[Qt-interest] QTouchEvent/QGestureEvent propagation

[Wathek LOUED]

Stephen you're right concerning getting simultanous gesture with the same
object. I didn't find a way to do that.

On Mon, Apr 11, 2011 at 5:48 PM, Sean Hayes <sean.t.hayes at vanderbilt.edu>wrote:

> On Mon, Apr 11, 2011 at 10:09 AM, Stephen M. Webb <
> stephen.webb at bregmasoft.ca> wrote:
>
>> On Sun, 2011-04-10 at 22:33 +0200, Wathek LOUED wrote:
>> > Hi all,
>> >
>> > I've noticed that the Events in Qt using the
>> > QGraphicsView/QGraphicsScene/QGraphicsItem are spread from the
>> QGraphicsView
>> > then to the QGraphicsScene and the to the item that got the lowest
>> Z-Index
>> > to the most top item.
>> >
>> > I think that that's a bit weird cause generally when using QTouchEvent
>> and
>> > QGesture we look at the most top element so imagine that you programmed
>> a
>> > gesture and that that gesture occured at position (x, y) and in that
>> > position there's 4 items that are grabbing the same gesture, so it'll be
>> > grabbed by all the item and not the top element won't it ?
>>
>> But imagine the scenario in which a multi-touch gesture is made with
>> four fingers spread across the scene?  Which element should receive the
>> event?  Should all elements receive a single-finger gesture or does a
>> 4-finger gesture have some significance?  Is the QGraphicsScene not the
>> right place to determine that?
>
>
> I would argue that to proper place is dependent on your design. If you have
> two separate gesture types (one for single finger gestures and one for
> 4-finger gestures), then the scene could grab 4-fingered gestures and
> QGraphicsObjects could grab the single-finger gestures. If that is what you
> want, they should receive "simultaneous" but different events.
>
> "Ignoring the gesture will mean the gesture will never be offered to you
> again. It *will *be offered to a parent widget or item as well." - from Qt
> 4.7 Gesture Overview Documentation<http://doc.qt.nokia.com/latest/gestures-overview.html#standard-procedure-for-event-handling>
> .
>
> Therefore, if a QGraphicsObject ignores a gesture and has
> a QGraphicsObject, the gesture event should be passed to the
> parent QGraphicsObject. Likewise, if the parent of the QGraphicsObject is a
> QGraphicsScene, it should then be passed to the parent scene. If the scene
> then ignores the event, it should then be passed to the scenes parent (which
> might be the QGraphicsView). As I understand the documentation, that should
> be the order of the event propagation. It does not make sense for the scene
> or the view to receive the gesture event on both sides of the QGraphicObject
> handling of the event. Therefore, if scene should not receive the event
> until after the QGraphicsObject ignores the event. That is my just opinion
> of how it should be based on my limited knowledge of the Qt event loop
> documentation. Any flows with that logic?
>
> Regards,
> Sean
>
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at qt.nokia.com
> http://lists.qt.nokia.com/mailman/listinfo/qt-interest
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20110411/bbddad33/attachment.html