Review MaterialX `namespaces`

[ashwinbhat]

The MaterialX specification allows for nodes that can be scoped in a namespace. MaterialX namespaces are most commonly used to define families of custom nodes (nodedefs), material libraries, or commonly-used network shaders or nodegraphs. The usage of the namespace node is in the form namespace:nodename

The rationale behind namespace was to allow DCCs to publish overridden nodes that have same names as stdlib nodes and include them in the data library so that DCC published nodes and stdlib nodes could coexist side by side to allow for interop of materials between DCCs.

Based on an informal survey, Autodesk is the only user of the namespaced nodes. It has be found that many implementations of MaterialX don't fully support MaterialX namespace. One of the main issues being the reason to process node names with : token. MateiralX namespace might become more easier to adopt if the namespace was just a prefix with _ token.

I'm not sure how USD handles MaterialX namespaced nodes when written to Sdr Shader Node so replacing the token might be easier.

[ashwinbhat]

@ld-kerley wanted your thought on this, does it align with what we discussed?

[ld-kerley]

Yes pretty much. The change from : to _ is really moving away from the additional namespace syntax in the specification of node names, and moving to a convention based approach where the namespace is just part of the actual name.

I would propose introducing validation to ensure that any node that declares a namespace attribute in its definition would be validated that its node attribute also started with the same prefix followed by an underscore.

We would still keep the namespace attribute for categorization purposes of the node definitions (think node creation menus in UI), but it would no longer need to be any sort of functional part of the core API, as its implementation would be realized directly from the concrete naming of the nodes.

I believe this is sufficient, as there is a desire that namespaces nodes do not fallback to their non-namespaces counterparts, and so we do not need to maintain a relationship between them.

[kwokcb]

For sanity checking I'd include:

• namespace id prepending on import, vs just reading in.
• what to use for nodedef references from namespaced implementations / graphs. Are they still namespaced ?