OCCTSwiftMesh

Mesh-domain algorithms for the OCCTSwift ecosystem. Operates on OCCTSwift.Mesh instances; complements the OCCT-side topology kernel rather than extending it.

Part of the OCCTSwift ecosystem — see the ecosystem map for how this package fits with the kernel, viewport, and sibling layers.

OCCTSwift           — B-Rep solid modelling kernel (wraps OpenCASCADE)
OCCTSwiftMesh       — mesh-domain algorithms (decimation, smoothing, repair, ...)
OCCTSwiftViewport   — Metal viewport for rendering
OCCTSwiftScripts    — script harness + occtkit CLI verbs

Why a separate package

OCCT's open-source distribution provides BRepMesh_* for mesh generation but no decimation, simplification, smoothing, hole-filling, remeshing, or other mesh-side post-processing. OCCT-Components ships a paywalled "Mesh Decimation" module — this package fills the same role with permissive, vendored implementations.

OCCTSwift itself stays focused on its mission as an OCCT wrapper. Mesh algorithms that happen to consume OCCT-produced meshes live here.

Status

✅ v1.1.0 — SemVer-stable. Ships Mesh.simplified(_:) (decimation, vendored meshoptimizer v1.1) and Mesh.crossSection(plane:) (planar slicing into closed contours). Requires OCCTSwift v1.0.1 or later. See docs/CHANGELOG.md.

API

Decimation — Mesh.simplified(_:)

import OCCTSwift
import OCCTSwiftMesh

let mesh: Mesh = shape.mesh()  // from OCCTSwift
let simplified = mesh.simplified(.init(
    targetTriangleCount: 5_000,
    preserveBoundary: true,
    preserveTopology: true
))

if let result = simplified {
    print("\(result.beforeTriangleCount) → \(result.afterTriangleCount)")
    print("Hausdorff: \(result.hausdorffDistance)")
    let reducedMesh = result.mesh
}

Slicing — Mesh.crossSection(plane:)

Intersect a mesh with a plane and recover the closed contours where it cuts the surface — the perimeter step a 3D-printer slicer performs. Works directly on open / unwelded scan meshes (no B-Rep sewing first). A thin-walled tube slices into separate outer and inner loops, so wall thickness is just their offset; inner-vs-outer comes from contour nesting, not triangle winding.

let section = mesh.crossSection(plane: CutPlane(point: p, normal: n))
for c in section!.contours {
    // c.depth == 0 → outer solid boundary; c.isHole → inner wall / pocket
    print(c.points.count, "pts, area", c.area, c.isHole ? "(hole)" : "")
}

// Or a whole slicer layer stack along an axis:
let stack = mesh.crossSections(axis: axis, through: p, spacing: 2.0)

Installation

// Package.swift
dependencies: [
    .package(url: "https://github.com/gsdali/OCCTSwiftMesh.git", from: "1.1.0"),
],
targets: [
    .target(
        name: "YourApp",
        dependencies: [
            .product(name: "OCCTSwiftMesh", package: "OCCTSwiftMesh"),
        ]
    )
]

License

LGPL-2.1, matching OCCTSwift. Vendored components retain their own permissive licenses (notably meshoptimizer under MIT). See NOTICE.md.

Roadmap

Beyond initial decimation:

• Subdivision (Catmull-Clark, Loop)
• Laplacian / Taubin smoothing
• Mesh repair (non-manifold cleanup, hole filling)
• Remeshing (uniform / adaptive)
• glTF mesh-export niceties (LOD chains, meshopt-encoded streams)
• GPU-accelerated mesh ops where worthwhile

Community needs drive priority — file an issue if you want one of these (or something else) sooner.

Related projects

• OCCTSwift — OCCT wrapper, source of Mesh
• OCCTSwiftScripts — script harness; simplify-mesh verb consumes this package (#22)
• OCCTMCP — MCP server; simplify_mesh tool consumes this package via OCCTSwiftScripts (#6)