Using Xlib With Tcl/Tk

WORK IN PROGRESS (for the next day or two (cleaning up old code and redocumenting how to do this) By George Peter Staplin

This tutorial demonstrates how to use Xlib with Tcl/Tk. In the example provided, Xlib is used to draw two boxes in a Tk window. A working C program is provided that should compile in OpenBSD, Linux, and other Unix-like systems. Most Tcl/Tk C programming examples provide information about writing a complete widget. This tutorial is designed in mind for using Tcl/Tk as a C library.

It is assumed that the reader knows the basics of C, Xlib, Tk, and compiling programs.

Xlib_TclTk.c:

 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <tcl.h>
 #include <tk.h>

 GC green_gc;
 GC red_gc;

 int create_colors (Tcl_Interp *interp) {
  XColor *col;
  Tk_Window tkwin;

  tkwin = Tk_MainWindow (interp);
  Tk_MakeWindowExist (tkwin);

  col = Tk_GetColor (interp, tkwin, "green");
  if (NULL == col)
   return TCL_ERROR;

  green_gc = Tk_GCForColor (col, Tk_WindowId (tkwin));
  col = Tk_GetColor (interp, tkwin, "red");
  if (NULL == col)
   return TCL_ERROR;

  red_gc = Tk_GCForColor (col, Tk_WindowId (tkwin));

  return TCL_OK;
 }

 int draw_pattern_cmd (
  ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]
 ) {
  Display *dis;
  Tk_Window tkwin;
  int i;

  if (2 != objc) {
   Tcl_WrongNumArgs (interp, 1, objv, "window-path");
   return TCL_ERROR;
  }

  tkwin = Tk_NameToWindow (interp, Tcl_GetString (objv[1]), Tk_MainWindow (interp));
  if (NULL == tkwin)
   return TCL_ERROR;

  Tk_MakeWindowExist (tkwin);
  dis = Tk_Display (tkwin);

  XClearWindow (dis, Tk_WindowId (tkwin));

  for (i = 0; i < 150; (i += 3)) {
   XFillRectangle (dis, Tk_WindowId (tkwin), green_gc, 1, 1, i, i);
   XFlush (dis);
   usleep (1);
  }

  for (i = 0; i < 150; (i += 3)) {
   XFillRectangle (dis, Tk_WindowId (tkwin), red_gc, 150, 150, i, i);
   XFlush (dis);
   usleep (1);
  }

  return TCL_OK;
 }

 int create_window_cmd (
  ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]
 ) {
  Tcl_Obj *r;
  Tk_Window tkwin;

  if (2 != objc) {
   Tcl_WrongNumArgs (interp, 1, objv, "window-path");
   return TCL_ERROR;
  }
  tkwin = Tk_CreateWindowFromPath (
   interp, Tk_MainWindow (interp), Tcl_GetString (objv[1]), NULL);

  r = Tcl_DuplicateObj (objv[1]);
  Tcl_SetObjResult (interp, r);
  return TCL_OK;
 }

 int app_init (Tcl_Interp *interp) {
  Tk_Window tkwin;

  if (TCL_OK != Tcl_Init (interp)) {
   fprintf (stderr, "Tcl_Init error: %s\n", Tcl_GetStringResult (interp));
   exit (EXIT_FAILURE);
  }

  if (TCL_OK != Tk_Init (interp)) {
   fprintf (stderr, "Tk_Init error: %s\n", Tcl_GetStringResult (interp));
   exit (EXIT_FAILURE);
  }

  Tcl_CreateObjCommand (interp, "create_window", create_window_cmd,
   (ClientData) NULL, (Tcl_CmdDeleteProc *) NULL);

  Tcl_CreateObjCommand (interp, "draw_pattern", draw_pattern_cmd,
   (ClientData) NULL, (Tcl_CmdDeleteProc *) NULL);

  if (TCL_OK != create_colors (interp))
   return TCL_ERROR;

  Tcl_EvalFile (interp, "script.tcl");

  Tk_MainLoop ();

  return TCL_OK;
 }

 int main(int argc, char *argv[]) {

  Tk_Main(argc, argv, app_init);
  return EXIT_SUCCESS;
 }

script.tcl:

 pack [create_window .w] -fill both -expand 1
 pack [button .b -text Draw -command {draw_pattern .w}]
 wm geometry . 400x400

See also: Drawing Into Foreign Windows. Also, BLT has a "container" widget, about which George Howlett has written [1].