7 @@ QPointF QEventPoint::globalGrabPosition() const
     \sa globalPosition, lastPosition, sceneLastPosition
 */
 QPointF QEventPoint::globalLastPosition() const
-{ return d->globalLastPos; }
+{ return d ? d->globalLastPos : QPointF(); }
 
 /*!
     \property QEventPoint::velocity
@@ -319,21 +304,21 @@ QPointF QEventPoint::globalLastPosition() const
     \sa QInputDevice::capabilities(), QInputEvent::device()
 */
 QVector2D QEventPoint::velocity() const
-{ return d->velocity; }
+{ return d ? d->velocity : QVector2D(); }
 
 /*!
     \property QEventPoint::state
     \brief the current state of the event point.
 */
 QEventPoint::State QEventPoint::state() const
-{ return d->state; }
+{ return d ? d->state : QEventPoint::State::Unknown; }
 
 /*!
     \property QEventPoint::device
     \brief the pointing device from which this event point originates.
 */
 const QPointingDevice *QEventPoint::device() const
-{ return d->device; }
+{ return d ? d->device : nullptr; }
 
 /*!
     \property QEventPoint::id
@@ -344,7 +329,7 @@ const QPointingDevice *QEventPoint::device() const
           the underlying drivers work.
 */
 int QEventPoint::id() const
-{ return d->pointId; }
+{ return d ? d->pointId : -1; }
 
 /*!
     \property QEventPoint::uniqueId
@@ -360,7 +345,7 @@ int QEventPoint::id() const
     in use with a touchscreen that supports them.
 */
 QPointingDeviceUniqueId QEventPoint::uniqueId() const
-{ return d->uniqueId; }
+{ return d ? d->uniqueId : QPointingDeviceUniqueId(); }
 
 /*!
     \property QEventPoint::timestamp
@@ -369,7 +354,7 @@ QPointingDeviceUniqueId QEventPoint::uniqueId() const
     \sa QPointerEvent::timestamp()
 */
 ulong QEventPoint::timestamp() const
-{ return d->timestamp; }
+{ return d ? d->timestamp : 0; }
 
 /*!
     \property QEventPoint::lastTimestamp
@@ -378,7 +363,7 @@ ulong QEventPoint::timestamp() const
     \sa globalLastPosition
 */
 ulong QEventPoint::lastTimestamp() const
-{ return d->lastTimestamp; }
+{ return d ? d->lastTimestamp : 0; }
 
 /*!
     \property QEventPoint::pressTimestamp
@@ -387,7 +372,7 @@ ulong QEventPoint::lastTimestamp() const
     \sa timestamp
 */
 ulong QEventPoint::pressTimestamp() const
-{ return d->pressTimestamp; }
+{ return d ? d->pressTimestamp : 0; }
 
 /*!
     \property QEventPoint::timeHeld
@@ -396,7 +381,7 @@ ulong QEventPoint::pressTimestamp() const
     \sa pressTimestamp, timestamp
 */
 qreal QEventPoint::timeHeld() const
-{ return (d->timestamp - d->pressTimestamp) / qreal(1000); }
+{ return d ? (d->timestamp - d->pressTimestamp) / qreal(1000) : 0.0; }
 
 /*!
     \property QEventPoint::pressure
@@ -405,7 +390,7 @@ qreal QEventPoint::timeHeld() const
     The return value is in the range \c 0.0 to \c 1.0.
 */
 qreal QEventPoint::pressure() const
-{ return d->pressure; }
+{ return d ? d->pressure : 0.0; }
 
 /*!
     \property QEventPoint::rotation
@@ -417,7 +402,7 @@ qreal QEventPoint::pressure() const
     Most touchscreens do not detect rotation, so zero is the most common value.
 */
 qreal QEventPoint::rotation() const
-{ return d->rotation; }
+{ return d ? d->rotation : 0.0; }
 
