Function simTri

js/smartResolution.js:121–166

(a, b, c, T, memo, depth)

  } else if (n === 1) {
    // 1→2 bisect: split edge a (longest), unsplit edges b and c stay intact in
    // separate children.  Median from opposite vertex to a's midpoint:
    //   m = ½ √(2b² + 2c² − a²)
    const m = 0.5 * Math.sqrt(Math.max(0, 2*b*b + 2*c*c - a*a));
    total = simTri(a / 2, b, m, T, memo, depth + 1)
          + simTri(a / 2, c, m, T, memo, depth + 1);
  } else {
    // n === 2: 1→3 fan.  Sorted descending → untouched edge is the smallest (c);
    // split neighbours are a and b.  Median from a's opposite vertex to a's
    // midpoint:  m = ½ √(2b² + 2c² − a²).
    const m = 0.5 * Math.sqrt(Math.max(0, 2*b*b + 2*c*c - a*a));
    total = simTri(c,     a / 2, m,     T, memo, depth + 1)
          + simTri(m,     c / 2, b / 2, T, memo, depth + 1)
          + simTri(b / 2, c / 2, a / 2, T, memo, depth + 1);
  }

  memo.set(key, total);
  return total;
}

// ── Decimation-target recommendation ─────────────────────────────────────────
//
// Estimates the post-decimation triangle count that preserves the texture's
// detail with minimum impact on visual quality.  Based on:
//
//   target_edge = COARSEN × pixelsPerEdge × pixMm × √(REF_AMP / max(amp, MIN_AMP))
//   N_tri       = K_geom × surfaceArea / target_edge²
//
// COARSEN = 1.0 → Nyquist target: triangle edge matches the texture's intrinsic
// detail spacing.  Earlier we tried 3× ("aggressive"), but that gave acceptable
// quality only on structured textures (logos, knurling) — on noise / fbm /
// leather textures, 3× coarsen produces visible faceting because every pixel
// of noise IS a feature, not just the high-gradient ones the analyser flags.
// At 1× the user can still drag the max-tri slider down for smaller files;
// the bench (bench-decim-quality.mjs) shows error becomes imperceptible at
// this ratio for both smooth and sharp test textures.
//
// Amplitude scaling: low amplitude needs fewer triangles to faithfully
// represent a gentle relief; high amplitude (heavy displacement) needs more.
const DECIM_COARSEN = 1.0;
const DECIM_REF_AMP = 0.5;
const DECIM_MIN_AMP = 0.1;
const DECIM_MIN_TRI = 10_000;
// Recommendation ceiling.  Sized for sensible default file sizes — much
// smaller than HARD_CAP_TRIANGLES (which is the OOM ceiling for what the
// pipeline can survive).  Users who want more can drag the Max Triangles
// slider up to its full range (20M); Smart just won't suggest above this
// by itself, since the downstream printable mesh rarely needs more.
const DECIM_MAX_TRI = 2_000_000;