libcruft-util/perlin.cpp

106 lines
2.4 KiB
C++

#include "perlin.hpp"
#include "debug.hpp"
#include "maths.hpp"
#include <cmath>
#include <limits>
namespace lerp {
double
linear (double a, double b, double weight) {
check (weight >= 0 && weight <= 1.0);
return (1.0 - weight) * a + weight * b;
}
double
cosine (double a, double b, double weight) {
check (weight >= 0 && weight <= 1.0);
double ft = weight * PI;
double f = (1.0 - cos (ft)) * 0.5;
return a * (1.0 - f) + b * f;
}
}
// Just a random generator [-1.0, 1.0]
static float
generate (intmax_t x, intmax_t y) {
uint32_t n = x + 257 * y;
n = (n << 13U) ^ n;
return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0f);
}
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;
}
double
curve (double t) {
return t * t * (3.0 - 2.0 * t);
}
double
sample2d (double x, double y) {
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;
double p0 = smooth2d (x_int, y_int);
double p1 = smooth2d (x_int + 1, y_int);
double p2 = smooth2d (x_int, y_int + 1);
double p3 = smooth2d (x_int + 1, y_int + 1);
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
perlin2d (double x, double y) {
size_t levels = 16;
double persistence = 0.7;
double total = 0.0;
for (size_t i = 0; i < levels; ++i) {
double frequency = powf (2.0, i);
double amplitude = powf (persistence, i);
total += sample2d (x * frequency, y * frequency) * amplitude;
}
return sigmoid (1.0 + total);
}
void
perlin2d (uint8_t *restrict pixels, size_t width, size_t height) {
for (size_t y = 0; y < height; ++y)
for (size_t x = 0; x < width; ++x) {
double p = perlin2d (x / 10.0, y / 10.0);
pixels[x + y * width] = p * std::numeric_limits<uint8_t>::max ();
}
}