[x3d-public] NIST conformance example behaviour

Wed Jan 25 18:22:52 PST 2017

> DEF/USE and bindable nodes
>
> * Discussion on public thread entitled NIST conformance example
> behaviour commencing at
> http://web3d.org/pipermail/x3d-public_web3d.org/2017-January/005848.html
>

I think Don described this by the idea that the USE node in the script
does not actually appear in the scenegraph and so is not subject to
routing or binding. This is the same for any node USEd in a script,
whether it is a bindable node or not.

Regarding whether or not the USEd node in a script must appear after
the DEFed node should not be an issue because the script does not need
access to the DEFed node until the script actually executes. So, order
of appearance should not matter  Only that the script actually has
access to the execution context of the DEFed node.

In a Script, the only reason to USE a node in a script is to enable
directOut.

The directOut is special. The USEd node fields are updated directly
without the use of ROUTE(s) or participation in any cascade. The USEd
node is not instantiated in this process. The DEFed node is already
instantiated and is read or updated directly, whether bound or not.

The next biggest understanding about directOut is that the set_ event
is essentially asynchronous. That is, a directOut to the USEd node
does not initiale a cascade, and can happen 'ouside' the cascade in
progress, at any time, as the script executes or when the script is
complete. So, while all events in the current cascade are defined to
be applied 'instantaneously, the directOut event may be outside the
current instant.

To me the directOut is like, well, you have everything running with
all your pertinent evens routed and accounted for, but then you detect
something and a little bang in the right place - a directOut 'kick' -
moves some dial someplace and improves the tune.

So, the directOut sort of happens in the event system background, or
maybe the event system foreground. However, the _changed event from
the updated field will be posted and may initiate a new cascade.

When a user understands how directOut is supposed to work then they
can make a better choice about when to use it. Best practice should
consider directOut to be less reliable with greater implementation
dependence than normal script operation.

Thanks and Best,
Joe

----- Original Message ----- 
From: "Roy Walmsley" <roy.walmsley at ntlworld.com>
To: <x3d at web3d.org>
Sent: Wednesday, January 25, 2017 3:18 AM
Subject: [x3d] Agenda for X3D WG Meeting Wednesday 25th January 2017

> Agenda for the X3D WG meeting to be held on Wednesday 25th  January
> 2017 at
> 0800 PST, 1600 GMT.
>
>
>
> Please add additional items if desired.
>
> All Web3D Consortium members are welcome to attend.
>
>
>
> Apologies received: None
>
>
>
> Preliminary:
>
> Approval of minutes of WG meeting held 18th January 2017
>
> http://web3d.org/mailman/private/x3d_web3d.org/2017-January/005702.html
>
>
>
> A. Outstanding matters
>
>
>
> 1. Invitation to Maxim Fedyukov
> 2. BoD approval of contribution submission guidelines page -
> http://www.web3d.org/standards/contribution-guidelines
> 3. Standards comment form page update -
> http://www.web3d.org/content/web3d-standards-comment-form
>
> * See Mantis issue 1133
> http://www.web3d.org/member-only/mantis/view.php?id=1133
>
>
>
> B. Summary and Technical reports
>
> Opportunity for anyone to make a short report on Web site,
> marketing,
> communication, specification or technical matters that is not
> already on the
> Agenda.
>
> * ISO/IEC JTC 1 study group on 3D printing and scanning. First
> meeting
> on Friday January 27th 2017 at 1300 UTC.
>
>
>
> C. Discussion Topics
>
>
>
> Update of X3D WG page at http://www.web3d.org/working-groups/x3d
>
> * General review of page
> * Specific review of first bullet point under activities - Call for
> Contributions for Compressed Binary Encoding for X3D
>
>
>
> DEF/USE and bindable nodes
>
> * Discussion on public thread entitled NIST conformance example
> behaviour commencing at
> http://web3d.org/pipermail/x3d-public_web3d.org/2017-January/005848.html
>
>
>
> D. Specification work, GitHub, and Mantis issues
>
>
>
> Mantis issue handling
>
> * New status values added (Mantis issue 1122,
> http://www.web3d.org/member-only/mantis/view.php?id=1122) for
> 'Commented'
> and 'Submitted'
> * Work through one example - Mantis issue 984
> http://www.web3d.org/member-only/mantis/view.php?id=984
>
>
>
> TimeSensor mailing list discussions
>
> * Mantis issue 1106 at
> http://www.web3d.org/member-only/mantis/view.php?id=1106
>
>
>
> E. Schedule review
>
>
>
> Other topics for discussion not yet assigned are:
>
>
>
> Invitation to Maxim Fedyukov to attend a meeting
>
> * e-mail thread on public list at
> http://web3d.org/pipermail/x3d-public_web3d.org/2016-December/005732.html
> entitled "Current X3D adoption"
>
> Submissions from Roy & Leonard
>
> X3D, VR, and mobile support, including dependence on WebGL, WebVR,
> glTF
>
>
>
> February 1st -
>
> February 8th -
>
> February 15th -
>
> February 22nd -
>
>
>
> F. Date and time of next meeting
>
>
>
> February 1st 2017 at 0800 PST 1600 GMT
>
>
>
> Roy Walmsley
>
> X3D WG co-chair
>
>
>
>
>
>

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----- Original Message ----- 
From: "Patrick Dähne" <patrick.daehne at igd.fraunhofer.de>
To: "Don Brutzman" <brutzman at nps.edu>
Cc: "Andreas Plesch" <andreasplesch at gmail.com>; "X3D Graphics public 
mailing list" <x3d-public at web3d.org>
Sent: Wednesday, January 25, 2017 4:50 PM
Subject: Re: [x3d-public] NIST conformance example behaviour

> 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.“
>
> 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
>
>
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