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exterior-coordinates.c
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exterior-coordinates.c
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#include <complex.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <omp.h> //OpenMP
/*
fork of
mandelbrot-book how to write a book about the Mandelbrot set by Claude Heiland-Alle
https://code.mathr.co.uk/mandelbrot-book/blob/HEAD:/book/
gcc exterior-coordinates.c -lm -Wall -fopenmp
./a.out >ec.pgm
*/
const double pi = 3.141592653589793;
double cnorm(double _Complex z)
{
return creal(z) * creal(z) + cimag(z) * cimag(z);
}
double cabs0(double _Complex z)
{
return fabs(creal(z)) + fabs(cimag(z));
}
int main()
{
int aa = 4;
int w = 800 * aa;
int h = 800 * aa;
int n = 1024;
double r = 2;
double r2 = 25 * 25 * 25 * 25;
unsigned char *img = malloc(w * h);
#pragma omp parallel for
for (int j = 0; j < h; ++j)
{
double y = (h/2 - (j + 0.5)) / (h/2) * r;
for (int i = 0; i < w; ++i)
{
double x = (i + 0.5 - w/2) / (h/2) * r;
double _Complex c = x + I * y;
double _Complex z = 0;
int k;
for (k = 0; k < n; ++k)
{
z = z * z + c;
if (cnorm(z) > r2)
break;
}
double g = 1;
if (k < n)
{
double _Complex e = fmod(1 + carg(z) / (2 * pi), 1) + I * (2 - log(cnorm(z))/log(r2));
if (cabs(e - (0.25 + 0.25 * I)) < 0.2) g = 0;
if (cabs0(e - (0.66 + 0.66 * I)) < 0.3) g = 0.67;
if (cabs(e - (0.17 + 0.75 * I)) < 0.1) g = 0.33;
}
img[j * w + i] = 255 * g;
}
}
printf("P5\n%d %d\n255\n", w, h);
fwrite(img, w * h, 1, stdout);
free(img);
return 0;
}