Topology-geometry graph over TopoDS / BRep.
Stores B-Rep topology as flat entity vectors (incidence-table model) with integer cross-references, enabling cache-friendly traversal, relation-table parent navigation, and parallel face-level geometry extraction.
Key design concepts:
- NodeId (Kind + Index): lightweight typed address into per-kind vectors.
- UID (Kind + Counter): persistent identity surviving compaction/reorder.
- RepId (Kind + Index): separate geometry/mesh addressing (Surface, Curve3D, Curve2D, Triangulation, Polygon) decoupled from topology nodes.
- CoEdge: half-edge entity owning PCurve data for each edge-face binding; seam edges use paired CoEdges with opposite Orientation (Parasolid convention).
- Lifecycle: Shapes().Add() populates from TopoDS_Shape; Editor() is the single mutation entry point for both structural creation/removal (Add*, Remove*, Append*) and field-level RAII-scoped mutation (Mut*()) with automatic cache invalidation and upward SubtreeGen propagation.
Per-occurrence data (orientation, location) lives on incidence refs. Definition types are aliases to BRepGraphInc entity structs.
Grouped View API
Related methods are grouped behind lightweight view objects. Include the corresponding header (e.g. BRepGraph_TopoView.hxx) to use.
Thread safety
Const query methods are safe for concurrent reads. Concurrent reads during active mutation still require external synchronization. Deferred invalidation (BRepGraph_DeferredScope) batches SubtreeGen propagation; concurrent Editor().Mut*() calls during deferred mode still require external serialization. Shapes().Add() is internally parallel when requested.
UID persistence
UIDs use monotonic counters (not vector indices), persisting across Compact() and node removal. Only BRepGraph::Clear() resets counters (new generation). See BRepGraph_UID.hxx for the serialization contract.
Extension model
Extend via BRepGraph_Layer (persistent metadata / observers) or BRepGraph_CacheRegistry (typed algorithm-computed transient cache services). Direct storage extension is not supported.
ID systems
Four ID types with different stability guarantees:
- NodeId (Kind + per-kind Index): fast graph-local address. NOT stable across Compact(). Use for in-graph traversal and short-lived algorithm temporaries.
- UID (Kind + monotonic Counter): persistent identity surviving Compact() and node removal. Use for cross-session storage, history tracking, and external references.
- RefId (Kind + per-kind Index): same stability as NodeId, but addresses reference entries (Shell->Solid binding, Face->Shell binding, CoEdge->Wire binding) rather than defs.
- RepId (Kind + per-kind Index): addresses owner-scoped geometry/mesh representation slots (Surface, Curve3D, Curve2D, Triangulation, Polygon).
Iterator guide
Choose the iterator that matches your traversal need:
- BRepGraph_Iterator<NodeType>: flat sequential scan of ALL definitions of one kind (e.g. every FaceDef, skipping removed). Use for bulk per-kind algorithms.
- BRepGraph_DefsIterator / BRepGraph_RefsIterator: single-level typed children of one parent (e.g. active shells of one solid, coedges of one wire). Zero allocation. Use when you have a specific parent and need its direct children.
- BRepGraph_ChildExplorer: depth-first downward walk from a root with accumulated location/orientation per step. Use when visiting descendants across multiple levels or when the global transform matters. Supports Recursive and DirectChildren modes.
- BRepGraph_ParentExplorer: upward walk via relation tables from a starting node. Use when tracing which shells/solids/compounds contain a given face or edge.
- BRepGraph_RelatedIterator: single-level semantic neighbors (adjacent faces, boundary edges, incident vertices). No structural descent; no location accumulation.
1.17.0