[x3d-public] Tony’s video; null Material considerations

Fri Aug 2 06:41:25 PDT 2024

Our X3D Architecture specification is the authoritative reference for what is supposed to happen.

We are careful to define expected functional results wherever possible.  This guides both implementations of X3D and authors as well.  A Shape node having a null material field is a fairly common occurrence, particularly when constructing models.

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Extensible 3D (X3D) v4.0 Part 1: Architecture and base components, 12 Shape component, 12.4.2 Appearance
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https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#Appearance

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The material field, if specified, shall contain a Material<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#Material>, PhysicalMaterial<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#PhysicalMaterial>, TwoSidedMaterial (deprecated)<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#TwoSidedMaterial> or UnlitMaterial<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#UnlitMaterial> node. If the material field is NULL or unspecified, lighting is off (all lights are ignored during rendering of the object that references this Appearance) and the unlit object colour is (1, 1, 1). Details of the X3D lighting model are in 17 Lighting component<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/lighting.html#PART8>.
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The backMaterial field, if specified, shall contain a Material<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#Material>, PhysicalMaterial<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#PhysicalMaterial> or UnlitMaterial<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#UnlitMaterial> node. It is only allowed to define a backMaterial if the material is also defined (not NULL). The node type provided to backMaterial (if any) shall match the node type provided to material. This field allows to render back faces with a different material parameters than the front faces. The meaning and all constraints of this field are explained in the section Two-sided materials<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/shape.html#TwoSidedMaterials>.

We are careful to define default results for missing fields whenever practical.  If the detection or correction of such edge cases remains ambiguous or poses an undesirable computational burden on browsers, then the specification typically states that expected results are undefined (meaning author and user beware, a browser can handle it as they see fit).

Clearly, guidance to authors and  validation tools can help complement the specification.

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X3D Tooltips, Appearance, material
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https://www.web3d.org/x3d/tooltips/X3dTooltips.html#Appearance.material
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[material accessType inputOutput<https://www.web3d.org/x3d/tooltips/X3dTooltips.html#accessType>, type SFNode<https://www.web3d.org/x3d/tooltips/X3dTooltips.html#SFNode> singleton, NULL node] [X3DMaterialNode<https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/nodeIndex.html#X3DMaterialNode>]
Single contained Material node that can specify visual attributes for lighting response (color types, transparency, etc.) applied to corresponding geometry.
Warning: if material is NULL or unspecified, lighting is off (all lights ignored) for this Shape and unlit object color is (1, 1, 1).

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X3D Resources, Quality Assurance (QA)
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https://www.web3d.org/x3d/content/examples/X3dResources.html#QualityAssurance
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X3D Quality Assurance (QA) identifies errors and warnings in order to make X3D scene content more portable and reliable. Improved Quality Assurance (QA) helps achieve intended results in X3D scenes and metadata.
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This is important. providing high confidence that when 3D modeling errors occur, they can be detected and then corrected. As a result, X3D models can run in many different file formats and programming languages, equivalently and correctly.

If anyone finds an apparent "hole" in X3D architecture coverage, or contrary implementations, then such reports are always appreciated.

Have fun with X3D4!   🙂

all the best, Don

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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

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