ludic/docs/language/noise/noise-perlin2.md
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feat(stdlib): add Noise.* — deterministic fixed-point procedural noise (#3)
A Noise.* namespace for procedural generation, implemented entirely in Q16.16
fixed point over an integer permutation hash so a seed reproduces the exact same
field on every platform and run (native/headless/wasm) — the determinism edge
over float noise that drifts across CPUs.

  - value2 / perlin2 / simplex2  — value, gradient, and simplex noise -> [-1,1]
  - fbm2(x,y,seed,octaves)       — fractal Brownian motion (octaves of simplex)
  - cellular2 / cellular2_id     — Worley F1 distance + nearest-cell id
  - unit(n)                      — remap [-1,1] -> [0,1]

Covers issue phases 1–2 fully plus cellular from phase 3; domain warp, ridged/
billow, and sample1/sample3 remain as follow-ups. Pure integer IR, C-free;
cellular/fbm reuse the math prelude's fx_sqrt.

- examples/library/noise.ludic: asserts the invariants a fixed-point generator
  must hold (Perlin == 0 at lattice points, every sampler within [-1,1],
  reproducibility, seed sensitivity, non-negative cellular distance). Wired into
  `x test` (now 52 passed).
- docs: a new Noise section + per-symbol pages; inventory and coverage pass.
- seed regenerated; `x bootstrap-cfree` fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-30 21:50:50 +03:00

1.3 KiB

id name category kind tokens sig tip order ns member
noise-perlin2 Noise.perlin2 noise namespace-method Noise.perlin2 Noise.perlin2(x, y, seed) -> fixed 2D Perlin gradient noise, deterministic, in [-1, 1]. 2 Noise perlin2

Samples 2D Perlin gradient noise at (x, y) for the given seed and returns a fixed in [-1, 1]. Instead of a random value per lattice point, Perlin places a random gradient at each corner and interpolates their dot products with the offset vectors — which gives smoother, more natural gradients than value noise, the familiar look of classic terrain and cloud fields. By construction the value is exactly 0 at every integer lattice point.

Deterministic in fixed point across platforms and runs. Scale the coordinates to set feature size, and stack octaves with Noise.fbm2 for richer detail.

Parameters:

  • x, y — the sample coordinates (fixed)
  • seed — the field selector
program Perlin {
  entry {
    let seed = 1337
    if Noise.perlin2(fixed(0), fixed(0), seed) == 0 { print(1) }   # zero at the lattice
    let n = Noise.perlin2(fixed(10) / fixed(3), fixed(7) / fixed(3), seed)
    print(Math.floor(n * fixed(1000)))
  }
}