 /*!
     \property QEventPoint::ellipseDiameters
@@ -429,7 +414,7 @@ qreal QEventPoint::rotation() const
     may be nonzero and always equal (the ellipse is approximated as a circle).
 */
 QSizeF QEventPoint::ellipseDiameters() const
-{ return d->ellipseDiameters; }
+{ return d ? d->ellipseDiameters : QSizeF(); }
 
 /*!
     \property QEventPoint::accepted
@@ -449,11 +434,12 @@ QSizeF QEventPoint::ellipseDiameters() const
 */
 void QEventPoint::setAccepted(bool accepted)
 {
-    d->accept = accepted;
+    if (d)
+        d->accept = accepted;
 }
 
 bool QEventPoint::isAccepted() const
-{ return d->accept; }
+{ return d ? d->accept : false; }
 
 
 /*!
@@ -474,6 +460,9 @@ bool QEventPoint::isAccepted() const
 */
 QPointF QEventPoint::normalizedPosition() const
 {
+    if (!d)
+        return {};
+
     auto geom = d->device->availableVirtualGeometry();
     if (geom.isNull())
         return QPointF();
@@ -488,6 +477,9 @@ QPointF QEventPoint::normalizedPosition() const
 */
 QPointF QEventPoint::startNormalizedPos() const
 {
+    if (!d)
+        return {};
+
     auto geom = d->device->availableVirtualGeometry();
     if (geom.isNull())
         return QPointF();
@@ -508,6 +500,9 @@ QPointF QEventPoint::startNormalizedPos() const
 */
 QPointF QEventPoint::lastNormalizedPos() const
 {
+    if (!d)
+        return {};
+
     auto geom = d->device->availableVirtualGeometry();
     if (geom.isNull())
         return QPointF();
@@ -523,19 +518,14 @@ QPointF QEventPoint::lastNormalizedPos() const
     event, or code that wants to save an eventpoint for later, has
     responsibility to detach before calling any setters, so as to hold and
     modify an independent copy. (The independent copy can then be used in a
-    subsequent event.) If detaching is unnecessary, because refCount shows that
-    there is only one QEventPoint referring to the QEventPointPrivate instance,
-    this function does nothing.
+    subsequent event.)
 */
 void QMutableEventPoint::detach()
 {
-    if (d->refCount == 1)
-        return; // no need: there is only one QEventPoint using it
-    qCDebug(lcEPDetach) << "detaching: refCount" << d->refCount << this;
-    auto old = d;
-    d = new QEventPointPrivate(*d);
-    d->refCount = 1;
-    --old->refCount;
+    if (d)
+        d.detach();
+    else
+        d.reset(new QEventPointPrivate(-1, nullptr));
 }
 
 /*! \internal
@@ -613,18 +603,20 @@ void QMutableEventPoint::setTimestamp(const ulong t)
     // then a press. Both events will get the same timestamp. So we need to set
     // the press timestamp and position even when the timestamp isn't advancing,
     // but skip setting lastTimestamp and velocity because those need a time delta.
-    if (state() == QEventPoint::State::Pressed) {
-        d->pressTimestamp = t;
-        d->globalPressPos = d->globalPos;
+    if (d) {
+        if (state() == QEventPoint::State::Pressed) {
+            d->pressTimestamp = t;
+            d->globalPressPos = d->globalPos;
+        }
+        if (d->timestamp == t)
+            return;
     }
-    if (d->timestamp == t)
-        return;
     detach();
     if (device()) {
         // get the persistent instance out of QPointingDevicePrivate::activePoints
         // (which sometimes might be the same as this instance)
         QEventPointPrivate *pd = QPointingDevicePrivate::get(
-                    const_cast<QPointingDevice *>(d->device))->pointById(id())->eventPoint.d;
+                    const_cast<QPointingDevice *>(d->device))->pointById(id())->eventPoint.d.get();
         if (t > pd->timestamp) {
             pd->lastTimestamp = pd->timestamp;
             pd->timestamp = t;
diff --git a/src/gui/kernel/qeventpoint.h b/src/gui/kernel/qeventpoint.h
index d4cce66b90..52b5c26039 100644
--- a/src/gui/kernel/qeventpoint.h
+++ b/src/gui/kernel/qeventpoint.h
@@ -43,10 +43,14 @@
 #include <QtGui/qtguiglobal.h>
 #include <QtGui/qvector2d.h>
 #include <QtGui/qpointingdevice.h>
+#include <QtCore/qshareddata.h>
+#include <QtCore/qmetatype.h>
 
