tweak

random.js

@@ -0,0 +1,51 @@
+import { clamp } from "./grid.js";
+
+export function hash2(x, y, seed) {
+  let h = Math.imul((x | 0) ^ (seed | 0), 374761393) + Math.imul((y | 0) ^ ((seed >>> 1) | 0), 668265263);
+  h = (h ^ (h >>> 13)) >>> 0;
+  h = Math.imul(h, 1274126177) >>> 0;
+  return ((h ^ (h >>> 16)) >>> 0) / 4294967295;
+}
+
+export function rand(seed, n) {
+  return hash2(n * 7919 + 17, n * 104729 + 31, seed);
+}
+
+export function smoothstep(t) {
+  t = clamp(t);
+  return t * t * (3 - 2 * t);
+}
+
+export function lerp(a, b, t) {
+  return a + (b - a) * t;
+}
+
+export function valueNoise(x, y, seed, scale) {
+  const sx = x / scale;
+  const sy = y / scale;
+  const x0 = Math.floor(sx);
+  const y0 = Math.floor(sy);
+  const tx = smoothstep(sx - x0);
+  const ty = smoothstep(sy - y0);
+
+  const a = hash2(x0, y0, seed);
+  const b = hash2(x0 + 1, y0, seed);
+  const c = hash2(x0, y0 + 1, seed);
+  const d = hash2(x0 + 1, y0 + 1, seed);
+
+  return lerp(lerp(a, b, tx), lerp(c, d, tx), ty);
+}
+
+export function fbm(x, y, seed) {
+  let amp = 1;
+  let scale = 54;
+  let sum = 0;
+  let norm = 0;
+  for (let i = 0; i < 5; i++) {
+    sum += valueNoise(x, y, seed + i * 101, scale) * amp;
+    norm += amp;
+    amp *= 0.5;
+    scale *= 0.5;
+  }
+  return sum / norm;
+}