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.
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.
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.
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.
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.
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).
This is the declaration of the gtk_box_pack_start function.
void gtk_box_pack_start (GtkBox *box,
GtkWidget *child,
gint expand,
gint fill,
gint padding);
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.
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.
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.
When creating a new box, the function looks like this:
GtkWidget * gtk_hbox_new (gint homogeneous,
gint spacing);
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.
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:
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.
#include "gtk/gtk.h"
void
destroy (GtkWidget *widget, gpointer *data)
{
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 (&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 destroy signal to the
* main window. This is very important for proper intuitive
* behavior */
gtk_signal_connect (GTK_OBJECT (window), "destroy",
GTK_SIGNAL_FUNC (destroy), 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_widget_destroy),
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;
}
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:
GtkWidget* gtk_table_new (gint rows,
gint columns,
gint homogeneous);
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:
0 1 2
0+----------+----------+
| | |
1+----------+----------+
| | |
2+----------+----------+
Note that the coordinate system starts in the upper left hand corner. To place a widget into a box, use the following function:
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);
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:
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:
void gtk_table_attach_defaults (GtkTable *table,
GtkWidget *widget,
gint left_attach,
gint right_attach,
gint top_attach,
gint bottom_attach);
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.
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.
void gtk_table_set_row_spacing (GtkTable *table,
gint row,
gint spacing);
void gtk_table_set_col_spacing (GtkTable *table,
gint column,
gint spacing);
Note that for columns, the space goes to the right of the column, and for rows, the space goes below the row.
You can also set a consistent spacing of all rows and/or columns with:
void gtk_table_set_row_spacings (GtkTable *table,
gint spacing);
And,
void gtk_table_set_col_spacings (GtkTable *table,
gint spacing);
Note that with these calls, the last row and last column do not get any spacing
For now, please refer to the table example in testgtk.c distributed with the gtk source.