dwm

/* cc transient.c -o transient -lX11 */

#include <stdlib.h>

#include <unistd.h>

#include <X11/Xlib.h>

#include <X11/Xutil.h>

int main(void) {

	Display *d;

	Window r, f, t = None;

	XSizeHints h;

	XEvent e;

	d = XOpenDisplay(NULL);

	if (!d)

		exit(1);

	r = DefaultRootWindow(d);

	f = XCreateSimpleWindow(d, r, 100, 100, 400, 400, 0, 0, 0);

	h.min_width = h.max_width = h.min_height = h.max_height = 400;

	h.flags = PMinSize | PMaxSize;

	XSetWMNormalHints(d, f, &h);

	XStoreName(d, f, "floating");

	XMapWindow(d, f);

	XSelectInput(d, f, ExposureMask);

	while (1) {

		XNextEvent(d, &e);

		if (t == None) {

			sleep(5);

			t = XCreateSimpleWindow(d, r, 50, 50, 100, 100, 0, 0, 0);

			XSetTransientForHint(d, t, f);

			XStoreName(d, t, "transient");

			XMapWindow(d, t);

			XSelectInput(d, t, ExposureMask);

		}

	}

	XCloseDisplay(d);

	exit(0);

}