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Posted on behalf of Khronos' 3D Formats Working Group - owners of
the glTF specification.
<p>This message addresses the proposed use of glTF in X3D V4.0,
specifically the means for lighting glTF V2.0 models.</p>
<p>glTF V2.0 primarily uses materials that are rendered using
physically-based rendering (<a
href="https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials"
target="_blank" moz-do-not-send="true">https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials</a>)
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. </p>
<p>To describe and illustrate lighting issues I wrote a blog post
"Importance of Environment Lights" (<a
class="moz-txt-link-freetext"
href="https://realism.com/blog/importance-environment-lights"
moz-do-not-send="true">https://realism.com/blog/importance-environment-lights</a>)
with an accompanying interactive demonstration "PBR Model &
Lighting Inspector" (<a class="moz-txt-link-freetext"
href="https://realism.com/Examples/pbr-lighting/"
moz-do-not-send="true">https://realism.com/Examples/pbr-lighting/</a>).
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
<a class="moz-txt-link-freetext" href="http://realism.com/Examples/pbr-lighting/FlightHelmet-3Points-IBL.png">http://realism.com/Examples/pbr-lighting/FlightHelmet-3Points-IBL.png</a><br>
</p>
<p>In the review copy of the X3D V4 specification, section 17 (<a
class="moz-txt-link-freetext"
href="https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/lighting.html"
moz-do-not-send="true">https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/lighting.html</a>)
describes the lighting component. There is no discussion of image
based lighting. Section 9.4.2 Inline (<a
class="moz-txt-link-freetext"
href="https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/networking.html#Inline"
moz-do-not-send="true">https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD3/Part01/components/networking.html#Inline</a>)
discusses the importing of glTF models into the X3D scene. There
is no discussion of lighting there.</p>
<p>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. </p>
<div class="moz-signature">-- <br>
<font class="tahoma,arial,helvetica san serif" color="#333366"> <font
size="+1"><b>Leonard Daly</b></font><br>
3D Systems & Cloud Consultant<br>
LA ACM SIGGRAPH Past Chair<br>
President, Daly Realism - <i>Creating the Future</i> </font></div>
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