106 lines
2.4 KiB
C++
106 lines
2.4 KiB
C++
#include "perlin.hpp"
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#include "debug.hpp"
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#include "maths.hpp"
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#include <cmath>
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#include <limits>
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namespace lerp {
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double
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linear (double a, double b, double weight) {
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check (weight >= 0 && weight <= 1.0);
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return (1.0 - weight) * a + weight * b;
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}
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double
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cosine (double a, double b, double weight) {
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check (weight >= 0 && weight <= 1.0);
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double ft = weight * PI;
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double f = (1.0 - cos (ft)) * 0.5;
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return a * (1.0 - f) + b * f;
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}
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}
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// Just a random generator [-1.0, 1.0]
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static float
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generate (intmax_t x, intmax_t y) {
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uint32_t n = x + 257 * y;
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n = (n << 13U) ^ n;
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return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0f);
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}
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double
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smooth2d (intmax_t x, intmax_t y) {
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double corners = (generate(x-1, y-1)+generate(x+1, y-1)+generate(x-1, y+1)+generate(x+1, y+1) ) / 16.0;
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double sides = (generate(x-1, y) +generate(x+1, y) +generate(x, y-1) +generate(x, y+1) ) / 8.0;
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double center = generate(x, y) / 4.0;
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return corners + sides + center;
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}
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double
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curve (double t) {
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return t * t * (3.0 - 2.0 * t);
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}
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double
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sample2d (double x, double y) {
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intmax_t x_int = intmax_t (x);
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double x_fac = x - x_int;
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intmax_t y_int = intmax_t (y);
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double y_fac = y - y_int;
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double p0 = smooth2d (x_int, y_int);
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double p1 = smooth2d (x_int + 1, y_int);
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double p2 = smooth2d (x_int, y_int + 1);
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double p3 = smooth2d (x_int + 1, y_int + 1);
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double i0 = lerp::cosine (p0, p1, curve (x_fac));
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double i1 = lerp::cosine (p2, p3, curve (x_fac));
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double value = lerp::cosine (i0, i1, curve (y_fac));
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return value;
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}
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double
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sigmoid (double x) {
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return -1.0 + 2.0 / (1.0 + exp (-2.0 * x));
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}
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double
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perlin2d (double x, double y) {
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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) {
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double frequency = powf (2.0, i);
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double amplitude = powf (persistence, i);
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total += sample2d (x * frequency, y * frequency) * amplitude;
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}
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return sigmoid (1.0 + total);
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}
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void
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perlin2d (uint8_t *restrict pixels, size_t width, size_t height) {
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for (size_t y = 0; y < height; ++y)
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for (size_t x = 0; x < width; ++x) {
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double p = perlin2d (x / 10.0, y / 10.0);
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pixels[x + y * width] = p * std::numeric_limits<uint8_t>::max ();
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}
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}
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