[osg-users] CompositeNodeCallback : useful addition?

Jean-Sébastien Guay jean-sebastien.guay at polymtl.ca
Fri Oct 26 07:18:36 PDT 2007


Hello Robert,

> You can nested callbacks within each other right now.  It's a bit
> awkward but does work for doing multiple callbacks.

Yes, as I said I find the current nested callback mechanism less  
intuitive. It would be better if it were transparent to users of the  
class, which is what I tried to do with CompositeNodeCallback's static  
methods.

> The issued you have with your approach is that you call the callbacks
> in series and don't provide a mechanism for traversal - rather it
> assumes that each callback would call the traverse on subgraph or not
> at all.  This might be OK for some callbacks types that fall into a
> pre or post callback style, but not ones that are in effect traversal
> callbacks.

OK, I'm totally open to improving the design and implementation... I  
haven't used traversal callbacks so I didn't know that was a widely  
used case. What is it that should be happening? Would it be something  
like this?


void CompositeNodeCallback::operator()(osg::Node* node, osg::NodeVisitor* nv)
{
     for (CallbackVector::iterator it = _callbacks.begin();
          it != _callbacks.end();
          ++it)
     {
         // Call (*it)->operator()(node, nv) on each callback.
         (**it)(node, nv);
         (*it)->traverse(node, nv);    // added
     }

     traverse(node, nv);    // added
}


Or is there more that is needed? As I see it, currently each class  
derived from NodeCallback is responsible for calling traverse() in its  
operator() anyways, if it needs to, so why do I need to call it in the  
composite? There must be something I don't understand.

As I said, my goal was to hide the complexity of managing multiple  
callbacks on one node, so if some tweaks are required to the  
implementation I'm totally open to doing them.

Thanks,

J-S
-- 
______________________________________________________
Jean-Sebastien Guay     jean-sebastien.guay at polymtl.ca
                         http://whitestar02.webhop.org/

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