@fourjs/geometry

Geometry primitives and buffers. Part of fourJS.

Implements the MVP tier of §50–53 in docs/SPECIFICATION.md; shipped in Phase 3 (§106). Coordinates follow the §7a right-handed Y-up convention.

What's here

• BufferGeometry — positions, optional normals, index (GeometryIndexArray), draw mode (GeometryDrawMode, including "lines"), and bounds (GeometryBounds).
• 2D primitive factories — boxGeometry, planeGeometry, circleGeometry2D, polygonGeometry2D, each with an options type.
• 3D primitive factories — sphereGeometry, cylinderGeometry, coneGeometry, capsuleGeometry, torusGeometry, latheGeometry, tubeGeometry, extrudeGeometry, heightFieldGeometry.
• Path (§51) — the six segment kinds, a fluent builder, flatten / subdivide / simplify / reverse / transform, length and point/tangent/normal evaluation, closest-point queries, fillRings for the two fill rules, and flatten-then-clip Booleans (booleanOp / union / intersect / subtract / xor).
• Tessellation (§52) — triangulatePolygon (ear clipping with bridged holes) behind the PolygonTessellator seam, and expandStroke, which widens polylines into §58's stroke band: alignment, butt/round/square caps, miter/round/bevel joins with a miter limit, and dashes with a phase offset. Path.polylines is the flattening it takes, closedness and all.
• SVG path data (§50) — parseSvgPathData reads a d attribute into a Path, formatSvgPathData writes one back out (optional { precision } is opt-in; the default stays String(value)). Coordinates are transcribed verbatim: SVG's Y-down user space is not flipped, because the transform that would land it in a Y-up world needs the document's viewBox. See the module header for the whole argument and the one-line correction.
• SVG documents (§50) — parseSvgDocument tokenizes <svg> markup in-process (no DOMParser): svg / g / path / rect / circle / ellipse / line / polyline / polygon, plus viewBox, transform, fill, stroke, and fill-rule. <!DOCTYPE and external entities are refused (§96).

Corrected 2026-08-09 (gap R-26): this section listed only BufferGeometry and "boxGeometry, planeGeometry, and circleGeometry2D", and the section below said the path model and tessellation were "staged / not yet implemented". Both shipped — tessellation on 2026-08-09 (R-25), the path model the same day (R-24), and the SVG bridge with this change.

Staged / not yet implemented

• Offset paths — §51's remaining staged operation. The offset now has §58's join model (expandStroke, gap R-16) but is a different output — a Path, not triangles.
• Anti-alias fringe generation — §52's remaining half. A fringe is a second band carrying a coverage ramp, and a ramp needs a per-vertex coverage attribute no §57 pipeline reads: it is a pipeline decision, and it lands with the ShapeMaterial packet that owns that pipeline.
• Curve-arrangement Booleans — booleanOp flattens first; a Bentley–Ottmann pass on the live segments is still the packet §52 wants for self-intersections.

Unit tests are colocated in tests/ per §92.

Workspace name @fourjs/geometry; publishes as @danielsimonjr/fourjs-geometry.