Converting SpecularGlossiness back to MetallicRoughness

[vpenades]

A while ago, I noticed SpecularGlossiness has been archived.

Also, more material extensions have been introduced, like Specular and IOR

I was wondering if it's possible to easily transfer the properties of SpecularGlossiness back to MetallicRoughness with the help of the newer extension.

Or is it a more complex process, which would require to do texture conversions?

Is there an official approach on how to deal with MetallicRoughness on models in the wild, now that it's been archived?

[donmccurdy]

Some resources:

• KHR_materials_specular / Conversions
• Discussion: KHR_materials_specular #1719 (comment)
• Implementation in glTF Transform: https://github.com/donmccurdy/glTF-Transform/blob/fad253d2925056f62b828137d5148d6a11c72e39/packages/functions/src/metal-rough.ts#L49-L127

It is necessary to either rewrite textures ,probably an offline process, or wrap textures in an expression – e.g. using a shader graph or custom GLSL containing the texture lookup as input to a PBR surface definition.

For three.js users we've encouraged doing the conversion offline, as the texture rewrites are a bit slow for runtime.

npm i --global @gltf-transform/cli

gltf-transform metalrough in.glb out.glb

[vpenades]

ouch!, I hoped there would be some easy conversion path, so I could get rid of the extension on load.

Given the conversion is non trivial, I guess I'll have to keep the extension around for backwards compatibility.

Thanks!