[x3d-public] X_ITE implementation of glTF material extensions

Thu Jun 27 05:55:54 PDT 2024

Thank you for the answers!

As for KHR_materials_pbrSpecularGlossiness:

Indeed some Sketchfab models use KHR_materials_pbrSpecularGlossiness ,
as internal Sketchfab exporter uses it in some cases. It seems
Sketchfab didn't update their tools to follow Khronos recommendations
(to use KHR_materials_specular instead of
KHR_materials_pbrSpecularGlossiness). Which is also understandable --
I don't think there's a straightforward conversion that exactly
preserves look from KHR_materials_pbrSpecularGlossiness to
KHR_materials_specular, even though they fulfill the same use-case. So
Sketchfab doesn't want to break compatibility (look of models).

That is why I wondered to implement
KHR_materials_pbrSpecularGlossiness in some way, though for now just
recommend users to ask model authors to not use this material type --
https://castle-engine.io/sketchfab . It's on our page about Sketchfab
integration, because that's where users in practice encounter this
issue :)

All good, I mean it is of course a practical and valid decision to
support KHR_materials_pbrSpecularGlossiness (by equivalent in X3D
SpecularGlossinessMaterial) for the time being, since real models use
it, despite what Khronos recommends. Thanks for the explanation!

As for unlit:

The "unlit" field in X3DOM PhysicalMaterial (
https://doc.x3dom.org/developer/x3dom/nodeTypes/PhysicalMaterial.html
) -- I'm not sure, but I think it predates the X3D 4.0 and
UnlitMaterial node. X3DOM doesn't implement UnlitMaterial for now at
all, looking at docs ( https://doc.x3dom.org/developer/classes.html )
.

So here I would vote for sticking to the standard, in both X3DOM and
X_ITE :) That is, UnlitMaterial should fulfill the need to translate
glTF unlit materials to X3D, and is simpler. X3DOM's
PhysicalMaterial.unlit, and X_ITE UnlitMaterialExtension, can
hopefully always be replaced by using UnlitMaterial.

As for sRGB workflow:

It is indeed not specified in X3D. X3DOM has their extension to
specify it ( https://doc.x3dom.org/tutorials/lighting/gamma/ ). Castle
Game Engine uses linear workflow it too ( though by default only for
PhysicalMaterial, see https://castle-engine.io/color_space , but you
can make it used always, it should actually affect Material and
UnlitMaterial too ). See
https://github.com/michaliskambi/x3d-tests/wiki/Gamma-correction-in-X3D-and-glTF
, https://github.com/michaliskambi/x3d-tests/wiki/Gamma-Correction-in-Future-X3D
for my knowledge.

I was recommending a "cautious" approach in X3D 4.0 here, because just
saying "use linear workflow for everything, like glTF" *will* change
the look of the existing models. But I think in the end we are in
situation when this is not specified, and everyone does something a
bit different. All in all, we should just all switch to "use linear
workflow for everything, like glTF" .

So, I'm older and wiser now :), and today I'm all after changing X3D
spec to just say it. That is, simply "use linear workflow for
everything, like glTF". The more exact wording what it should mean are
on https://github.com/michaliskambi/x3d-tests/wiki/Gamma-correction-in-X3D-and-glTF
, https://github.com/michaliskambi/x3d-tests/wiki/Gamma-Correction-in-Future-X3D
, these were made looking at glTF and they just seem to make sense.

