NCP-OUSD flashcards
NCP-OUSD · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Stage vs layer
- A layer is a single file of opinions; a stage is the composed in-memory result of stacking layers through composition arcs. Editing a stage writes to its layers.
- LIVRPS order
- Opinion strength across arcs: Local, Inherits, Variants, References, Payloads, Specializes. Local opinions in the root layer are strongest; specializes are weakest.
- Sublayer ordering
- Sublayers compose in reverse order: the last sublayer listed is weakest, and the root layer's own opinions beat every sublayer.
- Time samples
- Per-attribute keyed values stored in Sdf.TimeSamples. They coexist with a default value, and get() resolves the value at the current Usd.TimeCode.
- Prim vs property path
- Prim paths are absolute (/World/Cube) or relative (../Cube); property paths append .attribute or .relationship to a prim path.
- Reference vs payload
- A reference pulls a prim or layer subtree in at reference strength. A payload is a deferred reference that can be loaded or unloaded to save memory.
- Inherits and specializes
- Inherits apply class opinions at inherit strength. Specializes are weaker than all other arcs and provide fallback behavior for a prim.
- Variant sets
- Named alternatives on a prim declared in variantSets metadata. Only the selected variant contributes opinions, at variant strength in the LIVRPS order.
- Composition query
- Usd.PrimCompositionQuery lists every arc contributing to a prim and its strength, which is the fastest way to find where an opinion comes from.
- Over prim
- An over adds or overrides opinions on a prim without redefining its type. It is common in stronger layers that only tweak a referenced asset.
- Flatten for debugging
- Usd.Stage.Flatten() bakes the composed result into one layer, making it easy to see the final opinions when composition is hard to trace.
- Schema generation
- Schemas are generated from usda definitions via usdGenSchema into C++ and Python classes declaring typed properties, API schemas, and fallback values.
- Applied API schema
- A schema attached to any prim via API schemas metadata, such as UsdShadeMaterialBindingAPI. Multiple-apply variants are namespaced by instance name.
- Fallback values
- Values returned when no authored opinion exists. They live in generated schema code, not in layers, so they never appear in composition.
- Custom vs schema property
- Custom properties are declared with custom = true and need no schema. Schema properties must match the declared type and variability of the schema.
- Schema registry
- Usd.SchemaRegistry maps type names to registered schemas and can report whether a type is concrete and instantiable.
- Hydra architecture
- Hydra adapts a stage into Hydra prims via UsdImagingDelegate and feeds a render delegate such as Storm, which consumes the render index or scene index.
- Scene index
- A graph of HdSceneIndexPrim entries keyed by SdfPath. Filters and observers wrap and transform the graph before a render delegate sees it.
- Dirty bits
- HdDirtyBits flags such as DirtyTransform, DirtyPoints, and DirtyVisibility tell a render delegate which data changed and must be re-synced.
- Storm delegate
- Storm is the reference rasterizing Hydra render delegate. UsdView's renderer menu selects among registered delegates, including Storm.
- UsdImagingStageSceneIndex
- Builds a scene index from a UsdStage. Tools can combine it with HdRetainedSceneIndex and HdMergingSceneIndex to inject or merge prims.
- USDZ packaging
- An uncompressed zip archive of USD files and textures with no external references. Some readers require 64-byte alignment of packaged files.
- Dependency computation
- UsdUtils.ComputeAllDependencies returns referenced layers and asset paths, letting a pipeline relocate or package an asset without broken references.
- MaterialX interop
- UsdMtlx.readMaterialX reads .mtlx networks into a stage as UsdShade nodes, and UsdShadeMaterialBindingAPI links materials to prims.
- Alembic interop
- Alembic import preserves baked geometry and transforms but not USD composition arcs; it is a snapshot, not a live reference.
- Native instancing
- Set instanceable = true on a prim with a reference or payload. All instances share one prototype, and per-instance overrides break the sharing.
- Point instancer
- UsdGeomPointInstancer places many copies via positions, orientations, and prototype indices. It is lighter than native instancing for very large counts.
- Payload loading
- Payloads defer heavy subtrees. Usd.Stage.Load and Unload or the payloads metadata control what is loaded, saving memory and load time.
- Asset layout convention
- A top-level asset prim with defaultPrim set, geometry under /Geom, materials under /Materials, and a sublayer or layer per department.
- Plugin discovery
- USD discovers plugInfo.json files via PXR_PLUGINPATH_NAME. Schema and file-format plugins register at runtime through this mechanism.
- Asset resolver
- ArResolver maps asset paths to files. Custom resolvers implement ArResolver for studio pathing, and PXR_AR_DEFAULT_SEARCH_PATH sets fallback search paths.
- Compliance checker
- UsdUtils.ComplianceChecker and the usdchecker CLI validate assets for missing defaultPrim, unresolved references, and usdz packaging issues before delivery.