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<!doctype linuxdoc system>

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

<article>
<title>GTK Tutorial
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<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"
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			      name="&lt;gale@gtk.org&gt;"></tt>
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<date>May 24th, 1998
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<!-- ***************************************************************** -->
<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
Drawing Kit)  which is basically wrapper around the Xlib functions.  It's
called the GIMP toolkit because it was original written for developing
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>

<p>
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).
<p>
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 
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g_strerror().   Some also contain enhancements to the libc versions, such as
g_malloc that has enhanced debugging utilities.
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<p>
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
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you had trouble with.
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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
Objective C wrapper, and guile bindings available, but I don't follow these.
<p>
I would very much like to hear any problems you have learning GTK from this
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
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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/">.
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GTK uses GNU autoconf for
configuration.  Once untar'd, type ./configure --help to see a list of options.
<p>
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>

All programs will of course include the gtk/gtk.h which declares the
variables, functions, structures etc. that will be used in your GTK 
application.
<p>
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/
</itemize>
<p>
It removes these from the argument list, leaving anything it does
not recognize for your application to parse or ignore.	This creates a set
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of standard arguments accepted by all GTK applications.
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<p>
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.
<p>
The gtk_widget_show() function, lets GTK know that we are done setting the
attributes of this widget, and it can display it.
<p>
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>
/* helloworld.c */

#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");
}

gint delete_event(GtkWidget *widget, gpointer data)
{
    g_print ("delete event occured\n");
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    /* if you return FALSE in the "delete_event" signal handler,
     * GTK will emit the "destroy" signal.  Returning TRUE means
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     * you don't want the window to be destroyed.
     * This is useful for popping up 'are you sure you want to quit ?'
     * type dialogs. */
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    /* Change TRUE to FALSE and the main window will be destroyed with
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     * a "delete_event". */
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    return (TRUE);
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}

/* 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
    * by the window manager (usually the 'close' option, or on the
    * titlebar), we ask it to call the delete_event () function
    * as defined above.  The data passed to the callback
    * function is NULL and is ignored in the callback. */
    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,
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     * or if we return 'FALSE' in the "delete_event" callback. */
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    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
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     * gtk_widget_destroy(window) when "clicked".  Again, the destroy
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     * 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;
}
</verb></tscreen>

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

<tscreen><verb>
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gcc -Wall -g helloworld.c -o hello_world `gtk-config --cflags` \
    `gtk-config --libs`
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</verb></tscreen>
<p>
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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.

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<p>
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The libraries that are usually linked in are:
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<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>
Before we look in detail at hello world, we'll discuss events and callbacks.
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.
<p>
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.  
This is how GTK does
most of its useful work.  To make a button perform an action, 
we set up a signal handler to catch these
signals and call the appropriate function.  This is done by using a 
function such as:

<tscreen><verb>
gint gtk_signal_connect (GtkObject *object,
                         gchar *name,
			 GtkSignalFunc func,
			 gpointer func_data);
</verb></tscreen>
<p>
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.
<p>
The function specified in the third argument is called a "callback
function", and should be of the form:

<tscreen><verb>
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void callback_func(GtkWidget *widget, gpointer callback_data);
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</verb></tscreen>
<p>
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.
<p>
Another call used in the hello world example, is:

<tscreen><verb>
gint gtk_signal_connect_object (GtkObject *object,
                                gchar  *name,
				GtkSignalFunc func,
				GtkObject *slot_object);
</verb></tscreen>
<p>
gtk_signal_connect_object() is the same as gtk_signal_connect() except that
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:

<tscreen><verb>
void callback_func (GtkObject *object);
</verb></tscreen>
<p>
Where the object is usually a widget.  We usually don't setup callbacks for
gtk_signal_connect_object however.  They are usually used 
to call a GTK function that accept a single widget or object as an
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.

<!-- ----------------------------------------------------------------- -->
<sect1>Stepping Through Hello World
<p>
Now that we know the theory behind this, lets clarify by walking through 
the example hello world program.
<p>
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>
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void hello (GtkWidget *widget, gpointer data)
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{
    g_print ("Hello World\n");
}
</verb></tscreen>

<p>
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.
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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 
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ask that "destroy" is emitted, which in turn will call our "destroy" 
signal handler.

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

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    return (TRUE); 
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}
</verb></tscreen>

<p>
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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.

