uber / h3-go / 27727545624

100%

master: 100%

Pull #130

github

feat: add pure-Go regions (polygon/cells, multipolygon) to x/h3go

Implements the full H3 regions API in pure Go, verified against the cgo
reference:

- PolygonToCells (legacy flood-fill polyfill) and GeoPolygon.Cells, with the
  GeoPolygon/GeoLoop types, bounding-box helpers, and a ray-casting
  point-in-polygon test.
- PolygonToCellsExperimental with the ContainmentMode options (center, full,
  overlapping, overlapping-bbox): a hierarchical traversal of the cell grid
  exposed as a native iter.Seq, with cellToBBox (res-0, pole, and edge-length
  tables), bbox overlap/contains/scale/normalization, and cell-boundary
  intersection tests.
- CellsToMultiPolygon via the arc/union-find outline algorithm, assembling
  cell sets into polygons (outer loop plus holes) ordered by area, including
  the eight-triangle globe representation for a fully covered set. A Go map
  replaces the C hash table, which only accelerates lookup without affecting
  the result.

Verified against the cgo reference as sets across many polygons, all
containment modes, resolutions, and cell sets (blobs, rings, disjoint
regions, pentagons, the whole globe), plus error parity. 100% per-package
statement coverage by in-package tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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4170 of 4170 relevant lines covered (100.0%)

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