The problem is that you are trying to cast a pointer to a base class to a pointer to a subclass. This would only work if the actual object being pointed to is an instance of that subclass (or a further subclass of that subclass). Geometry is derived from Drawable, not the other way around - which seems to be the mistake that you are making.
Please refer to the inheritance diagrams for osg::Drawable and osg::Geometry. Matthew W. Fuesz Software Engineer Asc. Lockheed Martin STS 1210 Massillon Road Akron, OH 44315 [EMAIL PROTECTED] ________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Franclin Foping Sent: Thursday, July 31, 2008 7:17 AM To: OpenSceneGraph Users Subject: [osg-users] RE : Re: RE : Re: Converting a Drawable object to a Geometry object Hi Ulrich, I don't think you get the trick, from what you said, the only thing wrong is the ShapeDrawable. I will post a new issue in a short while which is not different from this post and you will see that even without using ShapeDrawable objects, the same issue still hang around. Just bear with me. Thanks for your help. Franclin. Ulrich Hertlein <[EMAIL PROTECTED]> a écrit : Hi Franclin, > Downcasting from a derived class to a parent class is possible with the > dynamic_cast operator. From what you have written in your mail, it looks like > the snippet won't compile at all, I can bet something it will as I tried it a > couple of hours ago. Try it yourself and let me know. The code is correct and will compile, it's just that the casts won't work as you expect. Okay, let's see: >> osg::Geode myGeode = new osg::Geode; >> myGeode->addDrawable(new osg::ShapeDrawable(new >> osg::Box(osg::Vec3(),1,1,1))); >> osg::Drawable* myDrawable = myGeode->getDrawable(0); myDrawable is a Drawable* to a ShapeDrawable This is fine since Drawable is a base class of ShapeDrawable. (I assume there aren't any other Drawables in myGeode and the first one is actually the ShapeDrawable you added.) > osg::Geometry* myGeom = myDrawable->asGeometry(); If you take a look at 'osg::Drawable' you'll see that this actually *always* returns 0 and ShapeDrawable doesn't override it (Geometry is the only class that overrides it). However, even doing what the comment says (and what you're doing for 'myGeom2'): osg::Geometry* geom = dynamic_cast(this) This cannot succeed since the *object* is-a ShapeDrawable (even though the pointer is Drawable*). > Of course, downcasting from shapedrawable to geometry would have not worked > and even worse would have not compiled at all. Agreed. But introducing a Drawable* doesn't help because it doesn't change the type of the object the pointer is pointing to. ShapeDrawable* shape = new ShapeDrawable(...) Drawable* drawable = dynamic_cast(shape); // OK, is a base class Geometry* geom = dynamic_cast(drawable); // is always 0 I'm probably not explaining this as clearly as possible but try to think of it this way: you have a base class 'Vehicle' and two derived classes 'Car' and 'Plane'. You can create a 'Plane' and have a 'Vehicle' pointer to it but you can't cast that pointer to a 'Car'. Hope this helps. Cheers, /ulrich _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ________________________________ Envoyé avec Yahoo! Mail <http://us.rd.yahoo.com/mailuk/taglines/isp/control/*http:/us.rd.yahoo.com/evt=52423/*http:/fr.docs.yahoo.com/mail/overview/index.html> . Une boite mail plus intelligente.
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