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<tscreen><verb>
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void destroy (GtkWidget *widget, gpointer data)
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{
    gtk_main_quit ();
}
</verb></tscreen>
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<p>
I assume you know about the main() function... yes, as with other
applications, all GTK applications will also have one of these.
<tscreen><verb>
int main (int argc, char *argv[])
{
</verb></tscreen>
<p>
This next part, declares a pointer to a structure of type GtkWidget.  These
are used below to create a window and a button.
<tscreen><verb>
    GtkWidget *window;
    GtkWidget *button;
</verb></tscreen>
<p>
Here is our gtk_init again.  As before, this initializes the toolkit, and
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.
<tscreen><verb>
    gtk_init (&amp;argc, &amp;argv);
</verb></tscreen>
<p>
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.
It sets up a new window, but it is not displayed until below where we call
gtk_widget_show(window) near the end of our program.
<tscreen><verb>
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
</verb></tscreen>
<p>
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
gtk_widget_destroy() call passing in the window widget as the object to
destroy.  By setting this up, we handle both cases with a single call.
Here, it just calls the destroy() function defined above with a NULL
argument, which quits GTK for us.  
<p>
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.
<tscreen><verb>
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
			GTK_SIGNAL_FUNC (destroy), NULL);
</verb></tscreen>
<p>
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">
<p>
And again, GTK_CONTAINER is a macro to perform type casting.
<tscreen><verb>
    gtk_container_border_width (GTK_CONTAINER (window), 10);
</verb></tscreen>
<p>
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
it.  It will have the label "Hello World" on it when displayed.
<tscreen><verb>
    button = gtk_button_new_with_label ("Hello World");
</verb></tscreen>
<p>
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",
			GTK_SIGNAL_FUNC (hello), NULL);
</verb></tscreen>
<p>
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
callback function as you need, and all will be executed in the order you
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>
    gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
			       GTK_SIGNAL_FUNC (gtk_widget_destroy),
			       GTK_OBJECT (window));
</verb></tscreen>
<p>
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 
placed in the window where it will be displayed.
<tscreen><verb>
    gtk_container_add (GTK_CONTAINER (window), button);
</verb></tscreen>
<p>
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
with such simple example, you'd never notice.
<tscreen><verb>
    gtk_widget_show (button);

    gtk_widget_show (window);
</verb></tscreen>
<p>
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.
<tscreen><verb>
    gtk_main ();
</verb></tscreen>
And the final return.  Control returns here after gtk_quit() is called.
<tscreen><verb>
    return 0;
</verb></tscreen>
<p>
Now, when we click the mouse button on a GTK button, the
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
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 
"destroy" signal, which is
caught, and calls our destroy() callback function, which simply exits GTK.
<p>
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
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"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
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"destroy" signal which of course, calls the "destroy" callback, exiting GTK.
<p>
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
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
typedefs are very straight forward and intuitive.  They are all defined in
glib/glib.h (which gets included from gtk.h).
<p>
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.

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

<tscreen><verb>
gint gtk_signal_connect (GtkObject *object, gchar *name,
			 GtkSignalFunc func, gpointer func_data);
</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
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object as you need, and each will be executed in turn, in the order they 
were attached.  

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This tag allows you to remove this callback from the list by using:
<tscreen><verb>
void gtk_signal_disconnect (GtkObject *object,
                            gint id);
</verb></tscreen>
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.
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Another function to remove all the signal handers from an object is:
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<tscreen><verb>
gtk_signal_handlers_destroy (GtkObject *object);
</verb></tscreen>
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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>
/* helloworld2.c */

#include <gtk/gtk.h>

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

/* another callback */
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void delete_event (GtkWidget *widget, gpointer data)
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{
    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;
}
</verb></tscreen>
707

708
Compile this program using the same linking arguments as our first example.
709 710 711
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
712 713 714
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.
715

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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>
When creating an application, you'll want to put more than one button
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
do you control where that widget is positioned ?  This is where packing
comes in.

<!-- ----------------------------------------------------------------- -->
<sect1>Theory of Packing Boxes
<p>
Most packing is done by creating boxes as in the example above.  These are
invisible widget containers that we can pack our widgets into and come in
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.
<p>
To create a new horizontal box, we use a call to gtk_hbox_new(), and for
vertical boxes, gtk_vbox_new().  The gtk_box_pack_start() and
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
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.	And in
fact, many widgets are actually containers themselves including the
button, but we usually only use a label inside a button.
<p>
By using these calls, GTK knows where you want to place your widgets so it
can do automatic resizing and other nifty things.  there's also a number
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
different styles you can get.

<p>
<? <CENTER> >
<?
774
<IMG SRC="gtk_tut_packbox1.gif" VSPACE="15" HSPACE="10" WIDTH="528" HEIGHT="235"
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
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
(i.e. same arguments to the gtk_box_pack_start () function).
<p>
This is the declaration of the gtk_box_pack_start function.

