[x3d-public] NIST conformance example behaviour

[Andreas Plesch]

Since a Script node can add a new node to the scene graph, it also should
be able to place a USE reference to a node somewhere in the scene graph in
the same (three) ways that it can place a new instance of a node into the
scene graph.

This is where then USEd bindable nodes as Script SFNode field default
values need to be considered. Since such USE references to bindable nodes
are discouraged/undefined outside of script nodes, using scripts to place
such node references is also discouraged/undefined.

There is a question if this script restriction needs to be made explicit in
the bindable nodes/script spec. sections or if it is implicit in the
existing language.

So how can one access a bindable node's fields from within a script ?

A) without directOut: route out event from script to bindable node's field;
others ?
B) with directOut: route bindable node itself to XFNode script field
(perhaps as children field of a group wrapper) to script field; use SAI
holder[0].set_headlight = ..
or set bindable node USE reference as default script field value and use
field name in script (as in example)

To me the last method (as used in the example) does feel like a shortcut or
a trick because it would be the only situation where a USEd bindable node
is required, establishing a sort of exception to a simple rule. The problem
in a way is that if a bindable node USE reference can be created as a
script field default value, there may be an expectation/temptation by
authors to then place this USE reference into the scene graph in some way.

So maybe this needs clarification:
"A Script node may define a field containing a USE reference to an existing
bindable node. However, this USE reference may not be placed into the scene
graph (see bindable nodes)." How does that sound ?

Ok, this turned out not very concise after all. Thanks for reading through
to the end,

Cheers

Andreas


On Jan 26, 2017 10:43 AM, "Andreas Plesch" <andreasplesch at gmail.com> wrote:

Here are my thoughts and I will try to be concise since I agree that this
really is not a major matter.

The script node is part of the scene graph but its position in it does not
matter. (So it is effectively always a root node).

Some script nodes will have (custom) SFNode fields which can be assigned a
default value. There are many other nodes which have SFNode fields such as
Shape.

Can a script node create an additional node in the scene graph, not
considering USE for a moment ? Yes, indirectly and directly:

A) Either a Route needs to place the created nodes in an existing 'holder'
(group) scene graph node:  See

http://www.web3d.org/x3d/content/examples/Basic/X3dSpecifica
tions/ECMAScriptSaiCreateNodesIndex.html

B) Or the script places the new node directly in the scene:

initialize()
  // Create nodes directly in the parent scene
    scene = Browser.currentScene;

  // Add the SFNode field value to the scene
    scene.rootNodes[0] = ScriptSFNodeFieldValue;

(is there an example ?   http://www.web3d.org/x3d/conte
nt/examples/Basic/ScriptConformance/CreateNodesFromPrototype
ECMAScriptIndex.html is close.)

C) or directOut is used:

USEdHolder.addchildren = ScriptSFNodeFieldValue; // or perhaps
USEdHolder.children.push(ScriptSFNodeFieldValue)

So I do believe that a Script field of type SFNode with a (non USE) default
value creates an instance of this node which then can be subsequently
placed into the scene graph by the script or with a route.

Ok, lets take a break. Continued later,

Andreas


Some discoveries:

http://www.web3d.org/x3d/content/examples/Vrml2Sourcebook/Si
ggraph98Course/LoaderIndex.html is a mind bender since the script uses
itself as a field value ....


Phrasing: "Instancing" is used here:

http://www.web3d.org/documents/specifications/19776-1/V3.3/P
art01/examples.html#Instancing

The annotated VRML reference which Patrick offered specifically discusses
how USE is supposed to represent the pointer concept. But instancing was
probably still used in VRML discussions.


On Thu, Jan 26, 2017 at 1:27 AM, Don Brutzman <brutzman at nps.edu> wrote:

