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Maya Reference Edit Router Documentation

The Maya USD plugin supports hosting a Maya reference inside the USD scene. This Maya reference can be edited as Maya data and then cached as USD prims. The caching process supports customization of its behaviour, even a full replacement of its logic through an edit router.

This document outlines the API of this edit router and what the default implementation does.

Edit Router Generalities

The edit router is a callback that receives information in a USD VtDictionary and fills another VtDictionary with information about what work it did.

The interface to declare and register an edit router is found in the file lib\mayaUsd\utils\editRouter.h. It declares the EditRouter class itself and functions to register and retrieve an edit router. The edit router is registered and retrieved by name.

Maya Reference Edit Router

The Maya Reference edit router is named "mayaReferencePush". The default implementation found in the file lib\mayaUsd\utils\editRouter.cpp as the function named cacheMayaReference does the following:

  • Extract all necessary inputs from the input VtDictionary.
  • Validate the path of the Maya Reference that was edited.
  • Validate the destination layer and destination prim.
  • Determine the file format of the USD cache.
  • Export the edited Maya data into a USD layer, the USD cache.
  • Copy the transform of the root of the Maya data into the Maya Reference.
  • Refer to the USD cache either as a reference or payload, optionally in a variant.
  • Fill the output VtDictionary with information about the layer and prim.

We will go into more details about these steps in the following sections.

Maya Reference Edit Router Inputs

The input information received by the Maya Reference edit router are:

  • "prim" (std::string): the SdfPath of the USD Maya Reference that was edited.
  • "defaultUSDFormat" (std::string): the USD file format used to create the cache.
  • "rn_layer" (std::string): the absolute file path to the cache. A layer will be created there.
  • "rn_relativePath" (int): if the file path should be converted to be relative to the layer containing the reference. 0 or 1.
  • "rn_primName" (std::string): the name of the root prim of the cache.
  • "rn_listEditType" (std::string): how the reference is added: "Append" or "Prepend".
  • "rn_payloadOrReference" (std::string): type of ref: "Reference" or "Payload".
  • "rn_defineInVariant" (int): if the cache is in a variant. 0 or 1.
  • "rn_variantSetName" (std::string): name of the variant set if in a variant.
  • "rn_variantName" (std::string): name of the variant in the set, if in a variant.
  • "src_stage" (UsdStageRefPtr): the source UsdStage to copy the transform.
  • "src_layer" (SdfLayerRefPtr): the source SdfLayer to copy the transform.
  • "src_path" (SdfPath): the source SdfPath to copy the transform.
  • "dst_stage" (UsdStageRefPtr): the destination UsdStage to copy the transform.
  • "dst_layer" (SdfLayerRefPtr): the destination SdfLayer to copy the transform.
  • "dst_path" (SdfPath): the destination SdfPath to copy the transform.

The last six inputs correspond to the parameters received by the Maya Reference updater pushCopySpecs function. That is the function that is calling the edit router.

Validation and Export

The Maya Reference default edit router validates various inputs to verify that the Maya Reference exists and was edited. It then exports the Maya scene nodes of the Maya Reference file to a USD layer file. That layer file will be used as the USD cache representing the contents of the Maya Reference.

Copy the Transform

To support that the user might have moved the root of the Maya Reference when editing as Maya data, the transform of this root is copied to the USD Maya Reference. This preserve the position of the data.

Create the Cache Prim

The USD cache must be referenced in the USD stage. The edit router creates a reference or payload, possibly in a variant, inside a USD prim. Remember that the path to that prim was given in "rn_primName".

Fill the Output VtDictionary

The output VtDictionary is filled with the following information:

  • "layer" (std::string): the identifier of the cache layer, will be equal to "rn_layer".
  • "save_layer" (std::string): "yes" if the layer should be saved. (Calling Save on it.)
  • "path" (std::string): the SdfPath to the prim that contains the cache.