libcruft-util/perlin.cpp

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#include "perlin.hpp"
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#include "bitwise.hpp"
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#include "debug.hpp"
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#include "hash.hpp"
#include "lerp.hpp"
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#include "maths.hpp"
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#include "random.hpp"
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#include <cmath>
#include <limits>
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struct params {
typedef size_t seed_t;
unsigned octaves;
double persistence;
seed_t seed;
double
generate (intmax_t x, intmax_t y) {
intmax_t mixed = rotate_left (x, sizeof (x) * 4) | y;
seed_t key = (seed_t)mixed ^ seed;
return util::hash (key) / (double)std::numeric_limits<intmax_t>::max ();
}
double
smooth2d (intmax_t x, intmax_t y) {
double corners = (generate(x - 1, y - 1) +
generate(x + 1, y - 1) +
generate(x - 1, y + 1) +
generate(x + 1, y + 1)) / 16.0;
double sides = (generate(x - 1, y ) +
generate(x + 1, y ) +
generate(x, y - 1) +
generate(x, y + 1)) / 8.0;
double center = generate(x, y ) / 4.0;
return corners + sides + center;
}
params ():
octaves (16),
persistence (0.7),
seed (util::random<size_t> ())
{ ; }
};
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// Just a random generator [-1.0, 1.0]
static float
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generate (intmax_t x, intmax_t y, size_t seed) {
intmax_t n = x + 257 * y;
n = (n << 13U) ^ n ^ seed;
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return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0f);
}
double
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smooth2d (intmax_t x, intmax_t y, size_t seed) {
double corners = (generate(x - 1, y - 1, seed) +
generate(x + 1, y - 1, seed) +
generate(x - 1, y + 1, seed) +
generate(x + 1, y + 1, seed)) / 16.0;
double sides = (generate(x - 1, y, seed) +
generate(x + 1, y, seed) +
generate(x, y - 1, seed) +
generate(x, y + 1, seed)) / 8.0;
double center = generate(x, y, seed) / 4.0;
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return corners + sides + center;
}
double
curve (double t) {
return t * t * (3.0 - 2.0 * t);
}
double
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sample2d (double x, double y, size_t seed) {
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intmax_t x_int = intmax_t (x);
double x_fac = x - x_int;
intmax_t y_int = intmax_t (y);
double y_fac = y - y_int;
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double p0 = smooth2d (x_int, y_int, seed);
double p1 = smooth2d (x_int + 1, y_int, seed);
double p2 = smooth2d (x_int, y_int + 1, seed);
double p3 = smooth2d (x_int + 1, y_int + 1, seed);
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double i0 = lerp::cosine (p0, p1, curve (x_fac));
double i1 = lerp::cosine (p2, p3, curve (x_fac));
double value = lerp::cosine (i0, i1, curve (y_fac));
return value;
}
double
sigmoid (double x) {
return -1.0 + 2.0 / (1.0 + exp (-2.0 * x));
}
double
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perlin2d (double x, double y, size_t seed) {
size_t levels = 16;
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double persistence = 0.7;
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double total = 0.0;
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for (size_t i = 0; i < levels; ++i) {
double frequency = powf (2.0, i);
double amplitude = powf (persistence, i);
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total += sample2d (x * frequency, y * frequency, seed) * amplitude;
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}
return sigmoid (1.0 + total);
}
void
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perlin2d (uint8_t *restrict pixels, size_t width, size_t height, const params& p) {
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for (size_t y = 0; y < height; ++y)
for (size_t x = 0; x < width; ++x) {
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double p = perlin2d (x / 10.0, y / 10.0, (size_t)pixels);
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pixels[x + y * width] = p * std::numeric_limits<uint8_t>::max ();
}
}
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void
perlin2d (uint8_t *restrict pixels, size_t width, size_t height) {
perlin2d (pixels, width, height, params ());
}