<tscreen><verb>
void gtk_box_pack_start (GtkBox    *box,
			 GtkWidget *child,
			 gint	    expand,
			 gint	    fill,
			 gint	    padding);
</verb></tscreen>

The first argument is the box you are packing the object into, the second
is this object.  The objects will all be buttons for now, so we'll be
packing buttons into boxes.
<p>
The expand argument to gtk_box_pack_start() or gtk_box_pack_end() controls
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).
Or the box is shrunk to just fit the widgets (FALSE).  Setting expand to
FALSE will allow you to do right and left
justifying of your widgets.  Otherwise, they will all expand to fit in the
box, and the same effect could be achieved by using only one of
gtk_box_pack_start or pack_end functions.
<p>
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.
<p>
When creating a new box, the function looks like this:

<tscreen><verb>
GtkWidget * gtk_hbox_new (gint homogeneous,
			  gint spacing);
</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.
<p>
What's the difference between spacing (set when the box is created) and
padding (set when elements are packed)? Spacing is added between objects,
and padding is added on either side of an object.  The following figure
should make it clearer:

<? <CENTER> >
<?
831
<IMG ALIGN="center" SRC="gtk_tut_packbox2.gif" WIDTH="509" HEIGHT="213"
832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848
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
heavily so hopefully you won't have any problems following it.  Compile it yourself
and play with it.

<!-- ----------------------------------------------------------------- -->
<sect1>Packing Demonstration Program
<p>
<tscreen><verb>
/* packbox.c */

#include "gtk/gtk.h"

void
849
delete_event (GtkWidget *widget, gpointer data)
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{
    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;
}
</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.

Using tables, we create a grid that we can place widgets in.  The widgets
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>
GtkWidget* gtk_table_new (gint rows,
                          gint columns,
                          gint homogeneous);
</verb></tscreen>
<p>
The first argument is the number of rows to make in the table, while the
second, obviously, the number of columns.

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.

The rows and columnts are laid out starting with 0 to n, where n was the
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>
<p>
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>
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);
</verb></tscreen>				       
<p>
Where the first argument ("table") is the table you've created and the second
("child") the widget you wish to place in the table.

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 
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 
top row of our 2x2 table, you'd use left_attach = 0, right_attach =2, top_attach = 0, 
bottom_attach = 1.

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>
void gtk_table_attach_defaults (GtkTable   *table,
                                GtkWidget  *widget,
				gint        left_attach,
				gint        right_attach,
				gint        top_attach,
				gint        bottom_attach);
</verb></tscreen>

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

1232 1233
We also have gtk_table_set_row_spacing() and gtk_table_set_col_spacing(). 
This places spacing between the rows at the specified row or column.
1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246

<tscreen><verb>
void gtk_table_set_row_spacing (GtkTable      *table,
                                gint           row,
				gint           spacing);
</verb></tscreen>
and
<tscreen><verb>
void       gtk_table_set_col_spacing  (GtkTable      *table,
                                       gint           column,
				       gint           spacing);
</verb></tscreen>

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Note that for columns, the space goes to the right of the column, and for 
rows, the space goes below the row.
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You can also set a consistent spacing of all rows and/or columns with:

<tscreen><verb>
void gtk_table_set_row_spacings (GtkTable *table,
                                 gint      spacing);
</verb></tscreen>
<p>
And,
<tscreen><verb>
void gtk_table_set_col_spacings (GtkTable  *table,
                                 gint       spacing);
</verb></tscreen>
<p>
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Note that with these calls, the last row and last column do not get any 
spacing.
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<!-- ----------------------------------------------------------------- -->
<sect1>Table Packing Example
<p>
Here we make a window with three buttons in a 2x2 table.
The first two buttons will be placed in the upper row.
A third, quit button, is placed in the lower row, spanning both columns.
Which means it should look something like this:
<p>
<? <CENTER> >
<?
1276
<IMG SRC="gtk_tut_table.gif" VSPACE="15" HSPACE="10" 
1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288
ALT="Table Packing Example Image" WIDTH="180" HEIGHT="120">
>
<? </CENTER> >

Here's the source code:

<tscreen><verb>
/* table.c */
#include <gtk/gtk.h>

/* our callback.
 * the data passed to this function is printed to stdout */
1289
void callback (GtkWidget *widget, gpointer data)
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{
    g_print ("Hello again - %s was pressed\n", (char *) data);
}

/* this callback quits the program */
1295
void delete_event (GtkWidget *widget, gpointer data)
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{
    gtk_main_quit ();
}

int main (int argc, char *argv[])
{
    GtkWidget *window;
    GtkWidget *button;
    GtkWidget *table;

    gtk_init (&amp;argc, &amp;argv);

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

    /* set the window title */
    gtk_window_set_title (GTK_WINDOW (window), "Table");

    /* 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), 20);

    /* create a 2x2 table */
    table = gtk_table_new (2, 2, TRUE);

    /* put the table in the main window */
    gtk_container_add (GTK_CONTAINER (window), table);

    /* create first button */
    button = gtk_button_new_with_label ("button 1");

    /* 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");


