Hypercurve

Exact, evidence-carrying planar curves, paths, contours, and regions for CAD topology.

Hypercurve is the two-dimensional curve kernel in the Hyper geometry stack. It models lines, circular arcs, Bézier curves, B-splines, and NURBS with hyperreal::Real coordinates, then builds intersection, classification, regularized Boolean, offset, reconstruction, and finite-projection operations on those carriers.

The crate owns planar curve geometry and topology. It deliberately does not own solid modeling or mesh topology: CSG grammar and operations such as extrusion, revolve, sweep, and loft belong in CSGRS, while triangle-mesh Boolean work belongs in Hypermesh.

This README describes crate version 0.3.1.

Primary types

Type	Role
Point2, Aabb2, Similarity2	Exact planar coordinates, bounds, and similarity transforms
CurvePoint2	Exact curve point retaining coordinates or selected geometric evidence
LineSeg2, CircularArc2, Segment2	Native line/arc primitives and their common enum
QuadraticBezier2, CubicBezier2, RationalQuadraticBezier2, RationalBezier2	Polynomial and rational Bézier carriers
PolynomialSplineCurve2, NurbsCurve2	Validated B-spline and NURBS curves
Curve2	Shared exact curve carrier with borrowed operations
CurveString2, CurvePath2, Contour2	Connected open strings, general paths, and closed line/arc contours
CurveRegion2	Native mixed-family filled planar region
CurveContext, CurvePreviewOptions, Classification<T>	One-byte predicate context, explicit lossy preview adapter, and decided/uncertain result
CurveError, ExactCurveError	Construction and exact-topology failure information

CurveRegion2 is the sole public filled-region carrier. Native line/arc specializations remain private fast paths inside the unified kernel.

Install

[dependencies]
hypercurve = "0.3.1"

Hyperreal, Hypersolve, and Hyperlimit are mandatory parts of the exact kernel; feature flags select only optional adapters and instrumentation.

Quick start

This builds a quadratic Bézier, constructs a square region from exact line segments, and classifies an interior point.

use hypercurve::{
    BezierDegree, Classification, Contour2, CurveContext, CurveRegion2, LineSeg2, Point2,
    QuadraticBezier2, Segment2,
};
use hyperreal::Real;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let p = |x, y| Point2::new(Real::from(x), Real::from(y));
    let bezier = QuadraticBezier2::new(p(0, 0), p(1, 2), p(2, 0));
    assert_eq!(bezier.structural_facts().degree, BezierDegree::Quadratic);

    let boundary = [
        ((0, 0), (2, 0)),
        ((2, 0), (2, 2)),
        ((2, 2), (0, 2)),
        ((0, 2), (0, 0)),
    ]
    .into_iter()
    .map(|(start, end)| LineSeg2::try_new(p(start.0, start.1), p(end.0, end.1)).map(Segment2::Line))
    .collect::<hypercurve::CurveResult<Vec<_>>>()?;

    let policy = CurveContext::STRICT;
    let contour = Contour2::try_new(boundary)?;
    let region =
        CurveRegion2::try_from_native_material_contours(vec![contour], &policy)?.into_value();
    let location = region.classify_point(&p(1, 1), &policy)?.into_value();
    assert!(matches!(location, Classification::Decided(_)));
    Ok(())
}

Run the checked copy:

cargo run --example basic

How the model fits together

Point2
  ├─ LineSeg2 / CircularArc2 ── Segment2 ── CurveString2 / Contour2
  └─ Bézier / B-spline / NURBS ── Curve2 ── CurvePath2
                                      │
                     arrange / classify / regularize
                                      │
                                CurveRegion2
                                      │
                  Boolean / offset / project / triangulate

A Contour2 is a closed, connected line/arc boundary with a fill rule. CurvePath2 generalizes connected paths to every supported curve family. CurveRegion2 stores filled topology as oriented native Bézier boundary fragments and is the main input to mixed-family region operations.

API guide

The following list covers the useful public front doors. Result and evidence types have accessors for inspecting counts, sources, blockers, and retained topology; consult docs.rs for those fields and exact signatures.

