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OpenUSD Exchange Samples: createSkeleton

This sample demonstrates how to open/create a stage with key metadata and create skeletal mesh with an animation using the OpenUSD Exchange SDK.

The OpenUSD documentation for using the UsdSkel API is very thorough and should be used as both an introduction and reference. This sample creates a UsdSkelRoot parent prim with a UsdSkelAnimation bound to a UsdSkelSkeleton. Then a UsdSkelBindingAPI is applied to a UsdGeomMesh and the skeleton joint indices and weights are applied. The result is a square "arm" with shoulder (j0), elbow (j1), and wrist(j2) joints. The sample animation contains timesamples for the elbow and wrist joints.

A diagram representing the vertices and joints in the skeletal mesh:

2---j2---3
|   |    |
1---j1---4
|   |    |
0---j0---5

USD Modules

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

OpenUSD Exchange SDK functions

  • createStage()
  • definePolyMesh()
  • getValidChildNames()
  • saveStage()
  • setLocalTransform()
  • Vec3fPrimvarData()

Languages

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

  • [./]run.[bat, sh] createSkeleton
  • python[3] source/python/createSkeleton.py

Hardcoded items

  • If a stage is created, it will have a default prim named "World", Y-up axis, 1 cm linear units
  • A 1 meter skinned mesh is created with an associated skeleton and animation under a SkelRoot called "skelRootGroup"
  • Stage metadata is set at 24 timecodes per second, end timecode is set to 48 to make a 2 second animation

Command Line Arguments

Usage:
  createSkeleton [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)