[x3d-public] gltf and x3d

[Andreas Plesch]

x3dom currently supports gltf 1.0 content with an ExternalGeometry and
an ExternalShape node. The ExternalGeometry node picks out just a
named geometry from a gltf scene, and the ExternalShape either a
single named node with geometry and material, or the complete scene,
as a group.

Lights,  cameras (viewpoints), animations, skinning, morphing are all ignored.

gltf 2.0 is aggressively pushed to phase out gltf 1.0 because it has a
better design and has required material support in the form of
PBR-metallic-roughness.  A lot of content is already available in gltf
2.0 format. So the question becomes if x3d should start to
interoperate with gltf directly or just in the form of translators.

The main benefit to support gltf for x3dom was to gain fast, efficient
loading of large meshes in a binary format (binary gltf or .glb is
very similar to src). It is possible to use blender for just geometry
modelling, and then to export as gltf 2.0. There are other and will be
more gltf exporting modellers as well. So this is still a valuable
goal and ExternalGeometry may persist.

If this is the case, we may start to ask if and how gltf geometry
support should be formalized in the standard. Presumably, gltf would
have to become an ISO standard first ?

It seems also nice to be able to place fully textured gltf models into
a x3d scenegraph (say a car) and then use x3d nodes to interact or
animate. But such ExternalShape integration requires quite a lot of
functionality. The x3d browser will have to know how to shade PBR
materials and how to use texture maps for all related parameters
similar to common surface shader nodes in view3dscene. Presumably
there will have to be then also consideration of how x3d lights work
with both, PBR and X3D materials. Since PBR materials would have to
able to be rendered, PBR materials may also be exposed outside of gltf
ExternalShape content, with a PhysicalMaterial node. However, in
x3dom, I think, it would be easier at first to restrict PBR to just
gltf content since it would use dedicated shader code anyways.

For ExternalShape use cases, a translator from gltf to x3d with
ExternalGeometry and PhysicalMaterial nodes may be also be a solution.

I think embedded keyframe animations would need a translator to
Interpolators rather than direct support.

I do not know enough about skinning and morphing and its relation to
HAnim to know if translation would be possible. One (key) aspect
aspect may be that morphing seems to be designed as deformation in the
shader. Not sure how collisions are then typically handled.

So thinking through this a bit, it may already be useful to start
supporting ExternalGeometry for gltf 2.0 in x3dom which may be
feasible.

Any feedback, comments, questions would be very welcome,

Andreas

-- 
Andreas Plesch
Waltham, MA 02453