Hi Rob, If you want to access the vertex attribute data (such as colours, normals, tex coords) then you are probably best to do a dynamic_cast<Geometry*> on the drawable and then access the data that way. If the drawable isn't a geometry then you'll need to use a cast to whatever object it is.
Robert. On Mon, Jul 26, 2010 at 11:07 PM, Rob Radtke <r...@stellarscience.com> wrote: > Thank you Robert for the detailed explanation of TriangleFunctor and > TriangleIndexFunctor. Those classes have proven to be very useful to me. > I'm curious to know if there is a good way to use those classes in a manner > that allows you to also access attributes for each vertex. In particular, > I'm interested in accessing texture coordinate and/or color attributes (for > v1, v2 and v3) inside of my 'operator()(const int v1, const int v2, const > int v3)' implementation. > > I have had some limited success using a custom ConstAttributeFunctor > subclass to accumlate attributes inside of a ' NodeVisitor::apply( > osg::Geode&)' override, but I'm struggling with devising the best plan for > mapping each vertex back to the appropriate attribute. My current solution > is very messy and I doublt it's very robust. Is there a prescribed way to > do this? > > Thanks, > Rob Radtke > > -----Original Message----- > From: osg-users-boun...@lists.openscenegraph.org > [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Robert > Osfield > Sent: 12 March 2010 10:57 > To: OpenSceneGraph Users > Subject: Re: [osg-users] Need help to understand this code snippet > withaccept > and operator > > Hi Fred, > > The TriangleIndexFunctor is a template helper class for making it > easier to access the triangles held in osg::Drawable. The actual > geometry primitives held within different osg::Drawable subclasses > could be of any type and any arrangement, so casting osg::Drawable to > osg::Geometry etc. and then accessing the primitives directly and then > working out how to interpret the triangles from this is rather > complex, tedious and prone to poor performance unless you are very > careful. > > To address the tight coupling of accessors to implementations, the > osg::Drawable has an accept(osg::Drawable::PrimitiveFunctor&) method > exists to allow a subclass from osg::Drawable to pass details on the > geometry primitives that it has to the functor in a generic way - thus > hiding the local implementation details of that Drawable and enabling > your own custom PrimitiveFunctor to work with a wide range of Drawable > without needing to know the implementation details. While this > achieves good decoupling the PrimitiveFunctor still has to handle all > the different types of primitives - polygons, tri strips, quads, qaud > strips, lines etc, which is still pretty complicated to implement. > > To address the complexity of handling all the different types of > primitives the TriangleIndexFunctor template class exists to decompose > all the descriptions of generic primitives into the simple triangles > marked by their corner indices. For you the app developer all you > then need to do is create you little functor that implements the void > operator()(const int v1, const int v2, const int v3) method as per the > example, and then pass the resulting templated class to the drawable > to get all the triangle information. The use of templates also > ensures good performance. > > If it wasn't for PrimtiiveFunctor and > TriangleFunctor/TriangleIndexFunctor accessing geometry would be very > tedious and error prone task - lots of casts, switch statements and > book keeping. These helper classes might seem a bit convoluted at > first look, they really make life much easier. Go have a search > through the OSG code base, there are plenty of examples of > TriangleFunctor/TriangleIndexFunctor in action - especially in > src/osgUtil. > > Cheers, > Robert. > > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
