If you want to import a model using pure PBR textures (metallic, roughness, AO and emissive),

New MTL and texture samples for previews and testing can be found in "mod/resource/entity/misc/materials/pbr" folder.

When both

• {height "xxx"}
  
• {lightmap "xxx"}

exist in mtl, shader will activate pure PBR mapping mode.

Among them:
The height entry, originally used for parallax mapping of ground texture, is now used to index indirect specular cube map.
The lightmap entry, originally used for pre-baked lightmap, is now used to store a four-channel mask texture.

In addition, additional parameters=
{parallax_scale 10000}: is used to enable automatic Phong to PBR conversion including indirect specular reflections.
{full_specular}: is used to enable support for emssive texture in pure PBR mode.

The indirect specular map is a texture that stores pre-filtered environment light information. We sample it to calculate the indirect specular reflections in PBR rendering.
The pre-made indirect specular map is stored in "mod/resource/texture/common/envmap".
This is not a mipmapped environment map! Textures stored in mipmaps are calculated using a special method, which is completely different from pure mipmaps.
These textures are obtained from Poly Haven under a CC0 license. Thanks to artist and website for their generosity!

You can simply access our pre-made indirect specular map using {height "$/envmap/env"}.

After enabling pure PBR texture mode with changes in section 3.1. Textures in MTL will be mapped to PBR according to following logic:
*Note: rgba= rad,green,blue,alpha= red,green,blue,alpha four texture channels

I will (sooooon!) be writing about this on my website and github.