Supporting occlusionTexture in Blender 2.8

I’m struggling to decide how to handle AO (occlusionTexture) in Blender 2.8. Overall the move to Principled BSDF is great, but it has no AO input.

One option would be to adopt a convention such that a disconnected Image Texture node, used in the same material as a Principled BSDF node, will automatically be treated as AO if (a) the node is named “AO”, or (b) the node uses a texture suffixed with “_ao”. Presumably the Importer and Exporter could use the same convention.

Other ideas? In general I don’t want to hack glTF features into this exporter when Blender doesn’t support them, but AO is a pretty critical feature…

[donmccurdy]

Are glTF 2.0 materials fundamentally so different from Principled BSDF, other than AO? If there were significant inconsistencies in the materials such that Blender Principled BSDF materials cannot accurately-enough match the glTF 2.0 spec I could be convinced that glTF-specific nodes would be a worthwhile addition. But otherwise, I’m much more interested in exporting native Blender features to native glTF than in asking Blender artists to use new format-specific materials, when Principled BSDF is already new, well-supported, and a rather good fit for glTF…

The problem as I see it is that Blender has very nicely-designed workflow for baking AO, and no mechanism at all for using or exporting that AO, except to export the image on its own. If we’re going to ask a favor of the Blender developers, I’d prefer to ask them to (a) allow AO input to Principled BSDF, or (b) provide some other mechanism of identifying a texture as a source of baked AO.

[emackey]

@ogierm Thanks. We considered that node, but it’s using the spec/gloss PBR workflow, which is an alternative to what now appears to be the more popular PBR workflow of metal/rough. We needed a solution for metal/rough PBR in Blender 2.80, and ultimately we went with a custom node for it.

The result is documented here in Blender Manual. Essentially a custom node group called glTF Settings is created, with an Occlusion input on it. The glTF format expects the red channel to contain the occlusion map.

The glTF importer will create a custom node if one doesn’t already exist by this name, when importing an occlusion map. Here’s a link to the Python code that does it.