path: root/libgnomecanvas/gnome-canvas.c

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: 8; c-basic-offset: 8 -*- */
/*
 * Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation
 * All rights reserved.
 *
 * This file is part of the Gnome Library.
 *
 * The Gnome 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.
 *
 * The Gnome 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 the Gnome Library; see the file COPYING.LIB.  If not,
 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
/*
  @NOTATION@
 */
/*
 * GnomeCanvas widget - Tk-like canvas widget for Gnome
 *
 * GnomeCanvas is basically a port of the Tk toolkit's most excellent canvas
 * widget.  Tk is copyrighted by the Regents of the University of California,
 * Sun Microsystems, and other parties.
 *
 *
 * Authors: Federico Mena <federico@nuclecu.unam.mx>
 *          Raph Levien <raph@gimp.org>
 */

/*
 * TO-DO list for the canvas:
 *
 * - Allow to specify whether GnomeCanvasImage sizes are in units or pixels
 *   (scale or don't scale).
 *
 * - Implement a flag for gnome_canvas_item_reparent() that tells the function
 *   to keep the item visually in the same place, that is, to keep it in the
 *   same place with respect to the canvas origin.
 *
 * - GC put functions for items.
 *
 * - Widget item (finish it).
 *
 * - GList *
 *   gnome_canvas_gimme_all_items_contained_in_this_area (GnomeCanvas *canvas,
 *                                                        Rectangle area);
 *
 * - Retrofit all the primitive items with microtile support.
 *
 * - Curve support for line item.
 *
 * - Arc item (Havoc has it; to be integrated in GnomeCanvasEllipse).
 *
 * - Sane font handling API.
 *
 * - Get_arg methods for items:
 *   - How to fetch the outline width and know whether it is in pixels or units?
 */

/*
 * Raph's TODO list for the antialiased canvas integration:
 *
 * - ::point() method for text item not accurate when affine transformed.
 *
 * - Clip rectangle not implemented in aa renderer for text item.
 *
 * - Clip paths only partially implemented.
 *
 * - Add more image loading techniques to work around imlib deficiencies.
 */

#include <config.h>

#include <math.h>
#include <string.h>
#include <stdio.h>
#include <gdk/gdkprivate.h>
#include <gtk/gtk.h>
#include "gailcanvas.h"
#include "gnome-canvas.h"
#include "gnome-canvas-i18n.h"
#include <libart_lgpl/art_rect.h>
#include <libart_lgpl/art_rect_uta.h>
#include <libart_lgpl/art_uta_rect.h>

#include "gnome-canvas-marshal.h"
#include "gnome-canvas-marshal.c"

#include "e-util/gtk-compat.h"

/* We must run our idle update handler *before* GDK wants to redraw. */
#define CANVAS_IDLE_PRIORITY (GDK_PRIORITY_REDRAW - 5)

static void gnome_canvas_request_update (GnomeCanvas      *canvas);
static void group_add                   (GnomeCanvasGroup *group,
                     GnomeCanvasItem  *item);
static void group_remove                (GnomeCanvasGroup *group,
                     GnomeCanvasItem  *item);
static void add_idle                    (GnomeCanvas      *canvas);

/*** GnomeCanvasItem ***/

/* Some convenience stuff */
#define GCI_UPDATE_MASK \
    (GNOME_CANVAS_UPDATE_REQUESTED | \
     GNOME_CANVAS_UPDATE_AFFINE | \
     GNOME_CANVAS_UPDATE_CLIP | \
     GNOME_CANVAS_UPDATE_VISIBILITY)
#define GCI_EPSILON 1e-18
#define GCI_PRINT_MATRIX(s,a) \
    g_print ("%s %g %g %g %g %g %g\n", \
    s, (a)[0], (a)[1], (a)[2], (a)[3], (a)[4], (a)[5])

enum {
    ITEM_PROP_0,
    ITEM_PROP_PARENT
};

enum {
    ITEM_EVENT,
    ITEM_LAST_SIGNAL
};

static void gnome_canvas_item_class_init     (GnomeCanvasItemClass *class);
static void gnome_canvas_item_init           (GnomeCanvasItem      *item);
static gint  emit_event                       (GnomeCanvas *canvas, GdkEvent *event);

static guint item_signals[ITEM_LAST_SIGNAL];

static GtkObjectClass *item_parent_class;

/**
 * gnome_canvas_item_get_type:
 *
 * Registers the &GnomeCanvasItem class if necessary, and returns the type ID
 * associated to it.
 *
 * Return value:  The type ID of the &GnomeCanvasItem class.
 **/
GType
gnome_canvas_item_get_type (void)
{
    static GType canvas_item_type;

    if (!canvas_item_type) {
        const GTypeInfo object_info = {
            sizeof (GnomeCanvasItemClass),
            (GBaseInitFunc) NULL,
            (GBaseFinalizeFunc) NULL,
            (GClassInitFunc) gnome_canvas_item_class_init,
            (GClassFinalizeFunc) NULL,
            NULL,           /* class_data */
            sizeof (GnomeCanvasItem),
            0,          /* n_preallocs */
            (GInstanceInitFunc) gnome_canvas_item_init,
            NULL            /* value_table */
        };

        canvas_item_type = g_type_register_static (GTK_TYPE_OBJECT, "GnomeCanvasItem",
                               &object_info, 0);
    }

    return canvas_item_type;
}

/* Object initialization function for GnomeCanvasItem */
static void
gnome_canvas_item_init (GnomeCanvasItem *item)
{
    item->flags |= GNOME_CANVAS_ITEM_VISIBLE;
}

