Re: [openvrml-develop] Problem in reading scene file

[Braden M. <br...@en...>]

On Mon, 2006-04-24 at 17:43 -0700, Dean Mann wrote:
> Hi Braden,
> 
> Thanks for the quick reply.
> 
> > > But still I cant get the coordinates, texture and their indices off the
> > > IndexedFaceSet
> > > node, either the file name of the texture image.
> >
> >What have you tried?
> 
> This is what I did, where the MyNodeTraverser class inherits from 
> openvrml::node_traverser.
> 
> void MyNodeTraverser::on_entering(openvrml::node & n)
> {
> 
> if (n.type().id() == "Material")
> {
> 	openvrml::vrml97_node::material_node mtrNode (n.type(),n.scope());

The above line creates a new node, which is probably not what you want
to do. You certainly don't want to do it by directly invoking this
class' constructor. You should avoid using anything in the
openvrml::vrml97node namespace; stick to what's in the openvrml
namespace when you possibly can. (The openvrml::vrml97node namespace
isn't part of the API at all in the forthcoming release of OpenVRML.)

> 	ambientIntensity = mtrNode.ambient_intensity();  // the value is always 0.2 
> no matter what is in the VRML file

Since you just created a new node, naturally the field has its default
value.

Rather than create a new node, you want to use the reference to the
existing one:

        openvrml::material_node * m =
          openvrml::node_cast<openvrml::material_node*>(&n);
        float ambient_intensity = m->ambient_intensity();

That approach works fine if the data you need to get is exposed via the
abstract node classes in the openvrml namespace. You can get arbitrary
field data like this:

        const openvrml::sffloat & ambient_intensity_field =
          static_cast<const openvrml::sffloat &>(n.field("ambientIntensity");
        float ambient_intensity = ambient_intensity_field.value;

> if (n.type().id() == "ImageTexture")
> {
> 	openvrml::vrml97_node::image_texture_node  imgTxtNode (n.type(),n.scope());
> 
> 	// no idea what to do next

I hope the above examples shed some light on this. You can use the
latter form to access any field you need--it's a generic mechanism.

> if (n.type().id() == "IndexedFaceSet")
> {
> 	openvrml::vrml97_node::indexed_face_set_node idxFSNode 
> (n.type(),n.scope());
> 
> 	openvrml::sfnode sfNode = (openvrml::sfnode)idxFSNode.GetCoord();

Is GetCoord something you've added? I don't know what it returns; but
converting it to a nonpointer, nonreference type with a C-style cast
isn't likely to end well. You should virtually never use C-style casts
in C++ code.

> 	openvrml::node* nodePtr = sfNode.value.get();  // here nodePtr becomes 
> undefined

If we assume the C-style cast wasn't somehow deleterious, the
explanation is that, as before, you created a new node so the field has
its default value. Again, I hope the code fragments I wrote above
sufficiently indicate what you need to do here.

Let me know if anything is still unclear.

-- 
Braden McDaniel                           e-mail: <br...@en...>
<http://endoframe.com>                    Jabber: <br...@ja...>