MeshIO

MeshIO is the pure-Swift mesh file I/O entry point — no OCCT. It reads STL / OBJ / PLY / glTF / GLB / 3MF / PMX / .x and writes everything except the two source-only formats (PMX, .x), all through the neutral Mesh value type. The companion MeshFormat enum and MeshError type live here too.

Topics

• MeshError · MeshFormat · MeshIO.readableExtensions · MeshIO.load(contentsOf:weldEpsilon:) · MeshIO.write(_:to:format:asciiSTL:)

MeshError

public enum MeshError: Error, Equatable, Sendable {
    case empty
    case notRecognized
    case unknownExtension(String)
    case unsupported(String)
}

• empty — input data was empty.
• notRecognized — bytes didn’t parse into a usable mesh.
• unknownExtension — the file extension maps to no MeshFormat.
• unsupported — operation not supported (e.g. writing PMX / .x, or big-endian PLY).

MeshFormat

The 3D mesh formats MeshIO handles. Mesh-only — CAD B-Rep and 2D vector formats live in OCCTSwiftIO.

public enum MeshFormat: String, Sendable, CaseIterable {
    case stl, obj, ply, pmx, x      // x = DirectX .x
    case threeMF = "3mf"
    case gltf, glb

    public init?(fileExtension ext: String)
    public var canRead: Bool   { true }
    public var canWrite: Bool  { self != .pmx && self != .x }
}

• init?(fileExtension:) — maps a case-insensitive extension (stl/obj/ply/pmx/x/3mf/gltf/glb) to a case, nil otherwise.
• canWrite — false for pmx and x (source-only formats); true for the rest.

MeshIO.readableExtensions

public static var readableExtensions: [String] { get }

• Returns: all readable format extensions: ["stl", "obj", "ply", "pmx", "x", "3mf", "gltf", "glb"].

MeshIO.load(contentsOf:weldEpsilon:)

Loads a mesh file, choosing the reader by extension. glTF / GLB load from the URL so external .bin buffers resolve relative to it; other formats read from in-memory Data.

public static func load(contentsOf url: URL, weldEpsilon: Float = 1e-4) throws -> Mesh

• Parameters: url — the mesh file; weldEpsilon — vertex-weld grid size (default 1e-4; pass 0 to skip welding).
• Returns: a welded Mesh.
• Throws: MeshError.unknownExtension for an unrecognised extension; .empty / .notRecognized for unparseable data; .unsupported for unsupported variants. PMX / .x are read via the SwiftPMX / SwiftX packages.
• Example:

  let mesh = try MeshIO.load(contentsOf: url)
  print(mesh.vertexCount, mesh.triangleCount)
  

MeshIO.write(_:to:format:asciiSTL:)

Writes a mesh, choosing the writer by format (or by the file extension when format is nil).

public static func write(
    _ mesh: Mesh,
    to url: URL,
    format: MeshFormat? = nil,
    asciiSTL: Bool = false
) throws

• Parameters:
  • mesh — the mesh to write.
  • url — destination file.
  • format — explicit format; if nil, inferred from url.pathExtension.
  • asciiSTL — write ASCII STL instead of binary (STL only; default false).
• Throws: MeshError.unsupported when the resolved format is pmx / x / nil.
• Example:

  try MeshIO.write(mesh, to: outURL)                            // by extension
  try MeshIO.write(mesh, to: stlURL, format: .stl, asciiSTL: true)