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9. Miscellaneous Widgets

9.1 Labels

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, place it inside a EventBox widget or a Button widget.

To create a new label, use:

GtkWidget *gtk_label_new( char *str );

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

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

void gtk_label_set_text( GtkLabel *label,
                         char     *str );

The first argument is the label you created previously (cast 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. You can produce multi-line labels by putting line breaks in the label string.

To retrieve the current string, use:

void gtk_label_get( GtkLabel  *label,
                    char     **str );

The first argument is the label you've created, and the second, the return for the string. Do not free the return string, as it is used internally by GTK.

The label text can be justified using:

void gtk_label_set_justify( GtkLabel         *label,
                            GtkJustification  jtype );

Values for jtype are:

  GTK_JUSTIFY_LEFT
  GTK_JUSTIFY_RIGHT
  GTK_JUSTIFY_CENTER (the default)
  GTK_JUSTIFY_FILL

The label widget is also capable of line wrapping the text automatically. This can be activated using:

void gtk_label_set_line_wrap (GtkLabel *label,
                              gboolean  wrap);

The wrap argument takes a TRUE or FALSE value.

If you want your label underlined, then you can set a pattern on the label:

void       gtk_label_set_pattern   (GtkLabel          *label,
                                    const gchar       *pattern);

The pattern argument indicates how the underlining should look. It consists of a string of underscore and space characters. An underscore indicates that the corresponding character in the label should be underlined. For example, the string

"__     __"
would underline the first two characters and eight and ninth characters.

Below is a short example to illustrate these functions. This example makes use of the Frame widget to better demonstrate the label styles. You can ignore this for now as the Frame widget is explained later on.

/* example-start label label.c */

#include <gtk/gtk.h>

int main( int   argc,
          char *argv[] )
{
  static GtkWidget *window = NULL;
  GtkWidget *hbox;
  GtkWidget *vbox;
  GtkWidget *frame;
  GtkWidget *label;

  /* Initialise GTK */
  gtk_init(&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_signal_connect (GTK_OBJECT (window), "destroy",
                      GTK_SIGNAL_FUNC(gtk_main_quit),
                      NULL);

  gtk_window_set_title (GTK_WINDOW (window), "Label");
  vbox = gtk_vbox_new (FALSE, 5);
  hbox = gtk_hbox_new (FALSE, 5);
  gtk_container_add (GTK_CONTAINER (window), hbox);
  gtk_box_pack_start (GTK_BOX (hbox), vbox, FALSE, FALSE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (window), 5);
  
  frame = gtk_frame_new ("Normal Label");
  label = gtk_label_new ("This is a Normal label");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Multi-line Label");
  label = gtk_label_new ("This is a Multi-line label.\nSecond line\n" \
                         "Third line");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Left Justified Label");
  label = gtk_label_new ("This is a Left-Justified\n" \
                         "Multi-line label.\nThird      line");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Right Justified Label");
  label = gtk_label_new ("This is a Right-Justified\nMulti-line label.\n" \
                         "Fourth line, (j/k)");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_RIGHT);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);

  vbox = gtk_vbox_new (FALSE, 5);
  gtk_box_pack_start (GTK_BOX (hbox), vbox, FALSE, FALSE, 0);
  frame = gtk_frame_new ("Line wrapped label");
  label = gtk_label_new ("This is an example of a line-wrapped label.  It " \
                         "should not be taking up the entire             " /* big space to test spacing */\
                         "width allocated to it, but automatically " \
                         "wraps the words to fit.  " \
                         "The time has come, for all good men, to come to " \
                         "the aid of their party.  " \
                         "The sixth sheik's six sheep's sick.\n" \
                         "     It supports multiple paragraphs correctly, " \
                         "and  correctly   adds "\
                         "many          extra  spaces. ");
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Filled, wrapped label");
  label = gtk_label_new ("This is an example of a line-wrapped, filled label.  " \
                         "It should be taking "\
                         "up the entire              width allocated to it.  " \
                         "Here is a sentence to prove "\
                         "my point.  Here is another sentence. "\
                         "Here comes the sun, do de do de do.\n"\
                         "    This is a new paragraph.\n"\
                         "    This is another newer, longer, better " \
                         "paragraph.  It is coming to an end, "\
                         "unfortunately.");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_FILL);
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Underlined label");
  label = gtk_label_new ("This label is underlined!\n"
                         "This one is underlined in quite a funky fashion");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_label_set_pattern (GTK_LABEL (label),
                         "_________________________ _ _________ _ ______     __ _______ ___");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  gtk_widget_show_all (window);

  gtk_main ();
  
  return(0);
}
/* example-end */

9.2 Arrows

The Arrow widget draws an arrowhead, facing in a number of possible directions and having a number of possible styles. It can be very useful when placed on a button in many applications. Like the Label widget, it emits no signals.

There are only two functions for manipulating an Arrow widget:

GtkWidget *gtk_arrow_new( GtkArrowType   arrow_type,
                          GtkShadowType  shadow_type );

void gtk_arrow_set( GtkArrow      *arrow,
                    GtkArrowType   arrow_type,
                    GtkShadowType  shadow_type );

The first creates a new arrow widget with the indicated type and appearance. The second allows these values to be altered retrospectively. The arrow_type argument may take one of the following values:

  GTK_ARROW_UP
  GTK_ARROW_DOWN
  GTK_ARROW_LEFT
  GTK_ARROW_RIGHT

These values obviously indicate the direction in which the arrow will point. The shadow_type argument may take one of these values:

  GTK_SHADOW_IN
  GTK_SHADOW_OUT (the default)
  GTK_SHADOW_ETCHED_IN
  GTK_SHADOW_ETCHED_OUT

Here's a brief example to illustrate their use.

/* example-start arrow arrow.c */

#include <gtk/gtk.h>

/* Create an Arrow widget with the specified parameters
 * and pack it into a button */
GtkWidget *create_arrow_button( GtkArrowType  arrow_type,
                                GtkShadowType shadow_type )
{
  GtkWidget *button;
  GtkWidget *arrow;

  button = gtk_button_new();
  arrow = gtk_arrow_new (arrow_type, shadow_type);

  gtk_container_add (GTK_CONTAINER (button), arrow);
  
  gtk_widget_show(button);
  gtk_widget_show(arrow);

  return(button);
}

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

  /* Initialize the toolkit */
  gtk_init (&argc, &argv);

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

  gtk_window_set_title (GTK_WINDOW (window), "Arrow Buttons");

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

  /* Sets the border width of the window. */
  gtk_container_set_border_width (GTK_CONTAINER (window), 10);

  /* Create a box to hold the arrows/buttons */
  box = gtk_hbox_new (FALSE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (box), 2);
  gtk_container_add (GTK_CONTAINER (window), box);

  /* Pack and show all our widgets */
  gtk_widget_show(box);

  button = create_arrow_button(GTK_ARROW_UP, GTK_SHADOW_IN);
  gtk_box_pack_start (GTK_BOX (box), button, FALSE, FALSE, 3);

  button = create_arrow_button(GTK_ARROW_DOWN, GTK_SHADOW_OUT);
  gtk_box_pack_start (GTK_BOX (box), button, FALSE, FALSE, 3);
  
  button = create_arrow_button(GTK_ARROW_LEFT, GTK_SHADOW_ETCHED_IN);
  gtk_box_pack_start (GTK_BOX (box), button, FALSE, FALSE, 3);
  
  button = create_arrow_button(GTK_ARROW_RIGHT, GTK_SHADOW_ETCHED_OUT);
  gtk_box_pack_start (GTK_BOX (box), button, FALSE, FALSE, 3);
  
  gtk_widget_show (window);
  
  /* Rest in gtk_main and wait for the fun to begin! */
  gtk_main ();
  
  return(0);
}
/* example-end */

9.3 The Tooltips Object

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 GTK.

Widgets that do not receive events (widgets that do not have their own window) will not work with tooltips.

The first call you will use creates a new tooltip. You only need to do this once for a set of tooltips as the GtkTooltips object this function returns can be used to create multiple tooltips.

GtkTooltips *gtk_tooltips_new( void );

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

void gtk_tooltips_set_tip( GtkTooltips *tooltips,
                           GtkWidget   *widget,
                           const gchar *tip_text,
                           const gchar *tip_private );

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 say. The last argument is a text string that can be used as an identifier when using GtkTipsQuery to implement context sensitive help. For now, you can set it to NULL.

Here's a short example:

GtkTooltips *tooltips;
GtkWidget *button;
.
.
.
tooltips = gtk_tooltips_new ();
button = gtk_button_new_with_label ("button 1");
.
.
.
gtk_tooltips_set_tip (tooltips, button, "This is button 1", NULL);

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

void gtk_tooltips_enable( GtkTooltips *tooltips );

Enable a disabled set of tooltips.

void gtk_tooltips_disable( GtkTooltips *tooltips );

Disable an enabled set of tooltips.

void gtk_tooltips_set_delay( GtkTooltips *tooltips,
                             gint         delay );

Sets how many milliseconds you have to hold your pointer over the widget before the tooltip will pop up. The default is 500 milliseconds (half a second).

void gtk_tooltips_set_colors( GtkTooltips *tooltips,
                              GdkColor    *background,
                              GdkColor    *foreground );

Set the foreground and background color of the tooltips.

And that's all the functions associated with tooltips. More than you'll ever want to know :-)

9.4 Progress Bars

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 calls to create a new progress bar.

There are two ways to create a progress bar, one simple that takes no arguments, and one that takes an Adjustment object as an argument. If the former is used, the progress bar creates its own adjustment object.

GtkWidget *gtk_progress_bar_new( void );

GtkWidget *gtk_progress_bar_new_with_adjustment( GtkAdjustment *adjustment );

The second method has the advantage that we can use the adjustment object to specify our own range parameters for the progress bar.

The adjustment of a progress object can be changed dynamically using:

void gtk_progress_set_adjustment( GtkProgress   *progress,
                                  GtkAdjustment *adjustment );

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

void gtk_progress_bar_update( GtkProgressBar *pbar,
                              gfloat          percentage );

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%. This is passed to the function as a real number ranging from 0 to 1.

GTK v1.2 has added new functionality to the progress bar that enables it to display its value in different ways, and to inform the user of its current value and its range.

A progress bar may be set to one of a number of orientations using the function

void gtk_progress_bar_set_orientation( GtkProgressBar *pbar,
                                       GtkProgressBarOrientation orientation );

The orientation argument may take one of the following values to indicate the direction in which the progress bar moves:

  GTK_PROGRESS_LEFT_TO_RIGHT
  GTK_PROGRESS_RIGHT_TO_LEFT
  GTK_PROGRESS_BOTTOM_TO_TOP
  GTK_PROGRESS_TOP_TO_BOTTOM

When used as a measure of how far a process has progressed, the ProgressBar can be set to display its value in either a continuous or discrete mode. In continuous mode, the progress bar is updated for each value. In discrete mode, the progress bar is updated in a number of discrete blocks. The number of blocks is also configurable.

The style of a progress bar can be set using the following function.

void gtk_progress_bar_set_bar_style( GtkProgressBar      *pbar,
                                     GtkProgressBarStyle  style );

The style parameter can take one of two values:

  GTK_PROGRESS_CONTINUOUS
  GTK_PROGRESS_DISCRETE

The number of discrete blocks can be set by calling

void gtk_progress_bar_set_discrete_blocks( GtkProgressBar *pbar,
                                           guint           blocks );

As well as indicating the amount of progress that has occured, the progress bar may be set to just indicate that there is some activity. This can be useful in situations where progress cannot be measured against a value range. Activity mode is not effected by the bar style that is described above, and overrides it. This mode is either TRUE or FALSE, and is selected by the following function.

void gtk_progress_set_activity_mode( GtkProgress *progress,
                                     guint        activity_mode );

The step size of the activity indicator, and the number of blocks are set using the following functions.

void gtk_progress_bar_set_activity_step( GtkProgressBar *pbar,
                                         guint           step );

void gtk_progress_bar_set_activity_blocks( GtkProgressBar *pbar,
                                           guint           blocks );

When in continuous mode, the progress bar can also display a configurable text string within its trough, using the following function.

void gtk_progress_set_format_string( GtkProgress *progress,
                                     gchar       *format);

The format argument is similiar to one that would be used in a C printf statement. The following directives may be used within the format string:

The displaying of this text string can be toggled using:

void gtk_progress_set_show_text( GtkProgress *progress,
                                 gint         show_text );

The show_text argument is a boolean TRUE/FALSE value. The appearance of the text can be modified further using:

void gtk_progress_set_text_alignment( GtkProgress   *progress,
                                      gfloat         x_align,
                                      gfloat         y_align );

The x_align and y_align arguments take values between 0.0 and 1.0. Their values indicate the position of the text string within the trough. Values of 0.0 for both would place the string in the top left hand corner; values of 0.5 (the default) centres the text, and values of 1.0 places the text in the lower right hand corner.