    /* insert button 1 into the upper left quadrant of the table */
    gtk_table_attach_defaults (GTK_TABLE(table), button, 0, 1, 0, 1);

    gtk_widget_show (button);

    /* create second button */

    button = gtk_button_new_with_label ("button 2");

    /* when the button is clicked, we call the "callback" function
     * with a pointer to "button 2" as it's argument */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
              GTK_SIGNAL_FUNC (callback), (gpointer) "button 2");
    /* insert button 2 into the upper right quadrant of the table */
    gtk_table_attach_defaults (GTK_TABLE(table), button, 1, 2, 0, 1);

    gtk_widget_show (button);

    /* create "Quit" button */
    button = gtk_button_new_with_label ("Quit");

    /* when the button is clicked, we call the "delete_event" function
     * and the program exits */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
                        GTK_SIGNAL_FUNC (delete_event), NULL);

    /* insert the quit button into the both 
     * lower quadrants of the table */
    gtk_table_attach_defaults (GTK_TABLE(table), button, 0, 2, 1, 2);

    gtk_widget_show (button);

    gtk_widget_show (table);
    gtk_widget_show (window);

    gtk_main ();

    return 0;
}
</verb></tscreen>
<!-- ***************************************************************** -->
<sect>Widget Overview
<!-- ***************************************************************** -->

<p>
The general steps to creating a widget in GTK are:
<enum>
<item> gtk_*_new - one of various functions to create a new widget.  These
are all detailed in this section.

<item> Connect all signals we wish to use to the appropriate handlers.

<item> Set the attributes of the widget.

<item> Pack the widget into a container using the appropriate call such as 
gtk_container_add() or gtk_box_pack_start().

<item> gtk_widget_show() the widget.
</enum>
<p>
gtk_widget_show() lets GTK know that we are done setting the attributes
of the widget, and it is ready to be displayed.  You may also use
gtk_widget_hide to make it disappear again.  The order in which you
show the widgets is not important, but I suggest showing the window
last so the whole window pops up at once rather than seeing the individual
widgets come up on the screen as they're formed.  The children of a widget
(a window is a widget too)
will not be displayed until the window itself is shown using the
gtk_widget_show() function.

<!-- ----------------------------------------------------------------- -->
<sect1> Casting
<p>
You'll notice as you go on, that GTK uses a type casting system.  This is
always done using macros that both test the ability to cast the given item,
and perform the cast.  Some common ones you will see are:

<itemize>
<item> GTK_WIDGET(widget)
<item> GTK_OBJECT(object)
<item> GTK_SIGNAL_FUNC(function)
<item> GTK_CONTAINER(container)
<item> GTK_WINDOW(window)
<item> GTK_BOX(box)
</itemize>

These are all used to cast arguments in functions.  You'll see them in the
examples, and can usually tell when to use them simply by looking at the
function's declaration.

As you can see below in the class hierarchy, all GtkWidgets are derived from
the GtkObject base class.  This means you can use an widget in any place the 
function asks for an object - simply use the GTK_OBJECT() macro.

For example:

<tscreen><verb>
gtk_signal_connect(GTK_OBJECT(button), "clicked",
                   GTK_SIGNAL_FUNC(callback_function), callback_data);
</verb></tscreen> 

This casts the button into an object, and provides a cast for the function
pointer to the callback.

Many widgets are also containers.  If you look in the class hierarchy below,
you'll notice that many widgets drive from the GtkContainer class.  Any one
of those widgets may use with the GTK_CONTAINER macro to
pass them to functions that ask for containers.

Unfortunately, these macros are not extensively covered in the tutorial, but I
recomend taking a look through the GTK header files.  It can be very
educational.  In fact, it's not difficult to learn how a widget works just
by looking at the function declarations.

<!-- ----------------------------------------------------------------- -->
<sect1>Widget Hierarchy
<p>
For your reference, here is the class hierarchy tree used to implement widgets.

