[x3d-public] Fwd: thinking about X3DJSONLD/X3DOM/glTF interoperability

[Andreas Plesch]

On Thu, Jul 6, 2017 at 12:33 PM, Leonard Daly <Leonard.Daly at realism.com>
wrote:

> John,
>
> XSeen is taking the approach of treating glTF as a model.   What are
> others doing?  Is anyone considering the whole scenegraph?  Why or why
> not?  Is glTF as a model done because Three.js treats glTF as a mesh (I
> don't know if three.js does this or not)?
>
>
> XSeen and A-Frame both use the glTF loader for THREE. The loader imports
> the entire model and texture (a mesh in THREE terminology). Both also
> include all of the animations and any scene graph structure. However, that
> structure (including animations) is sort-of encapsulated from the rest of
> the scene graph. There are no events that are fired during animation
> sequences.
>


> X3DOM treats the glTF file as what can be represented in a single Shape
> node - geometry + appearance. Transforms and animation are not included.
>
>
X3DOM should be able to apply the gltf transforms in the latest dev.
versions. Animations would need serious work to support, I believe.
A concern is that X3DOM only supports glTF1 while glTF2 will take over
pretty quickly now that it is out.

What do people think of the low level nature of glTF as opposed to X3D?
>
>
> glTF ranges from low-level (geometry + basic appearance) to full scene
> graph. I am not sure how to interpret your question.
>
> glTF is becoming the standard exchange format. It includes (more or less)
> everything in FBX, but it is open. It has more options than OBJ, and is
> smaller in size. I think it is necessary to be able to process glTF and
> include it in a scene graph, much like the glTF importer for THREE. Yes, it
> does overlap with X3D.
>
>
I think this is a nice characterization. glTF = gl Transport Format.


> While it makes it less understandable, I can see how keeping glTF low
> level would improve performance at the expense of file size.   Has anyone
> compared and contrasted the two standards?
>
>
> Which two standards - X3D & glTF? glTF has better animation, it has been
> adopted by more users and content creators (people & software). It comes in
> a binary and text forms. It has the potential for being the entire scene
> graph. It includes shaders and advanced appearance (bump maps, ambient
> occlusion, etc.).
>
> On the downside, I don't think it has audio, movie textures, environmental
> effects (fog, background, etc.), or sensors. I may be wrong about some of
> these items because I haven't studied glTF in its entirety -- I just
> haven't come across those capabilities yet.
>
>
One could probably include a textured big box or sphere as background in
glTF file. Fog may be possible with a custom shader. After all, glTF by
itself requires definition of shaders. Only the glTF extensions provide
predefined shaders for standard (KHR,PBR) materials. Apart from audio, the
biggest difference may be that glTF content is not supposed to interact
with the outside including the viewer, as far as I can tell. glTF does not
support internal scripting. It has internal reuse (DEF/USE) of resources.

>
> Are there glTF importer/exporters for blender yet? If not, why not?
>
>
> There will be a BOF at SIGGRAPH about Blender exporters including a glTF
> exporter. I am not sure about an importer. Since there is a THREE loader, I
> suspect it would not be that difficult to build an importer.
>

Meshes, lights, animations, standard materials should be able to be
digested.It could be difficult to have a lossless import -edit - export
cycle.

-Andreas


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