The current text setting of a progress object can be retrieved using the current or a specified adjustment value using the following two functions. The character string returned by these functions should be freed by the application (using the g_free() function). These functions return the formatted string that would be displayed within the trough.

gchar *gtk_progress_get_current_text( GtkProgress   *progress );

gchar *gtk_progress_get_text_from_value( GtkProgress *progress,
                                         gfloat       value );

There is yet another way to change the range and value of a progress object using the following function:

void gtk_progress_configure( GtkProgress  *progress,
                             gfloat        value,
                             gfloat        min,
                             gfloat        max );

This function provides quite a simple interface to the range and value of a progress object.

The remaining functions can be used to get and set the current value of a progess object in various types and formats:

void gtk_progress_set_percentage( GtkProgress *progress,
                                  gfloat       percentage );

void gtk_progress_set_value( GtkProgress *progress,
                             gfloat       value );

gfloat gtk_progress_get_value( GtkProgress *progress );

gfloat gtk_progress_get_current_percentage( GtkProgress *progress );

gfloat gtk_progress_get_percentage_from_value( GtkProgress *progress,
                                               gfloat       value );

These functions are pretty self explanatory. The last function uses the the adjustment of the specified progess object to compute the percentage value of the given range value.

Progress Bars are usually used with timeouts or other such functions (see section on 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.

/* example-start progressbar progressbar.c */

#include <gtk/gtk.h>

typedef struct _ProgressData {
    GtkWidget *window;
    GtkWidget *pbar;
    int timer;
} ProgressData;

/* Update the value of the progress bar so that we get
 * some movement */
gint progress_timeout( gpointer data )
{
    gfloat new_val;
    GtkAdjustment *adj;

    /* Calculate the value of the progress bar using the
     * value range set in the adjustment object */

    new_val = gtk_progress_get_value( GTK_PROGRESS(data) ) + 1;

    adj = GTK_PROGRESS (data)->adjustment;
    if (new_val > adj->upper)
      new_val = adj->lower;

    /* Set the new value */
    gtk_progress_set_value (GTK_PROGRESS (data), new_val);

    /* As this is a timeout function, return TRUE so that it
     * continues to get called */
    return(TRUE);
} 

/* Callback that toggles the text display within the progress
 * bar trough */
void toggle_show_text( GtkWidget    *widget,
                       ProgressData *pdata )
{
    gtk_progress_set_show_text (GTK_PROGRESS (pdata->pbar),
                                GTK_TOGGLE_BUTTON (widget)->active);
}

/* Callback that toggles the activity mode of the progress
 * bar */
void toggle_activity_mode( GtkWidget    *widget,
                           ProgressData *pdata )
{
    gtk_progress_set_activity_mode (GTK_PROGRESS (pdata->pbar),
                                    GTK_TOGGLE_BUTTON (widget)->active);
}

/* Callback that toggles the continuous mode of the progress
 * bar */
void set_continuous_mode( GtkWidget    *widget,
                          ProgressData *pdata )
{
    gtk_progress_bar_set_bar_style (GTK_PROGRESS_BAR (pdata->pbar),
                                    GTK_PROGRESS_CONTINUOUS);
}

/* Callback that toggles the discrete mode of the progress
 * bar */
void set_discrete_mode( GtkWidget    *widget,
                        ProgressData *pdata )
{
    gtk_progress_bar_set_bar_style (GTK_PROGRESS_BAR (pdata->pbar),
                                    GTK_PROGRESS_DISCRETE);
}
 
/* Clean up allocated memory and remove the timer */
void destroy_progress( GtkWidget     *widget,
                       ProgressData *pdata)
{
    gtk_timeout_remove (pdata->timer);
    pdata->timer = 0;
    pdata->window = NULL;
    g_free(pdata);
    gtk_main_quit();
}

int main( int   argc,
          char *argv[])
{
    ProgressData *pdata;
    GtkWidget *align;
    GtkWidget *separator;
    GtkWidget *table;
    GtkAdjustment *adj;
    GtkWidget *button;
    GtkWidget *check;
    GtkWidget *vbox;

    gtk_init (&argc, &argv);

    /* Allocate memory for the data that is passwd to the callbacks */
    pdata = g_malloc( sizeof(ProgressData) );
  
    pdata->window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_policy (GTK_WINDOW (pdata->window), FALSE, FALSE, TRUE);

    gtk_signal_connect (GTK_OBJECT (pdata->window), "destroy",
                        GTK_SIGNAL_FUNC (destroy_progress),
                        pdata);
    gtk_window_set_title (GTK_WINDOW (pdata->window), "GtkProgressBar");
    gtk_container_set_border_width (GTK_CONTAINER (pdata->window), 0);

    vbox = gtk_vbox_new (FALSE, 5);
    gtk_container_set_border_width (GTK_CONTAINER (vbox), 10);
    gtk_container_add (GTK_CONTAINER (pdata->window), vbox);
    gtk_widget_show(vbox);
  
    /* Create a centering alignment object */
    align = gtk_alignment_new (0.5, 0.5, 0, 0);
    gtk_box_pack_start (GTK_BOX (vbox), align, FALSE, FALSE, 5);
    gtk_widget_show(align);

    /* Create a Adjusment object to hold the range of the
     * progress bar */
    adj = (GtkAdjustment *) gtk_adjustment_new (0, 1, 150, 0, 0, 0);

    /* Create the GtkProgressBar using the adjustment */
    pdata->pbar = gtk_progress_bar_new_with_adjustment (adj);

    /* Set the format of the string that can be displayed in the
     * trough of the progress bar:
     * %p - percentage
     * %v - value
     * %l - lower range value
     * %u - upper range value */
    gtk_progress_set_format_string (GTK_PROGRESS (pdata->pbar),
                                    "%v from [%l-%u] (=%p%%)");
    gtk_container_add (GTK_CONTAINER (align), pdata->pbar);
    gtk_widget_show(pdata->pbar);

    /* Add a timer callback to update the value of the progress bar */
    pdata->timer = gtk_timeout_add (100, progress_timeout, pdata->pbar);

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

    /* rows, columns, homogeneous */
    table = gtk_table_new (2, 3, FALSE);
    gtk_box_pack_start (GTK_BOX (vbox), table, FALSE, TRUE, 0);
    gtk_widget_show(table);

    /* Add a check button to select displaying of the trough text */
    check = gtk_check_button_new_with_label ("Show text");
    gtk_table_attach (GTK_TABLE (table), check, 0, 1, 0, 1,
                      GTK_EXPAND | GTK_FILL, GTK_EXPAND | GTK_FILL,
                      5, 5);
    gtk_signal_connect (GTK_OBJECT (check), "clicked",
                        GTK_SIGNAL_FUNC (toggle_show_text),
                        pdata);
    gtk_widget_show(check);

    /* Add a check button to toggle activity mode */
    check = gtk_check_button_new_with_label ("Activity mode");
    gtk_table_attach (GTK_TABLE (table), check, 0, 1, 1, 2,
                      GTK_EXPAND | GTK_FILL, GTK_EXPAND | GTK_FILL,
                      5, 5);
    gtk_signal_connect (GTK_OBJECT (check), "clicked",
                        GTK_SIGNAL_FUNC (toggle_activity_mode),
                        pdata);
    gtk_widget_show(check);

    separator = gtk_vseparator_new ();
    gtk_table_attach (GTK_TABLE (table), separator, 1, 2, 0, 2,
                      GTK_EXPAND | GTK_FILL, GTK_EXPAND | GTK_FILL,
                      5, 5);
    gtk_widget_show(separator);

    /* Add a radio button to select continuous display mode */
    button = gtk_radio_button_new_with_label (NULL, "Continuous");
    gtk_table_attach (GTK_TABLE (table), button, 2, 3, 0, 1,
                      GTK_EXPAND | GTK_FILL, GTK_EXPAND | GTK_FILL,
                      5, 5);
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
                        GTK_SIGNAL_FUNC (set_continuous_mode),
                        pdata);
    gtk_widget_show (button);

    /* Add a radio button to select discrete display mode */
    button = gtk_radio_button_new_with_label(
               gtk_radio_button_group (GTK_RADIO_BUTTON (button)),
               "Discrete");
    gtk_table_attach (GTK_TABLE (table), button, 2, 3, 1, 2,
                      GTK_EXPAND | GTK_FILL, GTK_EXPAND | GTK_FILL,
                      5, 5);
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
                        GTK_SIGNAL_FUNC (set_discrete_mode),
                        pdata);
    gtk_widget_show (button);

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

    /* Add a button to exit the program */
    button = gtk_button_new_with_label ("close");
    gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
                               (GtkSignalFunc) gtk_widget_destroy,
                               GTK_OBJECT (pdata->window));
    gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);

    /* This makes it so the button is the default. */
    GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT);

    /* This grabs this button to be the default button. Simply hitting
     * the "Enter" key will cause this button to activate. */
    gtk_widget_grab_default (button);
    gtk_widget_show(button);

    gtk_widget_show (pdata->window);

    gtk_main ();
    
    return(0);
}
/* example-end */

9.5 Dialogs

The Dialog widget is very simple, and is actually just a window with a few things pre-packed into it for you. The structure for a Dialog is:

struct GtkDialog
{
      GtkWindow window;
    
      GtkWidget *vbox;
      GtkWidget *action_area;
};

So you see, it simply creates a window, and then packs a vbox into the top, which contains a separator and then an hbox called the "action_area".

The Dialog widget can be used for pop-up messages to the user, and other similar tasks. It is really basic, and there is only one function for the dialog box, which is:

GtkWidget *gtk_dialog_new( void );

So to create a new dialog box, use,

    GtkWidget *window;
    window = gtk_dialog_new ();

This will create the dialog box, and it is now up to you to use it. You could pack a button in the action_area by doing something like this:

    button = ...
    gtk_box_pack_start (GTK_BOX (GTK_DIALOG (window)->action_area),
                        button, TRUE, TRUE, 0);
    gtk_widget_show (button);

And you could add to the vbox area by packing, for instance, a label in it, try something like this:

    label = gtk_label_new ("Dialogs are groovy");
    gtk_box_pack_start (GTK_BOX (GTK_DIALOG (window)->vbox),
                        label, TRUE, TRUE, 0);
    gtk_widget_show (label);

As an example in using the dialog box, you could put two buttons in the action_area, a Cancel button and an Ok button, and a label in the vbox area, asking the user a question or giving an error etc. Then you could attach a different signal to each of the buttons and perform the operation the user selects.

If the simple functionality provided by the default vertical and horizontal boxes in the two areas doesn't give you enough control for your application, then you can simply pack another layout widget into the boxes provided. For example, you could pack a table into the vertical box.

9.6 Pixmaps

Pixmaps are data structures that contain pictures. These pictures can be used in various places, but most commonly as icons on the X desktop, or as cursors.

A pixmap which only has 2 colors is called a bitmap, and there are a few additional routines for handling this common special case.

To understand pixmaps, it would help to understand how X window system works. Under X, applications do not need to be running on the same computer that is interacting with the user. Instead, the various applications, called "clients", all communicate with a program which displays the graphics and handles the keyboard and mouse. This program which interacts directly with the user is called a "display server" or "X server." Since the communication might take place over a network, it's important to keep some information with the X server. Pixmaps, for example, are stored in the memory of the X server. This means that once pixmap values are set, they don't need to keep getting transmitted over the network; instead a command is sent to "display pixmap number XYZ here." Even if you aren't using X with GTK currently, using constructs such as Pixmaps will make your programs work acceptably under X.

To use pixmaps in GTK, we must first build a GdkPixmap structure using routines from the GDK layer. Pixmaps can either be created from in-memory data, or from data read from a file. We'll go through each of the calls to create a pixmap.

