gtk_tut.sgml 351 KB
Newer Older
1 2 3 4 5 6 7 8
<!doctype linuxdoc system>

<!-- This is the tutorial marked up in SGML
     (just to show how to write a comment)
-->

<article>
<title>GTK Tutorial
9 10 11
<author>Ian Main <tt><htmlurl url="mailto:imain@gtk.org"
			      name="&lt;imain@gtk.org&gt;"></tt>,
Tony Gale <tt><htmlurl url="mailto:gale@gtk.org"
12
			      name="&lt;gale@gtk.org&gt;"></tt>
13
<date>June 24th, 1998
14 15 16 17 18 19 20

<!-- ***************************************************************** -->
<sect>Introduction
<!-- ***************************************************************** -->
<p>
GTK (GIMP Toolkit) was originally developed as a toolkit for the GIMP
(General Image Manipulation Program).  GTK is built on top of GDK (GIMP
21 22
Drawing Kit) which is basically a wrapper around the Xlib functions.  It's
called the GIMP toolkit because it was originally written for developing
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
the GIMP, but has now been used in several free software projects.  The
authors are
<itemize>
<item> Peter Mattis   <tt><htmlurl url="mailto:petm@xcf.berkeley.edu"
			   name="petm@xcf.berkeley.edu"></tt>
<item> Spencer Kimball <tt><htmlurl url="mailto:spencer@xcf.berkeley.edu"
			   name="spencer@xcf.berkeley.edu"></tt>
<item> Josh MacDonald <tt><htmlurl url="mailto:jmacd@xcf.berkeley.edu"
			   name="jmacd@xcf.berkeley.edu"></tt>
</itemize>

GTK is essentially an object oriented application programmers interface (API).  
Although written completely in
C, it is implemented using the idea of classes and callback functions
(pointers to functions).
38

39 40 41 42 43
There is also a third component called glib which contains a few
replacements for some standard calls, as well as some additional functions
for handling linked lists etc.  The replacement functions are used to 
increase GTK's portability, as some of the functions implemented 
here are not available or are nonstandard on other unicies such as 
44 45
g_strerror().   Some also contain enhancements to the libc versions, such as
g_malloc that has enhanced debugging utilities.
46

47 48 49 50 51 52
This tutorial is an attempt to document as much as possible of GTK, it is by 
no means complete.  This
tutorial assumes a good understanding of C, and how to create C programs.
It would be a great benefit for the reader to have previous X programming
experience, but it shouldn't be necessary.  If you are learning GTK as your
first widget set, please comment on how you found this tutorial, and what
53
you had trouble with.
54 55
Note that there is also a C++ API for GTK (GTK--) in the works, so if you
prefer to use C++, you should look into this instead.  There's also an
56 57 58
Objective C wrapper, and Guile bindings available, but I don't follow these.

I would very much like to hear of any problems you have learning GTK from this
59 60 61 62 63 64 65 66
document, and would appreciate input as to how it may be improved.

<!-- ***************************************************************** -->
<sect>Getting Started
<!-- ***************************************************************** -->

<p>
The first thing to do of course, is download the GTK source and install
67 68 69
it.  You can always get the latest version from ftp.gtk.org in /pub/gtk.
You can also view other sources of GTK information on http://www.gtk.org/
<htmlurl url="http://www.gtk.org/" name="http://www.gtk.org/">.
70 71
GTK uses GNU autoconf for
configuration.  Once untar'd, type ./configure --help to see a list of options.
72

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
To begin our introduction to GTK, we'll start with the simplest program 
possible.  This program will
create a 200x200 pixel window and has no way of exiting except to be
killed using the shell.

<tscreen><verb>
#include <gtk/gtk.h>

int main (int argc, char *argv[])
{
    GtkWidget *window;
    
    gtk_init (&amp;argc, &amp;argv);
    
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_widget_show (window);
    
    gtk_main ();
    
    return 0;
}
</verb></tscreen>

96
All programs will of course include gtk/gtk.h which declares the
97 98
variables, functions, structures etc. that will be used in your GTK 
application.
99

100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
The next line:

<tscreen><verb>
gtk_init (&amp;argc, &amp;argv);
</verb></tscreen>

calls the function gtk_init(gint *argc, gchar ***argv) which will be
called in all GTK applications.  This sets up a few things for us such
as the default visual and color map and then proceeds to call
gdk_init(gint *argc, gchar ***argv).  This function initializes the
library for use, sets up default signal handlers, and checks the
arguments passed to your application on the command line, looking for one
of the following:

<itemize>
<item> <tt/--display/
<item> <tt/--debug-level/
<item> <tt/--no-xshm/
<item> <tt/--sync/
<item> <tt/--show-events/
<item> <tt/--no-show-events/
121 122
<item> <tt/--name/
<item> <tt/--class/
123
</itemize>
124

125
It removes these from the argument list, leaving anything it does
126
not recognize for your application to parse or ignore. This creates a set
127
of standard arguments accepted by all GTK applications.
128

129 130 131 132 133 134 135 136 137 138 139
The next two lines of code create and display a window.

<tscreen><verb>
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_widget_show (window);
</verb></tscreen>

The GTK_WINDOW_TOPLEVEL argument specifies that we want the window to
undergo window manager decoration and placement. Rather than create a
window of 0x0 size, a window without children is set to 200x200 by default
so you can still manipulate it.
140 141 142 143

The gtk_widget_show() function lets GTK know that we are done setting the
attributes of this widget, and that it can display it.

144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161
The last line enters the GTK main processing loop.

<tscreen><verb>
gtk_main ();
</verb></tscreen>

gtk_main() is another call you will see in every GTK application.  When
control reaches this point, GTK will sleep waiting for X events (such as
button or key presses), timeouts, or file IO notifications to occur.
In our simple example however, events are ignored.

<!-- ----------------------------------------------------------------- -->
<sect1>Hello World in GTK
<p>
OK, now for a program with a widget (a button).  It's the classic hello
world ala GTK.