<tscreen><verb>
  GtkObject
   +GtkData
   | +GtkAdjustment
   | `GtkTooltips
   `GtkWidget
     +GtkContainer
     | +GtkBin
     | | +GtkAlignment
     | | +GtkEventBox
     | | +GtkFrame
     | | | `GtkAspectFrame
     | | +GtkHandleBox
     | | +GtkItem
     | | | +GtkListItem
     | | | +GtkMenuItem
     | | | | `GtkCheckMenuItem
     | | | |   `GtkRadioMenuItem
     | | | `GtkTreeItem
     | | +GtkViewport
     | | `GtkWindow
     | |   +GtkColorSelectionDialog
     | |   +GtkDialog
     | |   | `GtkInputDialog
     | |   `GtkFileSelection
     | +GtkBox
     | | +GtkButtonBox
     | | | +GtkHButtonBox
     | | | `GtkVButtonBox
     | | +GtkHBox
     | | | +GtkCombo
     | | | `GtkStatusbar
     | | `GtkVBox
     | |   +GtkColorSelection
     | |   `GtkGammaCurve
     | +GtkButton
     | | +GtkOptionMenu
     | | `GtkToggleButton
     | |   `GtkCheckButton
     | |     `GtkRadioButton
     | +GtkCList
1497
     |  `GtkCTree
1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637
     | +GtkFixed
     | +GtkList
     | +GtkMenuShell
     | | +GtkMenuBar
     | | `GtkMenu
     | +GtkNotebook
     | +GtkPaned
     | | +GtkHPaned
     | | `GtkVPaned
     | +GtkScrolledWindow
     | +GtkTable
     | +GtkToolbar
     | `GtkTree
     +GtkDrawingArea
     | `GtkCurve
     +GtkEditable
     | +GtkEntry
     | | `GtkSpinButton
     | `GtkText
     +GtkMisc
     | +GtkArrow
     | +GtkImage
     | +GtkLabel
     | | `GtkTipsQuery
     | `GtkPixmap
     +GtkPreview
     +GtkProgressBar
     +GtkRange
     | +GtkScale
     | | +GtkHScale
     | | `GtkVScale
     | `GtkScrollbar
     |   +GtkHScrollbar
     |   `GtkVScrollbar
     +GtkRuler
     | +GtkHRuler
     | `GtkVRuler
     `GtkSeparator
       +GtkHSeparator
       `GtkVSeparator
</verb></tscreen>

<!-- ----------------------------------------------------------------- -->
<sect1>Widgets Without Windows
<p>
The following widgets do not have an associated window.  If you want to
capture events, you'll have to use the GtkEventBox.  See the section on   
<ref id="sec_The_EventBox_Widget" name="The EventBox Widget">

<tscreen><verb>
GtkAlignment
GtkArrow
GtkBin
GtkBox
GtkImage
GtkItem
GtkLabel
GtkPixmap
GtkScrolledWindow
GtkSeparator
GtkTable
GtkAspectFrame
GtkFrame
GtkVBox
GtkHBox
GtkVSeparator
GtkHSeparator
</verb></tscreen>
<p>
We'll further our exploration of GTK by examining each widget in turn,
creating a few simple functions to display them.  Another good source is
the testgtk.c program that comes with GTK.  It can be found in
gtk/testgtk.c.

<!-- ***************************************************************** -->
<sect>The Button Widget
<!-- ***************************************************************** -->

<!-- ----------------------------------------------------------------- -->
<sect1>Normal Buttons
<p>
We've almost seen all there is to see of the button widget.  It's pretty
simple.  There is however two ways to create a button.	You can use the
gtk_button_new_with_label() to create a button with a label, or use
gtk_button_new() to create a blank button.  It's then up to you to pack a
label or pixmap into this new button.  To do this, create a new box, and
then pack your objects into this box using the usual gtk_box_pack_start,
and then use gtk_container_add to pack the box into the button.
<p>
Here's an example of using gtk_button_new to create a button with a
picture and a label in it.  I've broken the code to create a box up from
the rest so you can use it in your programs.

<tscreen><verb>
/* buttons.c */

#include <gtk/gtk.h>

/* create a new hbox with an image and a label packed into it
 * and return the box.. */

GtkWidget *xpm_label_box (GtkWidget *parent, gchar *xpm_filename, gchar *label_text)
{
    GtkWidget *box1;
    GtkWidget *label;
    GtkWidget *pixmapwid;
    GdkPixmap *pixmap;
    GdkBitmap *mask;
    GtkStyle *style;

    /* create box for xpm and label */
    box1 = gtk_hbox_new (FALSE, 0);
    gtk_container_border_width (GTK_CONTAINER (box1), 2);

    /* get style of button.. I assume it's to get the background color.
     * if someone knows the real reason, please enlighten me. */
    style = gtk_widget_get_style(parent);

    /* now on to the xpm stuff.. load xpm */
    pixmap = gdk_pixmap_create_from_xpm (parent->window, &amp;mask,
					 &amp;style->bg[GTK_STATE_NORMAL],
					 xpm_filename);
    pixmapwid = gtk_pixmap_new (pixmap, mask);

    /* create label for button */
    label = gtk_label_new (label_text);

    /* pack the pixmap and label into the box */
    gtk_box_pack_start (GTK_BOX (box1),
			pixmapwid, FALSE, FALSE, 3);

    gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 3);

    gtk_widget_show(pixmapwid);
    gtk_widget_show(label);

    return (box1);
}

/* our usual callback function */
1638
void callback (GtkWidget *widget, gpointer data)
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{
    g_print ("Hello again - %s was pressed\n", (char *) data);
}


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

    gtk_init (&amp;argc, &amp;argv);

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

    gtk_window_set_title (GTK_WINDOW (window), "Pixmap'd Buttons!");

