[x3d-public] Sorry for not being able to attend today's teleconference, glTF stuff that I planned to mention

[Leonard Daly]

Michalis,

I am curious how you handle the differences in texture/appearance. glTF 
only handles PBR. It is possible to create the equivalent appearance of 
Phong-shaded material, but it takes quite a bit of work during 
modeling/texturing. If that work was not done, then you need to merge 
multiple maps for texture (aka base color), metallic, roughness, plus 
optionally those for normals (already in place in X3D), ambient 
occlusion, emissive (as a map, not just a scalar), and environmental 
light map.

I see some obvious mappings from glTF --> X3D. [This material included 
for those not deeply familiar with PBR or glTF's implementation of PBR.]

Things with obvious relationships
*glTF        -->        X3D*
base color    ->    texture
normals        ->    normals

Things with obvious relationships, but dimension reduction
*glTF (map)        --> X3D (scalar)*
emissive        ->    emissive
environment    -> multiple discrete lights

Things that don't map
*glTF*
metallic
roughness
ambient occlusion

Things that don't receive
*X3D*
diffuseColor (unless the texture is flat)
specular (computer in PBR)
emissive (unless the emissive map is flat -- see above)


Note that transparency and discrete lighting is separate and handled in 
both systems.

The page at https://github.com/KhronosGroup/glTF-WebGL-PBR is a good 
place to start for a description of the glTF implementation.

Leonard Daly



> Hi,
>
> My apologies, I will not be able to attend today's web3d
> teleconference. I'm falling asleep after 24h of work :) Man, I thought
> I'm stronger! :)
>
> For anyone interested, I wanted to briefly mention what has happened
> in Castle Game Engine / view3dscene about glTF. I can talk about it
> next Friday, but those interested can also read links below:
>
> - Castle Game Engine / view3dscene can now read glTF 2.0 (without
> animations): https://castle-engine.io/wp/2018/12/23/gltf-2-0/ . Both
> .gltf and .glb versions, images/buffers can be provided either as
> separate files or packed into a single file. You can open glTF files,
> you can refer to them using X3D "Inline" or "Anchor", you can use
> view3dscene/tovrmlx3d to convert glTF to X3D. The resulting X3D uses
> CommonSurfaceShader to express a Phong material with possible
> normalmaps.
>
> - I wanted to mention important "mismatch" between glTF and X3D, and
> how we deal with it by a new "flipVertically" field at texture nodes
> (like "ImageTexture.flipVertically"):
> https://castle-engine.io/x3d_implementation_texturing_extensions.php#section_flip_vertically
>
> - I wanted to mention "Appearance.alphaChannel", which is a CGE
> extension to X3D:
> https://castle-engine.io/x3d_implementation_shape_extensions.php#section_ext_alpha_channel
> . It is generally useful (even if you don't care about glTF), and also
> it allows to perfectly express the glTF "alphaMode" field at glTF
> materials.
>
> Best regards,
> Michalis
>
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>

-- 
*Leonard Daly*
3D Systems & Cloud Consultant
LA ACM SIGGRAPH Past Chair
President, Daly Realism - /Creating the Future/
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