<tscreen><verb>
162
/* example-start helloworld helloworld.c */
163 164 165 166 167 168 169 170 171 172

#include <gtk/gtk.h>

/* this is a callback function. the data arguments are ignored in this example..
 * More on callbacks below. */
void hello (GtkWidget *widget, gpointer data)
{
    g_print ("Hello World\n");
}

173
gint delete_event(GtkWidget *widget, GdkEvent *event, gpointer data)
174 175
{
    g_print ("delete event occured\n");
176 177
    /* if you return FALSE in the "delete_event" signal handler,
     * GTK will emit the "destroy" signal.  Returning TRUE means
178 179 180
     * you don't want the window to be destroyed.
     * This is useful for popping up 'are you sure you want to quit ?'
     * type dialogs. */
181 182

    /* Change TRUE to FALSE and the main window will be destroyed with
183
     * a "delete_event". */
184 185

    return (TRUE);
186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207
}

/* another callback */
void destroy (GtkWidget *widget, gpointer data)
{
    gtk_main_quit ();
}

int main (int argc, char *argv[])
{
    /* GtkWidget is the storage type for widgets */
    GtkWidget *window;
    GtkWidget *button;
    
    /* this is called in all GTK applications.  arguments are parsed from
     * the command line and are returned to the application. */
    gtk_init (&amp;argc, &amp;argv);
    
    /* create a new window */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    
    /* when the window is given the "delete_event" signal (this is given
208
    * by the window manager, usually by the 'close' option, or on the
209 210
    * titlebar), we ask it to call the delete_event () function
    * as defined above.  The data passed to the callback
211
    * function is NULL and is ignored in the callback function. */
212 213 214 215 216
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
			GTK_SIGNAL_FUNC (delete_event), NULL);
    
    /* here we connect the "destroy" event to a signal handler.  
     * This event occurs when we call gtk_widget_destroy() on the window,
217
     * or if we return 'FALSE' in the "delete_event" callback. */
218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
			GTK_SIGNAL_FUNC (destroy), NULL);
    
    /* sets the border width of the window. */
    gtk_container_border_width (GTK_CONTAINER (window), 10);
    
    /* creates a new button with the label "Hello World". */
    button = gtk_button_new_with_label ("Hello World");
    
    /* When the button receives the "clicked" signal, it will call the
     * function hello() passing it NULL as it's argument.  The hello() function is
     * defined above. */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
			GTK_SIGNAL_FUNC (hello), NULL);
    
    /* This will cause the window to be destroyed by calling
234
     * gtk_widget_destroy(window) when "clicked".  Again, the destroy
235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254
     * signal could come from here, or the window manager. */
    gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
			       GTK_SIGNAL_FUNC (gtk_widget_destroy),
			       GTK_OBJECT (window));
    
    /* this packs the button into the window (a gtk container). */
    gtk_container_add (GTK_CONTAINER (window), button);
    
    /* the final step is to display this newly created widget... */
    gtk_widget_show (button);
    
    /* and the window */
    gtk_widget_show (window);
    
    /* all GTK applications must have a gtk_main().	Control ends here
     * and waits for an event to occur (like a key press or mouse event). */
    gtk_main ();
    
    return 0;
}
255
/* example-end */
256 257 258 259 260 261 262 263
</verb></tscreen>

<!-- ----------------------------------------------------------------- -->
<sect1>Compiling Hello World
<p>
To compile use:

<tscreen><verb>
264 265
gcc -Wall -g helloworld.c -o hello_world `gtk-config --cflags` \
    `gtk-config --libs`
266
</verb></tscreen>
267 268 269 270 271 272 273 274 275

This uses the program <tt>gtk-config</>, which comes with gtk. This
program 'knows' what compiler switches are needed to compile programs
that use gtk. <tt>gtk-config --cflags</> will output a list of include
directories for the compiler to look in, and <tt>gtk-config --libs</>
will output the list of libraries for the compiler to link with and
the directories to find them in.

The libraries that are usually linked in are:
276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291
<itemize>
<item>The GTK library (-lgtk), the widget library, based on top of GDK.
<item>The GDK library (-lgdk), the Xlib wrapper.
<item>The glib library (-lglib), containing miscellaneous functions, only
g_print() is used in this particular example.  GTK is built on top
of glib so you will always require this library.  See the section on 
<ref id="sec_glib" name="glib"> for details.  
<item>The Xlib library (-lX11) which is used by GDK.
<item>The Xext library (-lXext).  This contains code for shared memory
pixmaps and other X extensions.
<item>The math library (-lm).  This is used by GTK for various purposes.
</itemize>

<!-- ----------------------------------------------------------------- -->
<sect1>Theory of Signals and Callbacks
<p>
292
Before we look in detail at hello world, we'll discuss signals and callbacks.
293 294 295
GTK is an event driven toolkit, which means it will sleep in
gtk_main until an event occurs and control is passed to the appropriate
function.
296

297 298 299
This passing of control is done using the idea of "signals".  When an 
event occurs, such as the press of a mouse button, the
appropriate signal will be "emitted" by the widget that was pressed.  
300 301 302 303 304
This is how GTK does most of its useful work. There are a set of signals
that all widgets inherit, such as "destroy", and there are signals that are
widget specific, such as "toggled" on a toggle button.

To make a button perform an action, we set up a signal handler to catch these
305 306 307 308
signals and call the appropriate function.  This is done by using a 
function such as:

<tscreen><verb>
309 310 311 312
gint gtk_signal_connect( GtkObject     *object,
                         gchar         *name,
                         GtkSignalFunc  func,
                         gpointer       func_data );
313
</verb></tscreen>
314

315 316 317 318
Where the first argument is the widget which will be emitting the signal, and
the second, the name of the signal you wish to catch.  The third is the function
you wish to be called when it is caught, and the fourth, the data you wish
to have passed to this function.
319

320
The function specified in the third argument is called a "callback
321
function", and should generally be of the form:
322 323

<tscreen><verb>
324 325
void callback_func( GtkWidget *widget,
                    gpointer   callback_data );
326
</verb></tscreen>
327 328 329 330 331 332 333 334 335 336

Where the first argument will be a pointer to the widget that emitted the 
signal, and the second, a pointer to the data given as the last argument
to the gtk_signal_connect() function as shown above.

Note that the above form for a signal callback function declaration is
only a general guide, as some widget specific signals generate different
calling parameters. For example, the GtkCList "select_row" signal provides
both row and column parameters.