GdkPixmap *gdk_bitmap_create_from_data( GdkWindow *window,
                                        gchar     *data,
                                        gint       width,
                                        gint       height );

This routine is used to create a single-plane pixmap (2 colors) from data in memory. Each bit of the data represents whether that pixel is off or on. Width and height are in pixels. The GdkWindow pointer is to the current window, since a pixmap's resources are meaningful only in the context of the screen where it is to be displayed.

GdkPixmap *gdk_pixmap_create_from_data( GdkWindow *window,
                                        gchar     *data,
                                        gint       width,
                                        gint       height,
                                        gint       depth,
                                        GdkColor  *fg,
                                        GdkColor  *bg );

This is used to create a pixmap of the given depth (number of colors) from the bitmap data specified. fg and bg are the foreground and background color to use.

GdkPixmap *gdk_pixmap_create_from_xpm( GdkWindow   *window,
                                       GdkBitmap  **mask,
                                       GdkColor    *transparent_color,
                                       const gchar *filename );

XPM format is a readable pixmap representation for the X Window System. It is widely used and many different utilities are available for creating image files in this format. The file specified by filename must contain an image in that format and it is loaded into the pixmap structure. The mask specifies which bits of the pixmap are opaque. All other bits are colored using the color specified by transparent_color. An example using this follows below.

GdkPixmap *gdk_pixmap_create_from_xpm_d( GdkWindow  *window,
                                         GdkBitmap **mask,
                                         GdkColor   *transparent_color,
                                         gchar     **data );

Small images can be incorporated into a program as data in the XPM format. A pixmap is created using this data, instead of reading it from a file. An example of such data is

/* XPM */
static const char * xpm_data[] = {
"16 16 3 1",
"       c None",
".      c #000000000000",
"X      c #FFFFFFFFFFFF",
"                ",
"   ......       ",
"   .XXX.X.      ",
"   .XXX.XX.     ",
"   .XXX.XXX.    ",
"   .XXX.....    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .........    ",
"                ",
"                "};

When we're done using a pixmap and not likely to reuse it again soon, it is a good idea to release the resource using gdk_pixmap_unref(). Pixmaps should be considered a precious resource, because they take up memory in the end-user's X server process. Even though the X client you write may run on a powerful "server" computer, the user may be running the X server on a small personal computer.

Once we've created a pixmap, we can display it as a GTK widget. We must create a GTK pixmap widget to contain the GDK pixmap. This is done using

GtkWidget *gtk_pixmap_new( GdkPixmap *pixmap,
                           GdkBitmap *mask );

The other pixmap widget calls are

guint gtk_pixmap_get_type( void );

void  gtk_pixmap_set( GtkPixmap  *pixmap,
                      GdkPixmap  *val,
                      GdkBitmap  *mask );

void  gtk_pixmap_get( GtkPixmap  *pixmap,
                      GdkPixmap **val,
                      GdkBitmap **mask);

gtk_pixmap_set is used to change the pixmap that the widget is currently managing. Val is the pixmap created using GDK.

The following is an example of using a pixmap in a button.

/* example-start pixmap pixmap.c */

#include <gtk/gtk.h>


/* XPM data of Open-File icon */
static const char * xpm_data[] = {
"16 16 3 1",
"       c None",
".      c #000000000000",
"X      c #FFFFFFFFFFFF",
"                ",
"   ......       ",
"   .XXX.X.      ",
"   .XXX.XX.     ",
"   .XXX.XXX.    ",
"   .XXX.....    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .XXXXXXX.    ",
"   .........    ",
"                ",
"                "};


/* when invoked (via signal delete_event), terminates the application.
 */
gint close_application( GtkWidget *widget,
                        GdkEvent  *event,
                        gpointer   data )
{
    gtk_main_quit();
    return(FALSE);
}


/* is invoked when the button is clicked.  It just prints a message.
 */
void button_clicked( GtkWidget *widget,
                     gpointer   data ) {
    g_print( "button clicked\n" );
}

int main( int   argc,
          char *argv[] )
{
    /* GtkWidget is the storage type for widgets */
    GtkWidget *window, *pixmapwid, *button;
    GdkPixmap *pixmap;
    GdkBitmap *mask;
    GtkStyle *style;
    
    /* create the main window, and attach delete_event signal to terminating
       the application */
    gtk_init( &argc, &argv );
    window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
    gtk_signal_connect( GTK_OBJECT (window), "delete_event",
                        GTK_SIGNAL_FUNC (close_application), NULL );
    gtk_container_set_border_width( GTK_CONTAINER (window), 10 );
    gtk_widget_show( window );

    /* now for the pixmap from gdk */
    style = gtk_widget_get_style( window );
    pixmap = gdk_pixmap_create_from_xpm_d( window->window,  &mask,
                                           &style->bg[GTK_STATE_NORMAL],
                                           (gchar **)xpm_data );

    /* a pixmap widget to contain the pixmap */
    pixmapwid = gtk_pixmap_new( pixmap, mask );
    gtk_widget_show( pixmapwid );

    /* a button to contain the pixmap widget */
    button = gtk_button_new();
    gtk_container_add( GTK_CONTAINER(button), pixmapwid );
    gtk_container_add( GTK_CONTAINER(window), button );
    gtk_widget_show( button );

    gtk_signal_connect( GTK_OBJECT(button), "clicked",
                        GTK_SIGNAL_FUNC(button_clicked), NULL );

    /* show the window */
    gtk_main ();
          
    return 0;
}
/* example-end */

To load a file from an XPM data file called icon0.xpm in the current directory, we would have created the pixmap thus

    /* load a pixmap from a file */
    pixmap = gdk_pixmap_create_from_xpm( window->window, &mask,
                                         &style->bg[GTK_STATE_NORMAL],
                                         "./icon0.xpm" );
    pixmapwid = gtk_pixmap_new( pixmap, mask );
    gtk_widget_show( pixmapwid );
    gtk_container_add( GTK_CONTAINER(window), pixmapwid );

A disadvantage of using pixmaps is that the displayed object is always rectangular, regardless of the image. We would like to create desktops and applications with icons that have more natural shapes. For example, for a game interface, we would like to have round buttons to push. The way to do this is using shaped windows.

A shaped window is simply a pixmap where the background pixels are transparent. This way, when the background image is multi-colored, we don't overwrite it with a rectangular, non-matching border around our icon. The following example displays a full wheelbarrow image on the desktop.

/* example-start wheelbarrow wheelbarrow.c */

#include <gtk/gtk.h>

/* XPM */
static char * WheelbarrowFull_xpm[] = {
"48 48 64 1",
"       c None",
".      c #DF7DCF3CC71B",
"X      c #965875D669A6",
"o      c #71C671C671C6",
"O      c #A699A289A699",
"+      c #965892489658",
"@      c #8E38410330C2",
"#      c #D75C7DF769A6",
"$      c #F7DECF3CC71B",
"%      c #96588A288E38",
"&      c #A69992489E79",
"*      c #8E3886178E38",
"=      c #104008200820",
"-      c #596510401040",
";      c #C71B30C230C2",
":      c #C71B9A699658",
">      c #618561856185",
",      c #20811C712081",
"<      c #104000000000",
"1      c #861720812081",
"2      c #DF7D4D344103",
"3      c #79E769A671C6",
"4      c #861782078617",
"5      c #41033CF34103",
"6      c #000000000000",
"7      c #49241C711040",
"8      c #492445144924",
"9      c #082008200820",
"0      c #69A618611861",
"q      c #B6DA71C65144",
"w      c #410330C238E3",
"e      c #CF3CBAEAB6DA",
"r      c #71C6451430C2",
"t      c #EFBEDB6CD75C",
"y      c #28A208200820",
"u      c #186110401040",
"i      c #596528A21861",
"p      c #71C661855965",
"a      c #A69996589658",
"s      c #30C228A230C2",
"d      c #BEFBA289AEBA",
"f      c #596545145144",
"g      c #30C230C230C2",
"h      c #8E3882078617",
"j      c #208118612081",
"k      c #38E30C300820",
"l      c #30C2208128A2",
"z      c #38E328A238E3",
"x      c #514438E34924",
"c      c #618555555965",
"v      c #30C2208130C2",
"b      c #38E328A230C2",
"n      c #28A228A228A2",
"m      c #41032CB228A2",
"M      c #104010401040",
"N      c #492438E34103",
"B      c #28A2208128A2",
"V      c #A699596538E3",
"C      c #30C21C711040",
"Z      c #30C218611040",
"A      c #965865955965",
"S      c #618534D32081",
"D      c #38E31C711040",
"F      c #082000000820",
"                                                ",
"          .XoO                                  ",
"         [email protected]#$%o&                                ",
"         *=-;#::o+                              ",
"           >,<12#:34                            ",
"             45671#:X3                          ",
"               +89<02qwo                        ",
"e*                >,67;ro                       ",
"ty>                 [email protected]>+&&                    ",
"$2u+                  ><ipas8*                  ",
"%$;=*                *3:.Xa.dfg>                ",
"Oh$;ya             *3d.a8j,Xe.d3g8+             ",
" Oh$;ka          *3d$a8lz,,xxc:.e3g54           ",
"  Oh$;kO       *pd$%svbzz,sxxxxfX..&wn>         ",
"   [email protected]    *3dthwlsslszjzxxxxxxx3:td8M4       ",
"    [email protected]& *3d$XNlvvvlllm,mNwxxxxxxxfa.:,B*     ",
"     [email protected],[email protected]#[email protected]:%j5&   ",
"      Oh$1hd5lllslllCCZrV#r#:#2AxxxxxxxxxcdwM*  ",
"       OXq6c.%8vvvllZZiqqApA:mq:Xxcpcxxxxxfdc9* ",
"        2r<[email protected]::qApxxxxxxfdcM ",
"        :,q-6MN.dfmZZrrSS:#[email protected]",
"         +A26jguXtAZZZC7iDiCCrVVii7Cmmmxxxxxx%3g",
"          *#16jszN..3DZZZZrCVSA2rZrV7Dmmwxxxx&en",
"           p2yFvzssXe:fCZZCiiD7iiZDiDSSZwwxx8e*>",
"           OA1<jzxwwc:$d%NDZZZZCCCZCCZZCmxxfd.B ",
"            3206Bwxxszx%et.eaAp77m77mmmf3&eeeg* ",
"             @26MvzxNzvlbwfpdettttttttttt.c,n&  ",
"             *;16=lsNwwNwgsvslbwwvccc3pcfu<o    ",
"              p;<69BvwwsszslllbBlllllllu<5+     ",
"              OS0y6FBlvvvzvzss,u=Blllj=54       ",
"               c1-699Blvlllllu7k96MMMg4         ",
"               *10y8n6FjvllllB<166668           ",
"                S-kg+>666<M<996-y6n<8*          ",
"                p71=4 m69996kD8Z-66698&&        ",
"                &i0ycm6n4 ogk17,0<6666g         ",
"                 N-k-<>     >=01-kuu666>        ",
"                 ,6ky&      &46-10ul,66,        ",
"                 Ou0<>       o66y<ulw<66&       ",
"                  *kk5       >66By7=xu664       ",
"                   <<M4      466lj<Mxu66o       ",
"                   *>>       +66uv,zN666*       ",
"                              566,xxj669        ",
"                              4666FF666>        ",
"                               >966666M         ",
"                                oM6668+         ",
"                                  *4            ",
"                                                ",
"                                                "};


/* When invoked (via signal delete_event), terminates the application */
gint close_application( GtkWidget *widget,
                        GdkEvent  *event,
                        gpointer   data )
{
    gtk_main_quit();
    return(FALSE);
}

int main (int argc,
          char *argv[] )
{
    /* GtkWidget is the storage type for widgets */
    GtkWidget *window, *pixmap, *fixed;
    GdkPixmap *gdk_pixmap;
    GdkBitmap *mask;
    GtkStyle *style;
    GdkGC *gc;
    
    /* Create the main window, and attach delete_event signal to terminate
     * the application.  Note that the main window will not have a titlebar
     * since we're making it a popup. */
    gtk_init (&argc, &argv);
    window = gtk_window_new( GTK_WINDOW_POPUP );
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
                        GTK_SIGNAL_FUNC (close_application), NULL);
    gtk_widget_show (window);

    /* Now for the pixmap and the pixmap widget */
    style = gtk_widget_get_default_style();
    gc = style->black_gc;
    gdk_pixmap = gdk_pixmap_create_from_xpm_d( window->window, &mask,
                                             &style->bg[GTK_STATE_NORMAL],
                                             WheelbarrowFull_xpm );
    pixmap = gtk_pixmap_new( gdk_pixmap, mask );
    gtk_widget_show( pixmap );

    /* To display the pixmap, we use a fixed widget to place the pixmap */
    fixed = gtk_fixed_new();
    gtk_widget_set_usize( fixed, 200, 200 );
    gtk_fixed_put( GTK_FIXED(fixed), pixmap, 0, 0 );
    gtk_container_add( GTK_CONTAINER(window), fixed );
    gtk_widget_show( fixed );

    /* This masks out everything except for the image itself */
    gtk_widget_shape_combine_mask( window, mask, 0, 0 );
    
    /* show the window */
    gtk_widget_set_uposition( window, 20, 400 );
    gtk_widget_show( window );
    gtk_main ();
          
    return(0);
}
/* example-end */

To make the wheelbarrow image sensitive, we could attach the button press event signal to make it do something. The following few lines would make the picture sensitive to a mouse button being pressed which makes the application terminate.

    gtk_widget_set_events( window,
                          gtk_widget_get_events( window ) |
                          GDK_BUTTON_PRESS_MASK );

   gtk_signal_connect( GTK_OBJECT(window), "button_press_event",
                       GTK_SIGNAL_FUNC(close_application), NULL );

9.7 Rulers

Ruler widgets are used to indicate the location of the mouse pointer in a given window. A window can have a vertical ruler spanning across the width and a horizontal ruler spanning down the height. A small triangular indicator on the ruler shows the exact location of the pointer relative to the ruler.

