[x3d-public] bboxDisplay considerations

[Andreas Plesch]

Working on a first version of bboxDisplay, I came across a few more decisions.

The spec. language says that "The bounding box is displayed regardless
of whether contained content is visible.".  This is useful for
debugging purposes. x3dom may not correctly update bboxes when
non-visible content changes.

There is also the reverse situation when the bounding box is contained
within a grouping node which is not visible. Because further traversal
into a non-visible grouping node is not normally needed, x3dom would
not display bboxes contained in non-visible nodes for performance
reasons.

Another perhaps somewhat surprising point is that bboxes are aligned
with the local, surrounding coordinate system of grouping nodes. This
means that displaying the bbox of a Transform does not adjust to any
changes to that transform, only to changes to the surrounding
transform. This is the sensible solution but may be surprising to
authors at first. Authors can always use the bbox of an additional
Group inside such a transform.

Any feedback welcome, Andreas

On Fri, Mar 24, 2023 at 11:26 PM Andreas Plesch <andreasplesch at gmail.com> wrote:
>
> These are good points. However, the author, not necessarily the
> browser, would typically know best how to use color for any intended
> purpose. After all, the author needs to decide when to display or hide
> the bbox. Of course, any browser can have user preferences which may
> override author choices.
>
> I believe browser debug and ui features would be independent of the
> bboxDisplay field. It is a field exposed for authoring purposes.
>
> I can also see the value in the argument that because it is a simple
> feature, its control should be simple. Richer bboxes would need to be
> custom made, perhaps with prototypes. On the other hand, from an
> implementation perspective, simple may mean "just another shape" to
> render which then could be easily exposed to the author.
>
> Well, enough looking. Perhaps time to proceed,
>
> Andreas
>
> On Fri, Mar 24, 2023 at 5:35 PM Brutzman, Donald (Don) (CIV)
> <brutzman at nps.edu> wrote:
> >
> > Thanks for close looks at this, it holds a lot of potential value.  Hopefully more-effective bounding boxes will improve authoring, debugging, and user interaction.
> >
> >
> >
> > We intentionally did not specify an X3D4 bboxColor field since
> >
> > Browsers might have their own algorithms or user preferences,
> > There is no “correct” color since farther objects and Background color might be the same or similar,
> > Browsers might decide to do color “negation” or some other technique for contrast,
> > Browsers might also use it for indication of picking, selection, collision.
> >
> >
> >
> > Authoritative references:
> >
> >
> >
> > X3D4 Architecture, Grouping component, 10.3.1 X3DBoundedObject
> > https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.review/Part01/components/grouping.html#X3DBoundedObject
> >
> >
> >
> > X3D4 Architecture, Grouping component, 10.2.2 Bounding boxes
> > https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.review/Part01/components/grouping.html#BoundingBoxes
> >
> >
> >
> > v/r Don
> >
> >
> >
> > From: x3d-public <x3d-public-bounces at web3d.org> On Behalf Of Holger Seelig
> > Sent: Friday, March 24, 2023 1:48 PM
> > To: Andreas Plesch <andreasplesch at gmail.com>
> > Cc: X3D <x3d-public at web3d.org>
> > Subject: Re: [x3d-public] bboxDisplay considerations
> >
> >
> >
> > Yes bboxSize and bboxCenter can be directly used as scale and translation for a transformation matrix for a bboxShape with size at 1.
> >
> >
> >
> > I also miss the possibility of setting the color of the box.
> >
> >
> >
> > Holger Seelig
> >
> > Leipzig, Germany
> >
> > holger.seelig at yahoo.de
> >
> >
> >
> >
> >
> >
> >
> > Am 24.03.2023 um 19:15 schrieb Andreas Plesch <andreasplesch at gmail.com>:
> >
> >
> >
> > Following up, I looked up the bboxDisplay implementation in x_ite, and
> > it does pretty much follow what I outlined, eg. using an additional
> > internal, on demand Shape. Instead of wrapping in a Transform, for
> > scaling it multiplies in a local transform matrix to the model view
