void           gtk_dial_set_adjustment         (GtkDial      *dial,
                                                GtkAdjustment *adjustment);
#ifdef __cplusplus
}
#endif /* __cplusplus */


#endif /* __GTK_DIAL_H__ */
/* example-end */
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H3>gtkdial.c</H3>

<P>
<BLOCKQUOTE><CODE>
<PRE>
/* example-start gtkdial gtkdial.c */

/* GTK - The GIMP Toolkit
 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
#include &lt;math.h>
#include &lt;stdio.h>
#include &lt;gtk/gtkmain.h>
#include &lt;gtk/gtksignal.h>

#include "gtkdial.h"

#define SCROLL_DELAY_LENGTH  300
#define DIAL_DEFAULT_SIZE 100

/* Forward declarations */

static void gtk_dial_class_init               (GtkDialClass    *klass);
static void gtk_dial_init                     (GtkDial         *dial);
static void gtk_dial_destroy                  (GtkObject        *object);
static void gtk_dial_realize                  (GtkWidget        *widget);
static void gtk_dial_size_request             (GtkWidget      *widget,
                                               GtkRequisition *requisition);
static void gtk_dial_size_allocate            (GtkWidget     *widget,
                                               GtkAllocation *allocation);
static gint gtk_dial_expose                   (GtkWidget        *widget,
                                                GdkEventExpose   *event);
static gint gtk_dial_button_press             (GtkWidget        *widget,
                                                GdkEventButton   *event);
static gint gtk_dial_button_release           (GtkWidget        *widget,
                                                GdkEventButton   *event);
static gint gtk_dial_motion_notify            (GtkWidget        *widget,
                                                GdkEventMotion   *event);
static gint gtk_dial_timer                    (GtkDial         *dial);

static void gtk_dial_update_mouse             (GtkDial *dial, gint x, gint y);
static void gtk_dial_update                   (GtkDial *dial);
static void gtk_dial_adjustment_changed       (GtkAdjustment    *adjustment,
                                                gpointer          data);
static void gtk_dial_adjustment_value_changed (GtkAdjustment    *adjustment,
                                                gpointer          data);

/* Local data */

static GtkWidgetClass *parent_class = NULL;

guint
gtk_dial_get_type ()
{
  static guint dial_type = 0;

  if (!dial_type)
    {
      GtkTypeInfo dial_info =
      {
        "GtkDial",
        sizeof (GtkDial),
        sizeof (GtkDialClass),
        (GtkClassInitFunc) gtk_dial_class_init,
        (GtkObjectInitFunc) gtk_dial_init,
        (GtkArgSetFunc) NULL,
        (GtkArgGetFunc) NULL,
      };

      dial_type = gtk_type_unique (gtk_widget_get_type (), &amp;dial_info);
    }

  return dial_type;
}

static void
gtk_dial_class_init (GtkDialClass *class)
{
  GtkObjectClass *object_class;
  GtkWidgetClass *widget_class;

  object_class = (GtkObjectClass*) class;
  widget_class = (GtkWidgetClass*) class;

  parent_class = gtk_type_class (gtk_widget_get_type ());

  object_class->destroy = gtk_dial_destroy;

  widget_class->realize = gtk_dial_realize;
  widget_class->expose_event = gtk_dial_expose;
  widget_class->size_request = gtk_dial_size_request;
  widget_class->size_allocate = gtk_dial_size_allocate;
  widget_class->button_press_event = gtk_dial_button_press;
  widget_class->button_release_event = gtk_dial_button_release;
  widget_class->motion_notify_event = gtk_dial_motion_notify;
}

static void
gtk_dial_init (GtkDial *dial)
{
  dial->button = 0;
  dial->policy = GTK_UPDATE_CONTINUOUS;
  dial->timer = 0;
  dial->radius = 0;
  dial->pointer_width = 0;
  dial->angle = 0.0;
  dial->old_value = 0.0;
  dial->old_lower = 0.0;
  dial->old_upper = 0.0;
  dial->adjustment = NULL;
}