A ruler must first be created. Horizontal and vertical rulers are created using

GtkWidget *gtk_hruler_new( void );    /* horizontal ruler */

GtkWidget *gtk_vruler_new( void );    /* vertical ruler   */

Once a ruler is created, we can define the unit of measurement. Units of measure for rulers can beGTK_PIXELS, GTK_INCHES or GTK_CENTIMETERS. This is set using

void gtk_ruler_set_metric( GtkRuler      *ruler,
                           GtkMetricType  metric );

The default measure is GTK_PIXELS.

    gtk_ruler_set_metric( GTK_RULER(ruler), GTK_PIXELS );

Other important characteristics of a ruler are how to mark the units of scale and where the position indicator is initially placed. These are set for a ruler using

void gtk_ruler_set_range( GtkRuler *ruler,
                          gfloat    lower,
                          gfloat    upper,
                          gfloat    position,
                          gfloat    max_size );

The lower and upper arguments define the extent of the ruler, and max_size is the largest possible number that will be displayed. Position defines the initial position of the pointer indicator within the ruler.

A vertical ruler can span an 800 pixel wide window thus

    gtk_ruler_set_range( GTK_RULER(vruler), 0, 800, 0, 800);

The markings displayed on the ruler will be from 0 to 800, with a number for every 100 pixels. If instead we wanted the ruler to range from 7 to 16, we would code

    gtk_ruler_set_range( GTK_RULER(vruler), 7, 16, 0, 20);

The indicator on the ruler is a small triangular mark that indicates the position of the pointer relative to the ruler. If the ruler is used to follow the mouse pointer, the motion_notify_event signal should be connected to the motion_notify_event method of the ruler. To follow all mouse movements within a window area, we would use

#define EVENT_METHOD(i, x) GTK_WIDGET_CLASS(GTK_OBJECT(i)->klass)->x

    gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event",
           (GtkSignalFunc)EVENT_METHOD(ruler, motion_notify_event),
           GTK_OBJECT(ruler) );

The following example creates a drawing area with a horizontal ruler above it and a vertical ruler to the left of it. The size of the drawing area is 600 pixels wide by 400 pixels high. The horizontal ruler spans from 7 to 13 with a mark every 100 pixels, while the vertical ruler spans from 0 to 400 with a mark every 100 pixels. Placement of the drawing area and the rulers is done using a table.

/* example-start rulers rulers.c */

#include <gtk/gtk.h>

#define EVENT_METHOD(i, x) GTK_WIDGET_CLASS(GTK_OBJECT(i)->klass)->x

#define XSIZE  600
#define YSIZE  400

/* This routine gets control when the close button is clicked */
gint close_application( GtkWidget *widget,
                        GdkEvent  *event,
                        gpointer   data )
{
    gtk_main_quit();
    return(FALSE);
}

/* The main routine */
int main( int   argc,
          char *argv[] ) {
    GtkWidget *window, *table, *area, *hrule, *vrule;

    /* Initialize GTK and create the main window */
    gtk_init( &argc, &argv );

    window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
            GTK_SIGNAL_FUNC( close_application ), NULL);
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);

    /* Create a table for placing the ruler and the drawing area */
    table = gtk_table_new( 3, 2, FALSE );
    gtk_container_add( GTK_CONTAINER(window), table );

    area = gtk_drawing_area_new();
    gtk_drawing_area_size( (GtkDrawingArea *)area, XSIZE, YSIZE );
    gtk_table_attach( GTK_TABLE(table), area, 1, 2, 1, 2,
                      GTK_EXPAND|GTK_FILL, GTK_FILL, 0, 0 );
    gtk_widget_set_events( area, GDK_POINTER_MOTION_MASK |
                                 GDK_POINTER_MOTION_HINT_MASK );

    /* The horizontal ruler goes on top. As the mouse moves across the
     * drawing area, a motion_notify_event is passed to the
     * appropriate event handler for the ruler. */
    hrule = gtk_hruler_new();
    gtk_ruler_set_metric( GTK_RULER(hrule), GTK_PIXELS );
    gtk_ruler_set_range( GTK_RULER(hrule), 7, 13, 0, 20 );
    gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event",
                               (GtkSignalFunc)EVENT_METHOD(hrule,
                                                        motion_notify_event),
                               GTK_OBJECT(hrule) );
    /*  GTK_WIDGET_CLASS(GTK_OBJECT(hrule)->klass)->motion_notify_event, */
    gtk_table_attach( GTK_TABLE(table), hrule, 1, 2, 0, 1,
                      GTK_EXPAND|GTK_SHRINK|GTK_FILL, GTK_FILL, 0, 0 );
    
    /* The vertical ruler goes on the left. As the mouse moves across
     * the drawing area, a motion_notify_event is passed to the
     * appropriate event handler for the ruler. */
    vrule = gtk_vruler_new();
    gtk_ruler_set_metric( GTK_RULER(vrule), GTK_PIXELS );
    gtk_ruler_set_range( GTK_RULER(vrule), 0, YSIZE, 10, YSIZE );
    gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event",
                               (GtkSignalFunc)
                                  GTK_WIDGET_CLASS(GTK_OBJECT(vrule)->klass)->
                                                         motion_notify_event,
                               GTK_OBJECT(vrule) );
    gtk_table_attach( GTK_TABLE(table), vrule, 0, 1, 1, 2,
                      GTK_FILL, GTK_EXPAND|GTK_SHRINK|GTK_FILL, 0, 0 );

    /* Now show everything */
    gtk_widget_show( area );
    gtk_widget_show( hrule );
    gtk_widget_show( vrule );
    gtk_widget_show( table );
    gtk_widget_show( window );
    gtk_main();

    return(0);
}
/* example-end */

9.8 Statusbars

Statusbars are simple widgets used to display a text message. They keep a stack of the messages pushed onto them, so that popping the current message will re-display the previous text message.

In order to allow different parts of an application to use the same statusbar to display messages, the statusbar widget issues Context Identifiers which are used to identify different "users". The message on top of the stack is the one displayed, no matter what context it is in. Messages are stacked in last-in-first-out order, not context identifier order.

A statusbar is created with a call to:

GtkWidget *gtk_statusbar_new( void );

A new Context Identifier is requested using a call to the following function with a short textual description of the context:

guint gtk_statusbar_get_context_id( GtkStatusbar *statusbar,
                                    const gchar  *context_description );

There are three functions that can operate on statusbars:

guint gtk_statusbar_push( GtkStatusbar *statusbar,
                          guint         context_id,
                          gchar        *text );

void gtk_statusbar_pop( GtkStatusbar *statusbar)
                        guint         context_id );

void gtk_statusbar_remove( GtkStatusbar *statusbar,
                           guint         context_id,
                           guint         message_id ); 

The first, gtk_statusbar_push, is used to add a new message to the statusbar. It returns a Message Identifier, which can be passed later to the function gtk_statusbar_remove to remove the message with the given Message and Context Identifiers from the statusbar's stack.

The function gtk_statusbar_pop removes the message highest in the stack with the given Context Identifier.

The following example creates a statusbar and two buttons, one for pushing items onto the statusbar, and one for popping the last item back off.

/* example-start statusbar statusbar.c */

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

GtkWidget *status_bar;

void push_item( GtkWidget *widget,
                gpointer   data )
{
  static int count = 1;
  char buff[20];

  g_snprintf(buff, 20, "Item %d", count++);
  gtk_statusbar_push( GTK_STATUSBAR(status_bar), GPOINTER_TO_INT(data), buff);

  return;
}

void pop_item( GtkWidget *widget,
               gpointer   data )
{
  gtk_statusbar_pop( GTK_STATUSBAR(status_bar), GPOINTER_TO_INT(data) );
  return;
}

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

    GtkWidget *window;
    GtkWidget *vbox;
    GtkWidget *button;

    gint context_id;

    gtk_init (&argc, &argv);

    /* create a new window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_widget_set_usize( GTK_WIDGET (window), 200, 100);
    gtk_window_set_title(GTK_WINDOW (window), "GTK Statusbar Example");
    gtk_signal_connect(GTK_OBJECT (window), "delete_event",
                       (GtkSignalFunc) gtk_exit, NULL);
 
    vbox = gtk_vbox_new(FALSE, 1);
    gtk_container_add(GTK_CONTAINER(window), vbox);
    gtk_widget_show(vbox);
          
    status_bar = gtk_statusbar_new();      
    gtk_box_pack_start (GTK_BOX (vbox), status_bar, TRUE, TRUE, 0);
    gtk_widget_show (status_bar);

    context_id = gtk_statusbar_get_context_id(
                          GTK_STATUSBAR(status_bar), "Statusbar example");

    button = gtk_button_new_with_label("push item");
    gtk_signal_connect(GTK_OBJECT(button), "clicked",
        GTK_SIGNAL_FUNC (push_item), GINT_TO_POINTER(context_id) );
    gtk_box_pack_start(GTK_BOX(vbox), button, TRUE, TRUE, 2);
    gtk_widget_show(button);              

    button = gtk_button_new_with_label("pop last item");
    gtk_signal_connect(GTK_OBJECT(button), "clicked",
        GTK_SIGNAL_FUNC (pop_item), GINT_TO_POINTER(context_id) );
    gtk_box_pack_start(GTK_BOX(vbox), button, TRUE, TRUE, 2);
    gtk_widget_show(button);              

    /* always display the window as the last step so it all splashes on
     * the screen at once. */
    gtk_widget_show(window);

    gtk_main ();

    return 0;
}
/* example-end */

9.9 Text Entries

The Entry widget allows text to be typed and displayed in a single line text box. The text may be set with function calls that allow new text to replace, prepend or append the current contents of the Entry widget.

There are two functions for creating Entry widgets:

GtkWidget *gtk_entry_new( void );

GtkWidget *gtk_entry_new_with_max_length( guint16 max );

The first just creates a new Entry widget, whilst the second creates a new Entry and sets a limit on the length of the text within the Entry.

There are several functions for altering the text which is currently within the Entry widget.

void gtk_entry_set_text( GtkEntry    *entry,
                         const gchar *text );

void gtk_entry_append_text( GtkEntry    *entry,
                            const gchar *text );

void gtk_entry_prepend_text( GtkEntry    *entry,
                             const gchar *text );

The function gtk_entry_set_text sets the contents of the Entry widget, replacing the current contents. The functions gtk_entry_append_text and gtk_entry_prepend_text allow the current contents to be appended and prepended to.

