QQuickSlider: add touchDragThreshold property

Add touchDragThreshold property for configuring the threshold to initiate a 'drag',
i.e. touch move, of the handle of the slider. The mouse 'drag' won't be affected
by the property.

This property may be also used to configure the drag events stealing priorities
of nested draggable items in the future.

[ChangeLog][Slider] Added touchDragThreshold property for configuring the threshold
to initiate the touch 'drag' of the handle of the slider. The mouse 'drag' won't be
affected by the property.

Task-number: QTBUG-62784
Change-Id: Ifaeea4653b48c44efbe7e1cb09d399a91359c16a
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 35 insertions, 2 deletions

diff --git a/src/quicktemplates2/qquickslider.cpp b/src/quicktemplates2/qquickslider.cpp
index ef2077af..9b922215 100644
--- a/src/quicktemplates2/qquickslider.cpp
+++ b/src/quicktemplates2/qquickslider.cpp
@@ -95,6 +95,7 @@ public:
           value(0),
           position(0),
           stepSize(0),
+          touchDragThreshold(-1), // in QQuickWindowPrivate::dragOverThreshold, '-1' implies using styleHints::startDragDistance()
           live(true),
           pressed(false),
           orientation(Qt::Horizontal),
@@ -121,6 +122,7 @@ public:
     qreal value;
     qreal position;
     qreal stepSize;
+    qreal touchDragThreshold;
     bool live;
     bool pressed;
     QPointF pressPoint;
@@ -636,6 +638,37 @@ void QQuickSlider::decrease()
     setValue(d->value - step);
 }
 
+/*!
+    \since QtQuick.Controls 2.5 (Qt 5.12)
+    \qmlproperty qreal QtQuick.Controls::Slider::touchDragThreshold
+
+    This property holds the threshold (in logical pixels) at which a touch drag event will be initiated.
+    The mouse drag threshold won't be affected.
+    The default value is \c Qt.styleHints.startDragDistance.
+
+    \sa QStyleHints
+*/
+qreal QQuickSlider::touchDragThreshold() const
+{
+    Q_D(const QQuickSlider);
+    return d->touchDragThreshold;
+}
+
+void QQuickSlider::setTouchDragThreshold(qreal touchDragThreshold)
+{
+    Q_D(QQuickSlider);
+    if (d->touchDragThreshold == touchDragThreshold)
+        return;
+
+    d->touchDragThreshold = touchDragThreshold;
+    emit touchDragThresholdChanged();
+}
+
+void QQuickSlider::resetTouchDragThreshold()
+{
+    setTouchDragThreshold(-1);
+}
+
 void QQuickSlider::keyPressEvent(QKeyEvent *event)
 {
     Q_D(QQuickSlider);
@@ -715,9 +748,9 @@ void QQuickSlider::touchEvent(QTouchEvent *event)
             case Qt::TouchPointMoved:
                 if (!keepTouchGrab()) {
                     if (d->orientation == Qt::Horizontal)
-                        setKeepTouchGrab(QQuickWindowPrivate::dragOverThreshold(point.pos().x() - d->pressPoint.x(), Qt::XAxis, &point));
+                        setKeepTouchGrab(QQuickWindowPrivate::dragOverThreshold(point.pos().x() - d->pressPoint.x(), Qt::XAxis, &point, qRound(d->touchDragThreshold)));
                     else
-                        setKeepTouchGrab(QQuickWindowPrivate::dragOverThreshold(point.pos().y() - d->pressPoint.y(), Qt::YAxis, &point));
+                        setKeepTouchGrab(QQuickWindowPrivate::dragOverThreshold(point.pos().y() - d->pressPoint.y(), Qt::YAxis, &point, qRound(d->touchDragThreshold)));
                 }
                 if (keepTouchGrab())
                     d->handleMove(point.pos());