337 338 339
Another call used in the hello world example, is:

<tscreen><verb>
340 341 342 343
gint gtk_signal_connect_object( GtkObject     *object,
                                gchar         *name,
                                GtkSignalFunc  func,
                                GtkObject     *slot_object );
344
</verb></tscreen>
345

346
gtk_signal_connect_object() is the same as gtk_signal_connect() except that
347 348 349
the callback function only uses one argument, a pointer to a GTK 
object.  So when using this function to connect signals, the callback
should be of the form:
350 351

<tscreen><verb>
352
void callback_func( GtkObject *object );
353
</verb></tscreen>
354

355 356
Where the object is usually a widget.  We usually don't setup callbacks for
gtk_signal_connect_object however.  They are usually used 
357
to call a GTK function that accepts a single widget or object as an
358 359 360 361 362 363 364 365
argument, as is the case in our hello world example.

The purpose of having two functions to connect signals is simply to allow
the callbacks to have a different number of arguments.  Many functions in
the GTK library accept only a single GtkWidget pointer as an argument, so you
want to use the gtk_signal_connect_object() for these, whereas for your 
functions, you may need to have additional data supplied to the callbacks.

366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487
<!-- ----------------------------------------------------------------- -->
<sect1>Events
<p>
In addition to the signal mechanism described above, there are a set of
<em>events</em> that reflect the X event mechanism. Callbacks may also be
attached to these events. These events are:

<itemize>
<item> event
<item> button_press_event
<item> button_release_event
<item> motion_notify_event
<item> delete_event
<item> destroy_event
<item> expose_event
<item> key_press_event
<item> key_release_event
<item> enter_notify_event
<item> leave_notify_event
<item> configure_event
<item> focus_in_event
<item> focus_out_event
<item> map_event
<item> unmap_event
<item> property_notify_event
<item> selection_clear_event
<item> selection_request_event
<item> selection_notify_event
<item> proximity_in_event
<item> proximity_out_event
<item> drag_begin_event
<item> drag_request_event
<item> drag_end_event
<item> drop_enter_event
<item> drop_leave_event
<item> drop_data_available_event
<item> other_event
</itemize>

In order to connect a callback function to one of these events, you use
the function gtk_signal_connect, as described above, using one of the
above event names as the <tt/name/ parameter. The callback function for
events has a slighty different form than that for signals:

<tscreen><verb>
void callback_func( GtkWidget *widget,
                    GdkEvent  *event,
                    gpointer   callback_data );
</verb></tscreen>

GdkEvent is a C <tt/union/ structure whose type will depend upon which of the
above events has occured. In order for us to tell which event has been issued
each of the possible alternatives has a <tt/type/ parameter which reflects the
event being issued. The other components of the event structure will depend
upon the type of the event. Possible values for the type are:

<tscreen><verb>
  GDK_NOTHING
  GDK_DELETE
  GDK_DESTROY
  GDK_EXPOSE
  GDK_MOTION_NOTIFY
  GDK_BUTTON_PRESS
  GDK_2BUTTON_PRESS
  GDK_3BUTTON_PRESS
  GDK_BUTTON_RELEASE
  GDK_KEY_PRESS
  GDK_KEY_RELEASE
  GDK_ENTER_NOTIFY
  GDK_LEAVE_NOTIFY
  GDK_FOCUS_CHANGE
  GDK_CONFIGURE
  GDK_MAP
  GDK_UNMAP
  GDK_PROPERTY_NOTIFY
  GDK_SELECTION_CLEAR
  GDK_SELECTION_REQUEST
  GDK_SELECTION_NOTIFY
  GDK_PROXIMITY_IN
  GDK_PROXIMITY_OUT
  GDK_DRAG_BEGIN
  GDK_DRAG_REQUEST
  GDK_DROP_ENTER
  GDK_DROP_LEAVE
  GDK_DROP_DATA_AVAIL
  GDK_CLIENT_EVENT
  GDK_VISIBILITY_NOTIFY
  GDK_NO_EXPOSE
  GDK_OTHER_EVENT	/* Deprecated, use filters instead */
</verb></tscreen>

So, to connect a callback function to one of these events we would use
something like

<tscreen><verb>
gtk_signal_connect( GTK_OBJECT(button), "button_press_event",
                    GTK_SIGNAL_FUNC(button_press_callback), 
		        NULL);
</verb></tscreen>

This assumes that <tt/button/ is a GtkButton widget. Now, when the mouse is
over the button and a mouse button is pressed, the function 
<tt/button_press_callback/ will be called. This function may be declared as:

<tscreen><verb>
static gint button_press_event (GtkWidget      *widget, 
                                GdkEventButton *event,
                                gpointer        data);
</verb></tscreen>

Note that we can declare the second argument as type <tt/GdkEventButton/
as we know what type of event will occur for this function to be called.

<!-- Need an Annex with all the event types in it - TRG -->

<!-- Need to check this - TRG
The value returned from this function indicates whether the event should
be processed further by the GTK event handling mechanism. Returning
TRUE indicates that the event has been handled, and that it should not
propogate further. Returning FALSE continues the normal event handling.
-->

488 489 490 491 492
<!-- ----------------------------------------------------------------- -->
<sect1>Stepping Through Hello World
<p>
Now that we know the theory behind this, lets clarify by walking through 
the example hello world program.
493

494 495 496 497 498 499
Here is the callback function that will be called when the button is
"clicked".  We ignore both the widget and the data in this example, but it 
is not hard to do things with them.  The next example will use the data 
argument to tell us which button was pressed.

<tscreen><verb>
500
void hello (GtkWidget *widget, gpointer data)
501 502 503 504 505 506 507 508 509 510 511
{
    g_print ("Hello World\n");
}
</verb></tscreen>

This callback is a bit special.  The "delete_event" occurs when the
window manager sends this event to the application.  We have a choice here
as to what to do about these events.  We can ignore them, make some sort of
response, or simply quit the application.

The value you return in this callback lets GTK know what action to take.
512 513
By returning TRUE, we let it know that we don't want to have the "destroy"
signal emitted, keeping our application running.  By returning FALSE, we 
514 515 516 517
ask that "destroy" is emitted, which in turn will call our "destroy" 
signal handler.

