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

[Chris Marrin]

On Jan 5, 2011, at 5:10 AM, Johannes Behr wrote:

> 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. 

> 
> 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.

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.

Once again, my apologies.

-----
~Chris
chris at marrin.com