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OBJ_MTL_PBR.md

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OBJ Material Entries (MTL file)

Keep in mind that this repository is using the following customized OBJ related three.js files: OBJ Loader, MTL Loader and OBJ Exporter.

These files have been synchronized to work with each other and process all custom PBR entries found in the MTL file, as listed further below, aiming at providing the GLTF alike functionality in the OBJ Viewer by taking advantage of the THREE.MeshPhysicalMaterial and a modified GLTF Loader.

All the entries have been set as such so they are compatible with three.js as well as the assimp library being used in this repository.

Most, if not all, of the available viewers do include the OBJ Exporter, thus can try to export their models to OBJ + MTL + textures format with whatever limitations there might be (like animations for example).

As for the textures, any of the following image formats should work with OBJ models when specified in the MTL file:

  • BMP, DDS, GIF, JPEG, PNG, TGA, WEBP

This document would represent a summary of PBR entries that can be found in the exported MTL file, with mentioning of some possibly utilized standard entries whose description can be seen online here.

Standard Entries:

  • Ka, Kd, Ke, Ks, Ns, Ni, Tr, Tf, d, illum, -bm, -s, -o
  • map_Ka, map_Kd, map_Ke, map_Ks, bump, map_bump, map_d, norm, disp

PBR Entries with associated textures (maps):

  • a - alphaTest (alphaCutoff)

  • s - material side

  • Pe - emissive intensity

  • Prf - reflectivity

  • Pac / Pad - attenuationColor / attenuationDistance

  • Pm - metalness

    • map_Pm - metalnessMap

  • Pr - roughness

    • map_Pr - roughnessMap

  • map_Px - replaces both map_Pm and map_Pr when they are identical

  • Pa/ Par - anisotropy (strength) / anisotropyRotation

    • map_Pa - anisotropyMap

  • Pi / Pii - iridescence / iridescenceIOR

    • map_Pi - iridescenceMap

  • Pitx / Pity - iridescenceThicknessMinimum / iridescenceThicknessMaximum (aka iridescenceThicknessRange[x, y] in three.js)

    • map_Pit - iridescenceThicknessMap

  • Pcc / Pcr - clearcoat / clearcoatRoughness

    • map_Pcc - clearcoatMap
    • map_Pcn - clearcoatNormalMap
    • map_Pcr - clearcoatRoughnessMap

  • Ps / Psr - sheenColor / sheenRoughness

    • map_Psc - sheenColorMap
    • map_Psr - sheenRoughnessMap`

  • Pth - thickness

    • map_Pth - thicknessMap

  • Ptr - transmission

    • map_Ptr - transmissionMap

  • Psp - specularColor

    • map_Psp - specularColorMap

  • Psi - specularIntensity

    • map_Psi - specularIntensityMap

Entries currently not compatible with the assimp library but working fine in the OBJ + MTL Viewer:

  • -c - texture center of rotation
  • -r - texture rotation value
  • -w - texture wrapping parameters (wrapS and wrapT)
  • Pns - normalScale
  • Pcn - clearcoatNormalScale
  • Pdt - depthTest
  • Pli - lightMapIntensity
  • disp_b - displacementBias
  • disp_s - displacementScale
  • Pbr_ps - sheen (layer intensity)
  • Pbr_pl_map - lightMap

Remember that other OBJ + MTL viewers will probably NOT be able to interpret most of these PBR entries.

Testing

This can be tested by using the Khronos Group glTF v2.0 examples and following these instructions:

  • Use my GLTF Viewer to load one of those example GLTF files via the viewer's URL option, here is an example url:
    • https://github.com/KhronosGroup/glTF-Sample-Models/blob/master/2.0/IridescenceMetallicSpheres/glTF/IridescenceMetallicSpheres.gltf
  • Use the viewer's OBJ export option to get OBJ + MTL + textures in a zip file
  • Extract all the files to a folder on your device (this needs to be done since my viewers currently don't support loading of zip files)
  • Examine the MTL file to see what the entries look like and then do the following:
    • Use my OBJ Viewer or ASSIMP Viewer and select its Browse option to load these extracted files all at once - your device will have to allow loading local files
  • After the model is loaded then make sure to check the Eq box in the viewer to get the environment texture / lights

Not all the examples will work properly but lots of them do.

Credits

Trademarks

  • Any and all trademarks, either directly or indirectly mentioned, belong to their respective owners.