#include <SDL.h>
#include <unistd.h>
#include <stdio.h>
#include <time.h>

static void putpixel(struct SDL_Surface *screen, const int x, const int y,
		     const unsigned char r, const unsigned char g,
		     const unsigned char b)
{
	int offset = y * screen->pitch + x * 4;
	unsigned char *buf = screen->pixels;

	buf[offset++] = b;
	buf[offset++] = g;
	buf[offset]   = r;
}

#define MAX_ITERATION 1000

int get_mandelbrot_iterations(double x0, double y0)
{
	double x = 0, y = 0, xtemp;
	int iteration = 0;

	while ((x * x + y * y < 2 * 2) && iteration < MAX_ITERATION) {

		xtemp = x * x - y * y + x0;
		y = 2 * x * y + y0;

		x = xtemp;
		iteration++;
	}

	return iteration;
}

int draw_mandelbrot(struct SDL_Surface *screen, double x1, double x2,
		double y1, double y2)
{
	double x0, y0, xlen, ylen, xstep, ystep;
	int iteration, xs, ys;

	xlen = x2 - x1;
	ylen = y2 - y1;
	xstep = xlen / (double)screen->w;
	ystep = ylen / (double)screen->h;

	for (ys = 0, y0 = y1; ys < screen->h; y0 += ystep, ys++) {
		for (xs = 0, x0 = x1; xs < screen->w; x0 += xstep, xs++) {
			iteration = get_mandelbrot_iterations(x0, y0);

			if (iteration == MAX_ITERATION)
				putpixel(screen, xs, ys, 255, 255, 255);
			else
				putpixel(screen, xs, ys,
					iteration * 8, iteration,
					iteration / 4);
		}

		SDL_Flip(screen);
	}

	return 0;
}

int main(int argc, char *argv[])
{
	SDL_Surface *screen;
	int flags = SDL_DOUBLEBUF | SDL_HWSURFACE | SDL_RESIZABLE;
	int xres = 800, yres = 600;

	if (SDL_Init(SDL_INIT_VIDEO) != 0) {
		fprintf(stderr, "Unable to initialize SDL: %s\n",
			SDL_GetError());

		return 1;
	}
	atexit(SDL_Quit);

	screen = SDL_SetVideoMode(xres, yres, 32, flags);
	if (screen == NULL) {
		fprintf(stderr, "Unable to set video mode: %s\n",
			SDL_GetError());
		return 2;
	}

	SDL_WM_SetCaption(argv[0], NULL);

	draw_mandelbrot(screen, -2.5, 1, -1, 1);

	yres = read(0, &xres, 1);

	return 0;
}