Flickable: use wheel event pixel deltas when available

Flickable can now handle wheel events which come from touchpads,
providing pixel deltas instead of angle deltas.  It will interpret
them as distance to flick, rather than using an average-velocity
physics model as it does when handling events from a physical mouse
wheel. This enables much finer control and limits the tendency
to "zing" way out of bounds accidentally.  It is achieved by
refactoring the direct-drag code which is needed for mouse dragging
and for touchpad gesture dragging (and eventually touchscreen dragging)
into a new internal drag() method.

[ChangeLog][QtQuick][Flickable] Flickable handles pixel deltas from
trackpad gestures as drags, for a more native feel

Task-number: QTBUG-22407
Change-Id: Ia613ddb25f46d452603f7cb567b74e80c95a346c
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/quick/items/qquickflickable_p_p.h b/src/quick/items/qquickflickable_p_p.h
index fa49c725f5..d7148ca57a 100644
--- a/src/quick/items/qquickflickable_p_p.h
+++ b/src/quick/items/qquickflickable_p_p.h
@@ -93,7 +93,7 @@ public:
         AxisData(QQuickFlickablePrivate *fp, void (QQuickFlickablePrivate::*func)(qreal))
             : move(fp, func)
             , transitionToBounds(0)
-            , viewSize(-1), lastPos(0), velocity(0), startMargin(0), endMargin(0)
+            , viewSize(-1), lastPos(0), previousDragDelta(0), velocity(0), startMargin(0), endMargin(0)
             , origin(0)
             , transitionTo(0)
             , continuousFlickVelocity(0), velocityTime(), vTime(0)
@@ -135,6 +135,7 @@ public:
         qreal dragStartOffset;
         qreal dragMinBound;
         qreal dragMaxBound;
+        qreal previousDragDelta;
         qreal velocity;
         qreal flickTarget;
         qreal startMargin;
@@ -151,6 +152,7 @@ public:
         bool transitionToSet : 1;
         bool fixingUp : 1;
         bool inOvershoot : 1;
+        bool inRebound : 1;
         bool moving : 1;
         bool flicking : 1;
         bool dragging : 1;
@@ -205,6 +207,7 @@ public:
     bool vMoved : 1;
     bool stealMouse : 1;
     bool pressed : 1;
+    bool scrollingPhase : 1;
     bool interactive : 1;
     bool calcVelocity : 1;
     bool pixelAligned : 1;
@@ -214,6 +217,7 @@ public:
     qint64 lastPressTime;
     QPointF lastPos;
     QPointF pressPos;
+    QVector2D accumulatedWheelPixelDelta;
     qreal deceleration;
     qreal maxVelocity;
     qreal reportedVelocitySmoothing;
@@ -244,7 +248,12 @@ public:
     void handleMouseMoveEvent(QMouseEvent *);
     void handleMouseReleaseEvent(QMouseEvent *);
 
+    void maybeBeginDrag(qint64 currentTimestamp, const QPointF &pressPosn);
+    void drag(qint64 currentTimestamp, QEvent::Type eventType, const QPointF &localPos,
+              const QVector2D &deltas, bool overThreshold, bool momentum, const QVector2D &velocity);
+
     qint64 computeCurrentTime(QInputEvent *event);
+    qreal devicePixelRatio();
 
     // flickableData property
     static void data_append(QQmlListProperty<QObject> *, QObject *);