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util/perlin.c

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+
+#include <math.h>
+
+double rawnoise(int n) {
+    n = (n << 13) ^ n;
+    return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0);
+}
+
+double noise2d(int x, int y, int octave, int seed) {
+    return rawnoise(x * 1619 + y * 31337 + octave * 3463 + seed * 13397);
+}
+
+double interpolate(double a, double b, double x) {
+    double f = (1 - cos(x * 3.141593)) * 0.5;
+
+    return a * (1 - f) + b * f;
+}
+
+double smooth2d(double x, double y, int octave, int seed) {
+    int intx = (int) x;
+    double fracx = x - intx;
+    int inty = (int) y;
+    double fracy = y - inty;
+
+    double v1 = noise2d(intx, inty, octave, seed);
+    double v2 = noise2d(intx + 1, inty, octave, seed);
+    double v3 = noise2d(intx, inty + 1, octave, seed);
+    double v4 = noise2d(intx + 1, inty + 1, octave, seed);
+
+    double i1 = interpolate(v1, v2, fracx);
+    double i2 = interpolate(v3, v4, fracx);
+
+    return interpolate(i1, i2, fracy);
+}
+
+
+double pnoise2d(double x, double y, double persistence, int octaves, int seed) {
+    double total = 0.0;
+    double frequency = 1.0;
+    double amplitude = 1.0;
+    double max = 0.0;
+
+    for (int i = 0; i < octaves; i++) {
+        total += smooth2d(x * frequency, y * frequency, i, seed) * amplitude;
+        max += amplitude;
+        frequency /= 2.0;
+        amplitude *= persistence;
+    }
+
+    // Normalize to [0, 1]
+    return (total + max) / (2.0 * max);
+}