GTK+ 2.0 Tutorial
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# 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 height and a horizontal ruler spanning down the width. 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 be `GTK_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,
                              gdouble   lower,
                              gdouble   upper,
                              gdouble   position,
                              gdouble   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_GET_CLASS(i)->x

        g_signal_connect_swapped (area, "motion_notify_event",
               G_CALLBACK (EVENT_METHOD (ruler, motion_notify_event)),
               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.

    #include <gtk/gtk.h>

    #define EVENT_METHOD(i, x) GTK_WIDGET_GET_CLASS(i)->x

    #define XSIZE  600
    #define YSIZE  400

    /* This routine gets control when the close button is clicked */
    static gboolean 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);
        g_signal_connect (window, "delete-event",
                          G_CALLBACK (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_widget_set_size_request (GTK_WIDGET (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);
        g_signal_connect_swapped (area, "motion_notify_event",
                                  G_CALLBACK (EVENT_METHOD (hrule, motion_notify_event)),
                                  hrule);
        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 );
        g_signal_connect_swapped (area, "motion_notify_event",
                                  G_CALLBACK (EVENT_METHOD (vrule, motion_notify_event)),
                                  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;
    }

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