The next function allows the current insertion point to be set.

void gtk_entry_set_position( GtkEntry *entry,
                             gint      position );

The contents of the Entry can be retrieved by using a call to the following function. This is useful in the callback functions described below.

gchar *gtk_entry_get_text( GtkEntry *entry );

The value returned by this function is used internally, and must not be freed using either free() or g_free()

If we don't want the contents of the Entry to be changed by someone typing into it, we can change its editable state.

void gtk_entry_set_editable( GtkEntry *entry,
                             gboolean  editable );

The function above allows us to toggle the editable state of the Entry widget by passing in a TRUE or FALSE value for the editable argument.

If we are using the Entry where we don't want the text entered to be visible, for example when a password is being entered, we can use the following function, which also takes a boolean flag.

void gtk_entry_set_visibility( GtkEntry *entry,
                               gboolean  visible );

A region of the text may be set as selected by using the following function. This would most often be used after setting some default text in an Entry, making it easy for the user to remove it.

void gtk_entry_select_region( GtkEntry *entry,
                              gint      start,
                              gint      end );

If we want to catch when the user has entered text, we can connect to the activate or changed signal. Activate is raised when the user hits the enter key within the Entry widget. Changed is raised when the text changes at all, e.g., for every character entered or removed.

The following code is an example of using an Entry widget.

/* example-start entry entry.c */

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

void enter_callback( GtkWidget *widget,
                     GtkWidget *entry )
{
  gchar *entry_text;
  entry_text = gtk_entry_get_text(GTK_ENTRY(entry));
  printf("Entry contents: %s\n", entry_text);
}

void entry_toggle_editable( GtkWidget *checkbutton,
                            GtkWidget *entry )
{
  gtk_entry_set_editable(GTK_ENTRY(entry),
                         GTK_TOGGLE_BUTTON(checkbutton)->active);
}

void entry_toggle_visibility( GtkWidget *checkbutton,
                              GtkWidget *entry )
{
  gtk_entry_set_visibility(GTK_ENTRY(entry),
                         GTK_TOGGLE_BUTTON(checkbutton)->active);
}

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

    GtkWidget *window;
    GtkWidget *vbox, *hbox;
    GtkWidget *entry;
    GtkWidget *button;
    GtkWidget *check;

    gtk_init (&argc, &argv);

    /* create a new window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_widget_set_usize( GTK_WIDGET (window), 200, 100);
    gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
    gtk_signal_connect(GTK_OBJECT (window), "delete_event",
                       (GtkSignalFunc) gtk_exit, NULL);

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

    entry = gtk_entry_new_with_max_length (50);
    gtk_signal_connect(GTK_OBJECT(entry), "activate",
                       GTK_SIGNAL_FUNC(enter_callback),
                       entry);
    gtk_entry_set_text (GTK_ENTRY (entry), "hello");
    gtk_entry_append_text (GTK_ENTRY (entry), " world");
    gtk_entry_select_region (GTK_ENTRY (entry),
                             0, GTK_ENTRY(entry)->text_length);
    gtk_box_pack_start (GTK_BOX (vbox), entry, TRUE, TRUE, 0);
    gtk_widget_show (entry);

    hbox = gtk_hbox_new (FALSE, 0);
    gtk_container_add (GTK_CONTAINER (vbox), hbox);
    gtk_widget_show (hbox);
                                  
    check = gtk_check_button_new_with_label("Editable");
    gtk_box_pack_start (GTK_BOX (hbox), check, TRUE, TRUE, 0);
    gtk_signal_connect (GTK_OBJECT(check), "toggled",
                        GTK_SIGNAL_FUNC(entry_toggle_editable), entry);
    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(check), TRUE);
    gtk_widget_show (check);
    
    check = gtk_check_button_new_with_label("Visible");
    gtk_box_pack_start (GTK_BOX (hbox), check, TRUE, TRUE, 0);
    gtk_signal_connect (GTK_OBJECT(check), "toggled",
                        GTK_SIGNAL_FUNC(entry_toggle_visibility), entry);
    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(check), TRUE);
    gtk_widget_show (check);
                                   
    button = gtk_button_new_with_label ("Close");
    gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
                               GTK_SIGNAL_FUNC(gtk_exit),
                               GTK_OBJECT (window));
    gtk_box_pack_start (GTK_BOX (vbox), 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);
}
/* example-end */

9.10 Spin Buttons

The Spin Button widget is generally used to allow the user to select a value from a range of numeric values. It consists of a text entry box with up and down arrow buttons attached to the side. Selecting one of the buttons causes the value to "spin" up and down the range of possible values. The entry box may also be edited directly to enter a specific value.

The Spin Button allows the value to have zero or a number of decimal places and to be incremented/decremented in configurable steps. The action of holding down one of the buttons optionally results in an acceleration of change in the value according to how long it is depressed.

The Spin Button uses an Adjustment object to hold information about the range of values that the spin button can take. This makes for a powerful Spin Button widget.

Recall that an adjustment widget is created with the following function, which illustrates the information that it holds:

GtkObject *gtk_adjustment_new( gfloat value,
                               gfloat lower,
                               gfloat upper,
                               gfloat step_increment,
                               gfloat page_increment,
                               gfloat page_size );

These attributes of an Adjustment are used by the Spin Button in the following way:

Additionally, mouse button 3 can be used to jump directly to the upper or lower values when used to select one of the buttons. Lets look at how to create a Spin Button:

GtkWidget *gtk_spin_button_new( GtkAdjustment *adjustment,
                                gfloat         climb_rate,
                                guint          digits );

The climb_rate argument take a value between 0.0 and 1.0 and indicates the amount of acceleration that the Spin Button has. The digits argument specifies the number of decimal places to which the value will be displayed.

A Spin Button can be reconfigured after creation using the following function:

void gtk_spin_button_configure( GtkSpinButton *spin_button,
                                GtkAdjustment *adjustment,
                                gfloat         climb_rate,
                                guint          digits );

The spin_button argument specifies the Spin Button widget that is to be reconfigured. The other arguments are as specified above.

The adjustment can be set and retrieved independantly using the following two functions:

void gtk_spin_button_set_adjustment( GtkSpinButton  *spin_button,
                                     GtkAdjustment  *adjustment );

GtkAdjustment *gtk_spin_button_get_adjustment( GtkSpinButton *spin_button );

The number of decimal places can also be altered using:

void gtk_spin_button_set_digits( GtkSpinButton *spin_button,
                                 guint          digits) ;

The value that a Spin Button is currently displaying can be changed using the following function:

void gtk_spin_button_set_value( GtkSpinButton *spin_button,
                                gfloat         value );

The current value of a Spin Button can be retrieved as either a floating point or integer value with the following functions:

gfloat gtk_spin_button_get_value_as_float( GtkSpinButton *spin_button );

gint gtk_spin_button_get_value_as_int( GtkSpinButton *spin_button );

If you want to alter the value of a Spin Value relative to its current value, then the following function can be used:

void gtk_spin_button_spin( GtkSpinButton *spin_button,
                           GtkSpinType    direction,
                           gfloat         increment );

The direction parameter can take one of the following values:

  GTK_SPIN_STEP_FORWARD
  GTK_SPIN_STEP_BACKWARD
  GTK_SPIN_PAGE_FORWARD
  GTK_SPIN_PAGE_BACKWARD
  GTK_SPIN_HOME
  GTK_SPIN_END
  GTK_SPIN_USER_DEFINED

This function packs in quite a bit of functionality, which I will attempt to clearly explain. Many of these settings use values from the Adjustment object that is associated with a Spin Button.

GTK_SPIN_STEP_FORWARD and GTK_SPIN_STEP_BACKWARD change the value of the Spin Button by the amount specified by increment, unless increment is equal to 0, in which case the value is changed by the value of step_increment in theAdjustment.

GTK_SPIN_PAGE_FORWARD and GTK_SPIN_PAGE_BACKWARD simply alter the value of the Spin Button by increment.

GTK_SPIN_HOME sets the value of the Spin Button to the bottom of the Adjustments range.

GTK_SPIN_END sets the value of the Spin Button to the top of the Adjustments range.

GTK_SPIN_USER_DEFINED simply alters the value of the Spin Button by the specified amount.

We move away from functions for setting and retreving the range attributes of the Spin Button now, and move onto functions that effect the appearance and behaviour of the Spin Button widget itself.

The first of these functions is used to constrain the text box of the Spin Button such that it may only contain a numeric value. This prevents a user from typing anything other than numeric values into the text box of a Spin Button:

void gtk_spin_button_set_numeric( GtkSpinButton *spin_button,
                                  gboolean       numeric );

You can set whether a Spin Button will wrap around between the upper and lower range values with the following function:

void gtk_spin_button_set_wrap( GtkSpinButton *spin_button,
                               gboolean       wrap );

You can set a Spin Button to round the value to the nearest step_increment, which is set within the Adjustment object used with the Spin Button. This is accomplished with the following function:

void gtk_spin_button_set_snap_to_ticks( GtkSpinButton  *spin_button,
                                        gboolean        snap_to_ticks );

The update policy of a Spin Button can be changed with the following function:

void gtk_spin_button_set_update_policy( GtkSpinButton  *spin_button,
                                    GtkSpinButtonUpdatePolicy policy );

The possible values of policy are either GTK_UPDATE_ALWAYS or GTK_UPDATE_IF_VALID.

These policies affect the behavior of a Spin Button when parsing inserted text and syncing its value with the values of the Adjustment.

In the case of GTK_UPDATE_IF_VALID the Spin Button only value gets changed if the text input is a numeric value that is within the range specified by the Adjustment. Otherwise the text is reset to the current value.

In case of GTK_UPDATE_ALWAYS we ignore errors while converting text into a numeric value.

The appearance of the buttons used in a Spin Button can be changed using the following function:

void gtk_spin_button_set_shadow_type( GtkSpinButton *spin_button,
                                      GtkShadowType  shadow_type );

As usual, the shadow_type can be one of:

  GTK_SHADOW_IN
  GTK_SHADOW_OUT
  GTK_SHADOW_ETCHED_IN
  GTK_SHADOW_ETCHED_OUT

Finally, you can explicitly request that a Spin Button update itself:

void gtk_spin_button_update( GtkSpinButton  *spin_button );

It's example time again.

/* example-start spinbutton spinbutton.c */

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

static GtkWidget *spinner1;

void toggle_snap( GtkWidget     *widget,
                  GtkSpinButton *spin )
{
  gtk_spin_button_set_snap_to_ticks (spin, GTK_TOGGLE_BUTTON (widget)->active);
}

void toggle_numeric( GtkWidget *widget,
                     GtkSpinButton *spin )
{
  gtk_spin_button_set_numeric (spin, GTK_TOGGLE_BUTTON (widget)->active);
}

void change_digits( GtkWidget *widget,
                    GtkSpinButton *spin )
{
  gtk_spin_button_set_digits (GTK_SPIN_BUTTON (spinner1),
                              gtk_spin_button_get_value_as_int (spin));
}

void get_value( GtkWidget *widget,
                gpointer data )
{
  gchar buf[32];
  GtkLabel *label;
  GtkSpinButton *spin;

  spin = GTK_SPIN_BUTTON (spinner1);
  label = GTK_LABEL (gtk_object_get_user_data (GTK_OBJECT (widget)));
  if (GPOINTER_TO_INT (data) == 1)
    sprintf (buf, "%d", gtk_spin_button_get_value_as_int (spin));
  else
    sprintf (buf, "%0.*f", spin->digits,
             gtk_spin_button_get_value_as_float (spin));
  gtk_label_set_text (label, buf);
}


int main( int   argc,
          char *argv[] )
{
  GtkWidget *window;
  GtkWidget *frame;
  GtkWidget *hbox;
  GtkWidget *main_vbox;
  GtkWidget *vbox;
  GtkWidget *vbox2;
  GtkWidget *spinner2;
  GtkWidget *spinner;
  GtkWidget *button;
  GtkWidget *label;
  GtkWidget *val_label;
  GtkAdjustment *adj;