    /* It's a good idea to do this for all windows. */
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
			GTK_SIGNAL_FUNC (gtk_exit), NULL);

    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
			GTK_SIGNAL_FUNC (gtk_exit), NULL);


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

    /* create a new button */
    button = gtk_button_new ();

    /* You should be getting used to seeing most of these functions by now */
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
			GTK_SIGNAL_FUNC (callback), (gpointer) "cool button");

    /* this calls our box creating function */
    box1 = xpm_label_box(window, "info.xpm", "cool button");

    /* pack and show all our widgets */
    gtk_widget_show(box1);

    gtk_container_add (GTK_CONTAINER (button), box1);

    gtk_widget_show(button);

    gtk_container_add (GTK_CONTAINER (window), button);

    gtk_widget_show (window);

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

    return 0;
}
</verb></tscreen>

The xpm_label_box function could be used to pack xpm's and labels into any
widget that can be a container.

<!-- ----------------------------------------------------------------- -->
<sect1> Toggle Buttons
<p>
Toggle buttons are very similar to normal buttons, except they will always
be in one of two states, alternated by a click.  They may be depressed, and
when you click again, they will pop back up.  Click again, and they will pop
back down. 

Toggle buttons are the basis for check buttons and radio buttons, as such,
many of the calls used for toggle buttons are inherited by radio and check
buttons.  I will point these out when we come to them.

Creating a new toggle button:

<tscreen><verb>
GtkWidget* gtk_toggle_button_new (void);

GtkWidget* gtk_toggle_button_new_with_label (gchar *label);
</verb></tscreen>
<p>
As you can imagine, these work identically to the normal button widget
calls.  The first creates a blank toggle button, and the second, a button 
with a label widget already packed into it.
<p>
To retrieve the state of the toggle widget, including radio and check
buttons, we use a macro as shown in our example below.  This tests the state
of the toggle in a callback.  The signal of interest emitted to us by toggle
buttons (the toggle button, check button, and radio button widgets), is the
"toggled" signal.  To check the state of these buttons, set up a signal
handler to catch the toggled signal, and use the macro to determine it's
state.  The callback will look something like:

<tscreen><verb>
void toggle_button_callback (GtkWidget *widget, gpointer   data)
{
    if (GTK_TOGGLE_BUTTON (widget)->active) 
    {
        /* If control reaches here, the toggle button is down */
    
    } else {
    
        /* If control reaches here, the toggle button is up */
    }
}
</verb></tscreen>

<!--

COMMENTED!

<tscreen><verb>
guint gtk_toggle_button_get_type (void);
</verb></tscreen>
<p>
No idea... they all have this, but I dunno what it is :)


<tscreen><verb>
void gtk_toggle_button_set_mode (GtkToggleButton *toggle_button,
                                 gint draw_indicator);
</verb></tscreen>
<p>
No idea.
-->

<tscreen><verb>
void gtk_toggle_button_set_state (GtkToggleButton *toggle_button,
                                  gint state);
</verb></tscreen>
<p>
The above call can be used to set the state of the toggle button, and it's
children the radio and check buttons.  Passing
in your created button as the first argument, and a TRUE or FALSE
for the second state argument to specify whether it should be up (released) or
down (depressed).  Default is up, or FALSE.

Note that when you use the gtk_toggle_button_set_state() function, and the
state is actually changed, it causes
the "clicked" signal to be emitted from the button.

<tscreen><verb>
void       gtk_toggle_button_toggled        (GtkToggleButton *toggle_button);
</verb></tscreen>
<p>
This simply toggles the button, and emits the "toggled" signal.

<!-- ----------------------------------------------------------------- -->
<sect1> Check Buttons
<p>
Check buttons inherent many properties and functions from the the toggle buttons above, 
but look a little
different.  Rather than being buttons with text inside them, they are small
squares with the text to the right of them.  These are often seen for
toggling options on and off in applications.

The two creation functions are the same as for the normal button.

<tscreen><verb>
GtkWidget* gtk_check_button_new (void);

GtkWidget* gtk_check_button_new_with_label (gchar *label);
</verb></tscreen>

The new_with_label function creates a check button with a label beside it.

Checking the state of the check button is identical to that of the toggle
button.

<!-- ----------------------------------------------------------------- -->
<sect1> Radio Buttons
<p>
Radio buttons are similar to check buttons except they are grouped so that
only one may be selected/depressed at a time.  This is good for places in
your application where you need to select from a short list of options.