 QT_BEGIN_NAMESPACE
 
-struct QEventPointPrivate;
+class QEventPointPrivate;
+QT_DECLARE_QESDP_SPECIALIZATION_DTOR_WITH_EXPORT(QEventPointPrivate, Q_GUI_EXPORT)
+
 class Q_GUI_EXPORT QEventPoint
 {
     Q_GADGET
@@ -87,14 +91,14 @@ public:
     Q_DECLARE_FLAGS(States, State)
     Q_FLAG(States)
 
-    QEventPoint(int id = -1, const QPointingDevice *device = nullptr);
+    explicit QEventPoint(int id = -1, const QPointingDevice *device = nullptr);
     QEventPoint(int pointId, State state, const QPointF &scenePosition, const QPointF &globalPosition);
-    QEventPoint(const QEventPoint &other);
-    QEventPoint(QEventPoint && other) noexcept : d(std::move(other.d)) { other.d = nullptr; }
-    QEventPoint &operator=(const QEventPoint &other);
-    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QEventPoint)
+    QEventPoint(const QEventPoint &other) noexcept;
+    QEventPoint &operator=(const QEventPoint &other) noexcept;
+    QEventPoint(QEventPoint && other) noexcept = default;
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QEventPoint)
     bool operator==(const QEventPoint &other) const noexcept;
-    inline bool operator!=(const QEventPoint &other) const noexcept { return !operator==(other); }
+    bool operator!=(const QEventPoint &other) const noexcept { return !operator==(other); }
     ~QEventPoint();
     inline void swap(QEventPoint &other) noexcept
     { qSwap(d, other.d); }
@@ -157,7 +161,7 @@ public:
     void setAccepted(bool accepted = true);
 
 private:
-    QEventPointPrivate *d;
+    QExplicitlySharedDataPointer<QEventPointPrivate> d;
     friend class QMutableEventPoint;
     friend class QPointerEvent;
 };
@@ -167,6 +171,8 @@ Q_GUI_EXPORT QDebug operator<<(QDebug, const QEventPoint *);
 Q_GUI_EXPORT QDebug operator<<(QDebug, const QEventPoint &);
 #endif
 
+Q_DECLARE_SHARED(QEventPoint)
+
 QT_END_NAMESPACE
 
 #endif // QEVENTPOINT_H
diff --git a/src/gui/kernel/qeventpoint_p.h b/src/gui/kernel/qeventpoint_p.h
index 147d134bda..f10739343f 100644
--- a/src/gui/kernel/qeventpoint_p.h
+++ b/src/gui/kernel/qeventpoint_p.h
@@ -62,7 +62,9 @@ Q_DECLARE_LOGGING_CATEGORY(lcEPDetach);
 
 class QPointingDevice;
 
-struct QEventPointPrivate {
+class QEventPointPrivate : public QSharedData
+{
+public:
     QEventPointPrivate(int id, const QPointingDevice *device)
       : device(device), pointId(id) { }
 
@@ -108,7 +110,6 @@ struct QEventPointPrivate {
     ulong lastTimestamp = 0;
     ulong pressTimestamp = 0;
     QPointingDeviceUniqueId uniqueId;
-    int refCount = 1;
     int pointId = -1;
     QEventPoint::State state = QEventPoint::State::Unknown;
     bool accept = false;