  /* Initialise GTK */
  gtk_init(&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  gtk_signal_connect (GTK_OBJECT (window), "destroy",
                      GTK_SIGNAL_FUNC (gtk_main_quit),
                      NULL);

  gtk_window_set_title (GTK_WINDOW (window), "Spin Button");

  main_vbox = gtk_vbox_new (FALSE, 5);
  gtk_container_set_border_width (GTK_CONTAINER (main_vbox), 10);
  gtk_container_add (GTK_CONTAINER (window), main_vbox);
  
  frame = gtk_frame_new ("Not accelerated");
  gtk_box_pack_start (GTK_BOX (main_vbox), frame, TRUE, TRUE, 0);
  
  vbox = gtk_vbox_new (FALSE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (vbox), 5);
  gtk_container_add (GTK_CONTAINER (frame), vbox);
  
  /* Day, month, year spinners */
  
  hbox = gtk_hbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (vbox), hbox, TRUE, TRUE, 5);
  
  vbox2 = gtk_vbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);
  
  label = gtk_label_new ("Day :");
  gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
  gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);
  
  adj = (GtkAdjustment *) gtk_adjustment_new (1.0, 1.0, 31.0, 1.0,
                                              5.0, 0.0);
  spinner = gtk_spin_button_new (adj, 0, 0);
  gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), TRUE);
  gtk_spin_button_set_shadow_type (GTK_SPIN_BUTTON (spinner),
                                   GTK_SHADOW_OUT);
  gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);
  
  vbox2 = gtk_vbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);
  
  label = gtk_label_new ("Month :");
  gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
  gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);
  
  adj = (GtkAdjustment *) gtk_adjustment_new (1.0, 1.0, 12.0, 1.0,
                                              5.0, 0.0);
  spinner = gtk_spin_button_new (adj, 0, 0);
  gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), TRUE);
  gtk_spin_button_set_shadow_type (GTK_SPIN_BUTTON (spinner),
                                   GTK_SHADOW_ETCHED_IN);
  gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);
  
  vbox2 = gtk_vbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);
  
  label = gtk_label_new ("Year :");
  gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
  gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);
  
  adj = (GtkAdjustment *) gtk_adjustment_new (1998.0, 0.0, 2100.0,
                                              1.0, 100.0, 0.0);
  spinner = gtk_spin_button_new (adj, 0, 0);
  gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), FALSE);
  gtk_spin_button_set_shadow_type (GTK_SPIN_BUTTON (spinner),
                                   GTK_SHADOW_IN);
  gtk_widget_set_usize (spinner, 55, 0);
  gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);
  
  frame = gtk_frame_new ("Accelerated");
  gtk_box_pack_start (GTK_BOX (main_vbox), frame, TRUE, TRUE, 0);
  
  vbox = gtk_vbox_new (FALSE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (vbox), 5);
  gtk_container_add (GTK_CONTAINER (frame), vbox);
  
  hbox = gtk_hbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);
  
  vbox2 = gtk_vbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);
  
  label = gtk_label_new ("Value :");
  gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
  gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);
  
  adj = (GtkAdjustment *) gtk_adjustment_new (0.0, -10000.0, 10000.0,
                                              0.5, 100.0, 0.0);
  spinner1 = gtk_spin_button_new (adj, 1.0, 2);
  gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner1), TRUE);
  gtk_widget_set_usize (spinner1, 100, 0);
  gtk_box_pack_start (GTK_BOX (vbox2), spinner1, FALSE, TRUE, 0);
  
  vbox2 = gtk_vbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);
  
  label = gtk_label_new ("Digits :");
  gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
  gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);
  
  adj = (GtkAdjustment *) gtk_adjustment_new (2, 1, 5, 1, 1, 0);
  spinner2 = gtk_spin_button_new (adj, 0.0, 0);
  gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner2), TRUE);
  gtk_signal_connect (GTK_OBJECT (adj), "value_changed",
                      GTK_SIGNAL_FUNC (change_digits),
                      (gpointer) spinner2);
  gtk_box_pack_start (GTK_BOX (vbox2), spinner2, FALSE, TRUE, 0);
  
  hbox = gtk_hbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);
  
  button = gtk_check_button_new_with_label ("Snap to 0.5-ticks");
  gtk_signal_connect (GTK_OBJECT (button), "clicked",
                      GTK_SIGNAL_FUNC (toggle_snap),
                      spinner1);
  gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
  gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE);
  
  button = gtk_check_button_new_with_label ("Numeric only input mode");
  gtk_signal_connect (GTK_OBJECT (button), "clicked",
                      GTK_SIGNAL_FUNC (toggle_numeric),
                      spinner1);
  gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
  gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE);
  
  val_label = gtk_label_new ("");
  
  hbox = gtk_hbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);
  button = gtk_button_new_with_label ("Value as Int");
  gtk_object_set_user_data (GTK_OBJECT (button), val_label);
  gtk_signal_connect (GTK_OBJECT (button), "clicked",
                      GTK_SIGNAL_FUNC (get_value),
                      GINT_TO_POINTER (1));
  gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);
  
  button = gtk_button_new_with_label ("Value as Float");
  gtk_object_set_user_data (GTK_OBJECT (button), val_label);
  gtk_signal_connect (GTK_OBJECT (button), "clicked",
                      GTK_SIGNAL_FUNC (get_value),
                      GINT_TO_POINTER (2));
  gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);
  
  gtk_box_pack_start (GTK_BOX (vbox), val_label, TRUE, TRUE, 0);
  gtk_label_set_text (GTK_LABEL (val_label), "0");
  
  hbox = gtk_hbox_new (FALSE, 0);
  gtk_box_pack_start (GTK_BOX (main_vbox), hbox, FALSE, TRUE, 0);
  
  button = gtk_button_new_with_label ("Close");
  gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
                             GTK_SIGNAL_FUNC (gtk_widget_destroy),
                             GTK_OBJECT (window));
  gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);

  gtk_widget_show_all (window);

  /* Enter the event loop */
  gtk_main ();
    
  return(0);
}
/* example-end */

9.11 Combo Box

The combo box is another fairly simple widget that is really just a collection of other widgets. From the user's point of view, the widget consists of a text entry box and a pull down menu from which the user can select one of a set of predefined entries. Alternatively, the user can type a different option directly into the text box.

The following extract from the structure that defines a Combo Box identifies several of the components:

struct _GtkCombo { 
        GtkHBox hbox; 
        GtkWidget *entry; 
        GtkWidget *button;
        GtkWidget *popup; 
        GtkWidget *popwin; 
        GtkWidget *list;
        ...  };

As you can see, the Combo Box has two principal parts that you really care about: an entry and a list.

First off, to create a combo box, use:

GtkWidget *gtk_combo_new( void );

Now, if you want to set the string in the entry section of the combo box, this is done by manipulating the entry widget directly:

    gtk_entry_set_text(GTK_ENTRY(GTK_COMBO(combo)->entry), "My String.");

To set the values in the popdown list, one uses the function:

void gtk_combo_set_popdown_strings( GtkCombo *combo,
                                    GList    *strings );

Before you can do this, you have to assemble a GList of the strings that you want. GList is a linked list implementation that is part of GLib, a library supporing GTK. For the moment, the quick and dirty explanation is that you need to set up a GList pointer, set it equal to NULL, then append strings to it with

GList *g_list_append( GList *glist, 
                      gpointer data );

It is important that you set the initial GList pointer to NULL. The value returned from the g_list_append function must be used as the new pointer to the GList.

Here's a typical code segment for creating a set of options:

    GList *glist=NULL;

    glist = g_list_append(glist, "String 1");
    glist = g_list_append(glist, "String 2");
    glist = g_list_append(glist, "String 3"); 
    glist = g_list_append(glist, "String 4");

    gtk_combo_set_popdown_strings( GTK_COMBO(combo), glist) ;

The combo widget makes a copy of the strings passed to it in the glist structure. As a result, you need to make sure you free the memory used by the list if that is appropriate for your application.

At this point you have a working combo box that has been set up. There are a few aspects of its behavior that you can change. These are accomplished with the functions:

void gtk_combo_set_use_arrows( GtkCombo *combo,
                               gint      val );

void gtk_combo_set_use_arrows_always( GtkCombo *combo,
                                      gint      val );

void gtk_combo_set_case_sensitive( GtkCombo *combo,
                                   gint      val );

gtk_combo_set_use_arrows() lets the user change the value in the entry using the up/down arrow keys. This doesn't bring up the list, but rather replaces the current text in the entry with the next list entry (up or down, as your key choice indicates). It does this by searching in the list for the item corresponding to the current value in the entry and selecting the previous/next item accordingly. Usually in an entry the arrow keys are used to change focus (you can do that anyway using TAB). Note that when the current item is the last of the list and you press arrow-down it changes the focus (the same applies with the first item and arrow-up).

If the current value in the entry is not in the list, then the function of gtk_combo_set_use_arrows() is disabled.

gtk_combo_set_use_arrows_always() similarly allows the use the the up/down arrow keys to cycle through the choices in the dropdown list, except that it wraps around the values in the list, completely disabling the use of the up and down arrow keys for changing focus.

gtk_combo_set_case_sensitive() toggles whether or not GTK searches for entries in a case sensitive manner. This is used when the Combo widget is asked to find a value from the list using the current entry in the text box. This completion can be performed in either a case sensitive or insensitive manner, depending upon the use of this function. The Combo widget can also simply complete the current entry if the user presses the key combination MOD-1 and "Tab". MOD-1 is often mapped to the "Alt" key, by the xmodmap utility. Note, however that some window managers also use this key combination, which will override its use within GTK.

Now that we have a combo box, tailored to look and act how we want it, all that remains is being able to get data from the combo box. This is relatively straightforward. The majority of the time, all you are going to care about getting data from is the entry. The entry is accessed simply by GTK_ENTRY(GTK_COMBO(combo)->entry). The two principal things that you are going to want to do with it are attach to the activate signal, which indicates that the user has pressed the Return or Enter key, and read the text. The first is accomplished using something like:

    gtk_signal_connect(GTK_OBJECT(GTK_COMB(combo)->entry), "activate",
                       GTK_SIGNAL_FUNC (my_callback_function), my_data);

Getting the text at any arbitrary time is accomplished by simply using the entry function:

gchar *gtk_entry_get_text(GtkEntry *entry);

Such as:

    char *string;

    string = gtk_entry_get_text(GTK_ENTRY(GTK_COMBO(combo)->entry));

That's about all there is to it. There is a function

void gtk_combo_disable_activate(GtkCombo *combo);

that will disable the activate signal on the entry widget in the combo box. Personally, I can't think of why you'd want to use it, but it does exist.

9.12 Calendar

The Calendar widget is an effective way to display and retrieve monthly date related information. It is a very simple widget to create and work with.

Creating a GtkCalendar widget is a simple as:

GtkWidget *gtk_calendar_new();

There might be times where you need to change a lot of information within this widget and the following functions allow you to make multiple change to a Calendar widget without the user seeing multiple on-screen updates.

void gtk_calendar_freeze( GtkCalendar *Calendar );

void gtk_calendar_thaw  ( GtkCalendar *Calendar );

They work just like the freeze/thaw functions of every other widget.

The Calendar widget has a few options that allow you to change the way the widget both looks and operates by using the function

void gtk_calendar_display_options( GtkCalendar               *calendar,
                                   GtkCalendarDisplayOptions  flags );

The flags argument can be formed by combining either of the following five options using the logical bitwise OR (|) operation:

The following functions are used to set the the currently displayed date:

gint gtk_calendar_select_month( GtkCalendar *calendar, 
                                guint        month,
                                guint        year );

void gtk_calendar_select_day( GtkCalendar *calendar,
                              guint        day );

The return value from gtk_calendar_select_month() is a boolean value indicating whether the selection was successful.

With gtk_calendar_select_day() the specified day number is selected within the current month, if that is possible. A day value of 0 will deselect any current selection.

In addition to having a day selected, any number of days in the month may be "marked". A marked day is highlighted within the calendar display. The following functions are provided to manipulate marked days:

gint gtk_calendar_mark_day( GtkCalendar *calendar,
                            guint        day);

gint gtk_calendar_unmark_day( GtkCalendar *calendar,
                              guint        day);

void gtk_calendar_clear_marks( GtkCalendar *calendar);

The currently marked days are stored within an array within the GtkCalendar structure. This array is 31 elements long so to test whether a particular day is currently marked, you need to access the corresponding element of the array (don't forget in C that array elements are numbered 0 to n-1). For example:

    GtkCalendar *calendar;
    calendar = gtk_calendar_new();

    ...

