#include <stdlib.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <iostream>

using namespace std;

// Globals--sue me.
Display *dpy;
GC gc;
Window win;

// The window needs repainting.  Do so.
void refresh() {
    XWindowAttributes xwa;
    if (XGetWindowAttributes(dpy, win, &xwa) == 0) return;

    // Draw a big thick X
    const auto w = xwa.width, h = xwa.height;

    XSetForeground(dpy, gc, random() & 0xffffff);
    XFillRectangle(dpy, win, gc, 0, 0, w, h);
    XSetForeground(dpy, gc, random() & 0xffffff);
    XSetLineAttributes(dpy, gc, w/6, LineSolid, CapButt, JoinMiter);
    XDrawLine(dpy, win, gc, 0, 0, w-1, h-1);
    XDrawLine(dpy, win, gc, w-1, 0, 0, h-1);

    XFlush(dpy);
}


int main() {
    dpy = XOpenDisplay(nullptr);
    if (dpy == nullptr) {
	cerr << "Can't open display\n";
	return 1;
    }

    const int screen = DefaultScreen(dpy);
    gc = DefaultGC(dpy, screen);

    win = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 50, 50,
			      800, 800, 0, 0xffffff, 0x000000);

    XSelectInput(dpy, win, ExposureMask);
    XMapWindow(dpy, win);

    for (int event_counter=0; ; ) {
	cout << "\rWaiting for event #" << ++event_counter << ' ' << flush;
	XEvent event;			// Event received
	XNextEvent(dpy, &event);	// Wait for the next event
	if (event.type == Expose && event.xexpose.count == 0)
	    refresh();
    }
}