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VertexIdentityTable.md

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title VertexIdentityTable
parent API Reference

VertexIdentityTable

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

Why it exists

ViewportBody.vertexIndices is the sequential index into Shape.vertices(), which (like Shape.edges()) is built from one deduplicating TopTools_IndexedMapOfShape over the shape's vertices, the same map Shape.vertex(at:) and Shape.subShapes(ofType: .vertex) use. A shared vertex between two shells already collapses to a single ordinal there.

VertexIdentityTable still earns its keep for the same reasons EdgeIdentityTable does: it captures the ordinal to Shape to GraphUID correspondence once, at tessellation time, so a consumer resolving a vertex pick does not have to re-walk the shape's vertex map itself, or hand-roll the graph.findNode(for:) plus graph.uid(ofNodeKind:index:) resolution FaceIdentityTable already does for faces.

API

public struct VertexIdentityTable: 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.vertexIndices, built from Shape.subShapes(ofType: .vertex).
  • 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 vertex could not be resolved in the graph.
  • 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 CADFileLoader.shapeToBodyMetadataAndIdentities.

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 vertexTable else { return }

// Resolve a B-Rep vertex pick back to its Shape and durable GraphUID.
let pickedOrdinal = Int(body.vertexIndices[0])
let pickedVertex = vertexTable.shape(forOrdinal: pickedOrdinal)
let pickedUID = vertexTable.uid(forOrdinal: pickedOrdinal)