GtkWidget*
gtk_dial_new (GtkAdjustment *adjustment)
{
  GtkDial *dial;

  dial = gtk_type_new (gtk_dial_get_type ());

  if (!adjustment)
    adjustment = (GtkAdjustment*) gtk_adjustment_new (0.0, 0.0, 0.0, 0.0, 0.0, 0.0);

  gtk_dial_set_adjustment (dial, adjustment);

  return GTK_WIDGET (dial);
}

static void
gtk_dial_destroy (GtkObject *object)
{
  GtkDial *dial;

  g_return_if_fail (object != NULL);
  g_return_if_fail (GTK_IS_DIAL (object));

  dial = GTK_DIAL (object);

  if (dial->adjustment)
    gtk_object_unref (GTK_OBJECT (dial->adjustment));

  if (GTK_OBJECT_CLASS (parent_class)->destroy)
    (* GTK_OBJECT_CLASS (parent_class)->destroy) (object);
}

GtkAdjustment*
gtk_dial_get_adjustment (GtkDial *dial)
{
  g_return_val_if_fail (dial != NULL, NULL);
  g_return_val_if_fail (GTK_IS_DIAL (dial), NULL);

  return dial->adjustment;
}

void
gtk_dial_set_update_policy (GtkDial      *dial,
                             GtkUpdateType  policy)
{
  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  dial->policy = policy;
}

void
gtk_dial_set_adjustment (GtkDial      *dial,
                          GtkAdjustment *adjustment)
{
  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  if (dial->adjustment)
    {
      gtk_signal_disconnect_by_data (GTK_OBJECT (dial->adjustment), (gpointer) dial);
      gtk_object_unref (GTK_OBJECT (dial->adjustment));
    }

  dial->adjustment = adjustment;
  gtk_object_ref (GTK_OBJECT (dial->adjustment));

  gtk_signal_connect (GTK_OBJECT (adjustment), "changed",
                      (GtkSignalFunc) gtk_dial_adjustment_changed,
                      (gpointer) dial);
  gtk_signal_connect (GTK_OBJECT (adjustment), "value_changed",
                      (GtkSignalFunc) gtk_dial_adjustment_value_changed,
                      (gpointer) dial);

  dial->old_value = adjustment->value;
  dial->old_lower = adjustment->lower;
  dial->old_upper = adjustment->upper;

  gtk_dial_update (dial);
}

static void
gtk_dial_realize (GtkWidget *widget)
{
  GtkDial *dial;
  GdkWindowAttr attributes;
  gint attributes_mask;

  g_return_if_fail (widget != NULL);
  g_return_if_fail (GTK_IS_DIAL (widget));

  GTK_WIDGET_SET_FLAGS (widget, GTK_REALIZED);
  dial = GTK_DIAL (widget);

  attributes.x = widget->allocation.x;
  attributes.y = widget->allocation.y;
  attributes.width = widget->allocation.width;
  attributes.height = widget->allocation.height;
  attributes.wclass = GDK_INPUT_OUTPUT;
  attributes.window_type = GDK_WINDOW_CHILD;
  attributes.event_mask = gtk_widget_get_events (widget) | 
    GDK_EXPOSURE_MASK | GDK_BUTTON_PRESS_MASK | 
    GDK_BUTTON_RELEASE_MASK | GDK_POINTER_MOTION_MASK |
    GDK_POINTER_MOTION_HINT_MASK;
  attributes.visual = gtk_widget_get_visual (widget);
  attributes.colormap = gtk_widget_get_colormap (widget);

  attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_COLORMAP;
  widget->window = gdk_window_new (widget->parent->window, &amp;attributes, attributes_mask);

  widget->style = gtk_style_attach (widget->style, widget->window);

  gdk_window_set_user_data (widget->window, widget);

  gtk_style_set_background (widget->style, widget->window, GTK_STATE_ACTIVE);
}

static void 
gtk_dial_size_request (GtkWidget      *widget,
                       GtkRequisition *requisition)
{
  requisition->width = DIAL_DEFAULT_SIZE;
  requisition->height = DIAL_DEFAULT_SIZE;
}

static void
gtk_dial_size_allocate (GtkWidget     *widget,
                        GtkAllocation *allocation)
{
  GtkDial *dial;

  g_return_if_fail (widget != NULL);
  g_return_if_fail (GTK_IS_DIAL (widget));
  g_return_if_fail (allocation != NULL);

  widget->allocation = *allocation;
  dial = GTK_DIAL (widget);

  if (GTK_WIDGET_REALIZED (widget))
    {

      gdk_window_move_resize (widget->window,
                              allocation->x, allocation->y,
                              allocation->width, allocation->height);

