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Three reviewer-meeting deliverables in one commit.
(1) output_uv_map for the two remaining DCE entries
─────────────────────────────────────────────────
* Discrete_inversive_distance.h: full implementation. After Newton,
reconstruct effective Euclidean edge lengths from the converged
log-radii via the Bowers-Stephenson identity
`ℓᵢⱼ² = rᵢ² + rⱼ² + 2·Iᵢⱼ·rᵢ·rⱼ`, populate a temporary
EuclideanMaps with `lambda0 = log(ℓᵢⱼ²)`, and reuse the existing
`euclidean_layout(mesh, 0, eucl)` priority-BFS. Per-vertex
Point_2 coordinates written into the user-supplied pmap.
Optional `normalise_layout(true)` applies the canonical PCA
centroid + major-axis rotation, same as the other 3 entries.
* Discrete_circle_packing.h: throws std::runtime_error with a
clear pointer to Phase 9c rather than silently producing
nonsense. CP-Euclidean is face-based; the faithful output is a
per-face circle packing in ℝ², not a per-vertex Point_2 map.
A true layout requires BPS-2010 §6 (~150 lines, on the porting
roadmap as Phase 9c). Failing loudly is the honest default.
Tests: 2 new cases in test_cgal_phase8b_lite.cpp
(OutputUvMap_InversiveDistance_PopulatesPmap;
OutputUvMap_CPEuclidean_ThrowsClearly). Both green.
Suite total now 259 (was 257, +2). CGAL subtotal: 234 → 236.
(2) Reviewer meeting documents
──────────────────────────
New directory doc/reviewer/ with three files:
* briefing.md — one-page orientation for the reviewer.
What the project is, where to look first
(https://tmoussa.codeberg.page/ConformalLabpp/), the headline
evidence (tests/coverage/sanitizers/license), what we want from
them, what's deferred and why, and the 5 questions in a separate
file.
* questions.md — the 5 concrete decisions we want their second
opinion on:
Q1 Phase 9c (port-literal vs re-derive)
Q2 Phase 9b-analytic (worth ~2 weeks for ~6× speedup?)
Q3 CP-Euclidean output_uv_map (build now or defer?)
Q4 CGAL submission strategy (one package or five?)
Q5 geometry-central cross-validation co-authorship
Plus an explicit "what would you say no to?" question at the
bottom — negative feedback is the highest-value information.
* agenda.md — my own internal playbook (NOT to be sent).
60-min flow: 5-min thank-you, 10-min architecture tour,
30-min for Q1-Q5 in the order Q4-Q1-Q2-Q5-Q3, 5-min "no"
question, 5-min wrap-up. Includes post-meeting memo template
to fill out in the 30 min after.
* README.md — index for the directory; says which file goes
to whom and when to send.
(3) locked-vs-flexible.md known-limitations update
─────────────────────────────────────────────
"output_uv_map covers 3 of 5 entries" → "covers 4 of 5".
CP-Euclidean's throws-clearly behaviour documented as a Phase 9c
deliverable rather than a passive gap.
Bonus: extended .codespellrc ignore list (acknowledgement, the
British-English spelling I used in agenda.md).
Verifications on this commit:
259/259 tests pass (0 skipped)
scripts/check-test-counts.sh: OK (23 + 236 = 259)
scripts/quality/license-headers.sh: OK (66/66 SPDX)
python3 scripts/quality/cgal-conventions.py: OK (0/6 violations)
scripts/quality/codespell.sh: OK (0 typos)
scripts/quality/shellcheck.sh: OK (0 findings)
python3 scripts/check-markdown-links.py: OK (143/143)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Markdown
# Questions for the external reviewer
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> Please skim this before the meeting. Each question is scoped so that
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> "do A" / "do B" / "either is fine" is a sufficient answer; deeper
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> dives are welcome but not required.
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These are the five decisions that would benefit most from a second
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opinion. Items 1-3 affect the porting roadmap directly; 4-5 affect
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the long-term goal (CGAL submission).
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---
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## Q1 — Phase 9c (4g-polygon canonical form): port-literal vs re-derive?
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The Java original has two utility classes:
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- `FundamentalPolygonUtility` (~600 lines)
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- `CanonicalFormUtility` (~900 lines)
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that together compute the canonical 4g-polygon for a higher-genus
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surface from its cut graph.
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We can either:
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- **(A) Port literally** (~2 weeks). Faithful, predictable, fixes
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the Java algorithm in C++. Down-side: we inherit the Java code's
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ad-hoc style and edge-case handling.
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- **(B) Re-derive from Springborn 2020 §5** (~3 weeks). Uses our
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existing `cut_graph.hpp` + holonomy infrastructure cleanly.
