[osg-users] GUIEventHandler called twice - possible bug(s)

[Riccardo Corsi]

Hi Robert,

please find attached a simple example that shows the issues I was trying to
explain:
- launch with no args to see the initial issue
- launch with "--crash" to get the crash i ran into when implementing the
callback deriving from osg::Callback
- launch with "--fix" to see the way I fixed it with the NodeCallback:
comments on the run() and operator() methods explain some concerns for this
solution

Hope this clarifies things :)
Ricky


On Mon, Aug 29, 2016 at 4:29 PM, Robert Osfield <robert.osfield at gmail.com>
wrote:

> Hi Ricky,
>
> The changes to Drawable and the knock on effect to the callbacks is an
> awkward one - it would be easy if it we could just discard backwards
> compatibility, so it's a far from ideal code, but alas you can't
> rewrite history once it's happened.
>
> From your description I don't have a clear idea of what is being
> called twice and whether this is a problem.  Could you create a small
> example that illustrates the problem, once I can see first hand I can
> review the behaviour and decide whether this is acceptable or is an
> bug.
>
> Thanks,
> Robert.
>
> On 29 August 2016 at 15:00, Riccardo Corsi <riccardo.corsi at kairos3d.it>
> wrote:
> > Hi all,
> >
> > I report what I believe could be considered a bug, probably introduced
> after
> > the promotion of the Drawable class to a node, together with the new
> > callback system.
> >
> > I have a GUIEventHandler derived class installed on a Drawable.
> > After some digging I've realized that it's called twice for every event
> due
> > to the EventVisitor code here:
> > https://github.com/openscenegraph/OpenSceneGraph/
> blob/master/include/osgGA/EventVisitor#L86
> >
> > GUIEventHandler happens to derive both from NodeCallback and
> > DrawableEventCallback, resulting in it being called twice. I think this
> > might be considered as a bug if the intended behavior was to keep using
> the
> > old GUIEventHandler interface the way it was (when attached to the viewer
> > for instance, it is called only once as expected).
> >
> > Relate issue:
> > I've re-implemented my callback deriving from osg::Callback, but this
> > results in a crash as the osg::CallbackObject interface is used even if
> the
> > cast does not succeed (first if condition)
> > https://github.com/openscenegraph/OpenSceneGraph/
> blob/master/include/osgGA/EventVisitor#L93
> >
> > I fixed that by deriving from osg::NodeCallback, but I had to reimplement
> > the operator() method instead of run(), as the second is not called by
> the
> > visitor - that also it's a bit counter-intuitive with respect to the
> > osg::Callback class interface.
> >
> > Ricky
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > osg-users mailing list
> > osg-users at lists.openscenegraph.org
> > http://lists.openscenegraph.org/listinfo.cgi/osg-users-
> openscenegraph.org
> >
> _______________________________________________
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>
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