GLTFExporter: Merge occlusion, roughness and metalness textures

[mrdoob]

Related issue: #14940 #16325

Description

The code in this PR only checks if texture has already been merged (which solves the actual issue in #14940).
Should we add additional parameters as suggested in #14940 (comment)?

/cc @fernandojsg @donmccurdy @elalish

[mrdoob]

This will need some tweaks probably but it'll easier to understand when people start using it. Merging.

[donmccurdy]

This looks good to me!

I'd also be fine with omitting .aoMap from the merging. While glTF has other material textures that can be merged (e.g. thickness texture only uses r), roughness/metallic are the only textures that must be merged, excluding the spec/gloss workflow. I don't think GLTFExporter should be automatically merging anything except O/R/M.

We could probably also change this line to just use PNG, if we're moving away from RGBFormat:

three.js/examples/jsm/exporters/GLTFExporter.js

Line 1053 in 0815182

const mimeType = format === RGBAFormat ? 'image/png' : 'image/jpeg';

^does that seem okay @Mugen87 ?

[Mugen87]

Yes, that makes sense!

[donmccurdy]

Opened #23385.

[repalash]

Hello, in the buildOrmTexture function, a Texture.image is returned when the textures are same on line 698, and a Texture is returned at 759. This gives an error when they are equal because processTexture expects a Texture.

Also, in the case where occlusion is null and roughness == metalness, what is the need to recreate the texture then?

[mrdoob]

Hello, in the buildOrmTexture function, a Texture.image is returned when the textures are same on line 698, and a Texture is returned at 759. This gives an error when they are equal because processTexture expects a Texture.

#23463 fixed that.

Also, in the case where occlusion is null and roughness == metalness, what is the need to recreate the texture then?

Yes, that logic needs to be improved.

[repalash]

Thanks for your reply.
@mrdoob In the case where the same aoMap is applied to multiple objects, will it be serialized separately for each object or is this handled somewhere?

[mrdoob]

@mrdoob In the case where the same aoMap is applied to multiple objects, will it be serialized separately for each object or is this handled somewhere?

Oh, I was not aware that could happen. Does that also happen with metalnessMap and/or roughnessMap?

[repalash]

Does that also happen with metalnessMap and/or roughnessMap?

Generally not. aoMaps use uv2, so it's possible to pack occlusion for multiple objects or even the complete scene in a single texture.

[mrdoob]

@repalash Fixed #23616