[x3d-public] [x3dom-users] bboxDisplay considerations; metadata nodes for new field extensions

Andreas Plesch andreasplesch at gmail.com
Sat Apr 1 14:41:27 PDT 2023

Hi Don,

Using metadata as an extension mechanism may be feasible. It would
require more thought on how to represent non-standard nodes in
metadata in addition to fields. For example, x3dom has the popular
BinaryGeometry node.

The metadata seem quite verbose. It would probably suffice to have a
single MetaDataMFString with all non-standard attributes:

<Shape bboxDisplay='true'>
   <MetadataString name='extension-fields' value=' " bboxColor=\'0.7
0.8 0.9\' " "bboxMargin=\'0.1\' " />

Instead of the "=" sequential name-value pairs may be preferable. The
meaning would be "add to the node as attribute name-value pairs in xml
encoding before initial parsing".

This makes parsing a bit harder but since MFtypes can generally only
be represented as strings in Metadata, such parsing is necessary in
any case.
For x3dom, the metadata values would only be used for initialization of fields.

Another way to think about validation of non-standard extensions is to
actually provide custom validation for such documents. This seems hard
but perhaps could be accomplished with a plug-in system for a base
validator system. Plug-ins could then be provided by extension

Finally, it is not unreasonable to keep the current semantics of
validation. Adding non-standard fields and nodes invalidates a

Best, Andreas

On Sat, Apr 1, 2023 at 3:57 PM Brutzman, Donald (Don) (CIV)
<brutzman at nps.edu> wrote:
> Thanks for continuing news about this excellent progress.
> Am thinking we might all agree to regularize addition of nonstandard fields in a way that still passes content validation.
> For example, non-standard experimental example
> <Shape bboxDisplay='true' bboxColor='0.7 0.8 0.9' bboxMargin='0.1' >
>    <Sphere/>
> </Shape>
> Might be equivalently and validly expressed as
> <Shape bboxDisplay='true'>
>    <MetadataSet name='extension'>
>         <MetadataString name='bboxColor' value='0.7 0.8 0.9'/>
>         <MetadataString name='bboxMargin' value='0.1' />
>    </MetadataSet>
>    <Sphere/>
> </Shape>
> A little more verbose perhaps... However, note that not only is model content validatable, but metadata content might also be validated if we build a metadata vocabulary that lists experimental field names, types and default values.  That way common extensions might be more sharable and model content remains confirmably correct.
> Seems like a useful good practice that isn't complex, so we could easily build <MetadataSet name='extension'> capabilities into our browser parsers and authoring tools.
> The X in X3D is Extensible... looking forward to continued innovation and practice/progress together.
> v/r Don
> -----Original Message-----
> From: Andreas Plesch <andreasplesch at gmail.com>
> Sent: Saturday, April 1, 2023 6:43 AM
> To: X3D <x3d-public at web3d.org>
> Cc: x3dom mlist <x3dom-users at lists.sourceforge.net>
> Subject: Re: [x3dom-users] [x3d-public] bboxDisplay considerations
> The bboxDisplay field is now available for bounded objects (grouping nodes and shapes) in the dev. version of x3dom.
> The color of the displayed bounding box can be customized with the non-standard bboxColor field, and the size expanded with the bboxMargin field.
> Enjoy ! Andreas
> On Thu, Mar 30, 2023 at 2:19 PM Andreas Plesch <andreasplesch at gmail.com> wrote:
> >
> > I think it will be very useful to allow different colors for different
> > sets of bounding boxes. Here are the rotating cubes with two sets of
> > bounding boxes. The yellow ones react to a TouchSensor, the orange
> > ones do not:
> > [...]

Andreas Plesch
Waltham, MA 02453

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