Module clipping 

Weiler-Atherton polygon clipping engine

Production-grade polygon clipping supporting Intersection, Union, Difference, and Symmetric Difference (XOR) operations. Handles holes, degeneracies, self-intersecting polygons, and floating-point edge cases.

Algorithm

The Weiler-Atherton algorithm proceeds in five phases:

1. Intersection detection – segment-segment tests between polygon boundaries
2. Entry/exit labeling – cross-product orientation classifies each intersection as entering or exiting the other polygon
3. Polygon tracing – walk along subject/clip polygons, switching at intersections to build result rings
4. Hole handling – process holes independently, classify output rings as exterior/interior by winding, assign holes via point-in-polygon
5. Degeneracy handling – epsilon snap, zero-length edge removal

Operations

• ClipOperation::Intersection – area in both A and B
• ClipOperation::Union – area in A or B (or both)
• ClipOperation::Difference – area in A but not B
• ClipOperation::SymmetricDifference – area in A or B but not both

Enums

ClipOperation

Polygon clipping operation kind.

Functions

clip_multi

Clip subject against a set of clip polygons in sequence.

clip_polygons

Clip two polygons with the given boolean operation.