[X3D-Public] Fwd: Re: [X3D] X3D HTML5 meeting discussions: Declarative 3D interest group at W3C

[Johannes Behr]

Hi,

>> 
>>> This is one of the biggest issues with X3DOM and any mapping from X3D to
>>> HTML (from my perspective) X3D inherently has a DAG model that shows up
>>> in subtle and not so subtle areas. This is foreign to HTML and adding a
>>> DAG under the hood making it look like a tree from the outside causes
>>> funny things to happen, if you make changes to one of the "copies" of a
>>> multiple referenced objects. Note that you run into CSS issues as well
>>> this way, which may be as difficult as those in SVG.
>> 
>> I agree. The DAG does not match the HTML tree and it's not just the
>> CSS assignments but makes serialization results really odd. However,
>> it's a very powerful feature for users to reuse other parts of scene with
>> a simple reference. References and deep-copies (e.g. with proto-instances)
>> are two generic solutions to the reuse problem. 
> 
> I think it's a mistake to go down the road of using a separate hierarchy for a 3D node set. Living in the HTML DOM is easy and gives you lots of features with little work. 

No question about this. The nodes will be in the DOM. This is one of the core ideas of this interest group.
The question is only, if this nodes represent a Tree or a DAG.
HTML uses the DOM as Tree, SVG as DAG. Both work today in almost every browser.

But maybe we have to step back and rethink the reuse issue. 

> 
>> 
>> Render/picking performance is  another good reason not to use
>> a DAG internally. Therefore we map the X3D graph to an OpenSG-Tree
>> internally in the native implementation. 
> 
> You should also be careful of citing performance problems of a particular approach before an implementation using that approach is attempted.

Well, this is not a new problem and the solutions are well understood. This is a ongoing discussion in the field of scene-graph design since
Performer (Tree) and Inventor (DAG) for 20 years :)

> 
> I may be attempting to steer this group in a direction it doesn't want to go. If so, I apologize and will stop. I think there is some promise of getting 3D nodes into many web browsers. But I think talking about changing the node hierarchy, DOM or event system will result in failure.

We all agree! This will not happen. We see the current DOM structure and event system as building ground. We build on existing W3C standards. 
The question is only how we utilize what is already there. 

best regards
johannes. 


> 
> Once again, my apologies.
> 
> -----
> ~Chris
> chris at marrin.com
> 

--
Dr. Johannes Behr
Leiter Projektbereich VR

Fraunhofer-Institut für Graphische Datenverarbeitung IGD
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