Creating a new radio button is done with one of these calls:

<tscreen><verb>
GtkWidget* gtk_radio_button_new (GSList *group);

GtkWidget* gtk_radio_button_new_with_label (GSList *group,
                                            gchar *label);
</verb></tscreen>
<p>
You'll notice the extra argument to these calls.  They require a group to
perform they're duty properly.  The first call should pass NULL as the first
argument.  Then create a group using:

<tscreen><verb>
GSList* gtk_radio_button_group (GtkRadioButton *radio_button);
</verb></tscreen>

<p>
The important thing to remember is that gtk_radio_button_group must be
called for each new button added to the group, with the previous button
passed in as an argument. The result is then passed into the call to
gtk_radio_button_new or gtk_radio_button_new_with_label. This allows a
chain of buttons to be established. The example below should make this
clear.

It is also a good idea to explicitly set which button should be the 
default depressed button with:

<tscreen><verb>
void gtk_toggle_button_set_state (GtkToggleButton *toggle_button,
                                  gint state);
</verb></tscreen>
<p>
This is described in the section on toggle buttons, and works in exactly the
same way.
<p>
The following example creates a radio button group with three buttons.

<tscreen><verb>
/* radiobuttons.c */

#include <gtk/gtk.h>
#include <glib.h>

1860
void close_application( GtkWidget *widget, gpointer data ) {
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  gtk_main_quit();
}

main(int argc,char *argv[])
{
  static GtkWidget *window = NULL;
  GtkWidget *box1;
  GtkWidget *box2;
  GtkWidget *button;
  GtkWidget *separator;
  GSList *group;
  
  gtk_init(&amp;argc,&amp;argv);          
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  
  gtk_signal_connect (GTK_OBJECT (window), "delete_event",
		      GTK_SIGNAL_FUNC(close_application),
		      NULL);

  gtk_window_set_title (GTK_WINDOW (window), "radio buttons");
  gtk_container_border_width (GTK_CONTAINER (window), 0);

  box1 = gtk_vbox_new (FALSE, 0);
  gtk_container_add (GTK_CONTAINER (window), box1);
  gtk_widget_show (box1);

  box2 = gtk_vbox_new (FALSE, 10);
  gtk_container_border_width (GTK_CONTAINER (box2), 10);
  gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0);
  gtk_widget_show (box2);

  button = gtk_radio_button_new_with_label (NULL, "button1");
  gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
  gtk_widget_show (button);

  group = gtk_radio_button_group (GTK_RADIO_BUTTON (button));
  button = gtk_radio_button_new_with_label(group, "button2");
  gtk_toggle_button_set_state (GTK_TOGGLE_BUTTON (button), TRUE);
  gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
  gtk_widget_show (button);

  group = gtk_radio_button_group (GTK_RADIO_BUTTON (button));
  button = gtk_radio_button_new_with_label(group, "button3");
  gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
  gtk_widget_show (button);

  separator = gtk_hseparator_new ();
  gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 0);
  gtk_widget_show (separator);

  box2 = gtk_vbox_new (FALSE, 10);
  gtk_container_border_width (GTK_CONTAINER (box2), 10);
  gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, TRUE, 0);
  gtk_widget_show (box2);

  button = gtk_button_new_with_label ("close");
  gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
			     GTK_SIGNAL_FUNC(close_application),
			     GTK_OBJECT (window));
  gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
  GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT);
  gtk_widget_grab_default (button);
  gtk_widget_show (button);
  gtk_widget_show (window);
     
  gtk_main();
  return(0);
}
</verb></tscreen>

You can shorten this slightly by using the following syntax, which
removes the need for a variable to hold the list of buttons:

<tscreen><verb>
     button2 = gtk_radio_button_new_with_label(
                 gtk_radio_button_group (GTK_RADIO_BUTTON (button1)),
                 "button2");
</verb></tscreen>

<!-- ***************************************************************** -->
<sect> Miscallaneous Widgets
<!-- ***************************************************************** -->

<!-- ----------------------------------------------------------------- -->
<sect1> Labels
<p>
Labels are used a lot in GTK, and are relatively simple.  Labels emit no
signals as they do not have an associated X window.  If you need to catch
signals, or do clipping, use the EventBox widget.

To create a new label, use:

<tscreen><verb>
GtkWidget* gtk_label_new (char *str);
</verb></tscreen>

Where the sole argument is the string you wish the label to display.

To change the label's text after creation, use the function:

<tscreen><verb>
void gtk_label_set (GtkLabel  *label,
		    char      *str);
</verb></tscreen>
<p>
Where the first argument is the label you created previously (casted using
the GTK_LABEL() macro), and the second is the new string.

The space needed for the new string will be automatically adjusted if needed.

To retrieve the current string, use:

<tscreen><verb>
void gtk_label_get (GtkLabel  *label,
		    char     **str);
</verb></tscreen>

Where the first arguement is the label you've created, and the second, the
return for the string.

