Hi John, Original Node callbacks didn't support multiple callbacks, but I worked out that I could add the functionality relatively non-intrusively by nesting callbacks. The key advantage with nesting is that it enables a callback retain data on the stack within the local scope of the callback - which makes things easy to implement and gives you thread safety for free, and enables the callback to take complete controlling traversal.
Providing similar support for Camera::DrawCallbacks would be possible, there isn't the same imperative for controlling traversal, but it'd keep the public Camera API simple - it's complicated enough as it is so am reluctant to add further API to it. The alternative would be to add a list of callbacks, but as you said this would break compatibility. Robert. On 9 April 2014 14:10, PCJohn <[email protected]> wrote: > Hi, > > I very like the capability of osg::Node to register any number of update, > event and cull callbacks. This allows for a nice modular approach with each > module registering callbacks for anything they wish without disturbing others. > > I came to a problem that Camera can register just one Initial-,Pre-,Post-, and > Final-DrawCallback. Surely, I can register my own "callback container" that > would call all my registered callback. But that is not compatible with OSG- > registered Callbacks, for instance OcclusionQueryNode would overwrite my > callback container. Could we possibly make the similar approach for the camera > as for osg::Node? I can volunteer to make the first iteration for osg- > submissions, if the community and Robert thinks that it is a good idea. > > > My idea for implementation would be to append > ref_ptr<DrawCallback> _nestedCallback into the Camera::DrawCallback structure, > append Camera::add*Callback() and Camera::remove*Callback() > and make Camera::callCallbacks(DrawCallback *cb) with a parameter giving > pointer to the first DrawCallback of Initial-,Pre-,Post-, and Final- > DrawCallback list. > An alternative would be to let the user call nested callbacks from > DrawCallback::operator(), but as we would always want (probably) to call all > the callbacks and never stop in the middle of the work, I personally like the > first approach more and it is more compatibility-friendly, as users will not > need to modify their existing callbacks to get the new multi-callback > capability. But I am ok with any approach. > > > Do you think it is a good idea? > John > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
