use-the-available-kernel

use-the-available-kernel

The from-reference loop fails most often not because kernelCAD lacks a primitive, but because the author did not reach for one that exists. This skill is a checklist of hard rules: when condition X holds in the reference, USE primitive Y.

Rule 1 — Non-uniform corner radii → variable fillet

If the reference shows a product where different corners have visibly different radii (Wayfarer brow: 4 mm at temple, 8 mm at outer-top wing corner; bottle shoulders; controller grips), USE the variable-radius form:

shape.fillet([
  { edges: { face: 'top', byNormal: '+Z' }, radius: 8 },
  { edges: { face: 'top', byNormal: '+Z', region: 'temple' }, radius: 4 },
]);

Do NOT author with repeated single-radius .fillet(r) calls and live with a uniform-look body. The scorer detects the sharp vs. rounded corner curvature mismatch in the silhouette gate.

Rule 2 — Symmetric parts → mirror, author one side

If the reference is symmetric about a cardinal plane (eyewear: YZ; most bottles: ZY axis; most consumer products: some cardinal plane), build the right half explicitly and call .mirror('YZ'):

const right = bodyHalf();
const full = right.mirror('YZ');

Do NOT author both halves manually with mirrored arcs. The cost is roughly 2× LoC and creates inevitable asymmetry bugs — the scorer will detect the SSIM break on the opposite side of the model.

Rule 3 — Cross-section varies along the body → surfaceFromCurves

If the body is visibly thicker at one end and thinner at another (acetate frames, handle grips, bottle necks), USE surfaceFromCurves with 2–3 cross-section profiles and .thicken(t):

const body = surfaceFromCurves([
  outlineAtTemple,
  outlineAtBridge,
  outlineAtTemple.mirror('YZ'),
]).thicken(15);

Do NOT uniform-extrude a single silhouette. The resulting slab is what the scorer detects as a "fake" body — the silhouette gate passes, but the SSIM gate fails because the depth profile is wrong.

Rule 4 — Organic curves → smoothSpline