code/mandelbrot/mandelbrot.c

#include <stdio.h>
#include "../libpng/img.h"


#define BAIL_OUT 8192
#define MAX_ITER 65536

#define WIDTH 4096
#define HEIGHT 4096

double map(int value, int min, int max, int map_min, int map_max)
{
	double R = (double) (map_max - map_min) / (double) (max - min);
	double y = map_min + (value * R) + R;
	return y;
}

void mandelbrot(double *field, int w, int h, int bail_out, int max_iter)
{
	double xPrime, yPrime, real, imaginary, realPrime,
	    imaginaryPrime, x2, y2;
	int  x, y, k;
	for (x = 0; x < w; x++) {
		for (y = 0; y < h; y++) {
			xPrime = map(x, 0, w, -2, 2);
			yPrime = map(y, 0, h, -2, 2);
			x2 = xPrime;
			y2 = yPrime;

			// iterate a^2 - b^2 + 2ab
			for (k = 0; k < max_iter; k++) {
				// a^2 - b^2
				real = xPrime * xPrime - yPrime * yPrime;
				// 2ab
				imaginary = 2 * xPrime * yPrime;

				// x = real + c
				xPrime = real + x2;
				// y = imaginary + c
				yPrime = imaginary + y2;

				if ((xPrime * xPrime + yPrime * yPrime) >
				    bail_out) {
					break;
				}
			}

			if (k == max_iter) {
				field[x * h + y] = max_iter;
			} else {
				field[x * h + y] = k;
			}
		}
	}
}

int main(int argc, char **argv)
{

	double * pix_field;

	pix_field = malloc(WIDTH * HEIGHT * sizeof(double));

	mandelbrot(pix_field, WIDTH, HEIGHT, BAIL_OUT,
		   MAX_ITER);

	pix_row rows[WIDTH];
	pix p;

	char filename[30];
	image img;
	p.r = 200;
	p.g = 200;
	p.b = 200;

	for (int i = 0; i < WIDTH; i++) {
		rows[i].p = malloc(HEIGHT * sizeof(pix));
		for (int j = 0; j < HEIGHT; j++) {
			p.r = map(pix_field[i * HEIGHT + j], 0, MAX_ITER, 0, 255);
			p.g = map(pix_field[i * HEIGHT + j], 0, MAX_ITER, 0, 255);
			p.b = map(pix_field[i * HEIGHT + j], 0, MAX_ITER, 0, 255);
			rows[i].p[j] = p;
		}
	}
	sprintf(filename, "mandel.png");
	img = initialize_png("mandelbrot", filename, WIDTH, HEIGHT);
	write_image(&img, rows);
	finish_image(&img);
	for (int i = 0; i < WIDTH; i++) {

		free(rows[i].p);
	}

	free(pix_field);

	return (0);
}