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OpenUSD Exchange Samples: createReferences

This sample demonstrates how to open/create a stage with key metadata and create a reference and payload using the OpenUSD Exchange SDK.

References are primarily used to compose smaller units of scene description into larger scenes. Payloads are a special kind of Reference that can be unloaded. Overs may be applied to these reference prims to override attributes.

When creating the component stage the sample uses a pattern that's different than simply creating a stage on disk and modifying it. The createComponentStage() function intentionally creates a new stage in memory, sets key metadata, adds prims to it, then exports it using OpenUSD Exchange's exportLayer() function. This is useful when generating USD data to prevent invalid or incomplete USD files on disk in the case of a failure.

  • UsdStage::CreateInMemory()
  • usdex::core::configureStage()
  • usdex::core::exportLayer()

This sample abuses mesh duplication by creating 8 mesh cubes in the component stage. A future optimization could use internal references or even scenegraph instances.

Note that OpenUSD Exchange doesn't currently have any functions for authoring references or payloads, so all of that functionality within the sample is accomplished with only the OpenUSD API.

USD Modules

The Gf, Sdf, Usd, and UsdGeom modules are used.

OpenUSD Exchange SDK functions

  • configureStage()
  • createStage()
  • definePolyMesh()
  • exportLayer()
  • getValidChildNames()
  • saveStage()
  • Vec3fPrimvarData()

Languages

This sample is implemented in both C++ and Python. To run:

  • [./]run.[bat, sh] createReferences
  • [./]python.[bat, sh] source/createReferences/createReferences.py

Hardcoded items

  • If a stage is created, it will have a default prim named "World", Y-up axis, 1 cm linear units
  • A new "component" stage is created that represents a prop, or component. It contains a 2x2x2 grouping of mesh cubes
  • The new "component" stage is then used in separate reference and payload prim
  • The reference prim gets a scale override on the last mesh prim in the component
  • The payload prim gets a display color override on the last mesh prim in the component

Command Line Arguments

Usage:
  createReferences [OPTION...]

  -a, --usda          Output a text stage rather than binary
  -h, --help          Print usage
  -p, --path arg      Alternate destination stage path (default: c:/Users/username/AppData/Local/Temp/usdex/sample.usdc)