[x3d-public] Comment of X3D V4, glTF, and Lighting

[Michalis Kamburelis]

I believe Don Brutzman created a related Mantis issue about it
recently, he will likely post a link.

Image-based lighting (in the form of "EnvironmentLight" node) is
indeed something I planned, but ultimately didn't find the time to
finalize for X3D 4.0. But I still very much want to have it. The only
question is "when" (for X3D 4.0 or postpone to X3D 4.1) and this
practically depends on me too (to find time to finish the work I
describe below).

My plan about it is on
https://github.com/michaliskambi/x3d-tests/wiki/Image-Based-Lighting-(EnvironmentLight-node)
. There is an initial node spec, and Castle Game Engine even
implements it and we have testcases in
https://github.com/michaliskambi/x3d-tests/tree/master/pbr/environment_light
.

That said, there are still important questions for the design, and
important holes in my current implementation.

One of the goals is of course to make it compatible with related glTF
extension, https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_lights_image_based
.

I do agree it is an important feature, we definitely want to have it
at one point in X3D. I do not think it is a blocker though -- punctual
light sources (point, spot, directional) work with physical (and
non-physical) materials as well, in both X3D and glTF.

Regards,
Michalis


pt., 15 sty 2021 o 20:47 Leonard Daly <Leonard.Daly at realism.com> napisał(a):
>
> Posted on behalf of Khronos' 3D Formats Working Group - owners of the glTF specification.
>
> This message addresses the proposed use of glTF in X3D V4.0, specifically the means for lighting glTF V2.0 models.
>
> glTF V2.0 primarily uses materials that are rendered using physically-based rendering (https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials) with the metallic-roughness model. Because of the potential for highly reflective materials, it is beneficial to simulate real-world lighting for the rendering to approximate what the eye would see with a real-world object. This simulation is typically done with image-based lighting (IBL). While IBL does not cover all situations (e.g., internal lighting in a model of a lamp), it does provide an excellent approximation of ambient and environment light source when there is a single model and the model/light interaction is not time dependent.
>
> To describe and illustrate lighting issues I wrote a blog post "Importance of Environment Lights" (https://realism.com/blog/importance-environment-lights) with an accompanying interactive demonstration "PBR Model & Lighting Inspector" (https://realism.com/Examples/pbr-lighting/). The tool allows the user to pick a model, image lighting, and environment image (Background node in X3D) and shows the real-time lighting effects. The tool uses Google's <model-viewer> custom HTML tag. Note that the lighting available in the demo is not indicative real-world lighting, but is simpler to illustrate the point. Another 3D Formats WG member (Eric Chadwick from Wayfair) rendered a different model (Fight Helmet) using closer to studio lighting and 3 Point lights (separate renders). The comparison image is at http://realism.com/Examples/pbr-lighting/FlightHelmet-3Points-IBL.png
>
> In the review copy of the X3D V4 specification, section 17 (https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/lighting.html) describes the lighting component. There is no discussion of image based lighting. Section 9.4.2 Inline (https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/networking.html#Inline) discusses the importing of glTF models into the X3D scene. There is no discussion of lighting there.
>
> Not including IBL with glTF model rendering creates appearances that are inaccurate and do not show off the capabilities of glTF materials and appearance. The 3D Formats Working Group highly recommends including IBL capability when rendering glTF models.
>
> --
> Leonard Daly
> 3D Systems & Cloud Consultant
> LA ACM SIGGRAPH Past Chair
> President, Daly Realism - Creating the Future
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