71 lines
2.6 KiB
C
71 lines
2.6 KiB
C
#include <math.h>
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#include "world/perlin.h"
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// adapted from: https://gist.github.com/nowl/828013#gistcomment-2807232
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static const uint8_t PERLIN_PERM_TABLE[] = {
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208,34,231,213,32,248,233,56,161,78,24,140,71,48,140,254,245,255,247,247,40,
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185,248,251,245,28,124,204,204,76,36,1,107,28,234,163,202,224,245,128,167,204,
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9,92,217,54,239,174,173,102,193,189,190,121,100,108,167,44,43,77,180,204,8,81,
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70,223,11,38,24,254,210,210,177,32,81,195,243,125,8,169,112,32,97,53,195,13,
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203,9,47,104,125,117,114,124,165,203,181,235,193,206,70,180,174,0,167,181,41,
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164,30,116,127,198,245,146,87,224,149,206,57,4,192,210,65,210,129,240,178,105,
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228,108,245,148,140,40,35,195,38,58,65,207,215,253,65,85,208,76,62,3,237,55,89,
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232,50,217,64,244,157,199,121,252,90,17,212,203,149,152,140,187,234,177,73,174,
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193,100,192,143,97,53,145,135,19,103,13,90,135,151,199,91,239,247,33,39,145,
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101,120,99,3,186,86,99,41,237,203,111,79,220,135,158,42,30,154,120,67,87,167,
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135,176,183,191,253,115,184,21,233,58,129,233,142,39,128,211,118,137,139,255,
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114,20,218,113,154,27,127,246,250,1,8,198,250,209,92,222,173,21,88,102,219
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};
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static int32_t perlin_noise2_sample(int32_t seed, int32_t x, int32_t y) {
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int32_t yindex = (y + seed) % 256;
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if (yindex < 0)
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yindex += 256;
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int32_t xindex = (PERLIN_PERM_TABLE[yindex] + x) % 256;
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if (xindex < 0)
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xindex += 256;
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return PERLIN_PERM_TABLE[xindex];
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}
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static double perlin_lerp(double x, double y, double t) {
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return x + t*(y - x);
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}
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static double perlin_smooth_lerp(double x, double y, double t) {
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return perlin_lerp(x, y, t * t * (3-2*t));
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}
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double perlin_noise2d(int32_t seed, double x, double y) {
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int32_t x_int = floor(x);
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int32_t y_int = floor(y);
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double x_frac = x - x_int;
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double y_frac = y - y_int;
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int32_t s = perlin_noise2_sample(seed, x_int, y_int);
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int32_t t = perlin_noise2_sample(seed, x_int+1, y_int);
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int32_t u = perlin_noise2_sample(seed, x_int, y_int+1);
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int32_t v = perlin_noise2_sample(seed, x_int+1, y_int+1);
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double low = perlin_smooth_lerp(s, t, x_frac);
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double high = perlin_smooth_lerp(u, v, x_frac);
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double result = perlin_smooth_lerp(low, high, y_frac);
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return result;
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}
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double perlin_fbm(int32_t seed, double x, double y, double freq, uint32_t octaves) {
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double xa = x*freq;
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double ya = y*freq;
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double amp = 1.0;
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double res = 0.0;
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double div = 0.0;
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for (uint32_t i=0; i<octaves; i++) {
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div += 256.0 * amp;
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res += perlin_noise2d(seed, xa, ya) * amp;
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amp *= 0.5;
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xa *= 2.0;
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ya *= 2.0;
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}
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return res/div;
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}
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