<tscreen><verb>
518
gint delete_event(GtkWidget *widget, GdkEvent *event, gpointer data)
519 520 521
{
    g_print ("delete event occured\n");

522
    return (TRUE); 
523 524 525
}
</verb></tscreen>

526 527 528 529
Here is another callback function which causes the program to quit by calling
gtk_main_quit().  This function tells GTK that it is to exit from gtk_main
when control is returned to it.

530
<tscreen><verb>
531
void destroy (GtkWidget *widget, gpointer data)
532 533 534 535
{
    gtk_main_quit ();
}
</verb></tscreen>
536

537 538
I assume you know about the main() function... yes, as with other
applications, all GTK applications will also have one of these.
539

540 541 542 543
<tscreen><verb>
int main (int argc, char *argv[])
{
</verb></tscreen>
544

545 546
This next part, declares a pointer to a structure of type GtkWidget.  These
are used below to create a window and a button.
547

548 549 550 551
<tscreen><verb>
    GtkWidget *window;
    GtkWidget *button;
</verb></tscreen>
552 553

Here is our gtk_init again. As before, this initializes the toolkit, and
554 555 556 557
parses the arguments found on the command line.  Any argument it
recognizes from the command line, it removes from the list, and modifies
argc and argv to make it look like they never existed, allowing your
application to parse the remaining arguments.
558

559 560 561
<tscreen><verb>
    gtk_init (&amp;argc, &amp;argv);
</verb></tscreen>
562

563 564
Create a new window.  This is fairly straight forward.  Memory is allocated
for the GtkWidget *window structure so it now points to a valid structure.
565
It sets up a new window, but it is not displayed until we call
566
gtk_widget_show(window) near the end of our program.
567

568 569 570
<tscreen><verb>
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
</verb></tscreen>
571 572 573 574 575

Here is an example of connecting a signal handler to an object, in
this case, the window.  Here, the "destroy" signal is caught.  This is
emitted when we use the window manager to kill the window (and we return
TRUE in the "delete_event" handler), or when we use the
576
gtk_widget_destroy() call passing in the window widget as the object to
577
destroy. By setting this up, we handle both cases with a single call.
578 579
Here, it just calls the destroy() function defined above with a NULL
argument, which quits GTK for us.  
580 581 582 583

The GTK_OBJECT and GTK_SIGNAL_FUNC are macros that perform type 
casting and checking for us, as well as aid the readability of the code.

584 585
<tscreen><verb>
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
586
                        GTK_SIGNAL_FUNC (destroy), NULL);
587
</verb></tscreen>
588

589 590 591 592 593 594
This next function is used to set an attribute of a container object.  
This just sets the window
so it has a blank area along the inside of it 10 pixels wide where no
widgets will go.  There are other similar functions which we will look at 
in the section on 
<ref id="sec_setting_widget_attributes" name="Setting Widget Attributes">
595

596
And again, GTK_CONTAINER is a macro to perform type casting.
597

598 599 600
<tscreen><verb>
    gtk_container_border_width (GTK_CONTAINER (window), 10);
</verb></tscreen>
601

602 603
This call creates a new button.  It allocates space for a new GtkWidget
structure in memory, initializes it, and makes the button pointer point to
604 605
it. It will have the label "Hello World" on it when displayed.

606 607 608
<tscreen><verb>
    button = gtk_button_new_with_label ("Hello World");
</verb></tscreen>
609

610 611 612 613 614 615 616 617
Here, we take this button, and make it do something useful.  We attach a
signal handler to it so when it emits the "clicked" signal, our hello()
function is called.  The data is ignored, so we simply pass in NULL to the
hello() callback function.  Obviously, the "clicked" signal is emitted when
we click the button with our mouse pointer.

<tscreen><verb>
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
618
                        GTK_SIGNAL_FUNC (hello), NULL);
619
</verb></tscreen>
620

621 622 623 624 625
We are also going to use this button to exit our program.  This will
illustrate how the "destroy"
signal may come from either the window manager, or our program.  When the
button is "clicked", same as above, it calls the first hello() callback function,
and then this one in the order they are set up.  You may have as many
626
callback functions as you need, and all will be executed in the order you
627 628 629 630 631
connected them.  Because the gtk_widget_destroy() function accepts only a
GtkWidget *widget as an argument, we use the gtk_signal_connect_object()
function here instead of straight gtk_signal_connect().

<tscreen><verb>
632 633 634
gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
                           GTK_SIGNAL_FUNC (gtk_widget_destroy),
                           GTK_OBJECT (window));
635
</verb></tscreen>
636

637 638
This is a packing call, which will be explained in depth later on.  But it
is fairly easy to understand.  It simply tells GTK that the button is to be 
639 640 641 642
placed in the window where it will be displayed. Note that a GTK container
can only contain one widget. There are other widgets, that are described later,
which are designed to layout multiple widgets in various ways.
 
643 644 645
<tscreen><verb>
    gtk_container_add (GTK_CONTAINER (window), button);
</verb></tscreen>
646

647 648 649 650 651
Now that we have everything setup the way we want it to be.  With all the
signal handlers in place, and the button placed in the window where it
should be, we ask GTK to "show" the widgets on the screen.  The window
widget is shown last so the whole window will pop up at once rather than
seeing the window pop up, and then the button form inside of it.  Although
652 653
with such a simple example, you'd never notice.

654 655 656 657 658
<tscreen><verb>
    gtk_widget_show (button);

    gtk_widget_show (window);
</verb></tscreen>
659

660 661
And of course, we call gtk_main() which waits for events to come from the X
server and will call on the widgets to emit signals when these events come.
662

663 664 665
<tscreen><verb>
    gtk_main ();
</verb></tscreen>
666

667
And the final return.  Control returns here after gtk_quit() is called.
668

669 670 671
<tscreen><verb>
    return 0;
</verb></tscreen>
672

673
Now, when we click the mouse button on a GTK button, the
674 675 676 677
widget emits a "clicked" signal.  In order for us to use this
information, our program sets up a signal handler to catch that signal, 
which dispatches the function of our choice. In our example, when the 
button we created is "clicked", the hello() function is called with a NULL
678 679 680
argument, and then the next handler for this signal is called.  This calls
the gtk_widget_destroy() function, passing it the window widget as it's
argument, destroying the window widget.  This causes the window to emit the 
681 682 683
"destroy" signal, which is caught, and calls our destroy() callback 
function, which simply exits GTK.

