feat(domain): onion-shaped hero domain for layers visualization

[domattioli]

Motivation

Need a domain shaped like a real onion — bulbous body, small stem nub at top, flat root-plate dimple at bottom — as a hero image for the QuADMESH layers concept. An onion cross-section is literally a nested-ring structure; the concentric CHILmesh skeleton layers map 1-to-1 onto the biological layers of the onion. Better than any abstract polygon for communicating what the algorithm does.

Geometry spec

         ___
        /   \      ← stem nub: small convex protrusion, ~5–8% of total height
       / ___  \
      |/     \|
     /  BODY   \   ← main body: oblate ellipse, width ≈ 1.4× height
    |           |
     \         /
      \_______/    ← root plate: slight inward concavity / flat dimple
         |||       ← root hairs (optional, decorative only)

Key geometric features:

• Body: oblate ellipse (a ≈ 1.0, b ≈ 0.70) — onions are wider than tall
• Stem nub: small convex bump at top (blend radius ~0.05), roughly centred
• Root plate: shallow concave indent at bottom (depth ~0.03–0.05), width ~30% of body diameter
• Silhouette should be recognisable at thumbnail scale (~300×300 px)

Intended use

1. Export .14 (ADCIRC fort.14 format) via ADMESH-Domains (see cross-post issue there).
2. Run QuADMESH faithful path → 30+ skeleton layers → screenshot the layer sweep.
3. Use rendered animation / still as README / docs hero image illustrating the layer-by-layer quad sweep.

Acceptance criteria

• Polygon is watertight, no self-intersections
• Triangulated mesh in .14 format, ~2 000–5 000 elements (fine enough for smooth layers, fast enough for demo)
• Recognisable onion silhouette with stem nub + root plate features
• ≥ 20 concentric CHILmesh skeleton layers (validates nested structure)
• Zero interior tris after tri2quad faithful pass
• Screenshot / render committed alongside mesh file

Cross-post

ADMESH-Domains issue for the .14 generation: domattioli/Valence#93

References

• README layers diagram (current placeholder uses rectangular grid)
• tests/fixtures/meshes/ — existing .14 fixtures for format reference

[domattioli]

might belong on the chilmesh repo

[domattioli]

Agent guidance — 2026-05-29

Cross-repo coordination required — do not duplicate work.

This issue is one of three that describe the same onion-domain deliverable:

• feat(domain): onion-shaped hero domain for layers visualization #46 (this) — onion domain for hero image + layer visualization
• domattioli/QuADMESH#101 — same onion domain, same acceptance criteria (duplicate tracking)
• feat(domain): onion-shaped domain for QuADMESH hero image Valence#93 — the .14 fort.14 mesh generation piece (the upstream step)

Correct execution order:

1. ADMESH-Domains#93 produces the watertight .14 mesh (polygon + triangulation)
2. This issue (QuADMESH#46 / #101) loads it via CHILmesh, validates n_layers ≥ 20, runs the faithful tri2quad sweep, screenshots the layer sweep

An agent working only in QuADMESH cannot create the .14 — it must either pull the artifact from ADMESH-Domains or coordinate with an ADMESH-Domains session. Do not re-implement domain generation here.

QuADMESH#101 appears to be a duplicate of this issue — consider closing #101 with a reference to #46 once the work is underway, to avoid split effort.

---

Generated by Claude Code