Write an image from a C program

blog1.c

#include <stdio.h>
#include <stdlib.h>


void get_color(int i, int j, char color[]) {
  static char r = 0, g = 0, b = 0;
  r++; g--; b++;
  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, 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;
}