684 685
Another course of events, is to use the window manager to kill the window.
This will cause the "delete_event" to be emitted.  This will call our
686 687
"delete_event" handler.  If we return TRUE here, the window will be left as
is and nothing will happen.  Returning FALSE will cause GTK to emit the
688
"destroy" signal which of course, calls the "destroy" callback, exiting GTK.
689

690 691 692 693 694 695 696 697 698 699 700 701
Note that these signals are not the same as the Unix system
signals, and are not implemented using them, although the terminology is
almost identical.

<!-- ***************************************************************** -->
<sect>Moving On
<!-- ***************************************************************** -->

<!-- ----------------------------------------------------------------- -->
<sect1>Data Types
<p>
There are a few things you probably noticed in the previous examples that
702 703 704 705 706 707
need explaining.  The gint, gchar etc. that you see are typedefs to int and 
char respectively.  This is done to get around that nasty dependency on the 
size of simple data types when doing calculations.

A good example is "gint32" which will be typedef'd to a 32 bit integer for
any given platform, whether it be the 64 bit alpha, or the 32 bit i386.  The
708 709
typedefs are very straight forward and intuitive.  They are all defined in
glib/glib.h (which gets included from gtk.h).
710 711 712

You'll also notice the ability to use GtkWidget when the function calls for 
a GtkObject. GTK is an object oriented design, and a widget is an object.
713 714 715 716 717 718 719

<!-- ----------------------------------------------------------------- -->
<sect1>More on Signal Handlers
<p>
Lets take another look at the gtk_signal_connect declaration.

<tscreen><verb>
720 721 722 723
gint gtk_signal_connect( GtkObject *object,
                         gchar *name,
                         GtkSignalFunc func,
                         gpointer func_data );
724 725 726 727
</verb></tscreen>

Notice the gint return value ?  This is a tag that identifies your callback
function.  As said above, you may have as many callbacks per signal and per
728
object as you need, and each will be executed in turn, in the order they 
729
were attached.
730

731
This tag allows you to remove this callback from the list by using:
732

733
<tscreen><verb>
734 735
void gtk_signal_disconnect( GtkObject *object,
                            gint id );
736
</verb></tscreen>
737

738 739 740
So, by passing in the widget you wish to remove the handler from, and the
tag or id returned by one of the signal_connect functions, you can
disconnect a signal handler.
741

742
Another function to remove all the signal handers from an object is:
743

744
<tscreen><verb>
745
void gtk_signal_handlers_destroy( GtkObject *object );
746
</verb></tscreen>
747

748 749 750 751 752 753 754 755 756 757 758
This call is fairly self explanatory.  It simply removes all the current
signal handlers from the object passed in as the first argument.

<!-- ----------------------------------------------------------------- -->
<sect1>An Upgraded Hello World
<p>
Let's take a look at a slightly improved hello world with better examples
of callbacks.  This will also introduce us to our next topic, packing
widgets.

<tscreen><verb>
759
/* example-start helloworld2 helloworld2.c */
760 761 762 763 764

#include <gtk/gtk.h>

/* Our new improved callback.  The data passed to this function is printed
 * to stdout. */
765
void callback (GtkWidget *widget, gpointer data)
766 767 768 769 770
{
    g_print ("Hello again - %s was pressed\n", (char *) data);
}

/* another callback */
771
void delete_event (GtkWidget *widget, GdkEvent *event, gpointer data)
772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849
{
    gtk_main_quit ();
}

int main (int argc, char *argv[])
{
    /* GtkWidget is the storage type for widgets */
    GtkWidget *window;
    GtkWidget *button;
    GtkWidget *box1;

    /* this is called in all GTK applications.	arguments are parsed from
     * the command line and are returned to the application. */
    gtk_init (&amp;argc, &amp;argv);

    /* create a new window */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

    /* this is a new call, this just sets the title of our
     * new window to "Hello Buttons!" */
    gtk_window_set_title (GTK_WINDOW (window), "Hello Buttons!");

    /* Here we just set a handler for delete_event that immediately
     * exits GTK. */
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
			GTK_SIGNAL_FUNC (delete_event), NULL);


    /* sets the border width of the window. */
    gtk_container_border_width (GTK_CONTAINER (window), 10);

    /* we create a box to pack widgets into.  this is described in detail
     * in the "packing" section below.  The box is not really visible, it
     * is just used as a tool to arrange widgets. */
    box1 = gtk_hbox_new(FALSE, 0);

    /* put the box into the main window. */
    gtk_container_add (GTK_CONTAINER (window), box1);

    /* creates a new button with the label "Button 1". */
    button = gtk_button_new_with_label ("Button 1");

    /* Now when the button is clicked, we call the "callback" function
     * with a pointer to "button 1" as it's argument */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
			GTK_SIGNAL_FUNC (callback), (gpointer) "button 1");

    /* instead of gtk_container_add, we pack this button into the invisible
     * box, which has been packed into the window. */
    gtk_box_pack_start(GTK_BOX(box1), button, TRUE, TRUE, 0);

    /* always remember this step, this tells GTK that our preparation for
     * this button is complete, and it can be displayed now. */
    gtk_widget_show(button);

    /* do these same steps again to create a second button */
    button = gtk_button_new_with_label ("Button 2");

    /* call the same callback function with a different argument,
     * passing a pointer to "button 2" instead. */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
			GTK_SIGNAL_FUNC (callback), (gpointer) "button 2");

    gtk_box_pack_start(GTK_BOX(box1), button, TRUE, TRUE, 0);

    /* The order in which we show the buttons is not really important, but I
     * recommend showing the window last, so it all pops up at once. */
    gtk_widget_show(button);

    gtk_widget_show(box1);

    gtk_widget_show (window);

    /* rest in gtk_main and wait for the fun to begin! */
    gtk_main ();

    return 0;
}
850
/* example-end */
851
</verb></tscreen>
852

853
Compile this program using the same linking arguments as our first example.
854 855 856
You'll notice this time there is no easy way to exit the program, you have 
to use your window manager or command line to kill it.  A good exercise 
for the reader would be to insert a third "Quit" button that will exit the
857 858 859
program.  You may also wish to play with the options to
gtk_box_pack_start() while reading the next section.  
Try resizing the window, and observe the behavior.
860

861 862 863 864 865 866 867 868
Just as a side note, there is another useful define for gtk_window_new() -
GTK_WINDOW_DIALOG.  This interacts with the window manager a little
differently and should be used for transient windows.

