brepkit

Solid modeling kernel for Rust and WebAssembly.

Architecture · Performance · Getting Started · Contributing

use brepkit_operations::primitives::{make_box, make_cylinder};
use brepkit_operations::boolean::{boolean, BooleanOp};
use brepkit_operations::measure::solid_volume;
use brepkit_io::step::writer::write_step;
use brepkit_topology::Topology;

let mut topo = Topology::new();

// Create a block with a cylindrical hole
let block = make_box(&mut topo, 30.0, 20.0, 10.0)?;
let hole = make_cylinder(&mut topo, 5.0, 15.0)?;
let drilled = boolean(&mut topo, BooleanOp::Cut, block, hole)?;

// Measure and export
let vol = solid_volume(&topo, drilled, 0.1)?;
let step = write_step(&topo, &[drilled])?;

Why build a CAD kernel?

Building a solid modeling kernel from scratch is one of those problems measured in developer-careers, not sprints. Parasolid, ACIS, and OpenCascade represent decades of accumulated effort — surface-surface intersection, robust boolean classification, exact geometric predicates, degenerate case handling. Each is a research domain in its own right.

brepkit grew out of building gridfinitylayouttool.com. I needed parametric CAD in the browser and the existing options were either proprietary or compiled-from-C++ with bridge overhead. OpenCascade works — brepjs proves that — but performance ceilings and an 11 MB WASM bundle kept getting in the way.

brepkit is the answer to a simple question: what if the kernel was built for WebAssembly from day one? Rust's type system, no unsafe, no unwrap, no panic — all operations return Result. The WASM bundle is 1.8 MB.

Status

Core operations work and are fast: primitives, booleans, fillets, chamfers, extrude, revolve, sweep, loft, pipe, STEP I/O. The math layer — NURBS evaluation, exact geometric predicates, all analytic surface intersections — is mature. Booleans preserve analytic surfaces (cylinders stay cylinders) and handle compound operations efficiently.

Still maturing: torus booleans fall back to the tessellated path, revolve/sweep/loft/pipe require planar profiles (extrude handles NURBS), and IGES round-trips lose analytic surface types.

For production use today, brepjs with the OpenCascade kernel is the stable path. brepkit is the faster replacement in progress — the kernel abstraction layer in brepjs means switching is a one-line change.

Features

Modeling — box, cylinder, cone, sphere, torus plus extrude, revolve, sweep, loft, pipe, helical sweep

Booleans — union, cut, intersect with analytic surface preservation

Modifiers — fillet (constant + variable radius), chamfer, shell, draft, offset, thicken, mirror, pattern

Sectioning — cross-section curves, split by plane or surface

Measurement — bounding box, area, volume, center of mass, distance, point classification (in/on/out)

Geometry — NURBS evaluation, surface-surface intersection, curve fitting (LSPIA), point projection, self-intersection detection

Tessellation — parallel CDT for planar faces, snap tessellation for analytic surfaces

Repair — healing, defeaturing, sewing, validation, face filling (Coons patch)

Feature Recognition — automatic detection of holes, pockets, slots, bosses, and ribs

Sketching — 2D constraint solver for sketch-driven modeling

Assemblies — hierarchical product structure with transforms, flattening, BOM

Evolution — face provenance tracking through booleans and modeling operations

Architecture

Layered Cargo workspace. Each layer depends only on layers below it, with one exception: brepkit-io also uses brepkit-operations for tessellation during mesh export. Boundaries are enforced by scripts/check-boundaries.sh and checked in CI.

Layer	Crate	What it does
L0	brepkit-math	Points, vectors, matrices, NURBS curves/surfaces, geometric predicates, CDT, convex hull
L1	brepkit-topology	Arena-allocated B-Rep: vertex, edge, wire, face, shell, solid. Half-edge adjacency graph
L2	brepkit-operations	Booleans, fillet, chamfer, extrude, revolve, sweep, loft, shell, measure
L2	brepkit-io	Import/export for 7 formats (2 B-Rep, 5 mesh). Uses operations for tessellation during mesh export
L3	brepkit-wasm	JavaScript API via wasm-bindgen

Performance

Median times from the brepjs benchmark suite (5 iterations, Node.js, Linux x86_64). WASM is single-threaded; native benchmarks use criterion with rayon.

Operation	brepkit (WASM)	OCCT (WASM)	Speedup	brepkit (native)
fuse(box, box)	5.7 ms	83.7 ms	15x	336 µs
cut(box, cylinder)	4.2 ms	123.8 ms	29x	221 µs
intersect(box, sphere)	31.9 ms	107.1 ms	3.4x	2.4 ms
box + chamfer	0.1 ms	7.8 ms	78x	55 µs
box + fillet	0.3 ms	8.1 ms	27x	75 µs
multi-boolean (16 holes)	1.7 ms	52.0 ms	31x	1.2 ms
mesh sphere (tol=0.01)	20.0 ms	61.3 ms	3.1x	1.8 ms
exportSTEP (×10)	0.9 ms	19.2 ms	21x	—

Booleans preserve analytic surfaces — cylinders and planes stay as exact geometry, keeping face counts low (72 vs ~7,000 for a 9-step compound boolean).

Native benchmarks: cargo bench -p brepkit-operations. WASM comparison: brepjs/benchmarks/.

Data Exchange

Format	Type	Import	Export
STEP	B-Rep	✓	✓
IGES	B-Rep	✓	✓*
STL	Mesh	✓	✓
3MF	Mesh	✓	✓
OBJ	Mesh	✓	✓
PLY	Mesh	✓	✓
glTF	Mesh	✓	✓

STEP preserves exact geometry on round-trip. *IGES export converts analytic surfaces to NURBS. Mesh formats export tessellated triangles.

Getting Started

As a Rust dependency

[dependencies]
brepkit-math = { git = "https://github.com/andymai/brepkit" }
brepkit-topology = { git = "https://github.com/andymai/brepkit" }
brepkit-operations = { git = "https://github.com/andymai/brepkit" }
brepkit-io = { git = "https://github.com/andymai/brepkit" }        # optional

As a WASM package

npm install brepkit-wasm

import init, { BrepKernel } from "brepkit-wasm";

await init();
const kernel = new BrepKernel();
const solid = kernel.makeBox(10, 20, 30);

For a higher-level TypeScript API, see brepjs.

Building from source

cargo build --workspace
cargo test --workspace
cargo clippy --all-targets -- -D warnings
cargo fmt --all

# WASM (full)
cargo build -p brepkit-wasm --target wasm32-unknown-unknown --release

# WASM (smaller, no IO)
cargo build -p brepkit-wasm --target wasm32-unknown-unknown --release --no-default-features

Projects Using brepkit

• brepjs - CAD modeling for JavaScript
• Gridfinity Layout Tool - Web-based Gridfinity storage layout generator

Open a PR to add your project.

License

AGPL-3.0-only