[Gnu3dkit-discuss] considering G3DGeometry

[Brent Gulanowski]

I have been struggling with the issue of what it means for a scene 
graph to be object oriented. I have been studying the MVC pattern 
recently as well, and the two have led to an idea.

It seems to be taken for granted that geometry data is part of the 
scene graph. What if this is not correct? What if the representation 
and the object were strictly distinct from one another? Not just a 
class distinction, as G3DNode is distinct form G3DGeometry, but a 
model/view distinction. It is taken for granted that the representation 
of 3D objects in interactive rendering is a vast simplification. So why 
is it not the case that the representation is considered a part of the 
renderer component, instead of the scene graph?

I would like to propose that, instead of holding a reference or pointer 
to a geometry object, that the scene graph merely holds a name. It uses 
this name when specifying itself to the renderer. The geometry used is 
specified --once -- at load time, and used from then on. It would even 
be best to store geometry data in a separate file or files from scene 
graph data. Then, whenever you change renderers, you will possibly also 
change geometric representations. For example, while an OpenGL renderer 
would use mesh objects, a ray tracer might use parametric objects. A 
scene graph could even be "rendered" to a text context, in which case 
objects would be represented by strings.

If there were some facility to ensure that the various representations 
used by different renderers were in fact parallel, so much the better, 
but I have not pursued that problem. My main purpose is to properly 
encapsulate object/model information, and to distinguish it from view 
information. I am more and more of the opinion that the on-screen 
representations of objects are view information, more to do with the 
display context than with the objects themselves. Likewise, I see the 
renderer as a view controller class, the complement to the drawable.

Comments and responses would be very welcome.