Expose drag threshold in MouseArea

In several cases such as for creating a Slider, it is useful to  have a
0 pixel threshold in order to initiate a drag operation. We have
previously hardcoded this to a platform dependent (usually 10 pixel)
value for MouseArea.

Note that we have no way of indicating the version/revision number
in a grouped property for documentation at the moment.

In addition we deliberately had to remove the REVISION from the
property because it is blocked by QTBUG-33179. However, since
this is not a user-creatable type it should not cause any
issues in practice.

This patch adds MouseArea.drag.threshold in order to improve on this.

Change-Id: Ia4871e64fab39e30c4494f00be99ad38cdd630df
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/quick/items/qquickmousearea.cpp b/src/quick/items/qquickmousearea.cpp
index 8a73a5d73d..39f07f2afd 100644
--- a/src/quick/items/qquickmousearea.cpp
+++ b/src/quick/items/qquickmousearea.cpp
@@ -48,10 +48,7 @@
 #include <private/qqmldata_p.h>
 
 #include <QtGui/private/qguiapplication_p.h>
-
 #include <QtGui/qevent.h>
-#include <QtGui/qguiapplication.h>
-#include <QtGui/qstylehints.h>
 
 #include <float.h>
 
@@ -695,8 +692,8 @@ void QQuickMouseArea::mouseMoveEvent(QMouseEvent *event)
             d->drag->target()->setPosition(dragPos);
 
         if (!keepMouseGrab()
-                && (QQuickWindowPrivate::dragOverThreshold(dragPos.x() - startPos.x(), Qt::XAxis, event)
-                || QQuickWindowPrivate::dragOverThreshold(dragPos.y() - startPos.y(), Qt::YAxis, event))) {
+                && (QQuickWindowPrivate::dragOverThreshold(dragPos.x() - startPos.x(), Qt::XAxis, event, d->drag->threshold())
+                || QQuickWindowPrivate::dragOverThreshold(dragPos.y() - startPos.y(), Qt::YAxis, event, d->drag->threshold()))) {
             setKeepMouseGrab(true);
             d->stealMouse = true;
             d->startScene = event->windowPos();
@@ -1189,6 +1186,7 @@ void QQuickMouseArea::setCursorShape(Qt::CursorShape shape)
     \qmlproperty real QtQuick2::MouseArea::drag.minimumY
     \qmlproperty real QtQuick2::MouseArea::drag.maximumY
     \qmlproperty bool QtQuick2::MouseArea::drag.filterChildren
+    \qmlproperty real QtQuick2::MouseArea::drag.threshold
 
     \c drag provides a convenient way to make an item draggable.
 
@@ -1213,6 +1211,10 @@ void QQuickMouseArea::setCursorShape(Qt::CursorShape shape)
     If \c drag.filterChildren is set to true, a drag can override descendant MouseAreas.  This
     enables a parent MouseArea to handle drags, for example, while descendants handle clicks:
 
+    \c drag.threshold determines the threshold in pixels of when the drag operation should
+    start. By default this is bound to a platform dependent value. This property was added in
+    Qt Quick 2.2.
+
     \snippet qml/mousearea/mouseareadragfilter.qml dragfilter
 
 */