[x3d-public] X3D Working Group meeting 23 SEP 2022: Mantis issues review, SvgTexture

[John Carlson]

@Michalis: can you confirm if you export  a glTF file from Blender, import
the same glTF in a new Blender instance, export the scene to a second glTF
file, that the 2 glTF files will be the same in form and function?   This
is important for importing any glTF into another tool besides
Blender—workflows.

Again, I lack experience.

On Thu, Sep 29, 2022 at 7:20 PM Michalis Kamburelis <
michalis.kambi at gmail.com> wrote:

> @John: glTF doesn't do any "lossy compression".
>
>     Don't read too deep into the saying "glTF is like JPG for 3D". The
> point of this is that "glTF wants to be a popular format for 3D
> interchange". It is not "storing as glTF means any lossy compression".
>
>     ( Of course you could use glTF with DRACO, and DRACO can be lossy
> (depending on settings). But using DRACO is just an optional extension in
> glTF, not required, not even specified  in glTF core. )
>
> @Don: I'm fine with your refinement ""Full X3D4 rendering support for
> glTF2 models includes both inline loading and native representations.",
> thank you!
>
> Though, just to point some details:
>
> 2.1. We talked in the past about why tangent information is useful in 3D
> file and "Normal" is not enough. There's a good reason why glTF has this
> information and I think X3D should have it too.
>
> See "[x3d-public] Allowing Normal node to accompany PointSet, then
> achieving well-defined rendering" thread, my post from 2019-12-12.
>
> In short, there are various algorithms to calculate tangent information
> from normals (and tex coords). They differ in some details and a practical
> application may also differ in precision. And when your renderer (that
> renders normalmap) and your 3D authoring tool (that creates the normalmap)
> use a bit different tangents, with a bit different outcomes -- then
> artifacts happen when you apply the normal map. The screenshot in answer on
> https://gamedev.stackexchange.com/questions/146855/how-do-you-compute-the-tangent-space-vectors-with-normals-given-in-the-mesh#comment259182_146855
> shows this nicely -- https://i.stack.imgur.com/FwKPO.png .
>
> 2.2. Interpolators are not an answer to the issue I mentioned there. The
> thing is that our X3DColorNode does "replace" of the color. Equivalent glTF
> concept does "modulate". I propose an extension to enable both modes:
> https://castle-engine.io/x3d_implementation_rendering_extensions.php#section_ext_color_mode
> .
>
> I do not see how interpolators could help here. They allow to animate
> stuff. They don't change that per-pertex X3DColorNode (animated or not
> animated) does "replace".
>
> Regards,
> Michalis
> On wrz 29 2022, at 11:44 pm, Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
> The relationship between a tangent and a normal is… orthogonal, literally.
>
>
>
>
>    - Wikipedia: Tangent
>    - https://en.wikipedia.org/wiki/Tangent
>
>
>
>
>    - Wikipedia: Normal (geometry)
>    - https://en.wikipedia.org/wiki/Normal_(geometry)
>
>
>
> Given a surface, you can convert a normal to a tangent (and vice versa).
>
>
>
> Regarding DOM, it is Document Object Model used to create a tree of
> element/attribute/value strings  corresponding to an HTML page.  Suggest
> reading the respective specifications, or summaries, in order to understand
> how it is a quite different from glTF.
>
>
>
> 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:* John Carlson <yottzumm at gmail.com>
> *Sent:* Thursday, September 29, 2022 12:05 PM
> *To:* Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>
> *Cc:* Michalis Kamburelis <michalis.kambi at gmail.com>; X3D Public Mailing
> List (x3d-public at web3d.org) <x3d-public at web3d.org>
> *Subject:* Re: [x3d-public] X3D Working Group meeting 23 SEP 2022: Mantis
> issues review, SvgTexture
>
>
> On Thu, Sep 29, 2022 at 12:42 PM Brutzman, Donald (Don) wrote
>
>
> 2.1.  Tangent vectors are normal to a surface.  X3D has a Normal node, so
> an
> advanced authoring can likely match such functionality.
>
>
> I don’t understand the first sentence.   Information is only needed if the
> first sentence is correct.
>
> I will try to me tomorrow or when the next meeting is.   The real purpose
> is to inquire into next meeting.
>
> If someone is preparing a glTF to DOM converter, can I participate?
>
> John
>
>
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