Overview.md

• value proposition
  • seamless interchage between DCC
  • distributed workflow
  • allow users to define high level semantics
  • provide superior read performance
  • provide superior tools for debugging and inspecting scenes
• What is USD?
  • A set of file formats, ascii and binary(named crate)
  • A closed grammar of composition operators
  • A set of consistent, high performance C++/Python libraries for interacting with USD assets
  • A set of tools for understanding and modifying USD assets
• USD Terminology
  • Stage is made up of layers, connected by composition arcs
  • Layers are composed of prims and properties, and also contain composition arcs
    • Objects=Prims+Properties, objects in USD are identified by scene paths(sdf)
      • Prims: named conteainer of data(specifier+optional typename)
        • Typenames are defined in schemas, which has semantic meaning
      • Properties are composed of attributes or relationships
        • Attribute values can be time sampled and/or default valued.
        • Relationships are pointers to other prims
          • a mesh points to another material system
        • Metadata can be authored on prims and properties, and can not be time varying
  • Composition arcs
    • Operators for combining individual units of scene description
      • Local Values + Sublayers -> Inherits -> Variant Sets -> References -> Payloads -> Specializes
    • Sublayers defined as a list of asset paths pointing to other layers
      • Work as photoshop layers, from top to down
    • References
      • Used for composing smaller units of scene description together
      • One of the most commonly used composition arcs in practice
    • Payloads
      • Very similar to references
      • Not eagerly loaded by composition
      • Can be loaded after initial composition
    • Variant sets
      • Allow a distinct set of options, from which downstream clients can select
      • Can be considered like a switchable reference
• Extendability
  • USD provides many points at which you can extend the system to fit your pipeline:
    • Asset Resolution Plugins, File Format Plugins, Schemas, Usdview Plugins
  • Asset Resolution Plugins
    • translate file refereces to real paths
  • File format plugins
    • usd allows users to define file format plugins, whihc enables a scene to read geometry in from foreign sources
  • Schemas
    • These allow users to define higher level concepts on top of prims and properties
  • Hydra
    • The imaging system backing USD, not a GL system
    • Allows for multiple backend implementations
  • usdview
    • Fast preview application for USD scenes