<!-- ***************************************************************** -->
<sect>Packing Widgets
<!-- ***************************************************************** -->
<p>
869
When creating an application, you'll want to put more than one widget
870 871 872
inside a window.  Our first hello world example only used one widget so we
could simply use a gtk_container_add call to "pack" the widget into the
window.  But when you want to put more than one widget into a window, how
873
do you control where that widget is positioned? This is where packing
874 875 876 877 878 879
comes in.

<!-- ----------------------------------------------------------------- -->
<sect1>Theory of Packing Boxes
<p>
Most packing is done by creating boxes as in the example above.  These are
880
invisible widget containers that we can pack our widgets into which come in
881 882 883 884 885 886
two forms, a horizontal box, and a vertical box.  When packing widgets
into a horizontal box, the objects are inserted horizontally from left to
right or right to left depending on the call used. In a vertical box,
widgets are packed from top to bottom or vice versa.  You may use any
combination of boxes inside or beside other boxes to create the desired
effect.
887

888
To create a new horizontal box, we use a call to gtk_hbox_new(), and for
889
vertical boxes, gtk_vbox_new(). The gtk_box_pack_start() and
890 891 892 893 894 895
gtk_box_pack_end() functions are used to place objects inside of these
containers.  The gtk_box_pack_start() function will start at the top and
work its way down in a vbox, and pack left to right in an hbox.
gtk_box_pack_end() will do the opposite, packing from bottom to top in a
vbox, and right to left in an hbox.  Using these functions allow us to
right justify or left justify our widgets and may be mixed in any way to
896 897 898
achieve the desired effect. We will use gtk_box_pack_start() in most of
our examples.  An object may be another container or a widget. In
fact, many widgets are actually containers themselves, including the
899
button, but we usually only use a label inside a button.
900

901
By using these calls, GTK knows where you want to place your widgets so it
902
can do automatic resizing and other nifty things. There's also a number
903 904 905 906 907 908 909 910 911 912
of options as to how your widgets should be packed. As you can imagine,
this method gives us a quite a bit of flexibility when placing and
creating widgets.

<!-- ----------------------------------------------------------------- -->
<sect1>Details of Boxes
<p>
Because of this flexibility, packing boxes in GTK can be confusing at
first. There are a lot of options, and it's not immediately obvious how
they all fit together.	In the end however, there are basically five
913
different styles.
914 915 916

<? <CENTER> >
<?
917
<IMG SRC="gtk_tut_packbox1.gif" VSPACE="15" HSPACE="10" WIDTH="528" HEIGHT="235"
918 919 920 921 922 923 924
ALT="Box Packing Example Image">
>
<? </CENTER> >

Each line contains one horizontal box (hbox) with several buttons. The
call to gtk_box_pack is shorthand for the call to pack each of the buttons
into the hbox. Each of the buttons is packed into the hbox the same way
925 926
(i.e. same arguments to the gtk_box_pack_start() function).

927 928 929
This is the declaration of the gtk_box_pack_start function.

<tscreen><verb>
930 931 932 933 934
void gtk_box_pack_start( GtkBox    *box,
                         GtkWidget *child,
                         gint       expand,
                         gint       fill,
                         gint       padding );
935 936 937
</verb></tscreen>

The first argument is the box you are packing the object into, the second
938
is the object. The objects will all be buttons for now, so we'll be
939
packing buttons into boxes.
940 941

The expand argument to gtk_box_pack_start() and gtk_box_pack_end() controls
942 943
whether the widgets are laid out in the box to fill in all the extra space
in the box so the box is expanded to fill the area alloted to it (TRUE).
944 945 946 947 948
Or the box is shrunk to just fit the widgets (FALSE). Setting expand to
FALSE will allow you to do right and left justification of your widgets.
Otherwise, they will all expand to fit into the box, and the same effect
could be achieved by using only one of gtk_box_pack_start or pack_end functions.

949 950 951 952
The fill argument to the gtk_box_pack functions control whether the extra
space is allocated to the objects themselves (TRUE), or as extra padding
in the box around these objects (FALSE). It only has an effect if the
expand argument is also TRUE.
953

954 955 956
When creating a new box, the function looks like this:

<tscreen><verb>
957 958
GtkWidget *gtk_hbox_new (gint homogeneous,
                         gint spacing);
959 960 961 962 963 964
</verb></tscreen>

The homogeneous argument to gtk_hbox_new (and the same for gtk_vbox_new)
controls whether each object in the box has the same size (i.e. the same
width in an hbox, or the same height in a vbox). If it is set, the expand
argument to the gtk_box_pack routines is always turned on.
965

966 967
What's the difference between spacing (set when the box is created) and
padding (set when elements are packed)? Spacing is added between objects,
968
and padding is added on either side of an object. The following figure
969 970 971 972
should make it clearer:

<? <CENTER> >
<?
973
<IMG ALIGN="center" SRC="gtk_tut_packbox2.gif" WIDTH="509" HEIGHT="213"
974 975 976 977 978
VSPACE="15" HSPACE="10" ALT="Box Packing Example Image">
>
<? </CENTER> >

Here is the code used to create the above images.  I've commented it fairly
979 980
heavily so hopefully you won't have any problems following it.  Compile it 
yourself and play with it.
981 982 983 984 985

<!-- ----------------------------------------------------------------- -->
<sect1>Packing Demonstration Program
<p>
<tscreen><verb>
986
/* example-start packbox packbox.c */
987 988 989 990

#include "gtk/gtk.h"

void
991
delete_event (GtkWidget *widget, GdkEvent *event, gpointer data)
992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268
{
    gtk_main_quit ();
}

