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title EdgeIdentityTable
parent API Reference

EdgeIdentityTable

Maps a render-path edge ordinal, the value stored in ViewportBody.edgeIndices, back to the Shape it was extracted from, and, when a BRepGraph was supplied, to the durable GraphUID minted from that graph. Mirrors FaceIdentityTable, but for edges.

Why it exists

Unlike the face ordinal, ViewportBody.edgeIndices is already keyed to Shape.edge(at:)'s index space: Shape.edge(at:), the bulk edge-polyline extractor behind ViewportBody.edgeIndices, and Shape.subShapes(ofType: .edge) all build one deduplicating TopTools_IndexedMapOfShape over the shape's edges, so a shared edge between two shells already collapses to a single ordinal there. There is no raw-vs-deduplicated split to reconcile the way there is for faces.

EdgeIdentityTable still earns its keep for the same reasons FaceIdentityTable does: it captures the ordinal to Shape to GraphUID correspondence once, at tessellation time, so a consumer resolving an edge pick does not have to re-walk the shape's edge map itself (Shape.subShape(type:index:) rebuilds it on every call), or hand-roll the graph.findNode(for:) plus graph.uid(ofNodeKind:index:) resolution FaceIdentityTable already does for faces. Edge identity also keeps working even if OCCT's edge traversal ever stopped deduplicating the way it does today.

API

public struct EdgeIdentityTable: Sendable {
    public let shapes: [Shape?]
    public let uids: [BRepGraph.GraphUID?]?

    public init(shapes: [Shape?], uids: [BRepGraph.GraphUID?]? = nil)
    public func shape(forOrdinal ordinal: Int) -> Shape?
    public func uid(forOrdinal ordinal: Int) -> BRepGraph.GraphUID?
}
  • shapes is indexed by the ordinal stored in ViewportBody.edgeIndices, built from Shape.edges().
  • An element is nil when that edge's Edge to Shape conversion failed. See ordinal alignment for why the array is optional rather than short.
  • uids is populated only when a BRepGraph was supplied to the entry point that produced this table. Each element is nil if that ordinal's edge could not be resolved in the graph, or has no entry in shapes.
  • shape(forOrdinal:) / uid(forOrdinal:) return nil for an out-of-range ordinal (or, for uid(forOrdinal:), when no graph was supplied at all).

Obtained from ShapeIdentity, which is the one builder for all three tables, from CADLoadResult.identity after a file load, or from CADFileLoader.shapeToBodyMetadataAndIdentities when meshing and identity are wanted from one call.

Example

let box = Shape.box(width: 10, height: 5, depth: 3)!
let graph = BRepGraph(shape: box)!
let (body, meta, faceTable, edgeTable, vertexTable) = CADFileLoader.shapeToBodyMetadataAndIdentities(
    box, id: "box", color: SIMD4<Float>(0.6, 0.6, 0.65, 1), graph: graph
)
guard let body, let edgeTable else { return }

// Resolve a wireframe edge pick back to its Shape and durable GraphUID.
let pickedOrdinal = Int(body.edgeIndices[0])
let pickedEdge = edgeTable.shape(forOrdinal: pickedOrdinal)
let pickedUID = edgeTable.uid(forOrdinal: pickedOrdinal)