Coordinates, primitives, and transforms

• Point2::{new, from_values, x, y, delta_from, distance_squared, lerp, translated, structural_facts} creates and inspects exact points.
• CurvePoint2::{from, coordinates, coincides_with, compare_coordinate, bounds} handles exact curve contacts through one opaque value. coordinates() is an optional view of stored Real coordinates; selected points retain their exact meaning and support geometric queries without that view. Predicates return their certainty under the requested CurveContext.
• LineSeg2::{try_new, point_at, reversed, classify_point, contains_point, structural_facts} covers checked segments and point predicates.
• CircularArc2::{try_from_center, from_bulge, contains_point, contains_sweep_point, point_at_sweep_fraction, reversed, structural_facts} covers directed circular arcs.
• Segment2::{from_bulge, kind, point_at, contains_point, reversed, structural_facts} dispatches over lines and arcs.
• Similarity2::{try_from_real_affine, try_from_f64_affine, transform_point, scale, reverses_orientation} validates exact translation, rotation, reflection, and uniform scale transforms. Curve and region types expose transform_similarity; CurveRegion2 also exposes transform_affine.

Bézier curves

• QuadraticBezier2::{new, from_line_segment, interpolate_point_at_parameter, interpolate_midpoint, point_at, control_hull_box, endpoint_tangent, structural_facts}.
• CubicBezier2::{new, interpolate_hermite, point_at, control_hull_box, endpoint_tangent, structural_facts}.
• RationalQuadraticBezier2 and RationalBezier2 provide checked rational construction, evaluation, derivatives, splitting, reversal, transforms, and topology/intersection evidence.
• RationalBezier2::from_homogeneous_controls retains exact Bernstein (X, Y, W) coefficients, including zero-weight intermediate controls. try_new accepts affine authoring points and weights; affine_control_points returns an optional finite view. Splitting and degree elevation preserve the homogeneous representation without forcing every control into affine space. Domain finiteness and local convex-hull certificates are separate proofs. Retained bounds and rational region point queries use the active finite interval, including exterior charts and finite restrictions excluding source poles.
• BezierParameter2, BezierParameterRange2, and BezierRootIsolationResult2 retain exact algebraic parameter information.
• Bézier analysis includes cusp and inflection classification, monotone spans, line/curve contacts, curve/curve intersection, length bounds, exact polynomial and rational area moments for conics, exact homogeneous degree elevations, arbitrary-degree carriers with at-most-quadratic weight polynomials, cubic-weight carriers with exactly classified discriminants, and arbitrary-degree weight carriers whose rational-root deflation leaves either a power of one irreducible quadratic or a quartic product of two, plus certified flattening, fitting, and split materialization.
• Parallel entry points include parallel_left, parallel_right, and approximate_parallel_blend2d_certified. Their result types retain error and singularity evidence; exact topology-producing offsets are owned by the unified CurveRegion2 engine below.
• BezierParallel2::{from_source, source, distance, point_at, derivative_at, reversed, split_at_exact, subcurve_between_exact, conservative_bounds, transform_similarity, point_incidence, supporting_line_incidence, intersections, parallel_intersection_candidates, parallel_intersections} is the compact exact procedural parallel carrier. General parallel pairs use complete polynomial projections, exact common-component saturation, selected normal and tangent-degeneracy predicates, refined tensor-Bernstein rejection, and preconditioned Poincare-Miranda box replay. Exact source overlap transport handles partial and reversed reparameterizations; materializable and structural overlap lanes remain cheaper. Its BezierParallelSource2 plus signed distance is the lossless structural export boundary.