/* Make a new hbox filled with button-labels. Arguments for the 
 * variables we're interested are passed in to this function. 
 * We do not show the box, but do show everything inside. */
GtkWidget *make_box (gint homogeneous, gint spacing,
		     gint expand, gint fill, gint padding) 
{
    GtkWidget *box;
    GtkWidget *button;
    char padstr[80];
    
    /* create a new hbox with the appropriate homogeneous and spacing
     * settings */
    box = gtk_hbox_new (homogeneous, spacing);
    
    /* create a series of buttons with the appropriate settings */
    button = gtk_button_new_with_label ("gtk_box_pack");
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    button = gtk_button_new_with_label ("(box,");
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    button = gtk_button_new_with_label ("button,");
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    /* create a button with the label depending on the value of
     * expand. */
    if (expand == TRUE)
	    button = gtk_button_new_with_label ("TRUE,");
    else
	    button = gtk_button_new_with_label ("FALSE,");
    
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    /* This is the same as the button creation for "expand"
     * above, but uses the shorthand form. */
    button = gtk_button_new_with_label (fill ? "TRUE," : "FALSE,");
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    sprintf (padstr, "%d);", padding);
    
    button = gtk_button_new_with_label (padstr);
    gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding);
    gtk_widget_show (button);
    
    return box;
}

int
main (int argc, char *argv[])
{
    GtkWidget *window;
    GtkWidget *button;
    GtkWidget *box1;
    GtkWidget *box2;
    GtkWidget *separator;
    GtkWidget *label;
    GtkWidget *quitbox;
    int which;
    
    /* Our init, don't forget this! :) */
    gtk_init (&amp;argc, &amp;argv);
    
    if (argc != 2) {
	fprintf (stderr, "usage: packbox num, where num is 1, 2, or 3.\n");
	/* this just does cleanup in GTK, and exits with an exit status of 1. */
	gtk_exit (1);
    }
    
    which = atoi (argv[1]);

    /* Create our window */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

    /* You should always remember to connect the destroy signal to the
     * main window.  This is very important for proper intuitive
     * behavior */
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
			GTK_SIGNAL_FUNC (delete_event), NULL);
    gtk_container_border_width (GTK_CONTAINER (window), 10);
    
    /* We create a vertical box (vbox) to pack the horizontal boxes into.
     * This allows us to stack the horizontal boxes filled with buttons one
     * on top of the other in this vbox. */
    box1 = gtk_vbox_new (FALSE, 0);
    
    /* which example to show.  These correspond to the pictures above. */
    switch (which) {
    case 1:
	/* create a new label. */
	label = gtk_label_new ("gtk_hbox_new (FALSE, 0);");
	
	/* Align the label to the left side.  We'll discuss this function and 
	 * others in the section on Widget Attributes. */
	gtk_misc_set_alignment (GTK_MISC (label), 0, 0);

	/* Pack the label into the vertical box (vbox box1).  Remember that 
	 * widgets added to a vbox will be packed one on top of the other in
	 * order. */
	gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0);
	
	/* show the label */
	gtk_widget_show (label);
	
	/* call our make box function - homogeneous = FALSE, spacing = 0,
	 * expand = FALSE, fill = FALSE, padding = 0 */
	box2 = make_box (FALSE, 0, FALSE, FALSE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);

	/* call our make box function - homogeneous = FALSE, spacing = 0,
	 * expand = FALSE, fill = FALSE, padding = 0 */
	box2 = make_box (FALSE, 0, TRUE, FALSE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (FALSE, 0, TRUE, TRUE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* creates a separator, we'll learn more about these later, 
	 * but they are quite simple. */
	separator = gtk_hseparator_new ();
	
	/* pack the separator into the vbox.  Remember each of these
	 * widgets are being packed into a vbox, so they'll be stacked
	 * vertically. */
	gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5);
	gtk_widget_show (separator);
	
	/* create another new label, and show it. */
	label = gtk_label_new ("gtk_hbox_new (TRUE, 0);");
	gtk_misc_set_alignment (GTK_MISC (label), 0, 0);
	gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0);
	gtk_widget_show (label);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (TRUE, 0, TRUE, FALSE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (TRUE, 0, TRUE, TRUE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* another new separator. */
	separator = gtk_hseparator_new ();
	/* The last 3 arguments to gtk_box_pack_start are: expand, fill, padding. */
	gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5);
	gtk_widget_show (separator);
	
	break;

    case 2:

	/* create a new label, remember box1 is a vbox as created 
	 * near the beginning of main() */
	label = gtk_label_new ("gtk_hbox_new (FALSE, 10);");
	gtk_misc_set_alignment (GTK_MISC (label), 0, 0);
	gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0);
	gtk_widget_show (label);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (FALSE, 10, TRUE, FALSE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (FALSE, 10, TRUE, TRUE, 0);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	separator = gtk_hseparator_new ();
	/* The last 3 arguments to gtk_box_pack_start are: expand, fill, padding. */
	gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5);
	gtk_widget_show (separator);
	
	label = gtk_label_new ("gtk_hbox_new (FALSE, 0);");
	gtk_misc_set_alignment (GTK_MISC (label), 0, 0);
	gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0);
	gtk_widget_show (label);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (FALSE, 0, TRUE, FALSE, 10);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* Args are: homogeneous, spacing, expand, fill, padding */
	box2 = make_box (FALSE, 0, TRUE, TRUE, 10);
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	separator = gtk_hseparator_new ();
	/* The last 3 arguments to gtk_box_pack_start are: expand, fill, padding. */
	gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5);
	gtk_widget_show (separator);
	break;
    
    case 3:

    /* This demonstrates the ability to use gtk_box_pack_end() to
	 * right justify widgets.  First, we create a new box as before. */
	box2 = make_box (FALSE, 0, FALSE, FALSE, 0);
	/* create the label that will be put at the end. */
	label = gtk_label_new ("end");
	/* pack it using gtk_box_pack_end(), so it is put on the right side
	 * of the hbox created in the make_box() call. */
	gtk_box_pack_end (GTK_BOX (box2), label, FALSE, FALSE, 0);
	/* show the label. */
	gtk_widget_show (label);
	
	/* pack box2 into box1 (the vbox remember ? :) */
	gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0);
	gtk_widget_show (box2);
	
