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<H2><A NAME="sec_packing_widgets"></A> <A NAME="s4">4. Packing Widgets </A></H2>
<P>When creating an application, you'll want to put more than one widget
inside a window. Our first <EM>helloworld</EM> 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.
<P>
<H2><A NAME="ss4.1">4.1 Theory of Packing Boxes</A>
</H2>
<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
which 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 allows 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. 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 are 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.
<P>
<H2><A NAME="ss4.2">4.2 Details of Boxes</A>
</H2>
<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.
<P> <CENTER >
<IMG SRC="gtk_tut_packbox1.gif" VSPACE="15" HSPACE="10" WIDTH="528"
HEIGHT="235" ALT="Box Packing Example Image"
> </CENTER
>
<P>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.
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_box_pack_start( GtkBox *box,
GtkWidget *child,
gint expand,
gint fill,
gint padding );
</PRE>
</CODE></BLOCKQUOTE>
<P>The first argument is the box you are packing the object into, the
second is the 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() and 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
allotted 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
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 gtk_box_pack_end.
<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:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget *gtk_hbox_new (gint homogeneous,
gint spacing);
</PRE>
</CODE></BLOCKQUOTE>
<P>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 gtk_box_pack routines function essentially
as if the <CODE>expand</CODE> argument was 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:
<P> <CENTER >
<IMG ALIGN="center" SRC="gtk_tut_packbox2.gif" WIDTH="509"
HEIGHT="213" VSPACE="15" HSPACE="10"
ALT="Box Packing Example Image"
> </CENTER
>
<P>Here is the code used to create the above images. I've commented it
fairly heavily so I hope you won't have any problems following
it. Compile it yourself and play with it.
<P>
<H2><A NAME="ss4.3">4.3 Packing Demonstration Program</A>
</H2>
<P>
<BLOCKQUOTE><CODE>
<PRE>
/* example-start packbox packbox.c */
#include <stdio.h>
#include <stdlib.h>
#include "gtk/gtk.h"
gint delete_event( GtkWidget *widget,
GdkEvent *event,
gpointer data )
{
gtk_main_quit();
return(FALSE);
}
/* 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 (&argc, &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 delete_event 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_set_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 = TRUE, 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 is 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);
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