#
#define MAXUSERS 4
#include <X11/Xlib.h>
#include <stdio.h>
#define TRUE 1
#define FALSE 0

main(argc,argv)
int argc;
char **argv;
{
  Display *display[MAXUSERS];
  Window root[MAXUSERS], window[MAXUSERS];
  long fgcolor, bgcolor;
  int screen, pointx, pointy;
  int eventmask = KeyPressMask|ExposureMask|ButtonPressMask;
  XEvent event;
  XGCValues gcval;
  GC draw[MAXUSERS];
  int FirstPt = TRUE;
  int NC;
  int i;

  if (argc == 1) NC = argc;
  else NC = argc-1;

  for (i=0; i< NC; i++){
    if (!(display[i] = XOpenDisplay(argv[i+1]))) {
      perror("XOpenDisplay");
      exit(1);
    }

    root[i] = RootWindow(display[i],screen = DefaultScreen(display[i]));
    fgcolor = BlackPixel(display[i],screen);
    bgcolor = WhitePixel(display[i],screen);

    window[i] = XCreateSimpleWindow(display[i],root[i],0,0,200,200,2,
        fgcolor,bgcolor);

    gcval.foreground = fgcolor;
    gcval.background = bgcolor;
    draw[i] = XCreateGC(display[i],window[i],GCForeground|GCBackground,&gcval);

    XMapWindow(display[i],window[i]);
    XFlush(display[i]);

  }
  XSelectInput(display[0],window[0],eventmask);

  for (;;) {
    XWindowEvent(display[0],window[0],eventmask,&event);
    switch (event.type) {
    case Expose:
      for (i=0; i<NC; i++){
        XClearWindow(display[i],window[i]);
    XFlush(display[i]);
}
      break;
    case ButtonPress:
        for (i=0; i<NC; i++) {
          XDrawPoint(display[i],window[i],draw[i],
              event.xbutton.x, event.xbutton.y);
          XFlush(display[i]);
        }
        break;
    case KeyPress:
      for (i=1; i<NC; i++)
        XDestroyWindow(display[i], window[i]);
      exit(0);
    default:
      fprintf(stderr,"Unexpected event: %d\n",event.type);
    }
  }
}