	/* a separator for the bottom. */
	separator = gtk_hseparator_new ();
	/* this explicitly sets the separator to 400 pixels wide by 5 pixels
	 * high.  This is so the hbox we created will also be 400 pixels wide,
	 * and the "end" label will be separated from the other labels in the
	 * hbox.  Otherwise, all the widgets in the hbox would be packed as
	 * close together as possible. */
	gtk_widget_set_usize (separator, 400, 5);
	/* pack the separator into the vbox (box1) created near the start 
	 * of main() */
	gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5);
	gtk_widget_show (separator);    
    }
    
    /* Create another new hbox.. remember we can use as many as we need! */
    quitbox = gtk_hbox_new (FALSE, 0);
    
    /* Our quit button. */
    button = gtk_button_new_with_label ("Quit");
    
    /* setup the signal to destroy the window.  Remember that this will send
     * the "destroy" signal to the window which will be caught by our signal
     * handler as defined above. */
    gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
			       GTK_SIGNAL_FUNC (gtk_main_quit),
			       GTK_OBJECT (window));
    /* pack the button into the quitbox.
     * The last 3 arguments to gtk_box_pack_start are: expand, fill, padding. */
    gtk_box_pack_start (GTK_BOX (quitbox), button, TRUE, FALSE, 0);
    /* pack the quitbox into the vbox (box1) */
    gtk_box_pack_start (GTK_BOX (box1), quitbox, FALSE, FALSE, 0);
    
    /* pack the vbox (box1) which now contains all our widgets, into the
     * main window. */
    gtk_container_add (GTK_CONTAINER (window), box1);
    
    /* and show everything left */
    gtk_widget_show (button);
    gtk_widget_show (quitbox);
    
    gtk_widget_show (box1);
    /* Showing the window last so everything pops up at once. */
    gtk_widget_show (window);
    
    /* And of course, our main function. */
    gtk_main ();

    /* control returns here when gtk_main_quit() is called, but not when 
     * gtk_exit is used. */
    
    return 0;
}
1269
/* example-end */
1270 1271 1272 1273 1274 1275 1276 1277
</verb></tscreen>

<!-- ----------------------------------------------------------------- -->
<sect1>Packing Using Tables
<p>
Let's take a look at another way of packing - Tables.  These can be
extremely useful in certain situations.

1278
Using tables, we create a grid that we can place widgets in. The widgets
1279 1280 1281 1282 1283
may take up as many spaces as we specify.

The first thing to look at of course, is the gtk_table_new function:

<tscreen><verb>
1284
GtkWidget *gtk_table_new( gint rows,
1285
                          gint columns,
1286
                          gint homogeneous );
1287
</verb></tscreen>
1288

1289
The first argument is the number of rows to make in the table, while the
1290
second, obviously, is the number of columns.
1291

1292 1293 1294 1295 1296
The homogeneous argument has to do with how the table's boxes are sized. If
homogeneous is TRUE, the table boxes are resized to the size of the largest
widget in the table. If homogeneous is FALSE, the size of a table boxes is 
dictated by the tallest widget in its same row, and the widest widget in its
column.
1297

1298
The rows and columnts are laid out from 0 to n, where n was the
1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309
number specified in the call to gtk_table_new.  So, if you specify rows = 2 and 
columns = 2, the layout would look something like this:

<tscreen><verb>
 0          1          2
0+----------+----------+
 |          |          |
1+----------+----------+
 |          |          |
2+----------+----------+
</verb></tscreen>
1310

1311 1312 1313 1314
Note that the coordinate system starts in the upper left hand corner.  To place a 
widget into a box, use the following function:

<tscreen><verb>
1315 1316 1317 1318 1319 1320 1321 1322 1323 1324
void gtk_table_attach( GtkTable  *table,
                       GtkWidget *child,
                       gint       left_attach,
                       gint       right_attach,
                       gint       top_attach,
                       gint       bottom_attach,
                       gint       xoptions,
                       gint       yoptions,
                       gint       xpadding,
                       gint       ypadding );
1325
</verb></tscreen>				       
1326

1327 1328 1329
Where the first argument ("table") is the table you've created and the second
("child") the widget you wish to place in the table.

1330 1331
The left and right attach arguments specify where to place the widget, and how
many boxes to use. If you want a button in the lower right table entry 
1332 1333 1334 1335
of our 2x2 table, and want it to fill that entry ONLY.  left_attach would be = 1, 
right_attach = 2, top_attach = 1, bottom_attach = 2.

Now, if you wanted a widget to take up the whole 
1336 1337
top row of our 2x2 table, you'd use left_attach = 0, right_attach = 2,
top_attach = 0, bottom_attach = 1.
1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362

The xoptions and yoptions are used to specify packing options and may be OR'ed 
together to allow multiple options.  

These options are:
<itemize>
<item>GTK_FILL - If the table box is larger than the widget, and GTK_FILL is
specified, the widget will expand to use all the room available.

<item>GTK_SHRINK - If the table widget was allocated less space then was
requested (usually by the user resizing the window), then the widgets would 
normally just be pushed off the bottom of
the window and disappear.  If GTK_SHRINK is specified, the widgets will
shrink with the table.

<item>GTK_EXPAND - This will cause the table to expand to use up any remaining
space in the window.
</itemize>

Padding is just like in boxes, creating a clear area around the widget
specified in pixels.  

gtk_table_attach() has a LOT of options.  So, there's a shortcut:

<tscreen><verb>
1363 1364 1365 1366 1367 1368
void gtk_table_attach_defaults( GtkTable  *table,
                                GtkWidget *widget,
                                gint       left_attach,
                                gint       right_attach,
                                gint       top_attach,
                                gint       bottom_attach );
1369 1370 1371
</verb></tscreen>

The X and Y options default to GTK_FILL | GTK_EXPAND, and X and Y padding
1372
are set to 0. The rest of the arguments are identical to the previous
1373 1374
function.

1375
We also have gtk_table_set_row_spacing() and gtk_table_set_col_spacing().
1376
This places spacing between the rows at the specified row or column.
1377 1378

<tscreen><verb>
1379 1380 1381
void gtk_table_set_row_spacing( GtkTable *table,
                                gint      row,
                                gint      spacing );
1382
</verb></tscreen>
1383

1384
and