X3D and glTF Model Differencing for Conversions, Comparison and Conformance Testing
- Rick Lentz – Naval Postgraduate School (NPS)
- Don Brutzman – Naval Postgraduate School (NPS)
- Michalis Kamburelis – Castle Game Engine
CATEGORY. Long Paper
KEYWORDS. X3D, glTF, Differencing, Conformance, VRML
ABSTRACT. The Extensible 3D (X3D) Graphics Architecture ISO/IEC 19775-1 International Standard version 4.0 is a major release that includes full support for version 2.0 of glTF, a standard file format for 3D scenes and models supporting geometry, appearance, a scene-graph hierarchical structure and model animation. X3D4 authors have the option to Inline (i.e. load) glTF models directly or else utilize native X3D nodes to create corresponding 3D models. Physically based rendering (PBR) and non-photorealistic rendering (NPR) and lighting are both important additions to the X3D4 rendering model. These lighting models are compatible and can coexist in real time with legacy X3D3 and VRML97 models (which utilize classic Phong shading and texturing) either independently or composed together into a single scene. The X3D4 approach to representing glTF 2.0 characteristics is defined in complete detail in order to be functionally identical, thus having the potential to achieve the greatest possible interoperability of 3D models across the Web. Nevertheless, a persistent problem remains in that glTF renderers do not always appear to produce visually identical results. Best practices for mapping glTF structures to X3D4 nodes are emerging to facilitate consistent conversion. This paper describes a variety of techniques to help confirm rendering consistency of X3D4 players, both when loading glTF assets and when representing native X3D4 conversions. Development of an X3D4 conformance archive corresponding to the publicly available glTF examples archive is expected to reinforce development of visually correct software renders capable of identical X3D4 and glTF presentation.