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feat(geometry): pn_geometry.hpp — Pn projective-metric substrate (jReality port)

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Ports the small but pervasive de.jreality.math.Pn surface that the Java
algorithmic core uses across every not-yet-ported geometric phase:
HyperbolicLayout, SphericalLayout, FundamentalPolygon (9c), KoebePolyhedron
(10c'), quasi-isothermic (10e), hyperelliptic theta, CircleDomain (11c).
Porting it once unblocks all downstream consumers instead of re-deriving
the metric ad hoc per phase.

pn_geometry.hpp — header-only, Eigen, ~120 LOC:
  PnMetric { EUCLIDEAN=0, ELLIPTIC=+1, HYPERBOLIC=-1 } matching jReality.
  pn_inner_product  — bilinear form per signature.
  pn_norm / pn_dehomogenize / pn_set_to_length / pn_normalize.
  pn_distance_between — Euclidean (spatial), elliptic (acos), hyperbolic (acosh).
  pn_linear_interpolation — affine (E) and slerp (S/H constant-speed geodesic).

HYPERBOLIC uses the timelike-positive ("upper-sheet") convention, identical to
the already-verified projective_math.hpp::hyperbolicDistance; pn_distance_between
is regression-anchored against it in the tests.

test_pn_geometry.cpp — 6 tests, all GREEN:
  InnerProductSignatures, EuclideanDistance, EllipticDistanceIsAngle,
  HyperbolicDistanceClosedFormAndAnchor (+ projective_math.hpp anchor),
  NormAndScaling, LinearInterpolationGeodesic.

doc/roadmap/java-parity.md — new "Infrastructure / support layers" section:
  de.jreality.math.Pn   → pn_geometry.hpp (partial, 6 fns covering core usage)
  de.jreality.math.Rn   → Eigen (no separate port needed)
  MatrixBuilder         → not yet (only needed for hyperelliptic theta)
  conformallab XML types → not planned (GUI persistence, not algorithmic)

246/246 cgal tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Tarik Moussa
2026-05-30 17:00:15 +02:00
parent 5de95a7a93
commit 149da15c64
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doc/roadmap/java-parity.md
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@@ -43,6 +43,20 @@ as the reference implementation for expected behaviour, edge cases, and test cas
---
## Infrastructure / support layers
These are not algorithmic phases but shared geometry substrates that multiple phases
depend on. Porting them once unblocks all downstream consumers.
| Java library | What it provides | C++ status | Notes |
|---|---|---|---|
| **`de.jreality.math.Pn`** | Projective-metric primitives: inner product, norm, distance, geodesic interpolation in Euclidean / Elliptic / Hyperbolic signatures | ⚠️ **partial** → `pn_geometry.hpp` (2026-05-30) | 6 functions (~30 LOC) cover the entire surface used by the Java algorithmic core (27 files, ≈106 imports). Unblocks: HyperbolicLayout, SphericalLayout, FundamentalPolygon (9c), KoebePolyhedron (10c'), quasi-isothermic (10e), hyperelliptic θ, CircleDomain (11c). |
| **`de.jreality.math.Rn`** | Real vector / matrix utilities (add, sub, scale, dot, norm, …) | ⚠️ partial → Eigen | The Rn surface used in the core (16 distinct methods) maps directly onto Eigen VectorXd / MatrixXd operations. No separate port needed; call-sites replace `Rn.foo(a,b)` with Eigen expressions inline. |
| **`de.jreality.math.MatrixBuilder`** | Isometry construction: `rotateFromTo`, `translateFromTo` in Euclidean / Hyperbolic models | ❌ not yet | Used only by `HyperIdealHyperellipticUtility` (hyperelliptic θ). Port on demand when that utility is needed. |
| **conformallab XML types** (`de.varylab.conformallab.types.*`) | JAXB-generated persistence format for Java GUI state (`HalfedgeEmbedding`, `UniformizationData`, …) | ❌ not planned | GUI / persistence layer, not an algorithmic substrate. conformallab++ has its own serialisation (`serialization.hpp`). Asset-specific parsers (e.g. for `lawson_curve_source.xml`) are added on demand, not as a general port. |
---
## Java utility classes not yet ported
These exist in `de.varylab.discreteconformal.util` in the Java library.