<!-- ----------------------------------------------------------------- -->
<sect1>The Tooltips Widget
<p>
These are the little text strings that pop up when you leave your pointer
over a button or other widget for a few seconds.  They are easy to use, so I
will just explain them without giving an example.  If you want to see some
code, take a look at the testgtk.c program distributed with GDK.
<p>
Some widgets (such as the label) will not work with tooltips.
<p>
The first call you will use to create a new tooltip.  You only need to do
1992 1993
this once in a given function.	The <tt/GtkTooltip/ this function 
returns can be used to create multiple tooltips.
1994 1995 1996 1997 1998 1999 2000 2001 2002

<tscreen><verb>
GtkTooltips *gtk_tooltips_new (void);
</verb></tscreen>

Once you have created a new tooltip, and the widget you wish to use it on,
simply use this call to set it.

<tscreen><verb>
2003 2004 2005 2006
void gtk_tooltips_set_tip (GtkTooltips *tooltips,
                           GtkWidget   *widget,
                           const gchar *tip_text,
                           const gchar *tip_private);
2007 2008 2009 2010
</verb></tscreen>

The first argument is the tooltip you've already created, followed by the
widget you wish to have this tooltip pop up for, and the text you wish it to
2011
say. The last argument can be set to NULL.
2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
<p>
Here's a short example:

<tscreen><verb>
GtkTooltips *tooltips;
GtkWidget *button;
...
tooltips = gtk_tooltips_new ();
button = gtk_button_new_with_label ("button 1");
...
2022
gtk_tooltips_set_tip (tooltips, button, "This is button 1", NULL);
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</verb></tscreen>

There are other calls used with tooltips.  I will just list them with a
brief description of what they do.

<tscreen><verb>
void gtk_tooltips_destroy    (GtkTooltips *tooltips);
</verb></tscreen>

Destroy the created tooltips.

<tscreen><verb>
void gtk_tooltips_enable     (GtkTooltips *tooltips);
</verb></tscreen>

Enable a disabled set of tooltips.

<tscreen><verb>
void gtk_tooltips_disable    (GtkTooltips *tooltips);
</verb></tscreen>

Disable an enabled set of tooltips.

<tscreen><verb>
void gtk_tooltips_set_delay  (GtkTooltips *tooltips,
			      gint	   delay);

</verb></tscreen>
Sets how many milliseconds you have to hold you pointer over the widget before the
tooltip will pop up.  The default is 1000 milliseconds or 1 second.

<tscreen><verb>
void	  gtk_tooltips_set_tips (GtkTooltips *tooltips,
			         GtkWidget   *widget,
			         gchar	  *tips_text);
</verb></tscreen>

Change the tooltip text of an already created tooltip.

<tscreen><verb>
void gtk_tooltips_set_colors (GtkTooltips *tooltips,
			      GdkColor	  *background,
			      GdkColor	  *foreground);
</verb></tscreen>

Set the foreground and background color of the tooltips.  Again, I have no
idea how to specify the colors.
<p>
And that's all the functions associated with tooltips.  More than you'll
ever want to know :)

<!-- ----------------------------------------------------------------- -->
<sect1> Progress Bars
<p>
Progress bars are used to show the status of an operation.  They are pretty 
easy to use, as you will see with the code below. But first lets start out 
with the call to create a new progress bar.

<tscreen><verb>
GtkWidget *gtk_progress_bar_new (void);
</verb></tscreen>

Now that the progress bar has been created we can use it.

<tscreen><verb>
void gtk_progress_bar_update (GtkProgressBar *pbar, gfloat percentage);
</verb></tscreen>

The first argument is the progress bar you wish to operate on, and the second 
argument is the amount 'completed', meaning the amount the progress bar has 
been filled from 0-100% (a real number between 0 and 1).

Progress Bars are usually used with timeouts or other such functions (see
section on <ref id="sec_timeouts" name="Timeouts, I/O and Idle Functions">) 
to give the illusion of multitasking.  All will employ 
the gtk_progress_bar_update function in the same manner.

Here is an example of the progress bar, updated using timeouts.  This 
code also shows you how to reset the Progress Bar.

<tscreen><verb>
/* progressbar.c */

#include <gtk/gtk.h>

static int ptimer = 0;
int pstat = TRUE;

/* This function increments and updates the progress bar, it also resets
 the progress bar if pstat is FALSE */
gint progress (gpointer data)
{
    gfloat pvalue;
    
    /* get the current value of the progress bar */
    pvalue = GTK_PROGRESS_BAR (data)->percentage;
    
    if ((pvalue >= 1.0) || (pstat == FALSE)) {
	pvalue = 0.0;
	pstat = TRUE;
    }
    pvalue += 0.01;
    
    gtk_progress_bar_update (GTK_PROGRESS_BAR (data), pvalue);
    
    return TRUE;
}

/* This function signals a reset of the progress bar */
void progress_r (void)
{  
    pstat = FALSE;  
}

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void destroy (GtkWidget *widget, gpointer data)
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