Flickable: add horizontal/verticalOvershoot properties

[ChangeLog][QtQuick][Flickable] Added horizontalOvershoot and
verticalOvershoot properties that can be used for implementing
boundary actions and effects.

Task-number: QTBUG-38515
Change-Id: I06379348a67d03507b56788d6fc7020bbb2d375f
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

4 files changed, 90 insertions, 3 deletions

diff --git a/src/quick/items/qquickflickable.cpp b/src/quick/items/qquickflickable.cpp
index 00a1306627..4ab604b30f 100644
--- a/src/quick/items/qquickflickable.cpp
+++ b/src/quick/items/qquickflickable.cpp
@@ -1570,12 +1570,52 @@ void QQuickFlickablePrivate::replayDelayedPress()
 //XXX pixelAligned ignores the global position of the Flickable, i.e. assumes Flickable itself is pixel aligned.
 void QQuickFlickablePrivate::setViewportX(qreal x)
 {
-    contentItem->setX(pixelAligned ? -Round(-x) : x);
+    Q_Q(QQuickFlickable);
+    if (pixelAligned)
+        x = -Round(-x);
+
+    contentItem->setX(x);
+    if (contentItem->x() != x)
+        return; // reentered
+
+    const qreal maxX = q->maxXExtent();
+    const qreal minX = q->minXExtent();
+
+    qreal overshoot = 0.0;
+    if (x <= maxX)
+        overshoot = maxX - x;
+    else if (x >= minX)
+        overshoot = minX - x;
+
+    if (overshoot != hData.overshoot) {
+        hData.overshoot = overshoot;
+        emit q->horizontalOvershootChanged();
+    }
 }
 
 void QQuickFlickablePrivate::setViewportY(qreal y)
 {
-    contentItem->setY(pixelAligned ? -Round(-y) : y);
+    Q_Q(QQuickFlickable);
+    if (pixelAligned)
+        y = -Round(-y);
+
+    contentItem->setY(y);
+    if (contentItem->y() != y)
+        return; // reentered
+
+    const qreal maxY = q->maxYExtent();
+    const qreal minY = q->minYExtent();
+
+    qreal overshoot = 0.0;
+    if (y <= maxY)
+        overshoot = maxY - y;
+    else if (y >= minY)
+        overshoot = minY - y;
+
+    if (overshoot != vData.overshoot) {
+        vData.overshoot = overshoot;
+        emit q->verticalOvershootChanged();
+    }
 }
 
 void QQuickFlickable::timerEvent(QTimerEvent *event)
@@ -1841,6 +1881,8 @@ QQmlListProperty<QQuickItem> QQuickFlickable::flickableChildren()
     beyond the boundary of the Flickable, and can overshoot the
     boundary when flicked.
     \endlist
+
+    \sa horizontalOvershoot, verticalOvershoot
 */
 QQuickFlickable::BoundsBehavior QQuickFlickable::boundsBehavior() const
 {
@@ -2638,4 +2680,38 @@ void QQuickFlickablePrivate::updateVelocity()
     emit q->verticalVelocityChanged();
 }
 
+/*!
+    \qmlproperty real QtQuick::Flickable::horizontalOvershoot
+    \since 5.9
+
+    This property holds the horizontal overshoot, that is, the horizontal distance by
+    which the contents has been dragged or flicked past the bounds of the flickable.
+    The value is negative when the content is dragged or flicked beyond the beginning,
+    and positive when beyond the end; \c 0.0 otherwise.
+
+    \sa verticalOvershoot, boundsBehavior
+*/
+qreal QQuickFlickable::horizontalOvershoot() const
+{
+    Q_D(const QQuickFlickable);
+    return d->hData.overshoot;
+}
+
+/*!
+    \qmlproperty real QtQuick::Flickable::verticalOvershoot
+    \since 5.9
+
+    This property holds the vertical overshoot, that is, the vertical distance by
+    which the contents has been dragged or flicked past the bounds of the flickable.
+    The value is negative when the content is dragged or flicked beyond the beginning,
+    and positive when beyond the end; \c 0.0 otherwise.
+
+    \sa horizontalOvershoot, boundsBehavior
+*/
+qreal QQuickFlickable::verticalOvershoot() const
+{
+    Q_D(const QQuickFlickable);
+    return d->vData.overshoot;
+}
+
 QT_END_NAMESPACE
diff --git a/src/quick/items/qquickflickable_p.h b/src/quick/items/qquickflickable_p.h
index 7384c7271a..78c8271525 100644
--- a/src/quick/items/qquickflickable_p.h
+++ b/src/quick/items/qquickflickable_p.h
@@ -106,6 +106,9 @@ class Q_QUICK_PRIVATE_EXPORT QQuickFlickable : public QQuickItem
 
