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Reformulate perlin into a struct

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This commit is contained in:
Danny Robson 2012-05-17 14:18:39 +10:00
parent d81537ba51
commit 3b8f4597bf
1 changed files with 47 additions and 98 deletions
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129
perlin.cpp
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@ -31,126 +31,76 @@
#include <limits>
#define LERP(a,b,t) lerp::quintic (a, b, t)
struct params {
typedef size_t seed_t;
unsigned octaves;
double persistence;
double frequency;
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> ())
{ ; }
};
// Just a random generator [-1.0, 1.0]
static float
generate (intmax_t x, intmax_t y, size_t seed) {
double
generate (intmax_t x, intmax_t y) const {
intmax_t n = x + 257 * y;
n = (n << 13U) ^ n ^ seed;
return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0f);
n = (n << 13U) ^ n ^ (intmax_t)seed;
return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0);
}
static double
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;
return corners + sides + center;
}
static double
curve (double t) {
return t * t * (3.0 - 2.0 * t);
}
static double
sample2d (double x, double y, size_t seed) {
double
eval (double x, double y) const {
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, 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);
// Generate the four corner values
double p0 = generate (x_int, y_int);
double p1 = generate (x_int + 1, y_int);
double p2 = generate (x_int, y_int + 1);
double p3 = generate (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;
// Interpolate on one dimension, then the other.
return LERP (LERP (p0, p1, x_fac),
LERP (p2, p3, x_fac),
y_fac);
}
static double
sigmoid (double x) {
return -1.0 + 2.0 / (1.0 + exp (-2.0 * x));
}
static double
perlin2d (double x, double y, size_t seed) {
size_t levels = 16;
double persistence = 0.7;
double
sample (double x, double y) const {
double total = 0.0;
for (size_t i = 0; i < levels; ++i) {
double frequency = powf (2.0, i);
for (size_t i = 0; i < octaves; ++i) {
double f = frequency * powf (2.0, i);
double amplitude = powf (persistence, i);
total += sample2d (x * frequency, y * frequency, seed) * amplitude;
total += eval (x * f, y * f) * amplitude;
total = max (-1.0, min (1.0, total));
}
return sigmoid (1.0 + total);
return (1.0 + total) / 2.0;
}
params ():
octaves (3),
persistence (0.5),
frequency (25.0),
seed (util::random<size_t> ())
{ ; }
};
void
static void
perlin2d (uint8_t *restrict pixels, size_t width, size_t height, const params& p) {
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, (size_t)pixels);
pixels[x + y * width] = p * std::numeric_limits<uint8_t>::max ();
double v = p.sample (x / double (width), y / double (height)); /*perlin2d (x / double (width),
y / double (height),
(size_t)pixels);*/
pixels[x + y * width] = v * std::numeric_limits<uint8_t>::max ();
}
}
@ -159,4 +109,3 @@ void
perlin2d (uint8_t *restrict pixels, size_t width, size_t height) {
perlin2d (pixels, width, height, params ());
}