> > matrix. it is not strictly part of the scene graph but gets added
> > during render traversal but not picking traversal. The bbox shape is
> > predefined as a white IndexedLineset but presumably could be
> > generalized/made customizable.
> >
> > I hope it is possible to avoid special treatment during traversal and
> > just manage as a regular, inert scene graph participant. Let's see.
> >
> > Ok, this was helpful. Andreas
> >
> > On Fri, Mar 24, 2023 at 12:10 PM Andreas Plesch <andreasplesch at gmail.com> wrote:
> >
> >
> > Please forgive me if I use this message to plan strategies for a
> > possible implementation of bboxDisplay for x3dom. There will be a few
> > questions at the end.
> >
> > To start, it is already quite straightforward to generate visual
> > feedback for selection purposes in x3dom. Here are a few examples:
> >
> > https://andreasplesch.github.io/Library/Examples/html5/highlight/turnyellow.html
> > https://andreasplesch.github.io/Library/Examples/html5/highlight/withBBox.html
> > https://andreasplesch.github.io/Library/Examples/html5/highlight/outline.html
> >
> > Thinking about generalizing to any X3DBoundedObject leads to the
> > following observations.
> >
> > In x3dom, only Shapes are collected for rendering during scene
> > traversal. Displaying a bbox for groups etc. breaks this basic
> > pattern.
> >
> > Although a custom shader would be most performant, this means it is
> > not really advantageous to expand the shader to include an option for
> > bbox rendering because it is restricted to shapes. Also a bbox needs
> > to be displayed even if the shape is not visible which complicates
> > logic.
> >
> > In turn, this means it appears to be necessary to add an internal bbox
> > Shape for each X3DBoundedObject to the scene graph which is managed by
> > the engine. Since the bbox size needs to be updated at each traversal
> > this will add some overhead. I guess if the updates are only performed
> > when the bbox is visible this may be ok but the check is still
> > necessary. Also the bbox shapes need to be created for a lot of
> > objects, perhaps on demand only which could be an optimization. It
> > will be necessary to be careful in cleaning up when a X3DBoundedObject
> > is deleted from the scene graph.
> >
> > Finally, I am considering adding an SFNode field to X3DBoundedObject
> > "bboxTemplate" which would be a Shape node or a Grouping node and
> > would let the scene designer customize the kind of bounding box used
> > for the display. By default it would be a green cage or such. It is
> > expected to be of unit size, and scaled internally (by a Transform
> > wrapper) to the actual bbox size. ( Hm, this would probably mean
> > allowing subShapes to Shape nodes as children. It may be possible to
> > deal with bboxes for Shapes as siblings, or in general as siblings,
> > eg. child of parent ).
> >
> > By default the size of the displayed bbox would be a tight fit but it
> > would look probably better to make it a little larger. So another
> > custom field could be SFFloat "bboxMargin", zero by default.
> >
> > What strategies do FreeWRL, x_ite or castle use to implement
> > bboxDisplay while keeping overhead at a minimum ? Check at each
> > traversal and insert a scaled bbox ? As an option in the shader ?
> >
> > Depending on the strategy, would it make sense to support a custom
> > bounding box ?
> >
> > A somewhat unrelated question is if a displayed bounding box is
> > eligible to be sensed by Sensors such as a TouchSensor ? Presumably,
> > it should be completely inert and be ignored but I am not sure if this
> > is how the spec. intends to be read. I think in x3dom it should be
> > possible to make sensing eligibility configurable.
> >
> > Thanks for any feedback,
> >
> > Andreas
> > --
> > Andreas Plesch
> > Waltham, MA 02453
> >
> >
> >
> >
> > --
> > Andreas Plesch
> > Waltham, MA 02453
> >
> > _______________________________________________
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> > x3d-public at web3d.org
> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
> >
> >
>
>
>
> --
> Andreas Plesch
> Waltham, MA 02453



-- 
Andreas Plesch
Waltham, MA 02453