[x3d-public] X3DParticleEmitter node inherit fromX3DChildNode(rather than X3DNode)

Thu Mar 10 14:32:12 PST 2022

> The right way to cache non-rendered content for DEF/USE libraries is to put them as children nodes within a Switch node with whichChoice=’-1’.

Indeed, "Switch" (with whichChoice left -1) is our (VRML, X3D)
traditional way of making a "library of nodes".

But the very reason why this thread exists is because Switch is not
sufficient :)

Switch only allows X3DChildNode as children. Which is of course
correct, it cannot allow "any X3DNode" as children, because it would
not make sense to traverse it, and Switch has to be designed with
assumption "one of these nodes can be active".

This means you cannot use Switch to have a library of e.g.
X3DParticleEmitter nodes. Which was the catalyst for this entire
thread -- Don wanted to make X3DParticleEmitter a X3DChildNode for
this reason, or make special exception to allow it as a root node, and
I argued that we should not make a special hack for
X3DParticleEmitter. Because one may also want to reUSE easily
Materials, ImageTextures etc.

This is why I proposed NodesLibrary. I suspect this is why X_ITE
decided to implement this by hacking MedataSet.

If we truly want functionality "library of any nodes", then I think we
really need something like NodesLibrary I described, probably in X3D
4.1. Switch is not enough (not for any node), and indeed we don't want
to encourage "hacking" MetadataSet to achieve this.

Regards,
Michalis

czw., 10 mar 2022 o 22:14 Brutzman, Donald (Don) (CIV)
<brutzman at nps.edu> napisał(a):
>
> Thanks for continued scrutiny and consideration.
>
>
>
> Likely we should create a set of examples from each of the languages you’ve listed (and more) to show how to do it.
>
>
>
> Metadata libraries are further exposable via Inline IMPORT/EXPORT or even as prototype declarations.  Such repurposing of MetadataSet structures can be automated if desirable.  Corresponding forms in Turtle for semantic web query will provide further use.
>
>
>
> Test cases welcome.
>
>
>
> 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 https:// faculty.nps.edu/brutzman
>
>
>
> From: Andreas Plesch <andreasplesch at gmail.com>
> Sent: Thursday, March 10, 2022 1:08 PM
> To: Joseph D Williams <joedwil at earthlink.net>
> Cc: Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>; X3D Graphics public mailing list <x3d-public at web3d.org>
> Subject: Re: [x3d-public] X3DParticleEmitter node inherit fromX3DChildNode(rather than X3DNode)
>
>
>
> Good comments.
>
> MetadataSet to have X3DNode nodes
>
> If I understand it, the idea of ending meta to include actual user code for the scenegraph is exactly the sort of extension wanting to be “worthwhile to deviate a bit and be more permissive than the spec” that dooms the long-term validation operation. Maybe good for something with simple structure that looks convenient and logical and seemingly convenient to implement at first thought and elementary usage, then ends up making something definitely not to be best practice. Please delineate the “worthwhile” parts that make a case.
>
>
>
> I only know that this construction shows up in most of x-ite examples, and is how the Titania editor saves a scene, simple or complex. I can only deduce that this decision was deliberate but cannot speak to the specific motivation by the author. Speculating, the feature seems to be valuable for authoring. It should be possible to convert to standard x3d automatically by moving the DEF node from the MetadataSet to the first USE node, perhaps by xslt.
>
>
>
> Not quite sure how validation would be affected.
>
>
>
> I agree that Metadata nodes should be limited to actual metadata but a library node seems sensible.
>
>
>
> Here is a list of other, well established scene graph systems which do have a concept of a non-renderable library which is separate and can then be referenced as needed:
>
>
>
> - svg
>
> - glTF
>
> - a-frame
>
> - collada (I believe)
>
>
>
> it is a natural concept and perhaps allows for cleaner user code organization. Having two alternative ways to define a DEF node (in a library, and as a first scene graph node) does seem to invite friction, and would need to be carefully considered.
>
>
>
> Andreas
>
>
>
>
>
> From: Andreas Plesch
> Sent: Tuesday, March 8, 2022 11:39 AM
> To: Brutzman, Donald (Don) (CIV)
> Cc: X3D Graphics public mailing list
> Subject: Re: [x3d-public] X3DParticleEmitter node inherit fromX3DChildNode(rather than X3DNode)
>
>
>
> Yes, I am pretty sure Holger is aware. I only brought it up because Titania/x-ite typically stays very close to the spec. But this is a capability where Titania/x-ite found it worthwhile to deviate a bit and be more permissive than the spec. This decision may point to the value of having a way to DEF any X3DNode (not just child nodes) outside of the scene graph, outweighing strict compliance.
>
>
>
> All the best, Andreas
>
>
>
> On Tue, Mar 8, 2022 at 2:22 PM Brutzman, Donald (Don) (CIV) <brutzman at nps.edu> wrote:
>
> MetadataSet is only allowed to contain other Metadata* nodes or comments.  Other content will fail validation (and will not load or import in the X3DJSAIL Java and X3DPSAIL Python libraries).
>
>
>
> The right way to cache non-rendered content for DEF/USE libraries is to put them as children nodes within a Switch node with whichChoice=’-1’.
>
>
>
> 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 https:// faculty.nps.edu/brutzman
>
>
>
> From: x3d-public <x3d-public-bounces at web3d.org> On Behalf Of Andreas Plesch
> Sent: Tuesday, March 8, 2022 10:11 AM
> To: X3D Graphics public mailing list <x3d-public at web3d.org>
> Subject: Re: [x3d-public] X3DParticleEmitter node inherit from X3DChildNode(rather than X3DNode)
>
>
>
> Of note is that Titania and x-ite allow MetadataSet to have X3DNode nodes, eg. any node, in the value field, not just X3DMetadataObject nodes.
>
>
>
> This allows MetadataSet to be used as a NodesLibrary for DEF/USE purposes. In fact, this kind of redirection is the default setup for scenes created in Titania.
>
>
>
> SVG also has a NodesLibrary equivalent, the <defs> element:
>
>
>
> https://developer.mozilla.org/en-US/docs/Web/SVG/Element/defs
>
>
>
> -Andreas
>
>
>
> Date: Mon, 7 Mar 2022 21:29:41 +0100
> From: Michalis Kamburelis <michalis.kambi at gmail.com>
> To: Joseph D Williams <joedwil at earthlink.net>
> Cc: GPU Group <gpugroup at gmail.com>,  "X3D Public Mailing List
>         (x3d-public at web3d.org)" <x3d-public at web3d.org>
> Subject: Re: [x3d-public] X3DParticleEmitter node inherit from
>         X3DChildNode(rather than X3DNode)
> Message-ID:
>         <CAKzBGZNToR-7CmaUzRxBE3xx9J6j2mPgmvKAjQKpGQxjdY_0hA at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Perhaps I should have written
>
> """
> The nodes within NodesLibrary don't make any effect, they are not
> traversed. They are only to be reUSEd (referenced) by other parts of
> the graph."
> """
>
> This makes the wording consistent with how e.g. Switch is described.
> Sure you have all the nodes in memory, you just don't traverse to
> inactive parts of Switch, LOD, NodesLibrary etc.
>
> Regards,
> Michalis
>
>
>
>
> --
>
> Andreas Plesch
> Waltham, MA 02453
>
>
>
>
>
>
> --
>
> Andreas Plesch
> Waltham, MA 02453
>
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