Progress reporting & cancellation

STEP and IGES imports can be slow on large assemblies. ShapeLoader.load / loadRobust accept an optional progress observer conforming to OCCTSwift’s ImportProgress protocol. OCCTSwiftIO ships ImportProgressClosure so you can pass a closure instead of writing a one-shot subclass.

(STL / OBJ / BREP loaders are single-call upstream and do not surface progress; the observer is honoured for STEP and IGES.)

Closure-based progress

import OCCTSwift
import OCCTSwiftIO

let result = try await ShapeLoader.load(
    from: stepURL,
    format: .step,
    progress: ImportProgressClosure { fraction, step in
        print("\(Int(fraction * 100))% — \(step)")   // fraction in 0.0...1.0
    }
)

fraction runs 0.0...1.0; step is a human-readable stage name (e.g. "Reading STEP file").

Threading note

The callback fires on whatever thread the importer runs on — typically a background thread, since ShapeLoader.load dispatches the work off a Task.detached. Hop to the main actor for UI updates:

progress: ImportProgressClosure { fraction, _ in
    Task { @MainActor in progressBar.doubleValue = fraction }
}

Cancellation

Pass a cancelCheck that returns true to cooperatively cancel. Wiring it to Task.isCancelled ties the import to Swift structured-concurrency cancellation; cancelling throws ImportError.cancelled:

progress: ImportProgressClosure(
    cancelCheck: { Task.isCancelled },
    progress: { fraction, step in /* … */ }
)

The ImportProgressClosure initializer signature:

public init(
    cancelCheck: @escaping @Sendable () -> Bool = { false },
    progress: @escaping @Sendable (Double, String) -> Void
)