utils/permutation

(no submodules)

Purpose

The permutation module provides the seeded 512-byte permutation table plus the fade and lerp helpers used by every gradient-noise function in @suaveplan/noise. Centralising these shared utilities here keeps Perlin, Simplex, and Value noise consistent with one another: they all consume a table shuffled by Sfc32Rng.

Features

buildPermutation(seed) — seeded 512-byte Uint8Array; first 256 entries are a Fisher-Yates shuffle of [0, 255], second 256 mirror the first (so hash wrap-around is free)
fade(t) — Perlin's quintic fade curve 6t^5 - 15t^4 + 10t^3
lerp(a, b, t) — standard linear interpolation

Usage: Basic Example

import { buildPermutation, fade } from "@suaveplan/noise";

const p = buildPermutation("terrain-42");
const f = fade(0.5); // 0.5

Usage: Advanced Example

import { buildPermutation, fade, lerp } from "@suaveplan/noise";

const perm = buildPermutation(0);
// Hash 2D integer coordinates through the table:
function hash2(xi: number, yi: number): number {
  return perm[((perm[xi & 0xff] as number) + (yi & 0xff)) & 0x1ff] as number;
}

API Reference

buildPermutation(seed: string | number): Uint8Array — deterministic 512-byte table.
fade(t: number): number — Perlin's quintic smoothing, returns 0 at t=0 and 1 at t=1.
lerp(a: number, b: number, t: number): number — returns a + (b-a)*t.

Implementation Notes

Uint8Array uses one byte per entry, so the full table fits in 512 bytes of memory and stays in L1 cache during long noise evaluation loops. The Fisher-Yates shuffle runs 255 steps and uses rng.nextUint32() % (i+1) — the small modulo bias is statistically irrelevant for noise-table generation. The second-half mirror lets consumers do perm[(a + b) & 0x1ff] without branching or masking a/b first.

1.9 KiB Raw Blame History