Module boolean 

Path boolean ops (M-BOOL.0 / AUT-161 → M-BOOL.5 / AUT-166).

In-house polygon-clipping engine. The full design rationale — algorithm choice, alternatives rejected, follow-up tickets — is captured in _docs/adr/M-BOOL-backend.md.

Quick API

use wisp::path::boolean::{combine, BooleanOp, BoolOptions};
use wisp::path::PathBuilder;

let circle_a = /* a closed Path */;
let circle_b = /* a closed Path */;
let union = combine(&circle_a, &circle_b, BooleanOp::Union, BoolOptions::default());

Algorithm (v1, polygon-only)

1. Flatten each Path to a list of closed polylines (one per MoveTo-rooted subpath).
2. Build a directed-edge list per polyline, labelled Subject (path A) or Clip (path B).
3. Find every pair-wise edge intersection in O(n·m). Subdivide both edges at each intersection so every output fragment has integer-multiplicity endpoints.
4. For each fragment, evaluate “inside A?” and “inside B?” at the fragment’s midpoint via the parity (even-odd) point-in-polygon test against the other polygon’s full edge list.
5. Keep each fragment iff it lies on the boundary of the desired output region — i.e. the op rule evaluates differently on the two sides of the fragment.
6. Stitch retained fragments tip-to-tail into closed contours; emit one MoveTo+LineTo*+Close subpath per contour.

Known v1 limitations

All deferred to follow-up tickets (AUT-167..179):

• Bezier curves flatten via crate::scene::path::Path::flatten before processing; curvature is lost. M-BOOL.7 lands a flatten_subpaths that preserves multi-subpath structure.
• Holes + FillRule::NonZero semantics are stubbed: BoolOptions::fill_rule is accepted but only EvenOdd is honoured today. M-BOOL.8 implements winding-number tracking.
• Self-intersecting inputs → undefined output. Match Clipper2 v1.
• O(n·m) intersection finding is fine for our typical path sizes (50–500 vertices). M-BOOL.17 benchmarks set the bar for a future Bentley-Ottmann sweep-line if needed.

Structs

BoolOptions

Tuning knobs for combine.

Edge 🔒

Enums

BooleanOp

The four primitive boolean ops on two paths.

EdgeLabel 🔒

FillRule

Fill-rule policy for self-overlapping inputs.

Functions

build_edges 🔒

combine

Combine two paths via the given boolean op.

combine_n

Convenience N-ary fold (M-BOOL.6 / AUT-167).

contours_to_path 🔒

flatten_cubic 🔒

flatten_quad 🔒

inside_any 🔒

keep_fragment 🔒

Decide whether a fragment is retained for the given op.

op_rule 🔒

perp_distance 🔒

ray_crossings 🔒

Parity / even-odd point-in-polygon. Returns the number of times a rightward ray from point crosses any edge of the polygon.

rebuild_from_polylines 🔒

segment_intersection 🔒

Robust-ish two-segment intersection. Returns (t_along_first, t_along_second, intersection_point) when the segments cross in the interior of both. Endpoint-only touches are filtered out by the caller via t > tolerance && t < 1 - tolerance. Returns None for parallel, collinear, or near-collinear pairs.

split_at_intersections 🔒

Split every edge at its intersections with every other edge. Returns the (possibly larger) fragment list.

stitch 🔒

Walk fragments tip-to-tail, building closed loops.

subpaths 🔒

Decompose a Path into closed polylines, one per MoveTo-rooted subpath. Open subpaths (without Close) are silently dropped — boolean ops are only meaningful on closed regions.