Regards,
Michalis

śr., 26 cze 2024 o 17:48 Holger Seelig <holger.seelig at yahoo.de> napisał(a):
>
> I have added SpecularGlossinessMaterial, as there are models on the internet that use it (sketchfab), so that these models can also be displayed. X3DOM also has a way to display this material. Furthermore, it is apparently not possible to convert this material with the associated textures by using PhysicalMaterial.
>
> I added UnlitMaterialExtension for now, because X3DOM also has an *unlit* field in PhysicalMaterial.
>
> https://doc.x3dom.org/developer/x3dom/nodeTypes/PhysicalMaterial.html
>
> An important aspect is also the sRGB workflow, which is specified in PhysicalMaterial, but is not mentioned in X3D (or are there texts about it).
>
> Best regards,
> Holger
>
> --
> Holger Seelig
> Leipzig, Germany
>
> holger.seelig at yahoo.de
> https://create3000.github.io/x_ite/
>
> Am 26.06.2024 um 14:54 schrieb Michalis Kamburelis <michalis.kambi at gmail.com>:
>
> Great news! I'm reading your node docs, excellent work in getting this
> specified and implemented!
>
> I have a plan to implement these material extensions in Castle Game
> Engine / Castle Model Viewer as well (
> https://castle-engine.io/roadmap#gltf_material_features ). Looks like
> you beat me to it with X_ITE, and it makes me very happy :)  (Also
> because it means I can look at your nodes and code and my task is much
> easier :) ).
>
> Some initial thoughts about the spec of new functionality:
>
> 1. Expressing functionality as "extensions" of PhysicalMaterial (I see
> you have "PhysicalMaterial.extensions", MFNode with
> X3DMaterialExtensionNode,
> https://create3000.github.io/x_ite/components/shape/physicalmaterial/
> ):
>
>    This is great solution, this expressed the intention nicely (this
> information is extra data, "extension", and without it things look
> worse but make sense).
>
>    I'm looking at this both from Castle Game Engine / Castle Model
> Viewer author perspective, also from the perspective of future X3D
> versions. A lot of your extensions, including the
> "PhysicalMaterial.extensions" field and nodes like
> SheenMaterialExtension, ClearcoatMaterialExtension could definitely be
> part of future X3D (4.1?) version.
>
> 2. Comments specifically about SpecularGlossinessMaterial (
> https://create3000.github.io/x_ite/components/x-ite/specularglossinessmaterial/
> ):
>
>    Note that KHR_materials_pbrSpecularGlossiness is deprecated, and
> the recommendation is to follow instead KHR_materials_specular which
> addresses a similar use-case. In Castle Game Engine / Castle Model
> Viewer we deliberately decided, for this reason, to not support
> KHR_materials_pbrSpecularGlossiness and just explain it to users (
> https://castle-engine.io/sketchfab ).
>
>    I of course understand it is a practical decision, if your users
> demand KHR_materials_pbrSpecularGlossiness then
> SpecularGlossinessMaterial makes sense. I'm just saying that this
> should probably not go to future X3D spec.
>
>    Just like Khronos recommends KHR_materials_specular over
> KHR_materials_pbrSpecularGlossiness, we should in X3D recommend
> SpecularMaterialExtension over SpecularGlossinessMaterial.
>
> 3. I see you added also UnlitMaterialExtension, can you expand why do
> you need it?
>
>    I know your approach is a bit more consistent with glTF, that has
> "physical material with KHR_materials_unlit".
>
>    That said, I deliberately deviated here for X3D 4.0, adding
> instead a separate node "UnlitMaterial". "UnlitMaterial" does feel
> more natural -- being unlit is, conceptually, not an extension of PBR
> lighting equations (or PBR specular, or Phong lighting equations...).
> Being unlit means you throw away the usual lighting equations, and
> just have very simple situation where resulting color is emissiveColor
> * optional emissiveTexture. This makes "UnlitMaterial" spec simple,
> this also sidesteps glTF question (that used to be ambiguous in older
> glTF spec version) of how to combine glTF base and emissive color in
> case of KHR_materials_unlit (because in X3D, we just have
> "UnlitMaterial" with "UnlitMaterial,emissiveColor" -- it's simpler),
> this also allows natural optimizations on the renderer side (unlit can
> use completely different set of simple shaders).
>
>    So ideally, I see "UnlitMaterial" as X3D-equivalent of
> "KHR_materials_unlit". If there is a need for UnlitMaterialExtension,
> I'm curious to know why, and can we avoid it, to keep X3D spec simple
> :)
>
> Many thanks for your work. This is great advancement for X3D! I
> absolutely recommend everyone on this list to click on Holger's links
> to demos and extensions, we absolutely should look at this
> functionality as potentially becoming available in other X3D browsers
> (I will definitely want to implement (subset of it) in Castle Game
> Engine / Castle Model Viewer) and in future X3D spec versions.
>
> Best regards,
> Michalis
>
>
> wt., 25 cze 2024 o 11:52 Holger Seelig via x3d-public
> <x3d-public at web3d.org> napisał(a):
>
>
> With the current release v10.0.1, all glTF material extensions are now available, i.e. when a glTF file is parsed, these extensions are automatically converted to X3D. There is now an X3D node for each glTF extension. These nodes can also be referenced directly in X3D files. Extensions for glTF materials are converted to the new X3DMaterialExtensionNode nodes, which can be used as a child of PhysicalMaterial node and the new SpecularGlossinessMaterial node. These material nodes now have a new field »extensions« for this purpose. The introduction of the »extensions« field has only a minimal impact and leads to the greatest possible compatibility.
>
> To get an idea of what a great difference these new material extensions make, check out our glTF Sample Viewer. Take some time and look through all the examples. I am sure you will be amazed.
>
> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/
>
> Here are three selected examples, but there are many more:
>
> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=AnisotropyBarnLamp
> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=DragonAttenuation
> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=MosquitoInAmber
> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=ToyCar
>
> Implemented glTF Extensions:
>
> All glTF extensions implemented with this version are listed below:
>
> X3DOneSidedMaterialNode
>
> * KHR_materials_pbrSpecularGlossiness implemented as SpecularGlossinessMaterial node.
>
> X3DMaterialExtensionNode
>
> * KHR_materials_anisotropy implemented as AnisotropyMaterialExtension node.
> * KHR_materials_clearcoat implemented as ClearcoatMaterialExtension node.
> * KHR_materials_dispersion implemented as DispersionMaterialExtension node.
> * KHR_materials_emissive_strength implemented as EmissiveStrengthMaterialExtension node.
> * KHR_materials_ior implemented as IORMaterialExtension node.
> * KHR_materials_iridescence implemented as IridescenceMaterialExtension node.
> * KHR_materials_sheen implemented as SheenMaterialExtension node.
> * KHR_materials_specular implemented as SpecularMaterialExtension node.
> * KHR_materials_transmission implemented as TransmissionMaterialExtension node.
> * KHR_materials_unlit implemented as UnlitMaterialExtension node.
> * KHR_materials_volume implemented as VolumeMaterialExtension node.
>
> Switch
>
> * KHR_materials_variants implemented as Switch node.
>
> These new nodes are initially available in the X_ITE component and documented here:
> https://create3000.github.io/x_ite/components/#x_ite
>
> Make X3D even better!
> Best regards,
> Holger
>
> --
> Holger Seelig
> Leipzig, Germany
>
> holger.seelig at yahoo.de
> https://create3000.github.io/x_ite/
>
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