#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <sys/ioctl.h>  /* for ioctl() and struct winsize*/

void drawLine (int m, int n, int x, int y, char *cell, int pause) {
 int dx, dy, dx2, dy2, f, inc, celli=0;
 char *dir;

	printf ("\e[%d;%dH", n+1, m+1);

	dx=x-m;
	dy=y-n;

	if (abs(dy) <= abs(dx)) {
		if (dx<0) { // Draw right to left
			inc = -1;
			dx *= -1;
		} else { // Draw left to right
			inc = 1;
		}

		if (dy<0) {
			dir="\e[A"; // IV.2 and II2
			dy *= -1;
		} else {  // I.1 and III1
			dir = "\e[B";
		}

		dx2=dx+dx, dy2=dy+dy;
		f=dy2-dx;

		while (printf ("%c", cell[celli++]), m != x) {
			if (!cell[celli]) celli=0;
			pause && usleep(pause*1000);
			m += inc;
			if (inc == -1) { printf (""); }
			if (f>0) {
				f -= dx2;
				printf (dir);
			}
			f = f + dy2;
		}
	} else {
		dx ^= dy; dy ^= dx;  dx ^= dy;

		if (dx<0) { // Draw right to left
			inc = -1;
			dx *= -1;
		} else { // Draw left to right
			inc = 1;
		}

		if (dy<0) {
			dir="\e[D"; // IV.2 and II2
			dy *= -1;
		} else {  // I.1 and III1
			dir = "\e[C";
		}

		dx2=dx+dx, dy2=dy+dy;
		f=dy2-dx;

		while (printf ("%c", cell[celli++]), n != y) {
			if (!cell[celli]) celli=0;
			pause && usleep(pause*1000);
			n += inc;
			if (inc == -1) { printf ("\e[A"); }
			else { printf ("\e[B"); }
			if (f>0) {
				f -= dx2;
				printf (dir);
			}
			f = f + dy2;
		}
	}
}

int newrand (void) {
	static int i[] = {1, -1, 2, -2, 3, -3, 4, -4};
	return i[random()%4];
}

int main (int argc, char *argv[]) {
 struct winsize win;
 int width, height;
 int d=50, i=0;
 int m, n, x, y;
 int mi, ni, xi, yi;

	srandom(time(0));
	ioctl(1, TIOCGWINSZ, &win);
	width = win.ws_col;
	height = win.ws_row;
	if (argc!=2) {
		printf ("Usage:: qix delay"
		        " Plots animated qix line with delay.\n"
		        " Default value: %d\n", d);
	} else {
		d = atoi(argv[1]);
	}

	setbuf(stdout, NULL);
	printf ("\e[0m\e[?25l");

	width*=4;
	height*=4;
	x=random()%width;
	y=random()%height;

	m=random()%width;
	n=random()%height;

	mi=newrand();
	ni=newrand();
	xi=newrand();
	yi=newrand();

	loop:

		d && usleep(d*10);
		if (!(++i%50)) {
			printf ("\e7\e[0m\e[%dH\n\e8", height);
			n--; y--;
			if (!(i%100)) printf ("\e[4%dm", (random()%7)+1);
		}

		drawLine (m>>2, n>>2, x>>2, y>>2, " ", 0);

		m += mi; n += ni;
		x += xi; y += yi;

		if (m<0) { m=0; mi=newrand(); }
		if (m>=width) { m=width; mi=newrand(); }

		if (n<0) { n=0; ni=newrand(); }
		if (n>=height) { n=height; ni=newrand(); }

		if (x<0) { x=0; xi=newrand(); }
		if (x>=width) { x=width; xi=newrand(); }

		if (y<0) { y=0; yi=newrand(); }
		if (y>=height) { y=height; yi=newrand(); }

	goto loop;

	return 0;
}