    /* Is day 7 marked? */
    if (calendar->marked_date[7-1])
       /* day is marked */

Note that marks are persistent across month and year changes.

The final Calendar widget function is used to retrieve the currently selected date, month and/or year.

void gtk_calendar_get_date( GtkCalendar *calendar, 
                            guint       *year,
                            guint       *month,
                            guint       *day );

This function requires you to pass the addresses of guint variables, into which the result will be placed. Passing NULL as a value will result in the corresponding value not being returned.

The Calendar widget can generate a number of signals indicating date selection and change. The names of these signals are self explanatory, and are:

That just leaves us with the need to put all of this together into example code.

 
/* example-start calendar calendar.c */
/*
 * Copyright (C) 1998 Cesar Miquel, Shawn T. Amundson, Mattias Grönlund
 * Copyright (C) 2000 Tony Gale
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <gtk/gtk.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

#define DEF_PAD 10
#define DEF_PAD_SMALL 5

#define TM_YEAR_BASE 1900

typedef struct _CalendarData {
  GtkWidget *flag_checkboxes[5];
  gboolean  settings[5];
  gchar     *font;
  GtkWidget *font_dialog;
  GtkWidget *window;
  GtkWidget *prev2_sig;
  GtkWidget *prev_sig;
  GtkWidget *last_sig;
  GtkWidget *month;
} CalendarData;

enum {
  calendar_show_header,
  calendar_show_days,
  calendar_month_change, 
  calendar_show_week,
  calendar_monday_first
};

/*
 * GtkCalendar
 */

void calendar_date_to_string( CalendarData *data,
                              char         *buffer,
                              gint          buff_len )
{
  struct tm tm;
  time_t time;

  memset (&tm, 0, sizeof (tm));
  gtk_calendar_get_date (GTK_CALENDAR(data->window),
                         &tm.tm_year, &tm.tm_mon, &tm.tm_mday);
  tm.tm_year -= TM_YEAR_BASE;
  time = mktime(&tm);
  strftime (buffer, buff_len-1, "%x", gmtime(&time));
}

void calendar_set_signal_strings( char         *sig_str,
                                  CalendarData *data)
{
  gchar *prev_sig;

  gtk_label_get (GTK_LABEL (data->prev_sig), &prev_sig);
  gtk_label_set (GTK_LABEL (data->prev2_sig), prev_sig);

  gtk_label_get (GTK_LABEL (data->last_sig), &prev_sig);
  gtk_label_set (GTK_LABEL (data->prev_sig), prev_sig);
  gtk_label_set (GTK_LABEL (data->last_sig), sig_str);
}

void calendar_month_changed( GtkWidget    *widget,
                             CalendarData *data )
{
  char buffer[256] = "month_changed: ";

  calendar_date_to_string (data, buffer+15, 256-15);
  calendar_set_signal_strings (buffer, data);
}

void calendar_day_selected( GtkWidget    *widget,
                            CalendarData *data )
{
  char buffer[256] = "day_selected: ";

  calendar_date_to_string (data, buffer+14, 256-14);
  calendar_set_signal_strings (buffer, data);
}

void calendar_day_selected_double_click( GtkWidget    *widget,
                                         CalendarData *data )
{
  struct tm tm;
  char buffer[256] = "day_selected_double_click: ";

  calendar_date_to_string (data, buffer+27, 256-27);
  calendar_set_signal_strings (buffer, data);

  memset (&tm, 0, sizeof (tm));
  gtk_calendar_get_date (GTK_CALENDAR(data->window),
                         &tm.tm_year, &tm.tm_mon, &tm.tm_mday);
  tm.tm_year -= TM_YEAR_BASE;

  if(GTK_CALENDAR(data->window)->marked_date[tm.tm_mday-1] == 0) {
    gtk_calendar_mark_day(GTK_CALENDAR(data->window),tm.tm_mday);
  } else { 
    gtk_calendar_unmark_day(GTK_CALENDAR(data->window),tm.tm_mday);
  }
}

void calendar_prev_month( GtkWidget    *widget,
                            CalendarData *data )
{
  char buffer[256] = "prev_month: ";

  calendar_date_to_string (data, buffer+12, 256-12);
  calendar_set_signal_strings (buffer, data);
}

void calendar_next_month( GtkWidget    *widget,
                            CalendarData *data )
{
  char buffer[256] = "next_month: ";

  calendar_date_to_string (data, buffer+12, 256-12);
  calendar_set_signal_strings (buffer, data);
}

void calendar_prev_year( GtkWidget    *widget,
                            CalendarData *data )
{
  char buffer[256] = "prev_year: ";

  calendar_date_to_string (data, buffer+11, 256-11);
  calendar_set_signal_strings (buffer, data);
}

void calendar_next_year( GtkWidget    *widget,
                            CalendarData *data )
{
  char buffer[256] = "next_year: ";

  calendar_date_to_string (data, buffer+11, 256-11);
  calendar_set_signal_strings (buffer, data);
}


void calendar_set_flags( CalendarData *calendar )
{
  gint i;
  gint options=0;
  for (i=0;i<5;i++) 
    if (calendar->settings[i])
      {
        options=options + (1<<i);
      }
  if (calendar->window)
    gtk_calendar_display_options (GTK_CALENDAR (calendar->window), options);
}

void calendar_toggle_flag( GtkWidget    *toggle,
                           CalendarData *calendar )
{
  gint i;
  gint j;
  j=0;
  for (i=0; i<5; i++)
    if (calendar->flag_checkboxes[i] == toggle)
      j = i;

  calendar->settings[j]=!calendar->settings[j];
  calendar_set_flags(calendar);
  
}

void calendar_font_selection_ok( GtkWidget    *button,
                                 CalendarData *calendar )
{
  GtkStyle *style;
  GdkFont  *font;

  calendar->font = gtk_font_selection_dialog_get_font_name(
                        GTK_FONT_SELECTION_DIALOG (calendar->font_dialog));
  if (calendar->window)
    {
      font = gtk_font_selection_dialog_get_font(GTK_FONT_SELECTION_DIALOG(calendar->font_dialog));
      if (font) 
        {
          style = gtk_style_copy (gtk_widget_get_style (calendar->window));
          gdk_font_unref (style->font);
          style->font = font;
          gdk_font_ref (style->font);
          gtk_widget_set_style (calendar->window, style);
        }
    }
}

void calendar_select_font( GtkWidget    *button,
                           CalendarData *calendar )
{
  GtkWidget *window;

  if (!calendar->font_dialog) {
    window = gtk_font_selection_dialog_new ("Font Selection Dialog");
    g_return_if_fail(GTK_IS_FONT_SELECTION_DIALOG(window));
    calendar->font_dialog = window;
    
    gtk_window_position (GTK_WINDOW (window), GTK_WIN_POS_MOUSE);
    
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
                        GTK_SIGNAL_FUNC (gtk_widget_destroyed),
                        &calendar->font_dialog);
    
    gtk_signal_connect (GTK_OBJECT (GTK_FONT_SELECTION_DIALOG (window)->ok_button),
                        "clicked", GTK_SIGNAL_FUNC(calendar_font_selection_ok),
                        calendar);
    gtk_signal_connect_object (GTK_OBJECT (GTK_FONT_SELECTION_DIALOG (window)->cancel_button),
                               "clicked",
                               GTK_SIGNAL_FUNC (gtk_widget_destroy), 
                               GTK_OBJECT (calendar->font_dialog));
  }
  window=calendar->font_dialog;
  if (!GTK_WIDGET_VISIBLE (window))
    gtk_widget_show (window);
  else
    gtk_widget_destroy (window);

}

void create_calendar()
{
  GtkWidget *window;
  GtkWidget *vbox, *vbox2, *vbox3;
  GtkWidget *hbox;
  GtkWidget *hbbox;
  GtkWidget *calendar;
  GtkWidget *toggle;
  GtkWidget *button;
  GtkWidget *frame;
  GtkWidget *separator;
  GtkWidget *label;
  GtkWidget *bbox;
  static CalendarData calendar_data;
  gint i;
  
  struct {
    char *label;
  } flags[] =
    {
      { "Show Heading" },
      { "Show Day Names" },
      { "No Month Change" },
      { "Show Week Numbers" },
      { "Week Start Monday" }
    };

  
  calendar_data.window = NULL;
  calendar_data.font = NULL;
  calendar_data.font_dialog = NULL;

  for (i=0; i<5; i++) {
    calendar_data.settings[i]=0;
  }

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title(GTK_WINDOW(window), "GtkCalendar Example");
  gtk_container_border_width (GTK_CONTAINER (window), 5);
  gtk_signal_connect(GTK_OBJECT(window), "destroy",
                     GTK_SIGNAL_FUNC(gtk_main_quit),
                     NULL);
  gtk_signal_connect(GTK_OBJECT(window), "delete-event",
                     GTK_SIGNAL_FUNC(gtk_false),
                     NULL);

  gtk_window_set_policy(GTK_WINDOW(window), FALSE, FALSE, TRUE);

  vbox = gtk_vbox_new(FALSE, DEF_PAD);
  gtk_container_add (GTK_CONTAINER (window), vbox);

  /*
   * The top part of the window, Calendar, flags and fontsel.
   */

  hbox = gtk_hbox_new(FALSE, DEF_PAD);
  gtk_box_pack_start (GTK_BOX(vbox), hbox, TRUE, TRUE, DEF_PAD);
  hbbox = gtk_hbutton_box_new();
  gtk_box_pack_start(GTK_BOX(hbox), hbbox, FALSE, FALSE, DEF_PAD);
  gtk_button_box_set_layout(GTK_BUTTON_BOX(hbbox), GTK_BUTTONBOX_SPREAD);
  gtk_button_box_set_spacing(GTK_BUTTON_BOX(hbbox), 5);

  /* Calendar widget */
  frame = gtk_frame_new("Calendar");
  gtk_box_pack_start(GTK_BOX(hbbox), frame, FALSE, TRUE, DEF_PAD);
  calendar=gtk_calendar_new();
  calendar_data.window = calendar;
  calendar_set_flags(&calendar_data);
  gtk_calendar_mark_day ( GTK_CALENDAR(calendar), 19);  
  gtk_container_add( GTK_CONTAINER( frame), calendar);
  gtk_signal_connect (GTK_OBJECT (calendar), "month_changed", 
                      GTK_SIGNAL_FUNC (calendar_month_changed),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "day_selected", 
                      GTK_SIGNAL_FUNC (calendar_day_selected),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "day_selected_double_click", 
                      GTK_SIGNAL_FUNC (calendar_day_selected_double_click),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "prev_month", 
                      GTK_SIGNAL_FUNC (calendar_prev_month),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "next_month", 
                      GTK_SIGNAL_FUNC (calendar_next_month),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "prev_year", 
                      GTK_SIGNAL_FUNC (calendar_prev_year),
                      &calendar_data);
  gtk_signal_connect (GTK_OBJECT (calendar), "next_year", 
                      GTK_SIGNAL_FUNC (calendar_next_year),
                      &calendar_data);


  separator = gtk_vseparator_new ();
  gtk_box_pack_start (GTK_BOX (hbox), separator, FALSE, TRUE, 0);

  vbox2 = gtk_vbox_new(FALSE, DEF_PAD);
  gtk_box_pack_start(GTK_BOX(hbox), vbox2, FALSE, FALSE, DEF_PAD);
  
  /* Build the Right frame with the flags in */ 

  frame = gtk_frame_new("Flags");
  gtk_box_pack_start(GTK_BOX(vbox2), frame, TRUE, TRUE, DEF_PAD);
  vbox3 = gtk_vbox_new(TRUE, DEF_PAD_SMALL);
  gtk_container_add(GTK_CONTAINER(frame), vbox3);

  for (i = 0; i < 5; i++)
    {
      toggle = gtk_check_button_new_with_label(flags[i].label);
      gtk_signal_connect (GTK_OBJECT (toggle),
                            "toggled",
                            GTK_SIGNAL_FUNC(calendar_toggle_flag),
                            &calendar_data);
      gtk_box_pack_start (GTK_BOX (vbox3), toggle, TRUE, TRUE, 0);
      calendar_data.flag_checkboxes[i]=toggle;
    }
  /* Build the right font-button */ 
  button = gtk_button_new_with_label("Font...");
  gtk_signal_connect (GTK_OBJECT (button),
                      "clicked",
                      GTK_SIGNAL_FUNC(calendar_select_font),
                      &calendar_data);
  gtk_box_pack_start (GTK_BOX (vbox2), button, FALSE, FALSE, 0);