     Q_PROPERTY(bool pixelAligned READ pixelAligned WRITE setPixelAligned NOTIFY pixelAlignedChanged)
 
+    Q_PROPERTY(qreal horizontalOvershoot READ horizontalOvershoot NOTIFY horizontalOvershootChanged REVISION 9)
+    Q_PROPERTY(qreal verticalOvershoot READ verticalOvershoot NOTIFY verticalOvershootChanged REVISION 9)
+
     Q_PROPERTY(QQmlListProperty<QObject> flickableData READ flickableData)
     Q_PROPERTY(QQmlListProperty<QQuickItem> flickableChildren READ flickableChildren)
     Q_CLASSINFO("DefaultProperty", "flickableData")
@@ -201,6 +204,9 @@ public:
     bool pixelAligned() const;
     void setPixelAligned(bool align);
 
+    qreal horizontalOvershoot() const;
+    qreal verticalOvershoot() const;
+
     Q_INVOKABLE void resizeContent(qreal w, qreal h, QPointF center);
     Q_INVOKABLE void returnToBounds();
     Q_INVOKABLE void flick(qreal xVelocity, qreal yVelocity);
@@ -243,6 +249,8 @@ Q_SIGNALS:
     void dragStarted();
     void dragEnded();
     void pixelAlignedChanged();
+    Q_REVISION(9) void horizontalOvershootChanged();
+    Q_REVISION(9) void verticalOvershootChanged();
 
 protected:
     bool childMouseEventFilter(QQuickItem *, QEvent *) Q_DECL_OVERRIDE;
@@ -286,6 +294,7 @@ protected:
 private:
     Q_DISABLE_COPY(QQuickFlickable)
     Q_DECLARE_PRIVATE(QQuickFlickable)
+    friend class QQuickFlickableContentItem;
     friend class QQuickFlickableVisibleArea;
     friend class QQuickFlickableReboundTransition;
 };
diff --git a/src/quick/items/qquickflickable_p_p.h b/src/quick/items/qquickflickable_p_p.h
index 0c3bc21071..1ceff22dfc 100644
--- a/src/quick/items/qquickflickable_p_p.h
+++ b/src/quick/items/qquickflickable_p_p.h
@@ -101,7 +101,7 @@ public:
             : move(fp, func)
             , transitionToBounds(0)
             , viewSize(-1), lastPos(0), previousDragDelta(0), velocity(0), startMargin(0), endMargin(0)
-            , origin(0)
+            , origin(0), overshoot(0)
             , transitionTo(0)
             , continuousFlickVelocity(0), velocityTime(), vTime(0)
             , smoothVelocity(fp), atEnd(false), atBeginning(true)
@@ -148,6 +148,7 @@ public:
         qreal startMargin;
         qreal endMargin;
         qreal origin;
+        qreal overshoot;
         qreal transitionTo;
         qreal continuousFlickVelocity;
         QElapsedTimer velocityTime;
diff --git a/src/quick/items/qquickitemsmodule.cpp b/src/quick/items/qquickitemsmodule.cpp
index b0ddbb0034..b8db5d76e4 100644
--- a/src/quick/items/qquickitemsmodule.cpp
+++ b/src/quick/items/qquickitemsmodule.cpp
@@ -374,6 +374,7 @@ static void qt_quickitems_defineModule(const char *uri, int major, int minor)
     qmlRegisterType<QQuickBorderImageMesh>("QtQuick", 2, 8, "BorderImageMesh");
 #endif
 
+    qmlRegisterType<QQuickFlickable, 9>(uri, 2, 9, "Flickable");
     qmlRegisterType<QQuickMouseArea, 9>(uri, 2, 9, "MouseArea");
 }