[x3d-public] getContainerField() [was cobweb DOM integration]

[Andreas Plesch]

On Mon, Oct 10, 2016 at 3:47 PM, Andreas Plesch <andreasplesch at gmail.com>
wrote:

> Hi Roy,
>
> On Oct 10, 2016 10:27 AM, "Roy Walmsley" <roy.walmsley at ntlworld.com>
> wrote:
> >...
> > Q1 – Usually (always) just one field for a given parent nodetype. I
> don’t have an exhaustive answer, but I will give an example. It may be the
> only one, not sure. Look at the Collision node, (19775-1, 23.4.2,
> http://www.web3d.org/documents/specifications/19775-1/V3.3/P
> art01/components/navigation.html#Collision. Note that there is a children
> field and a proxy field, both of which accept X3DChildNode. In other words,
> what can go in one can also go in the other.
> >
>
> This may not be the best example since children is a mfnode and proxy is a
> sfnode. So based on the node type of the child it would be still possible
> to determine which field is targeted ?
>
> I was grepping through the web3d and savage examples to get a quick sense
of how containerField is used. One type of usage seems to be just repeating
the default containerField value, presumably as an aid for a human
interpreter of the x3d, particularly in the savage archive. Another type of
usage is with user defined fields in proto instances where the default
container field value necessarily does not apply. A third type is with
certain components: H-Anim, Rigid Body seem to use it most. Volume
Rendering, as Doug noticed, also requires containerField='voxels' for
VolumeData.

I can see why for XML it was decided to have containerField rather than
wrapper tags. It is awkward to have a <Children> element under grouping
nodes when the wrapped elements are actually child nodes, and particularly
so when repeated many times. But containerField is also a rather
unintuitive concept, requiring to think 'backwards', eg. up the hierarchy.
Well, I am sure this was discussed at length and it would be difficult to
come up with a better solution without deep changes.

-Andreas
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