Re: [Gnu3dkit-discuss] considering G3DGeometry

[Brent Gulanowski]

On Friday, March 21, 2003, at 01:24  PM, Philippe C.D. Robert wrote:

> the topics you mention are definitely worth spending more thoughts, 
> but I doubt that this affects the core design of the 3DKit. On the 
> other hand, transformation techniques and level of detail concepts are 
> indeed very interesting and important. But be aware that these are 
> very mathematical areas (you sound like you are less interested in 
> maths)!

I learn maths as required, and avoid them when possible! It depends on 
the application.
> To remain on-topic, what are your concrete interests here, what kind 
> of object representations, what do you want to address/solve exactly?
>
> BTW the current design (frontend/backend separation) allows us to 
> easily introduce mechanisms to achieve such concepts. To give an 
> example, you could write a GL based renderer backend which tessellates 
> algebraic surfaces, performs surface subdivision etc. on the fly and 
> then renders them using application specific detail settings.

OK. This is all good. I guess I'm thinking more about pre-rendered 
stuff being used later, and making it easy to swap different reps in 
and out. Consider two applications: one to model individual 
representations (where you'd do the tessellation and other procedural 
work), and another to display a large scene made up of these reps. You 
want to save the procedurally generated rep as a fixed mesh, and then 
just load it up later. Maybe you'd pre-render a bunch of them at 
different levels of detail, and then load them up as appropriate. I can 
think of ways that it would be a lot easier to just swap one rep for 
another inside a resource file, than to have to manipulate the scene 
graph directly. I'm sure you can do any of this by manipulating the 
scene graph, but I'm postulating ways that would avoid that if 
possible, for users' benefit, the same way you can substitute images 
and strings in resources that are used to describe user interfaces now.

I also had an idea for using the renderer interface for a data source 
for an NSOutlineView. The scene graph would think it was drawing 
things, but really it would just be passing object references which the 
data source would convert into hierarchy and string information. You 
save yourself having to write a second interface for the data source. 
If, however, the shape nodes tried to submit geometry, that would all 
just be ignored, and would be a waste of time. Instead the groups call 
-objectInstance, and the "renderer" just finds a suitable retained 
object representation: in this case, a dictionary of strings.

That's one example. I'm thinking of a couple more, but they are still 
too vague. I'll readily admit that I'm sort of pushing an AppKit 
concept onto a pretty different application, and maybe I'm seeing 
parallels that aren't really there. What are your feelings about 3D 
user interfaces? I know they have been tried and usually fail 
miserably, but I am curious about them. But then there is the hassle of 
having a conceptual domain model (say, a company organizational chart, 
or a visual representation of a call tree of a program, or a langauge 
structure, or a shape grammar) and trying to integrate it with the 3D 
scene model that portrays it.

So on the one hand I'm wondering about 2D views of 3D data, and on the 
other hand, 3D interpreted views of non-graphical data. If there was 
one interface that could handle all of it, that would be pretty cool. 
But it's a lot to ask for.

Brent Gulanowski                address@hidden
--
If you paid a million monkeys to type on a million keyboards, 
eventually they would produce Micro$oft Windows.