arris

A B-Rep geometric kernel written from scratch in Rust.

An arris is the sharp edge where two surfaces meet — the thing a B-Rep kernel exists to compute.

Arris is a library, not an application: it builds solids, cuts and fuses them, blends their edges, measures, tessellates and exports them. It carries a tolerance on every entity rather than one global epsilon, returns a typed error naming the entities involved rather than panicking on geometry it cannot do, and returns a provenance record from every operation so that a parametric application can name the faces an operation made. Same input, same output, same entity ids, on every platform. Pure Rust, no unsafe, builds for wasm32.

State

Pre-1.0 and under development. The public API breaks between minor versions, and each break is listed in the release's commit. What is in today:

• primitives, rigid transforms, and extrude and revolve of a profile of lines, arcs and elliptic arcs;
• booleans — cut, fuse, common — over planar and cylindrical faces, with multi-shell results (cavities, split cuts, disjoint fuses) and a typed refusal for the surface pairs that are not in yet;
• constant-radius fillet and chamfer on plane–plane and plane–cylinder edges, with miters, corners and hole rims;
• cone, sphere and torus faces, checked and measured, meeting through their meridians on a shared axis;
• tessellation to a chord tolerance, mass properties (volume, centroid, inertia), plane projection and face frames;
• STEP AP214 export, STL and OBJ export, and a deterministic native format in JSON and bytes.

Not in yet: free-form NURBS surfaces and curves, variable-radius blends, sheet and non-manifold bodies, a STEP reader, booleans on cone, sphere, torus or elliptic-cylinder faces, and booleans whose operands would meet in a quartic intersection curve. Each of those is a typed refusal today, never a wrong answer.

Correctness

Every operation returns a shape that passes the invariant checker, and the checker runs after every operation in debug builds. Every fixture in the test corpus carries an oracle value — volume, area, centroid, counts, point classifications — computed by Open CASCADE, which Arris must match within the fixture's stated tolerance. Open CASCADE is run as the oracle through Python; it is never a build or runtime dependency, and PROVENANCE.md says how it is used and read. Properties (volume additivity, cut-then-fuse, commutativity, STEP round-trip) are tested over random operands in random poses from a fixed seed.

Workspace

Arris is a Cargo workspace. crates/arris is the facade a consumer depends on; it re-exports the layered crates beneath it — arris-math, arris-geom, arris-topo (the representation), arris-check (the invariant checker), arris-ops, arris-mesh, arris-io (the algorithms) and arris-debug (dev-facing: rasteriser, fixtures, property-test strategies; it is not published). A crate never depends on one above it; tools/check-layers.sh enforces that in CI and in the pre-commit hook. The layout and the reasons are in docs/ARCHITECTURE.md; tools/oracle/ is the Open CASCADE test oracle, run through Python and never linked.

Licence

MIT or Apache-2.0, at your option. See LICENSE-MIT and LICENSE-APACHE.