  /*
   *  Build the Signal-event part.
   */

  frame = gtk_frame_new("Signal events");
  gtk_box_pack_start(GTK_BOX(vbox), frame, TRUE, TRUE, DEF_PAD);

  vbox2 = gtk_vbox_new(TRUE, DEF_PAD_SMALL);
  gtk_container_add(GTK_CONTAINER(frame), vbox2);
  
  hbox = gtk_hbox_new (FALSE, 3);
  gtk_box_pack_start (GTK_BOX (vbox2), hbox, FALSE, TRUE, 0);
  label = gtk_label_new ("Signal:");
  gtk_box_pack_start (GTK_BOX (hbox), label, FALSE, TRUE, 0);
  calendar_data.last_sig = gtk_label_new ("");
  gtk_box_pack_start (GTK_BOX (hbox), calendar_data.last_sig, FALSE, TRUE, 0);

  hbox = gtk_hbox_new (FALSE, 3);
  gtk_box_pack_start (GTK_BOX (vbox2), hbox, FALSE, TRUE, 0);
  label = gtk_label_new ("Previous signal:");
  gtk_box_pack_start (GTK_BOX (hbox), label, FALSE, TRUE, 0);
  calendar_data.prev_sig = gtk_label_new ("");
  gtk_box_pack_start (GTK_BOX (hbox), calendar_data.prev_sig, FALSE, TRUE, 0);

  hbox = gtk_hbox_new (FALSE, 3);
  gtk_box_pack_start (GTK_BOX (vbox2), hbox, FALSE, TRUE, 0);
  label = gtk_label_new ("Second previous signal:");
  gtk_box_pack_start (GTK_BOX (hbox), label, FALSE, TRUE, 0);
  calendar_data.prev2_sig = gtk_label_new ("");
  gtk_box_pack_start (GTK_BOX (hbox), calendar_data.prev2_sig, FALSE, TRUE, 0);

  bbox = gtk_hbutton_box_new ();
  gtk_box_pack_start (GTK_BOX (vbox), bbox, FALSE, FALSE, 0);
  gtk_button_box_set_layout(GTK_BUTTON_BOX(bbox), GTK_BUTTONBOX_END);

  button = gtk_button_new_with_label ("Close");
  gtk_signal_connect (GTK_OBJECT (button), "clicked", 
                      GTK_SIGNAL_FUNC (gtk_main_quit), 
                      NULL);
  gtk_container_add (GTK_CONTAINER (bbox), button);
  GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT);
  gtk_widget_grab_default (button);

  gtk_widget_show_all(window);
}


int main(int   argc,
         char *argv[] )
{
  gtk_set_locale ();
  gtk_init (&argc, &argv);

  create_calendar();

  gtk_main();

  return(0);
}
/* example-end */

9.13 Color Selection

The color selection widget is, not surprisingly, a widget for interactive selection of colors. This composite widget lets the user select a color by manipulating RGB (Red, Green, Blue) and HSV (Hue, Saturation, Value) triples. This is done either by adjusting single values with sliders or entries, or by picking the desired color from a hue-saturation wheel/value bar. Optionally, the opacity of the color can also be set.

The color selection widget currently emits only one signal, "color_changed", which is emitted whenever the current color in the widget changes, either when the user changes it or if it's set explicitly through gtk_color_selection_set_color().

Lets have a look at what the color selection widget has to offer us. The widget comes in two flavours: gtk_color_selection and gtk_color_selection_dialog.

GtkWidget *gtk_color_selection_new( void );

You'll probably not be using this constructor directly. It creates an orphan ColorSelection widget which you'll have to parent yourself. The ColorSelection widget inherits from the VBox widget.

 
GtkWidget *gtk_color_selection_dialog_new( const gchar *title );

This is the most common color selection constructor. It creates a ColorSelectionDialog. It consists of a Frame containing a ColorSelection widget, an HSeparator and an HBox with three buttons, "Ok", "Cancel" and "Help". You can reach these buttons by accessing the "ok_button", "cancel_button" and "help_button" widgets in the ColorSelectionDialog structure, (i.e., GTK_COLOR_SELECTION_DIALOG(colorseldialog)->ok_button)).

void gtk_color_selection_set_update_policy( GtkColorSelection *colorsel, 
                                            GtkUpdateType      policy );

This function sets the update policy. The default policy is GTK_UPDATE_CONTINUOUS which means that the current color is updated continuously when the user drags the sliders or presses the mouse and drags in the hue-saturation wheel or value bar. If you experience performance problems, you may want to set the policy to GTK_UPDATE_DISCONTINUOUS or GTK_UPDATE_DELAYED.

void gtk_color_selection_set_opacity( GtkColorSelection *colorsel,
                                      gint               use_opacity );

The color selection widget supports adjusting the opacity of a color (also known as the alpha channel). This is disabled by default. Calling this function with use_opacity set to TRUE enables opacity. Likewise, use_opacity set to FALSE will disable opacity.

void gtk_color_selection_set_color( GtkColorSelection *colorsel,
                                    gdouble           *color );

You can set the current color explicitly by calling this function with a pointer to an array of colors (gdouble). The length of the array depends on whether opacity is enabled or not. Position 0 contains the red component, 1 is green, 2 is blue and opacity is at position 3 (only if opacity is enabled, see gtk_color_selection_set_opacity()). All values are between 0.0 and 1.0.

void gtk_color_selection_get_color( GtkColorSelection *colorsel,
                                    gdouble           *color );

When you need to query the current color, typically when you've received a "color_changed" signal, you use this function. Color is a pointer to the array of colors to fill in. See the gtk_color_selection_set_color() function for the description of this array.

Here's a simple example demonstrating the use of the ColorSelectionDialog. The program displays a window containing a drawing area. Clicking on it opens a color selection dialog, and changing the color in the color selection dialog changes the background color.

/* example-start colorsel colorsel.c */

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

GtkWidget *colorseldlg = NULL;
GtkWidget *drawingarea = NULL;

/* Color changed handler */

void color_changed_cb( GtkWidget         *widget,
                       GtkColorSelection *colorsel )
{
  gdouble color[3];
  GdkColor gdk_color;
  GdkColormap *colormap;

  /* Get drawingarea colormap */

  colormap = gdk_window_get_colormap (drawingarea->window);

  /* Get current color */

  gtk_color_selection_get_color (colorsel,color);

  /* Fit to a unsigned 16 bit integer (0..65535) and
   * insert into the GdkColor structure */

  gdk_color.red = (guint16)(color[0]*65535.0);
  gdk_color.green = (guint16)(color[1]*65535.0);
  gdk_color.blue = (guint16)(color[2]*65535.0);

  /* Allocate color */

  gdk_color_alloc (colormap, &gdk_color);

  /* Set window background color */

  gdk_window_set_background (drawingarea->window, &gdk_color);

  /* Clear window */

  gdk_window_clear (drawingarea->window);
}

/* Drawingarea event handler */

gint area_event( GtkWidget *widget,
                 GdkEvent  *event,
                 gpointer   client_data )
{
  gint handled = FALSE;
  GtkWidget *colorsel;

  /* Check if we've received a button pressed event */

  if (event->type == GDK_BUTTON_PRESS && colorseldlg == NULL)
    {
      /* Yes, we have an event and there's no colorseldlg yet! */

      handled = TRUE;

      /* Create color selection dialog */

      colorseldlg = gtk_color_selection_dialog_new("Select background color");

      /* Get the ColorSelection widget */

      colorsel = GTK_COLOR_SELECTION_DIALOG(colorseldlg)->colorsel;

      /* Connect to the "color_changed" signal, set the client-data
       * to the colorsel widget */

      gtk_signal_connect(GTK_OBJECT(colorsel), "color_changed",
        (GtkSignalFunc)color_changed_cb, (gpointer)colorsel);

      /* Show the dialog */

      gtk_widget_show(colorseldlg);
    }

  return handled;
}

/* Close down and exit handler */

gint destroy_window( GtkWidget *widget,
                     GdkEvent  *event,
                     gpointer   client_data )
{
  gtk_main_quit ();
  return(TRUE);
}

/* Main */

gint main( gint   argc,
           gchar *argv[] )
{
  GtkWidget *window;

  /* Initialize the toolkit, remove gtk-related commandline stuff */

  gtk_init (&argc,&argv);

  /* Create toplevel window, set title and policies */

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title (GTK_WINDOW(window), "Color selection test");
  gtk_window_set_policy (GTK_WINDOW(window), TRUE, TRUE, TRUE);

  /* Attach to the "delete" and "destroy" events so we can exit */

  gtk_signal_connect (GTK_OBJECT(window), "delete_event",
    (GtkSignalFunc)destroy_window, (gpointer)window);
  
  /* Create drawingarea, set size and catch button events */

  drawingarea = gtk_drawing_area_new ();

  gtk_drawing_area_size (GTK_DRAWING_AREA(drawingarea), 200, 200);

  gtk_widget_set_events (drawingarea, GDK_BUTTON_PRESS_MASK);

  gtk_signal_connect (GTK_OBJECT(drawingarea), "event", 
    (GtkSignalFunc)area_event, (gpointer)drawingarea);
  
  /* Add drawingarea to window, then show them both */

  gtk_container_add (GTK_CONTAINER(window), drawingarea);

  gtk_widget_show (drawingarea);
  gtk_widget_show (window);
  
  /* Enter the gtk main loop (this never returns) */

  gtk_main ();

  /* Satisfy grumpy compilers */

  return(0);
}
/* example-end */

9.14 File Selections

The file selection widget is a quick and simple way to display a File dialog box. It comes complete with Ok, Cancel, and Help buttons, a great way to cut down on programming time.

To create a new file selection box use:

GtkWidget *gtk_file_selection_new( gchar *title );

To set the filename, for example to bring up a specific directory, or give a default filename, use this function:

void gtk_file_selection_set_filename( GtkFileSelection *filesel,
                                      gchar            *filename );

To grab the text that the user has entered or clicked on, use this function:

gchar *gtk_file_selection_get_filename( GtkFileSelection *filesel );

There are also pointers to the widgets contained within the file selection widget. These are:

  dir_list
  file_list
  selection_entry
  selection_text
  main_vbox
  ok_button
  cancel_button
  help_button

Most likely you will want to use the ok_button, cancel_button, and help_button pointers in signaling their use.

Included here is an example stolen from testgtk.c, modified to run on its own. As you will see, there is nothing much to creating a file selection widget. While in this example the Help button appears on the screen, it does nothing as there is not a signal attached to it.

/* example-start filesel filesel.c */

#include <gtk/gtk.h>

/* Get the selected filename and print it to the console */
void file_ok_sel( GtkWidget        *w,
                  GtkFileSelection *fs )
{
    g_print ("%s\n", gtk_file_selection_get_filename (GTK_FILE_SELECTION (fs)));
}

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

int main( int   argc,
          char *argv[] )
{
    GtkWidget *filew;
    
    gtk_init (&argc, &argv);
    
    /* Create a new file selection widget */
    filew = gtk_file_selection_new ("File selection");
    
    gtk_signal_connect (GTK_OBJECT (filew), "destroy",
                        (GtkSignalFunc) destroy, &filew);
    /* Connect the ok_button to file_ok_sel function */
    gtk_signal_connect (GTK_OBJECT (GTK_FILE_SELECTION (filew)->ok_button),
                        "clicked", (GtkSignalFunc) file_ok_sel, filew );
    
    /* Connect the cancel_button to destroy the widget */
    gtk_signal_connect_object (GTK_OBJECT (GTK_FILE_SELECTION
                                            (filew)->cancel_button),
                               "clicked", (GtkSignalFunc) gtk_widget_destroy,
                               GTK_OBJECT (filew));
    
    /* Lets set the filename, as if this were a save dialog, and we are giving
     a default filename */
    gtk_file_selection_set_filename (GTK_FILE_SELECTION(filew), 
                                     "penguin.png");
    
    gtk_widget_show(filew);
    gtk_main ();
    return 0;
}
/* example-end */


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