Splines and unified curves

• PolynomialSplineCurve2::{try_new, try_new_periodic, point_at, derivative_at, insert_knot, split_at, subcurve, clamped_subcurve, reversed, transform_similarity, bezier_decomposition, bezier_spans}.
• NurbsCurve2::{try_new, try_new_periodic, from_homogeneous_controls, point_at, derivative_at, insert_knot, insert_knots, remove_knot, degree_elevation, elevated_to_degree, split_at, subcurve, clamped_subcurve, reversed, transform_similarity, bezier_decomposition, bezier_spans, native_subcurves}.
• NURBS and rational Bézier spans share HomogeneousControl2 coefficients. Extraction, knot insertion/removal, and degree recomposition preserve zero and mixed control weights without affine projection. homogeneous_controls is authoritative; affine_control_points is an optional finite view. Homogeneous NURBS construction takes an expanded knot vector and explicit SplinePeriodicity2; span evaluators retain their exact source knot intervals. Conic and polynomial specializations are optional, and linear rational spans retain degree one. Bounds and monotonicity use the actual curve denominator.
• Wrapped evaluation and one-sided evaluation are available on periodic spline carriers through the *_wrapped and *_side method families.
• Curve2::{new, try_polynomial_bspline, try_nurbs, try_periodic_polynomial_bspline, try_periodic_nurbs, family, point_at, derivative_at, bounds, split_at, subcurve, reversed, transform_similarity, native_bezier_fragments, trim_inside_region, trim_inside_region_with_parameters} is the common owned carrier. Exact region trimming returns reusable Curve2 pieces from authored and generated supports. The parameter-retaining form reports their oriented source locations as CurveLocation2, exact parameter ranges and boundary contacts. Positive-length boundary overlaps are retained; isolated tangencies add no curve. Path trimming keeps disconnected spline spans in separate chunks. These operations borrow &Curve2 directly and reuse its retained calculations. Borrow paths as &CurvePath2; iterate their curves with path.curves().iter(). Curve2 also retains generated analytic parallels, selected circles, chords, and algebraic cuts. start and end return CurvePoint2; parameter_domain returns CurveParameterRange2, preserving selected endpoint evidence. geometry() is an optional native definition, and coordinates() is an optional scalar view of a point. Neither view is required for lossless CurveRegion2::boundary_paths export or subsequent region construction. point_at and point_at_side accept CurveParameter2 and return CurvePoint2, retaining selected roots and local fibers without requiring coordinate images. A Real or BezierParameter2 converts directly into the common parameter. parameter.scalar() and range.scalar_endpoints() expose stored Real views. Selected parameters remain exact when these views are absent. Intersections return CurveLocation2 contacts and CurveParameterRange2 overlap ranges. A location retains its support parameter and span chart; location.parameter(&policy) maps it into the authored curve domain on demand, preserving selected roots for evaluation and subdivision. CurveParameter2::compare compares parameters in a shared support chart without requiring scalar payloads and reports predicate certainty. Curve and open-path intersections consume retained rational-source cuts and exact chords directly, clipping contacts and overlaps to both active domains. Overlap boundaries retain their certified correspondence, including a shared endpoint when clipping leaves no positive-length span. Chord pairs and chord/rational-source pairs share the region intersection kernels while retaining endpoint contacts for open paths. Overlap ranges pair corresponding endpoints in the first curve's traversal order, including reversed overlaps. Selected overlap cuts reuse their source-interval certificates, and evaluation reuses finite-chord parameter certificates without reconstructing incidence. Self-crossings of projectively corresponding supports retain their off-diagonal contacts. Curve and path intersection_topology results expose reusable Curve2 pieces in traversal order. They preserve selected source parameters and one-sided spline endpoints without requiring native Bézier materialization. A path's CurvePathSplit2::curves() groups pieces by authored curve. The borrowed arrangement_graph() shares the topology's retained graph; its source indices identify authored curves, followed by fragment indices in traversal order. Graph preparation participates in the topology operation's certainty result. Retraced components, exterior source domains, and generated circle and parallel pair kernels still report explicit blockers where their common dispatch is unfinished. Generated curves keep their source chart when traversal is reversed. Subdivision accepts the same common parameters. Selected ranges retain their source chart and endpoint evidence, share one authored source through repeated cuts, and cover every intersected arc or spline span. Splitting returns pieces in traversal order and preserves both one-sided endpoints at spline jumps. Reversal, similarity transforms, bounds, and path corner edits consume these retained carriers. General differential and pair-intersection APIs are still being unified; operations report an explicit blocker for carriers they cannot yet consume.

Strings, paths, contours, and regions

• CurveString2::{try_new, from_bulge_vertices, link_connected_endpoints, connect_endpoints_with_line, merge_adjacent_collinear_lines, remove_adjacent_reversed_duplicates, trim_between_parameters, trim_between_points} edits connected line/arc strings without owning corner construction semantics.
• CurvePath2::{try_new, reversed, transform_similarity, chamfer_vertex_by_setbacks, fillet_vertex_by_radius, bounds, classify_point, native_bezier_fragments, bezier_boundary_loop} is the sole connected-curve corner-edit authority and handles general connected curves. Corner edits enumerate exact solutions from design setbacks or radius; callers do not supply a preselected trim/contact answer.
• Contour2::{try_new, try_new_with_fill_rule, from_bulge_vertices, signed_area, winding_number, classify_point, point_on_boundary, intersect_contour, intersect_self, split_at_intersections, split_at_self_intersections} handles closed line/arc boundaries.
• CurveRegion2::{empty, arrange_unordered_segments, try_from_native_contours, try_from_native_material_contours, try_from_native_boundary_contours, try_from_boundary_paths, classify_point, signed_depth, signed_area, filled_area, boundary_profiles, boundary_paths, segment_certified, offset} is the mixed-family region API. offset is the sole region offset operation and takes an explicit OffsetCornerStyle2; unsupported exact carriers remain explicit blockers. segment_certified is a separate lossy output adapter and never participates in offset topology.
• CurveRegion2::{intersect_region, boolean_region, boolean_regions} returns intersection topology between regularized boundaries, or regularized union, intersection, difference, and xor results. Authored winding and canceled seams are resolved first. BooleanOp selects an operation; batched CurveRegionBooleanResults2 exposes all four from one evaluation.
• CurveRegion2::straight_skeleton and the straight_skeleton_*_events methods expose staged skeleton construction and blockers. translation_obstacle_convex constructs the exact translational configuration-space obstacle for supported convex contours.

