BRepGraph (page 2 of 2)

Centralized transient cache for algorithm-computed per-reference values.
Symmetric counterpart of BRepGraph_TransientCache, keyed by BRepGraph_RefId instead of BRepGraph_NodeId. Freshness is tracked via BaseRef::OwnGen rather than BaseDef::SubtreeGen, because references do not own subtrees.
Shares the same BRepGraph_CacheKind descriptors and BRepGraph_CacheKindRegistry as the node cache; the same kind GUID can address values in both caches.
OwnGen-based freshness
Each stored slot records OwnGen at write time. On read, if the stored OwnGen differs from the reference's current OwnGen the cached value is considered stale.
Lifecycle
NOT a Layer. Cleared on BRepGraph_Builder::Add() and Compact(). No explicit removal callback

• stale data is auto-detected by OwnGen mismatch.
  Thread safety
  After Reserve(), Get() and Set() for in-range indices bypass the mutex entirely. Out-of-range access falls back to mutex-protected vector growth.

Unique reference identifier within a BRepGraph.
Identity = (RefKind, Counter). Generation is excluded from equality/hash. Counter 0 is an invalid sentinel.
Serialization Contract
Entity UIDs (BRepGraph_UID) and reference UIDs (BRepGraph_RefUID) share a single monotonic counter (BRepGraph_Data::myNextUIDCounter). To persist a BRepGraph across sessions:

1. Write: for each reference entry, serialize (RefKind, Counter, OwnGen).
2. Read: reconstruct reference entries, populate RefUID vectors with deserialized (RefKind, Counter) values, set myNextUIDCounter to max(all_entity_counters, all_ref_counters) + 1.
3. myGeneration resets to 0 on load (session-scoped).
4. VersionStamps from a previous session will correctly detect staleness via Generation mismatch.

Single-level iterator over semantically related topology nodes.
The iterator yields immediate related nodes for one source node together with the relation kind explaining why each node is returned. Results are not deduplicated; callers that need uniqueness should filter on top.

Lightweight typed index into a per-kind representation vector inside BRepGraph.
The pair (Kind, Index) forms a unique representation identifier within one graph instance. Default-constructed RepId has Index = UINT32_MAX (invalid).
Representations are NOT topology nodes - they hold geometry or mesh data referenced by topology entities. They do not participate in BFS traversal, reverse index, or parent-child relationships.
RepId is a value type: cheap to copy, compare, hash.

Allocation-free iterator over root product identifiers.
Iterates directly over BRepGraph::RootProductIds() - products not referenced by any active occurrence.

Centralized geometry access for BRepGraph - analogue of BRep_Tool.
Geometry in BRepGraph is stored in the definition frame (representation Location baked via applyRepresentationLocation). Instance Locations live on topology Instance/Ref structs (VertexInstance, CoEdgeInstance, WireInstance, FaceInstance, ShellInstance, SolidInstance, OccurrenceInstance). This class applies ref Locations automatically when accessing 3D geometry.
Instance structs are lightweight read-only projections produced during traversal, while Ref structs are stored reference entries from RefsView; this API accepts whichever form naturally carries the required context for the queried property.
Methods are grouped by topology kind via nested classes: BRepGraph_Tool::Vertex, Edge, CoEdge, Face, Wire.