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

main(argc,argv)
int argc;
char **argv;
{
  int i;
  int j;
  Display *display[MAXUSERS];
  Window root[MAXUSERS], window[MAXUSERS];
  long fgcolor, bgcolor;
  int screen, pointx[MAXUSERS], pointy[MAXUSERS];
  int eventmask = KeyPressMask|ExposureMask|ButtonPressMask;
  XEvent event;
  XGCValues gcval;
  GC draw[MAXUSERS];
  int FirstPt[MAXUSERS];
  int NC;
  if (argc == 1) NC = argc;
  else NC = argc-1;
printf("NC %d\n", NC);
  for (i=0; i< NC; i++){
    if (!(display[i] = XOpenDisplay(argv[i+1]))) {
      perror("XOpenDisplay");
      exit(1);
    }

    FirstPt[i] = TRUE;
    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[i],window[i],eventmask);
  }

  for (;;) {
    for (j=0; j<NC; j++){
    if (XCheckWindowEvent(display[j],window[j],eventmask,&event))
    switch (event.type) {
    case Expose:
      for (i=0; i<NC; i++)
        XClearWindow(display[i],window[i]);
     for (i=0; i<NC; i++)
           XFlush(display[i]);


      break;
    case ButtonPress:
      if (FirstPt[j]) {
        FirstPt[j]=FALSE;
        pointx[j] = event.xbutton.x;
        pointy[j] = event.xbutton.y;
        for (i=0; i<NC; i++)
          XDrawPoint(display[i],window[i],draw[i],pointx[j],pointy[j]);
     for (i=0; i<NC; i++)
           XFlush(display[i]);


        break;
      }
      else {
        FirstPt[j]=TRUE;
        for (i=0; i<NC; i++)
        {
          XDrawLine(display[i],window[i],draw[i],pointx[j],pointy[j],
              event.xbutton.x, event.xbutton.y);
        }
        for (i=0; i<NC; i++)
           XFlush(display[i]);

        break;
      }
    case KeyPress:
      for (i=1; i<NC; i++)
        XDestroyWindow(display[i], window[i]);
     for (i=0; i<NC; i++)
           XFlush(display[i]);


      exit(0);
    default:
      fprintf(stderr,"Unexpected event: %d\n",event.type);
    }
  }
  }
}