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@bedekelly bedekelly/blog2.c
Created Nov 19, 2017

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Draw the Mandelbrot Set
#include <stdio.h>
#include <stdlib.h>
#include <complex.h>
#define MAX_X 384
#define MAX_Y 216
#define X_LOWER -2.5
#define X_UPPER 1.0555555
#define Y_LOWER -1
#define Y_UPPER 1
#define MAX_ITERATIONS 255
/* Calculate the number of iterations a point takes to leave a bound. */
int iterations(double cr, double ci, int max_it) {
// Create our initial numbers, c and z, along with a counter for iterations, i.
double complex z = 0 + 0*I;
double complex c = cr + ci*I;
int i = 0;
// Keep iterating z until:
// (a) z gets higher than our upper bound, or
// (b) we hit the maximum number of iterations
for (; i<max_it; i++) {
z = z*z + c;
if (cabs(z) > 4)
break;
}
return i;
}
/* Linearly map a value from one range into another. */
double linmap(double val, double lower1, double upper1, double lower2, double upper2) {
return ((val - lower1) / (upper1 - lower1)) * (upper2 - lower2) + lower2;
}
/* Calculate the colour for coordinates (x, y) and write into color[]. */
void get_color(int x, int y, int maxX, int maxY, char color[]) {
// Map the screen coordinates to the Mandelbrot coordinates.
double x1 = linmap(x, 0, maxX, X_LOWER, X_UPPER);
double y1 = linmap(y, 0, maxY, Y_LOWER, Y_UPPER);
int its = iterations(x1, y1, MAX_ITERATIONS);
// Map the number of iterations to a colour between 0 and 255.
char r = linmap(its, 0, MAX_ITERATIONS, 0, 255);
char g = r;
char b = g;
// Write the colours.
color[0] = r;
color[1] = g;
color[2] = b;
}
/* Write the header for a PPM file. */
void write_header(FILE *fp, int dimx, int dimy) {
fprintf(fp, "P6\n"); // Write magic chars.
fprintf(fp, "%d %d\n", dimx, dimy); // Write width and height.
fprintf(fp, "255\n"); // Write max colour value.
}
/* Generate a Mandelbrot image. */
void generate_file(int dimx, int dimy) {
// Create a file and write to it.
FILE *fp = fopen("mandelbrot.ppm", "wb");
write_header(fp, dimx, dimy);
// For each coordinate, calculate its color then write to file.
char color[3];
for (int j=0; j<dimy; ++j)
for (int i=0; i<dimx; ++i)
{
get_color(i, j, dimx, dimy, color);
fwrite(color, 1, 3, fp);
}
// Close the file pointer to clean up.
fclose(fp);
}
int main(int argc, char *argv[]) {
// Grab our parameters from the system args.
int dimx = atoi(argv[1]);
int dimy = atoi(argv[2]);
// Write the file with the given resolution.
generate_file(dimx, dimy);
return EXIT_SUCCESS;
}
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