> Sincere thanks for your follow-up note Patrick.
>
> On 1/25/2017 4:50 PM, Patrick Dähne wrote:
>
>> Hello Don,
>>
>> "A Script node with a field containing a USE reference to a bindable node
>>> has the ability to bind a node directly by changing the value of the bind
>>> field.  Setting the bind value is equivalent to receiving a set_bind event.“
>>>
>>
> This statement was the result of 20-30 minutes careful discussion on the
> weekly teleconference today.
>
> I should have also noted that it was refined and documented as part of
> Mantis issue 749, which was previously submitted.  Web3D Consortium Member
> access on the website is necessary to view these issues.
>
>         Mantis 0000749: 7.2.2 Bindable children nodes - Amend prose
>         http://www.web3d.org/member-only/mantis/view.php?id=749
>
> It seems to me that most everything said by everyone on this topic (both
> email and teleconference) has essentially agreed on functionality: that a
> Script field USE node does not get processed as part of the scene-graph
> traversal, nor does it get bound simply by being referenced as an SFNode
> field.  We carefully discussed the specification prose today to ensure that
> all cases were considered.
>
> Interestingly the participants (Dick Roy Joe Leonard Vince and myself,
> maybe Nicholas was still with us) looked quite closely at the exact same
> sentence identified by you.  We tried a few prose variations along the
> lines of what you are suggesting as well.  We decided eventually that the
> words there were still the best we could achieve.  Perhaps your phrasing is
> more helpful, but functionality is agreed upon at least.
>
> So, for your question below, why do we want to add this additional
> sentence quoted at the top of this message?  Continued review of paragraph
> 7.2.2 steps (a) through (i) describes binding behaviors on the basis of
> events being received.  The case of a Script node with a field USE
> reference and directOutput='true' which subsequently sets the value of
> 'bind' field during Script invocation wasn't addressed... so this extra
> sentence was added for clarity, to explicitly note that the bind/unbind
> operations are equivalent for event access and direct access.
>
> I hope this helps explain the additional sentence.
>
> Of note is that the in-person discussions are really helpful. Interpreting
> the specification prose can be a tricky business!  We do our best to listen
> to every option together and achieve concise descriptions.  We also
> reference the email thread and every direct suggestion in Mantis for future
> reference as well.  Also essential is the presence of a good example scene
> with agreed-upon semantics for rendering and user interaction.
>
> Since Fraunhofer is a member you are of course welcome to join.  If you or
> anyone else wants to propose a further improvement, we will be happy to
> schedule a good time for that.  Member connection information is online,
> non-member invitations are not a problem for these topics.
>
>         http://www.web3d.org/member/teleconference-information
>
> So... lots of careful listening and due diligence.  We are further paying
> close attention to using Mantis when performing the corresponding X3D
> specification editing in Github.
>
> Please check out the mantis issue if you still have concerns, and let's
> review again at a good time for you (and Andreas as well).  There is little
> value in "winning" an email debate, rather we always want to achieve common
> ground, shared understanding and (hopefully!) consensus so that all
> implementations can consistently handle X3D content.  So these efforts are
> all worthwhile, especially for the special semantics of bindable nodes,
> Script execution and DEF/USE referencing.
>
> More specification issues await... but we are certainly operating at a
> greater level of working group + community knowledge than ever before.
> Apparently benefits are cumulative!  8)
>
> Hope we're looking ~ acceptable now.  Further improvement always welcome.
> Looking forward to continuing progress together with all of X3D, again
> thanks to all involved.
>
> v/r Don
>
>
> Sorry, I did not want to resume that nitpicking discussion, but you are
>> taking the wrong direction :-(
>>
>> My point is:
>>
>> 1. There is this sentence in section 7.2.2 of the specification: „The
>> results are undefined if a multiply instanced (DEF/USE) bindable node is
>> bound.“
>>
>> 2. In the NIST example we exactly do have that case - a bindable node
>> (DEF nav1 NavigationInfo) that is multiply instanced - once as a child of
>> the (implicit) root Group node, and once as a child of the Script node.
>>
>> 3. => According to the specification, the example is undefined. Q.E.D.
>>
>> I do not claim that there *actually* is a problem with the NIST example,
>> I just say that *formally* the example is invalid because of that sentence
>> in section 7.2.2 of the specification.
>>
>> So what is the rationale behind that sentence? That is explained in the
>> Annotated VRML97 Reference. The browser needs to determine the
>> transformation of the currently bound Viewpoint, Background or Fog node.
>> The NavigationInfo node actually is a special case, because for that node
>> the transformation of the currently bound Viewpoint is taken. Now, when you
>> DEF/USE a bindable node (or any group node above a bindable node), you have
>> to take care that you do not add the bindable node more than once to the
>> transformation hierarchy, because otherwise the browser cannot decide which
>> of the transformations to take. Adding a bindable node to the Script node
>> does *not* add it to the transformation hierarchy (see section 4.3.5 of the
>> specification) - that is why there is no problem in the NIST example.
>>
>> So, what to do with that awkward sentence in section 7.2.2? My
>> recommendation would be to replace it with a sentences like this: „A
>> bindable node may only be bound when it is part of the transformation
>> hierarchy exactly once, otherwise the result is undefined.“ But I’m sure a
>> native english speaker can word that much better.
>>
>> Bye,
>>
>> Patrick
>>
>
>
> all the best, Don
> --
> Don Brutzman  Naval Postgraduate School, Code USW/Br
> brutzman at nps.edu
> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
> +1.831.656.2149
> X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzma
> n
>



-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
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