MouseArea: add scrollGestureEnabled property

If true, scroll gestures coming from the operating system can cause
wheel to be emitted; if false, only an actual mouse wheel will do that.
The photosurface example demostrates the use case.
1) the flick gesture on a trackpad should flick the underlying
Flickable, not zoom an individual image
2) mouse wheel should zoom an individual image if the cursor is
pointing to it
3) dragging an image on a touchscreen should be possible, independently
of flicking the Flickable.  This means multiPointTouchEnabled should be
true, so we cannot interpret multiPointTouchEnabled to mean that
multipoint touch scroll gestures should be disabled.

Change-Id: Ie063556866f07b3fbadc53990b110edeed532710
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

1 files changed, 32 insertions, 2 deletions

diff --git a/src/quick/items/qquickmousearea.cpp b/src/quick/items/qquickmousearea.cpp
index dc7ba96c35..d6aa30835c 100644
--- a/src/quick/items/qquickmousearea.cpp
+++ b/src/quick/items/qquickmousearea.cpp
@@ -50,7 +50,7 @@ QT_BEGIN_NAMESPACE
 DEFINE_BOOL_CONFIG_OPTION(qmlVisualTouchDebugging, QML_VISUAL_TOUCH_DEBUGGING)
 
 QQuickMouseAreaPrivate::QQuickMouseAreaPrivate()
-: enabled(true), hovered(false), longPress(false),
+: enabled(true), scrollGestureEnabled(true), hovered(false), longPress(false),
   moved(false), stealMouse(false), doubleClick(false), preventStealing(false),
   propagateComposedEvents(false), pressed(0)
 #ifndef QT_NO_DRAGANDDROP
@@ -497,6 +497,36 @@ void QQuickMouseArea::setEnabled(bool a)
 }
 
 /*!
+    \qmlproperty bool QtQuick::MouseArea::scrollGestureEnabled
+
+    This property controls whether this MouseArea responds to scroll gestures
+    from non-mouse devices, such as the 2-finger flick gesture on a trackpad.
+    If set to false, the \l wheel signal be emitted only when the wheel event
+    comes from an actual mouse with a wheel, while scroll gesture events will
+    pass through to any other Item that will handle them. For example, the user
+    might perform a flick gesture while the cursor is over an item containing a
+    MouseArea, intending to interact with a Flickable which is underneath.
+    Setting this property to false will allow the PinchArea to handle the mouse
+    wheel or the pinch gesture, while the Flickable handles the flick gesture.
+
+    By default, this property is true.
+*/
+bool QQuickMouseArea::isScrollGestureEnabled() const
+{
+    Q_D(const QQuickMouseArea);
+    return d->scrollGestureEnabled;
+}
+
+void QQuickMouseArea::setScrollGestureEnabled(bool e)
+{
+    Q_D(QQuickMouseArea);
+    if (e != d->scrollGestureEnabled) {
+        d->scrollGestureEnabled = e;
+        emit scrollGestureEnabledChanged();
+    }
+}
+
+/*!
     \qmlproperty bool QtQuick::MouseArea::preventStealing
     This property holds whether the mouse events may be stolen from this
     MouseArea.
@@ -821,7 +851,7 @@ void QQuickMouseArea::hoverLeaveEvent(QHoverEvent *event)
 void QQuickMouseArea::wheelEvent(QWheelEvent *event)
 {
     Q_D(QQuickMouseArea);
-    if (!d->enabled) {
+    if (!d->enabled || (!isScrollGestureEnabled() && event->source() != Qt::MouseEventNotSynthesized)) {
         QQuickItem::wheelEvent(event);
         return;
     }