neco-brep

日本語

Analytical B-Rep modeling for constructive solid geometry, profile-driven solid generation, and mesh export.

A Japanese mathematical note is available in MATH-ja.md.

Modeling workflow

Shell is the main boundary representation. It stores vertices, edge curves, and face surfaces. Surfaces can stay analytic (Plane, Cylinder, Cone, Sphere, Ellipsoid, Torus) or remain NURBS-backed for revolve, sweep, and loft workflows.

The crate covers both primitive construction and profile-driven solids. Primitive shells include shell_from_box, shell_from_cylinder, shell_from_cone, shell_from_sphere, shell_from_ellipsoid, and shell_from_torus. Profile-driven shells use shell_from_extrude, shell_from_revolve, shell_from_sweep, or shell_from_loft with neco-nurbs profiles.

shell_from_sweep expects the spine as Bezier-decomposed control points. shell_from_loft operates on &[LoftSection] with a LoftMode, and corresponding sections must decompose to the same number of Bezier spans.

Boolean and export

boolean_2d_all and boolean_3d keep the result in B-Rep form, so downstream steps can stay analytic until tessellation is needed. Shell::tessellate converts the shell to triangles, and the resulting mesh can be exported with write_stl_binary or write_stl_ascii.

General solid representation is stable for ordinary analytic primitives and standard profile-driven construction. shell_from_extrude and shell_from_revolve are in better shape than the more complex loft and sweep routes, which still need more hardening.

For 2D boolean, the main result type is RegionSet, which can represent empty results, a single region, or multiple disjoint regions. The older boolean_2d function remains as a compatibility helper for callers that only accept single-region results.

For 3D boolean, lower-dimensional contact is treated as non-overlap. Point contact, line contact, and other zero-volume contact states produce an empty shell for Intersect and keep the minuend unchanged for Subtract. Union still requires a single connected shell result.

3D boolean operations are experimental. Result completeness is not yet guaranteed, and the tessellation / rendering path still has known bugs. Use them for evaluation, controlled workflows, and incremental validation rather than as a fully reliable production boolean pipeline.

Usage

Primitive boolean and tessellation

use neco_brep::{
    boolean_3d, shell_from_box, shell_from_cylinder, BooleanOp,
};
use neco_brep::stl::write_stl_binary;

let a = shell_from_box(2.0, 2.0, 2.0);
let b = shell_from_cylinder(0.4, None, 2.0);

let result = boolean_3d(&a, &b, BooleanOp::Subtract)?;
let mesh = result.tessellate(24)?;

let mut bytes = Vec::new();
write_stl_binary(&mesh, &mut bytes)?;
# Ok::<(), Box<dyn std::error::Error>>(())

Extrude a NURBS profile

use neco_brep::shell_from_extrude;
use neco_nurbs::{NurbsCurve2D, NurbsRegion};

let profile = NurbsRegion {
    outer: vec![NurbsCurve2D::circle([0.0, 0.0], 1.0)],
    holes: vec![],
};

let shell = shell_from_extrude(&profile, [0.0, 0.0, 1.0], 2.0)?;
# let _ = shell;
# Ok::<(), String>(())

API

License

MIT