    }
  dial->radius = MIN(allocation->width,allocation->height) * 0.45;
  dial->pointer_width = dial->radius / 5;
}

static gint
gtk_dial_expose (GtkWidget      *widget,
                 GdkEventExpose *event)
{
  GtkDial *dial;
  GdkPoint points[6];
  gdouble s,c;
  gdouble theta, last, increment;
  GtkStyle      *blankstyle;
  gint xc, yc;
  gint upper, lower;
  gint tick_length;
  gint i, inc;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  if (event->count > 0)
    return FALSE;
  
  dial = GTK_DIAL (widget);

/*  gdk_window_clear_area (widget->window,
                         0, 0,
                         widget->allocation.width,
                         widget->allocation.height);
*/
  xc = widget->allocation.width/2;
  yc = widget->allocation.height/2;

  upper = dial->adjustment->upper;
  lower = dial->adjustment->lower;

  /* Erase old pointer */

  s = sin(dial->last_angle);
  c = cos(dial->last_angle);
  dial->last_angle = dial->angle;

  points[0].x = xc + s*dial->pointer_width/2;
  points[0].y = yc + c*dial->pointer_width/2;
  points[1].x = xc + c*dial->radius;
  points[1].y = yc - s*dial->radius;
  points[2].x = xc - s*dial->pointer_width/2;
  points[2].y = yc - c*dial->pointer_width/2;
  points[3].x = xc - c*dial->radius/10;
  points[3].y = yc + s*dial->radius/10;
  points[4].x = points[0].x;
  points[4].y = points[0].y;

  blankstyle = gtk_style_new ();
  blankstyle->bg_gc[GTK_STATE_NORMAL] =
                widget->style->bg_gc[GTK_STATE_NORMAL];
  blankstyle->dark_gc[GTK_STATE_NORMAL] =
                widget->style->bg_gc[GTK_STATE_NORMAL];
  blankstyle->light_gc[GTK_STATE_NORMAL] =
                widget->style->bg_gc[GTK_STATE_NORMAL];
  blankstyle->black_gc =
                widget->style->bg_gc[GTK_STATE_NORMAL];

  gtk_draw_polygon (blankstyle,
                    widget->window,
                    GTK_STATE_NORMAL,
                    GTK_SHADOW_OUT,
                    points, 5,
                    FALSE);

  gtk_style_unref(blankstyle);


  /* Draw ticks */

  if ((upper - lower) == 0)
    return;

  increment = (100*M_PI)/(dial->radius*dial->radius);

  inc = (upper - lower);

  while (inc &lt; 100) inc *=10;
  while (inc >= 1000) inc /=10;
  last = -1;

  for (i=0; i&lt;=inc; i++)
    {
      theta = ((gfloat)i*M_PI/(18*inc/24.) - M_PI/6.);

      if ((theta - last) &lt; (increment))
        continue;     
      last = theta;

      s = sin(theta);
      c = cos(theta);

      tick_length = (i%(inc/10) == 0) ? dial->pointer_width : dial->pointer_width/2;

      gdk_draw_line (widget->window,
                     widget->style->fg_gc[widget->state],
                     xc + c*(dial->radius - tick_length),
                     yc - s*(dial->radius - tick_length),
                     xc + c*dial->radius,
                     yc - s*dial->radius);
    }

  /* Draw pointer */

  s = sin(dial->angle);
  c = cos(dial->angle);
  dial->last_angle = dial->angle;

  points[0].x = xc + s*dial->pointer_width/2;
  points[0].y = yc + c*dial->pointer_width/2;
  points[1].x = xc + c*dial->radius;
  points[1].y = yc - s*dial->radius;
  points[2].x = xc - s*dial->pointer_width/2;
  points[2].y = yc - c*dial->pointer_width/2;
  points[3].x = xc - c*dial->radius/10;
  points[3].y = yc + s*dial->radius/10;