Supply an Image-based Light file

At TPAC we agreed that specifying an image-based light (IBL) is an important component of a V1 implementation and specification. In addition to the specific name (environment map, lighting environment, IBL etc), there is the matter of structural representation, i.e. how it resides within the tree structure of the <model> markup itself.

I don't have a strong opinion but some candidates I can see are:

1. An attribute on the <model> tag:

<model environment-map="warehouse.hdr">
  <source src="shelf.usdz"/>
</model>

3. An attribute on the <source> tag

<model>
  <source src="shelf.usdz" environment-map="warehouse.hdr"  />
</model>

4. An independent tag inside the <model> block

<model>
  <environment-map src="warehouse.hdr" />
  <source src="shelf.usdz"/>
</model>

Or some more complex nesting of <source> elements within such a tag. It should be simple, but my expectation is that the role and complexity of <model> will increase over time, so something expressive enough to meet some obvious needs would be useful.

The issue contains the candidate HTML structures for representing an image-based light but names no implementation files or tests. Start by reviewing the proposed , , and relationships and the unresolved naming and nesting questions. Done means the representation and its role in the V1 specification are agreed and documented.