Add dragThreshold property to Event Handlers

We need drag threshold to be adjustable on each handler instance instead
of relying only on the system default drag threshold. For example in
some use cases DragHandler needs to work with a threshold of 0 or 1 to
start dragging as soon as the point is pressed or as soon as the point
is moved, with no "jump", to enable fine adjustment of a value on some
control such as a Slider.

This involves moving the dragOverThreshold() functions that handlers are
using from QQuickWindowPrivate to QQuickPointerHandlerPrivate, so that
they can use the adjustable threshold value.

Task-number: QTBUG-68075
Change-Id: Ie720cbbf9f30abb40d1731d92f8e7f1e6534eeb5
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/quick/handlers/qquickpointerhandler_p_p.h b/src/quick/handlers/qquickpointerhandler_p_p.h
index 2ea4905643..5727b1ef55 100644
--- a/src/quick/handlers/qquickpointerhandler_p_p.h
+++ b/src/quick/handlers/qquickpointerhandler_p_p.h
@@ -68,9 +68,16 @@ public:
 
     QQuickPointerHandlerPrivate();
 
+    template<typename TEventPoint>
+    bool dragOverThreshold(qreal d, Qt::Axis axis, const TEventPoint *p) const;
+
+    bool dragOverThreshold(QVector2D delta) const;
+    bool dragOverThreshold(const QQuickEventPoint *point) const;
+
     QQuickPointerEvent *currentEvent = nullptr;
     QQuickItem *target = nullptr;
     qreal m_margin = 0;
+    qint16 dragThreshold = -1;   // -1 means use the platform default
     uint8_t grabPermissions : 8;
     bool enabled : 1;
     bool active : 1;