#include <X11/Xlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void) {
   Display *d;
   Window w, ww;
   XEvent e;
   int s;

   int width = 100, height = 100;

   d = XOpenDisplay(NULL);
   if (d == NULL) {
      fprintf(stderr, "Cannot open display\n");
      exit(1);
   }

   s = DefaultScreen(d);
   w = XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, 120, 120, 1,
                            WhitePixel(d, s), BlackPixel(d, s));

   ww = XCreateSimpleWindow(d, w, 10, 10, width, height, 1, BlackPixel(d, s), WhitePixel(d, s));

   XSelectInput(d, w, ExposureMask | KeyPressMask | StructureNotifyMask );
   XSelectInput(d, ww, ExposureMask | KeyPressMask);
   XMapWindow(d, w);
   XMapWindow(d, ww);

   while (1) {
      XNextEvent(d, &e);
      if (e.type == Expose) {
         XFillRectangle(d, ww, DefaultGC(d, s), 20, 20, 10, 10);
         XFillRectangle(d, ww, DefaultGC(d, s), width-30, height-30, 10, 10);
         XFillRectangle(d, ww, DefaultGC(d, s), 20, height-30, 10, 10);
         XFillRectangle(d, ww, DefaultGC(d, s), width-30, 20, 10, 10);
      }
      if (e.type == KeyPress)
         break;

      if (e.type == ConfigureNotify) {
        width = e.xconfigure.width - 20;
        if (width < 100) width = 100;
        height = e.xconfigure.height - 20;
        if (height < 100) height = 100;
        XMoveResizeWindow (d, ww, 10, 10, width, height);
      }
   }

   XCloseDisplay(d);
   return 0;
}