Add API to allow input reordering on node graphs

[kwokcb]

Workflow Motivation

In order for users to specify interface ordering for node graphs they need to re-order the storage order of child inputs. Additionally, when creating new definitions (nodedef) they may which to specify the ordering of child inputs as part of definition publishing.

Proposal

Provide a simple atomic API to allow for inputs on node graphs to be re-ordered without affecting non-input child ordering.
The proposed API name is: NodeGraph::setInputOrdering() where a list all input names specifies the desired ordering.

[meshula]

Would this need some work on the usd side to capture the ordering somewhere? Perhaps UsdUI or something?

[kwokcb]

Hi @meshula,
This doesn't add any additional metadata to specify the UI ordering. It's just a way to re-order inputs on a nodegraph.

Does USD already have separate specifiers for UI ordering (e.g. is this this stacking order in UsdUITokenType ?
I'm guessing from your comment it does not, but If it does then it might be worthwhile to look at the equivalent support for MaterialX as a related but separate change.

[meshula]

Stacking order relates to the screen depth of nodes (this node should appear over that node if they overlap).

Reading the mx code, I see that childOrder is not a user imposed reordering of the nodes, but rather encodes a construction order. Since hdMtlx iterates that list, there's no reordering hints necessary at that end as order is implicit in that loop.

✅ #does-it-usd