Conversion, finite output, and adapters

• CurveString2::{from_real_line_string, from_finite_line_string, reconstruct_from_polyline} and Contour2::{from_real_ring, from_finite_ring, reconstruct_from_closed_polyline} import or reconstruct line/arc geometry.
• CurveRegion2::recover_from_finite_profiles reconstructs a region from finite material/hole profiles. PolylineReconstructionOptions controls the distance tolerance.
• project_to_finite_polyline, project_to_finite_curve_paths, project_to_finite_profiles, and project_to_finite_region provide explicit finite approximations. FiniteProjectionOptions makes the curve chord-error budget visible at the boundary.
• With triangulation, FiniteRegionProfile2::triangulate and triangulate_finite_rings produce finite triangles through Hypertri.
• With svg, SvgGeometry2::{from_svg, from_svg_with_options, to_svg, to_svg_with_options}, parse_svg_path_data, import_svg_document, and export_svg_document provide SVG exchange. Native L, A, Q, and C commands are used where possible; a versioned data-hypercurve-path attribute preserves curve families and exact values for Hypercurve round-trips.

Precision, guarantees, and boundaries

Hypercurve separates exact values from decisions about them:

• Coordinates are Real values, not an implicit f64 tolerance model.
• Checked constructors reject malformed or structurally invalid input.
• Topological branches use an explicit CurveContext. CurveContext::STRICT accepts only certified decisions, while CurveContext::APPROXIMATE_512 may consume Hyperlimit's terminal 512-bit interpretation.
• CurvePreviewOptions owns finite display tolerances separately. Its scoped preview results are never exact topology or construction provenance.
• Classification::Decided(value) is a supported conclusion. Classification::Uncertain(reason) preserves an undecidable or unsupported predicate instead of silently choosing a side.
• CurveResult<T> reports ordinary construction/operation failures. ExactCurveResult<T> can additionally report the precise exact-topology blocker.
• Native output remains exact where the implementation has complete evidence. Projection to f64, polyline segmentation, SVG rendering, and triangulation are explicit conversion boundaries with caller-visible options or evidence.
• Boolean and arrangement result types retain contacts, overlaps, blockers, source provenance, and completeness rather than exposing private caches or sweep internals.

Support is deliberately operation-specific. A curve family being representable does not imply that every topology operation is decidable for every symbolic input. Inspect returned status and blocker evidence instead of treating uncertainty as empty geometry.

Feature flags

Feature	Default	Purpose
dispatch-trace	no	Hyperreal/Hyperlimit dispatch instrumentation
triangulation	no	Finite-region triangulation through Hypertri
svg	no	SVG import/export and exact round-trip extension
hershey	no	Compiled Hershey stroke fonts and native curve-string text
comparative-benchmarks	no	Third-party benchmark adapters only

Common configurations:

cargo check
cargo test --all-features
cargo run --example arrangement
cargo check --features svg

The browser demo lives in examples/hypercurve_ui and is built separately with Trunk. It is not part of the library API.

Validation and performance

The quick start is compiled as examples/basic.rs and checked byte-for-byte against this README. The test suite also covers adversarial exact predicates, mixed-family region Booleans, regression corpora, and finite adapters.

The rank-independent public-Boolean matrix, recursive radial/projective regressions (including fourth-generation offsets), and release-scale PCB corpora run in the normal suite. Longer selected-fiber and source-cusp stroke corpora can also be run explicitly:

cargo test --release --locked --all-features --lib selected_fiber_genuinely_analytic_contacts_complete_region_booleans -- --ignored
cargo test --release --locked --all-features --test hypercurve_curve_region_stroke -- --ignored

Detailed benchmark definitions and interpretation live in PERFORMANCE.md and COMPARATIVE_BENCHMARKS.md. Fuzz target ownership and replay instructions live in fuzz/README.md. These are maintainer validation resources, not API guarantees.

References

These sources describe algorithms or numerical principles used by the crate; they are not claims of source-code derivation.