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Down-side: longer; potential for new bugs not seen by the Java
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original's test cases.
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**Question**: which route do you prefer, and is there a Springborn-era
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reference implementation (Mathematica notebook, paper appendix) we
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should cross-validate against?
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Context: `doc/roadmap/phases.md` §Phase 9c, `doc/roadmap/porting-status.md`.
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---
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## Q2 — Phase 9b-analytic Hessian: implement now or later?
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We have:
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- **Done**: per-face block-FD Hessian (96× faster than naive full-FD).
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- **Derived but not implemented**: analytic Hessian via the Schläfli
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identity, expected ~6× further speedup over block-FD.
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- **Derivation document**:
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[`doc/math/hyperideal-hessian-derivation.md`](../math/hyperideal-hessian-derivation.md)
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(805 lines, all sign pitfalls covered, references Schläfli 1858,
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Milnor 1982, Vinberg 1993, Cho-Kim 1999, Glickenstein 2011,
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Springborn 2020).
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**Question**:
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- At what mesh size does the ~6× become user-visible enough to
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justify ~2 weeks of implementation work?
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- Are you aware of subtleties in the Schläfli-based derivation our
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document might be missing?
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If the answer is "implement", we'd target Phase 9b-analytic right
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after the meeting.
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---
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## Q3 — `output_uv_map` for CP-Euclidean: build now or defer?
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For CP-Euclidean (face-based DOFs, BPS 2010) the natural output is a
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**per-face circle packing** in ℝ² — not a per-vertex `Point_2` map
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the way the other four DCE entries produce.
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Today the entry throws `std::runtime_error` with a helpful pointer if
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the caller passes `output_uv_map(...)`. A faithful layout would be
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~150 lines implementing BPS-2010 §6.
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**Question**: do *your* CP-Euclidean use cases need a UV-like output,
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or are the face circle radii themselves the deliverable? The answer
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shapes whether Phase 9c gets it now or later.
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---
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## Q4 — CGAL submission strategy: one package or five?
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For the long-term CGAL submission:
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- **(A) One package** "Discrete_conformal_map" — single entry header,
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five solver functions, one set of named parameters. Easier for
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users to find; harder to compartmentalise reviews.
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- **(B) Five packages** "Discrete_*" — each DCE model is its own
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CGAL package with its own concept + reference manual. More
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ceremony for users; more familiar review surface for CGAL editors.
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Today the code is structured per-functional (Strategy C — see
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[`locked-vs-flexible.md`](../architecture/locked-vs-flexible.md) §7).
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Either submission packaging is achievable from this base.
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**Question**: what's the CGAL editor convention for related-but-distinct
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algorithms — Polygon_mesh_processing as one example (one package, many
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algorithms), vs Triangulation_2/Triangulation_3/Periodic_*/Hyperbolic_*
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as another (multiple packages for related algorithms)?
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---
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## Q5 — geometry-central cross-validation (GC-1)
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Two libraries solve the DCE problem from opposite algorithmic
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directions:
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- **conformallab++**: Newton on the fixed mesh (no intrinsic flips).
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- **geometry-central**: Ptolemy flips on an intrinsic triangulation.
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An automated comparison on common meshes would be:
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- A nice paper (the disagreement modes are interesting in their own
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right).
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- A confidence-building tool for both libraries (we benefit from
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catching corner-case bugs, they benefit from cross-validation
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against a Newton baseline).
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- ~3 days of plumbing (CMake-fetch geometry-central, write 5 common
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test meshes, compare `u_per_vertex` to a tolerance).
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**Question**: would you be interested in co-authoring such a comparison
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note (with us doing the implementation)? Or do you know someone in
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the Crane group who would?
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---
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## Things you do *not* need to comment on (unless you want)
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- C++ style choices captured in `.clang-format` + `.clang-tidy`.
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- Test framework choice (GTest).
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- License (MIT, with vendored deps catalogued in
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[`code/deps/THIRD-PARTY-LICENSES.md`](../../code/deps/THIRD-PARTY-LICENSES.md)).
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- Build system (CMake ≥ 3.20, header-only consumer + optional
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CLI/Viewer).
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These are conscious decisions matched to CGAL conventions and aren't
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load-bearing in the sense that revisiting them later is cheap.
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---
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## What I'm hoping you'll say "no" to
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This is a deliberately blunt question because positive feedback is
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nice but negative feedback is rarer and more valuable:
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**Looking at any of the 12 architecture decisions in
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[`locked-vs-flexible.md`](../architecture/locked-vs-flexible.md), is
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there one where you think "no, that's the wrong call, here's why"?**
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The 🔴 load-bearing decisions are the most consequential to revisit,
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because waiting longer makes them more expensive. No is the most
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useful answer.
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