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perlin.h
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perlin.h
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#pragma once
#include "rtweekend.h"
class perlin {
public:
perlin() {
randvec = new vec3[point_count];
for (int i = 0; i < point_count; i++) {
randvec[i] = normalize(vec3::random(-1, 1));
}
perm_x = perlin_generate_perm();
perm_y = perlin_generate_perm();
perm_z = perlin_generate_perm();
}
~perlin() {
delete[] randvec;
delete[] perm_x;
delete[] perm_y;
delete[] perm_z;
}
double noise(const point3& p) const {
auto u = p.x() - floor(p.x());
auto v = p.y() - floor(p.y());
auto w = p.z() - floor(p.z());
auto i = static_cast<int>(floor(p.x()));
auto j = static_cast<int>(floor(p.y()));
auto k = static_cast<int>(floor(p.z()));
vec3 vector[2][2][2];
for (int di = 0; di < 2; di++) {
for (int dj = 0; dj < 2; dj++) {
for (int dk = 0; dk < 2; dk++) {
vector[di][dj][dk] = randvec[
perm_x[(i + di) & 255] ^
perm_y[(j + dj) & 255] ^
perm_z[(k + dk) & 255]
];
}
}
}
return perlin_trilinear_interp(vector, u, v, w);
}
double turb(const point3& p, int depth = 7) const {
auto accum = 0.0;
auto temp_p = p;
auto weight = 1.0;
for (int i = 0; i < depth; i++) {
accum += weight * noise(temp_p);
weight *= 0.5;
temp_p *= 2;
}
return fabs(accum);
}
private:
const int point_count = 256;
vec3* randvec;
int* perm_x;
int* perm_y;
int* perm_z;
int* perlin_generate_perm() {
auto p = new int[point_count];
for (int i = 0; i < point_count; i++) {
p[i] = i;
}
permuate(p, point_count);
return p;
}
void permuate(int* p, int count) {
for (int i = count - 1; i > 0; i--) {
int target = random_int(0, i);
int temp = p[target];
p[target] = p[i];
p[i] = temp;
}
}
static double perlin_trilinear_interp(vec3 vec[2][2][2], double u, double v, double w) {
// hermitian interpolation: to get rid of Mach-Band.
auto uu = u * u * (3 - 2 * u);
auto vv = v * v * (3 - 2 * v);
auto ww = w * w * (3 - 2 * w);
double accum = 0.0;
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
for (int k = 0; k < 2; k++) {
vec3 weight(u - i, v - j, w - k);
accum += dot(vec[i][j][k], weight) *
(i * uu + (1 - i) * (1 - uu)) *
(j * vv + (1 - j) * (1 - vv)) *
(k * ww + (1 - k) * (1 - ww));
}
}
}
return accum;
}
};