#include <X11/Xlib.h>
#include <X11/X.h>
#include <X11/keysym.h>
#include <X11/cursorfont.h>
#include <stdio.h>
#include <string.h>
#define BUFFERSIZE 20
#define WIDTH 200
#define HIEGHT 200
int charwidth, charascent, chardescent;

char buffer[BUFFERSIZE];
int bufsize=BUFFERSIZE;
KeySym keysym;
long statinout;
int charcount;

XFontStruct *font_info;

Display *display;
Window root, window;
GC draw, erase;

main(argc,argv)
int argc;
char **argv;
{
  long fgcolor, bgcolor;
  int screen, pointx, pointy;
  long eventmask = ExposureMask|KeyPressMask;
  XEvent event;
  XGCValues gcval;

  if (!(display = XOpenDisplay(argv[1]))) {
    perror("XOpenDisplay");
    exit(1);
  }

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

  window = XCreateSimpleWindow(display,root,0,0,WIDTH,HIEGHT,2,
      fgcolor,bgcolor);

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

  gcval.foreground = bgcolor;
  gcval.background = fgcolor;
  erase= XCreateGC(display,window,GCForeground|GCBackground,&gcval);

  load_font();
  defineCtrl();
  XSelectInput(display,window,eventmask);
  XMapWindow(display,window);

  for (;;) {
    XWindowEvent(display,window,eventmask,&event);
    switch (event.type) {
    case Expose:
      XClearWindow(display,window);
      break;
    case KeyPress:
      charcount = XLookupString(&event,buffer,bufsize,
          &keysym, &statinout);
      buffer[charcount]='\0';
      if (strcmp (buffer, "quit") == 0 )  exit(0);
      else if (charcount == 1){
        if (keysym >= XK_space && keysym <= XK_asciitilde)
          PutChar (buffer);
        else if (keysym == XK_BackSpace  ||  keysym ==XK_Delete)
          DelChar(buffer);
      }
      break;

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

  char   *fontname = "9x15";
  if ((font_info = XLoadQueryFont(display, fontname)) == NULL) {
    (void) fprintf(stderr,"Could not get font\n");
    exit( -1 );
  }
  XSetFont(display, draw, font_info->fid);
  charwidth = font_info -> max_bounds.width;
  charascent = font_info -> max_bounds.ascent;
  chardescent = font_info -> max_bounds.descent;
}

defineCtrl()
{
  KeySym modlist[2];
  unsigned int list_len = 1;
  modlist[0] = XK_Control_L;
  XRebindKeysym(display,XK_q,modlist,list_len,"quit",4);
}

PutChar(buffer)
char buffer[];
{
  int winx, winy;
  int rwinx, rwiny;
  unsigned int maskret;
  Window rootret, childret;
  int j;
  XQueryPointer(display, window, &rootret, &childret,
      &rwinx, &rwiny, &winx, &winy, &maskret);
  if (winx >= WIDTH-8 || winy >= HIEGHT-8) XBell(display,0);
  XDrawString(display,window,draw,winx,winy,buffer,strlen(buffer));
  XWarpPointer(display, NULL, NULL, 0,0,0,0,charwidth,0);
}

DelChar( buffer)
char buffer[];
{
  int winx, winy;
  int rwinx, rwiny;
  unsigned int maskret;
  Window rootret, childret;
  int j;
  XWarpPointer(display, NULL, NULL, 0,0,0,0,-charwidth,0);
  XQueryPointer(display, window, &rootret, &childret,
      &rwinx, &rwiny, &winx, &winy, &maskret);
  XFillRectangle(display,window,erase,winx,
      winy-charascent,charwidth,charascent+chardescent);
}