• Aichholzer, O., Aurenhammer, F., Alberts, D., and Gärtner, B. “A Novel Type of Skeleton for Polygons.” Journal of Universal Computer Science 1(12), 1995, 752–761. DOI: 10.3217/jucs-001-12-0752.
• Bentley, J. L., and Ottmann, T. A. “Algorithms for Reporting and Counting Geometric Intersections.” IEEE Transactions on Computers C-28(9), 1979, 643–647. DOI: 10.1109/TC.1979.1675432.
• Boehm, W. “Inserting New Knots into B-Spline Curves.” Computer-Aided Design 12(4), 1980, 199–201. DOI: 10.1016/0010-4485(80)90154-2.
• de Boor, C. A Practical Guide to Splines. Springer, 1978. DOI: 10.1007/978-1-4612-6333-3.
• de Berg, M., Cheong, O., van Kreveld, M., and Overmars, M. Computational Geometry: Algorithms and Applications, 3rd ed. Springer, 2008. DOI: 10.1007/978-3-540-77974-2.
• Farouki, R. T., and Neff, C. A. “Analytic Properties of Plane Offset Curves.” Computer Aided Geometric Design 7(1–4), 1990, 83–99. DOI: 10.1016/0167-8396(90)90002-N.
• Farouki, R. T., and Rajan, V. T. “Algorithms for Polynomials in Bernstein Form.” Computer Aided Geometric Design 5(1), 1988, 1–26. DOI: 10.1016/0167-8396(88)90016-7.
• Foster, E. L., Hormann, K., and Popa, R. T. “Clipping Simple Polygons with Degenerate Intersections.” Computers & Graphics: X 2, 2019, 100007. DOI: 10.1016/j.cagx.2019.100007.
• Greiner, G., and Hormann, K. “Efficient Clipping of Arbitrary Polygons.” ACM Transactions on Graphics 17(2), 1998, 71–83. DOI: 10.1145/274363.274364.
• Hormann, K., and Agathos, A. “The Point in Polygon Problem for Arbitrary Polygons.” Computational Geometry 20(3), 2001, 131–144. DOI: 10.1016/S0925-7721(01)00012-8.
• Martinez, F., Rueda, A. J., and Feito, F. R. “A New Algorithm for Computing Boolean Operations on Polygons.” Computers & Geosciences 35(6), 2009, 1177–1185. DOI: 10.1016/j.cageo.2008.08.009.
• Patrikalakis, N. M., Maekawa, T., and Cho, W. Shape Interrogation for Computer Aided Design and Manufacturing. MIT Hyperbook, 2009. MIT.
• Sederberg, T. W., and Nishita, T. “Curve Intersection Using Bézier Clipping.” Computer-Aided Design 22(9), 1990, 538–549. DOI: 10.1016/0010-4485(90)90039-F.
• Shewchuk, J. R. “Adaptive Precision Floating-Point Arithmetic and Fast Robust Geometric Predicates.” Discrete & Computational Geometry 18(3), 1997, 305–363. DOI: 10.1007/PL00009321.
• Tiller, W., and Hanson, E. G. “Offsets of Two-Dimensional Profiles.” IEEE Computer Graphics and Applications 4(9), 1984, 36–46. DOI: 10.1109/MCG.1984.275995.
• Vatti, B. R. “A Generic Solution to Polygon Clipping.” Communications of the ACM 35(7), 1992, 56–63. DOI: 10.1145/129902.129906.
• Weiss, M., Jüttler, B., and Aurenhammer, F. “Mitered Offsets and Skeletons for Circular Arc Polygons.” Mathematics of Computation 90, 2021, 251–283. DOI: 10.1090/mcom/3551.
• Yap, C. K. “Towards Exact Geometric Computation.” Computational Geometry 7(1–2), 1997, 3–23. DOI: 10.1016/0925-7721(95)00040-2.

Acknowledgements

Hypercurve builds on Hyperreal, Hyperlimit, and Hypersolve, with optional Hypertri integration. The wider Hyper ecosystem provides the three-dimensional and engineering layers.

The bibliography above acknowledges the research traditions that inform the implementation. Optional comparison dependencies are benchmark or validation peers and do not provide Hypercurve’s native topology.

The optional compiled single-stroke font catalog was created by Dr. A. V. Hershey at the U.S. National Bureau of Standards. Its source distribution format was created by James Hurt of Cognition, Inc.; the integrated Rust representation is not the U.S. NTIS distribution format. The complete required acknowledgement is available as hypercurve::hershey::FONT_DATA_NOTICE.

License and contributing

Licensed under the Apache License 2.0.

Bug reports should include the smallest exact input, selected features, policy, operation, and returned blocker or uncertainty evidence. Before proposing a change, run cargo fmt --all -- --check, the relevant focused test, and cargo test --all-features.