Adding example materials

[AntonPalmqvist]

Here's a collection of example materials, in .mtlx format, that cover most of the parameters found in the OpenPBR specification, as suggested in this Slack thread: https://academysoftwarefdn.slack.com/archives/C06365EAQMP/p1698709666974279

• Any parameters that would’ve been the same as the default have been omitted, to keep the files as minimal as possible, with potential loss of clarity in some cases. Let me know if there are any concerns with this.
• Scene unit for the test renders was set to centimeters. This brings up something I find a bit confusing, why the Subsurface Radius unit isn’t specified in the mtlx file, when the goal is to unify material parameters across applications? Subsurface materials will look different depending on the users scene units. Why is the unit not specified, as it is with Thin Film Thickness, and Emission Luminance?
• Tests were rendered using aiOpenPBRSurface in Arnold 7.2.5.0 Beta 60, kindly provided by @portsmouth
• transmission_dispersion_abbe_number and transmission_dispersion_scale from the white paper are not yet in the reference implementation. Do we want to wait with them for the Glass material, or should I keep them, for future compatibility? They are functional in Arnold at least.
• For the above reason, all materials except Glass are confirmed working in MaterialX Viewer, using the OpenPBR reference implementation.
• I added the default material as well. Let me know if it doesn't belong here.
• All materials are thoroughly researched to be as physically accurate as possible

Brushed Aluminum

<input name="base_color" type="color3" value="0.912, 0.914, 0.920" />
<input name="base_metalness" type="float" value="1.0" />
<input name="specular_color" type="color3" value="0.970, 0.979, 0.988" />
<input name="specular_roughness" type="float" value="0.2" />
<input name="specular_anisotropy" type="float" value="0.9" />
<input name="specular_rotation" type="float" value="0.25" />

Car Paint

<input name="base_color" type="color3" value="0.1, 0.6, 0.9" />
<input name="specular_ior" type="float" value="1.6" />
<input name="specular_roughness" type="float" value="0.3" />
<input name="coat_weight" type="float" value="1" />
<input name="coat_roughness" type="float" value="0.02" />
<input name="coat_ior" type="float" value="1.6" />

Glass

<input name="specular_roughness" type="float" value="0.0" />
<input name="specular_ior" type="float" value="1.52" />
<input name="transmission_weight" type="float" value="1.0" />
<input name="transmission_dispersion_abbe_number" type="float" value="64" />
<input name="transmission_dispersion_scale" type="float" value="1.0" />

Honey

<input name="specular_roughness" type="float" value="0.0" />
<input name="specular_ior" type="float" value="1.504" />
<input name="transmission_weight" type="float" value="1.0" />
<input name="transmission_color" type="color3" value="0.83, 0.4, 0.04" />
<input name="transmission_depth" type="float" value="2" />
<input name="transmission_scatter" type="color3" value="0.9, 0.9, 0.9" />

Ketchup

<input name="base_color" type="color3" value="0.164, 0.006, 0.002" />
<input name="specular_roughness" type="float" value="0" />
<input name="specular_ior" type="float" value="1.3" />
<input name="subsurface_weight" type="float" value="1.0" />
<input name="subsurface_color" type="color3" value="0.164, 0.006, 0.002" />
<input name="subsurface_radius_scale" type="color3" value="0.476, 0.058, 0.039" />

Light Bulb

<input name="emission_color" type="color3" value="1.000, 0.415, 0.099" />
<input name="emission_luminance" type="float" value="10000" />

Pearl

<input name="base_color" type="color3" value="0.8, 0.75, 0.7" />
<input name="specular_roughness" type="float" value="0.35" />
<input name="specular_ior" type="float" value="1.5" />
<input name="subsurface_weight" type="float" value="1.0" />
<input name="subsurface_color" type="color3" value="0.8, 0.75, 0.7" />
<input name="subsurface_radius_scale" type="color3" value="0.3, 0.5, 0.3" />
<input name="coat_weight" type="float" value="1" />
<input name="coat_roughness" type="float" value="0.15" />
<input name="coat_ior" type="float" value="1.68" />
<input name="thin_film_thickness" type="float" value="420" />
<input name="thin_film_ior" type="float" value="2" />

Soap Bubble

<input name="specular_roughness" type="float" value="0" />
<input name="specular_ior" type="float" value="1.0" />
<input name="transmission_weight" type="float" value="1.0" />
<input name="thin_film_thickness" type="float" value="500" />
<input name="thin_film_ior" type="float" value="1.4" />
<input name="geometry_thin_walled" type="boolean" value="true" />

Velvet

<input name="base_color" type="color3" value="0.02, 0.02, 0.02" />
<input name="specular_roughness" type="float" value="0.8" />
<input name="fuzz_weight" type="float" value="1" />
<input name="fuzz_color" type="color3" value="0.4, 0.4, 0.4" />
<input name="fuzz_roughness" type="float" value="0.2" />

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: AntonPalmqvist / name: Anton Palmqvist (239f8aa)
• ✅ login: jstone-lucasfilm / name: Jonathan Stone (d280b95)

[meshula]

these demonstrate the material's versatility nicely!

[jstone-lucasfilm]

Thanks for this great initial work, @AntonPalmqvist, and I'll just highlight these renders of the first three examples in the MaterialX render test suite, comparing their visual output in GLSL and OSL:

[AntonPalmqvist]

Feel free to merge whenever you feel ready, as I don't have write access to this repository.

[jstone-lucasfilm]

Thanks @AntonPalmqvist, and I'd agree that we should move forward and merge this work, which we can continue to build upon as we approach an OpenPBR 1.0 release.

[virtualzavie]

This is a fantastic idea. Thank you @AntonPalmqvist.