noise.mjs

Blame: the commit that last changed each line · file · history

`1de9dc7c` 2026-09-07 Pavel Safronov	1	/**
	2	* Deterministic value noise with fBm, wrapping on the y (theta) axis.
	3	*
	4	* The map is a cylinder: y wraps and x does not. Noise that ignores that leaves a
	5	* visible seam down the map, so the lattice wraps at a caller-supplied period.
	6	*/
	7
	8	/**
	9	* 32-bit integer hash. Uses Math.imul throughout: the obvious float version
	10	* silently loses precision on large products and leaves axis-aligned streaks
	11	* across the terrain.
	12	*/
	13	function hash(x, y, seed) {
	14	let h = Math.imul(x \| 0, 374761393) ^ Math.imul(y \| 0, 668265263) ^ Math.imul(seed \| 0, 1274126177)
	15	h = Math.imul(h ^ (h >>> 15), 2246822519)
	16	h = Math.imul(h ^ (h >>> 13), 3266489917)
	17	return ((h ^ (h >>> 16)) >>> 0) / 4294967295
	18	}
	19
	20	const smooth = (t) => t * t * (3 - 2 * t)
	21
	22	/** Value noise at (x, y) on a lattice, wrapping y every `wrapY` cells. */
	23	function value(x, y, seed, wrapY) {
	24	const xi = Math.floor(x)
	25	const yi = Math.floor(y)
	26	const xf = smooth(x - xi)
	27	const yf = smooth(y - yi)
	28	const wrap = (v) => (wrapY > 0 ? ((v % wrapY) + wrapY) % wrapY : v)
	29	const y0 = wrap(yi)
	30	const y1 = wrap(yi + 1)
	31	const a = hash(xi, y0, seed)
	32	const b = hash(xi + 1, y0, seed)
	33	const c = hash(xi, y1, seed)
	34	const d = hash(xi + 1, y1, seed)
	35	return (a + (b - a) * xf) * (1 - yf) + (c + (d - c) * xf) * yf
	36	}
	37
	38	/** Fractal Brownian motion in [0,1]. `wrapY` is the lattice period on the y axis. */
	39	export function fbm(x, y, { octaves = 4, seed = 1, wrapY = 0, lacunarity = 2, gain = 0.5 } = {}) {
	40	let sum = 0
	41	let amp = 1
	42	let norm = 0
	43	let freq = 1
	44	for (let o = 0; o < octaves; o++) {
	45	sum += value(x * freq, y * freq, seed + o * 101, wrapY * freq) * amp
	46	norm += amp
	47	amp *= gain
	48	freq *= lacunarity
	49	}
	50	return sum / norm
	51	}
	52
	53	/** Ridged fBm — absolute-valued and inverted, which makes mountain crests. */
	54	export function ridged(x, y, opts = {}) {
	55	const { octaves = 4 } = opts
	56	let sum = 0
	57	let amp = 1
	58	let norm = 0
	59	let freq = 1
	60	for (let o = 0; o < octaves; o++) {
	61	const v = 1 - Math.abs(value(x * freq, y * freq, (opts.seed ?? 1) + o * 211, (opts.wrapY ?? 0) * freq) * 2 - 1)
	62	sum += v * v * amp
	63	norm += amp
	64	amp *= 0.5
	65	freq *= 2
	66	}
	67	return sum / norm
	68	}