/**
 * gnome_canvas_item_new:
 * @parent: The parent group for the new item.
 * @type: The object type of the item.
 * @first_arg_name: A list of object argument name/value pairs, NULL-terminated,
 * used to configure the item.  For example, "fill_color", "black",
 * "width_units", 5.0, NULL.
 * @Varargs:
 *
 * Creates a new canvas item with @parent as its parent group.  The item is
 * created at the top of its parent's stack, and starts up as visible.  The item
 * is of the specified @type, for example, it can be
 * gnome_canvas_rect_get_type().  The list of object arguments/value pairs is
 * used to configure the item. If you need to pass construct time parameters, you
 * should use g_object_new() to pass the parameters and
 * gnome_canvas_item_construct() to set up the canvas item.
 *
 * Return value: The newly-created item.
 **/
GnomeCanvasItem *
gnome_canvas_item_new (GnomeCanvasGroup *parent,
                       GType type,
                       const gchar *first_arg_name, ...)
{
    GnomeCanvasItem *item;
    va_list args;

    g_return_val_if_fail (GNOME_IS_CANVAS_GROUP (parent), NULL);
    g_return_val_if_fail (g_type_is_a (type, gnome_canvas_item_get_type ()), NULL);

    item = GNOME_CANVAS_ITEM (g_object_new (type, NULL));

    va_start (args, first_arg_name);
    gnome_canvas_item_construct (item, parent, first_arg_name, args);
    va_end (args);

    return item;
}

/* Performs post-creation operations on a canvas item (adding it to its parent
 * group, etc.)
 */
static void
item_post_create_setup (GnomeCanvasItem *item)
{
    group_add (GNOME_CANVAS_GROUP (item->parent), item);

    gnome_canvas_request_redraw (
        item->canvas, item->x1, item->y1, item->x2 + 1, item->y2 + 1);
    item->canvas->need_repick = TRUE;
}

/* Set_property handler for canvas items */
static void
gnome_canvas_item_set_property (GObject *gobject, guint param_id,
                const GValue *value, GParamSpec *pspec)
{
    GnomeCanvasItem *item;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (param_id) {
    case ITEM_PROP_PARENT:
        if (item->parent != NULL) {
            g_warning ("Cannot set `parent' argument after item has "
                   "already been constructed.");
        } else if (g_value_get_object (value)) {
            item->parent = GNOME_CANVAS_ITEM (g_value_get_object (value));
            item->canvas = item->parent->canvas;
            item_post_create_setup (item);
        }
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, param_id, pspec);
        break;
    }
}

/* Get_property handler for canvas items */
static void
gnome_canvas_item_get_property (GObject *gobject, guint param_id,
                GValue *value, GParamSpec *pspec)
{
    GnomeCanvasItem *item;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (param_id) {
    case ITEM_PROP_PARENT:
        g_value_set_object (value, item->parent);
        break;

    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, param_id, pspec);
        break;
    }
}

/**
 * gnome_canvas_item_construct:
 * @item: An unconstructed canvas item.
 * @parent: The parent group for the item.
 * @first_arg_name: The name of the first argument for configuring the item.
 * @args: The list of arguments used to configure the item.
 *
 * Constructs a canvas item; meant for use only by item implementations.
 **/
void
gnome_canvas_item_construct (GnomeCanvasItem *item, GnomeCanvasGroup *parent,
                 const gchar *first_arg_name, va_list args)
{
    g_return_if_fail (GNOME_IS_CANVAS_GROUP (parent));
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    item->parent = GNOME_CANVAS_ITEM (parent);
    item->canvas = item->parent->canvas;

    g_object_set_valist (G_OBJECT (item), first_arg_name, args);

    item_post_create_setup (item);
}

/* If the item is visible, requests a redraw of it. */
static void
redraw_if_visible (GnomeCanvasItem *item)
{
    if (item->flags & GNOME_CANVAS_ITEM_VISIBLE)
        gnome_canvas_request_redraw (
            item->canvas, item->x1, item->y1,
            item->x2 + 1, item->y2 + 1);
}

/* Standard object dispose function for canvas items */
static void
gnome_canvas_item_dispose (GObject *object)
{
    GnomeCanvasItem *item;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (object));

    item = GNOME_CANVAS_ITEM (object);

    if (item->canvas)
        redraw_if_visible (item);

    /* Make the canvas forget about us */

    if (item->canvas && item == item->canvas->current_item) {
        item->canvas->current_item = NULL;
        item->canvas->need_repick = TRUE;
    }

    if (item->canvas && item == item->canvas->new_current_item) {
        item->canvas->new_current_item = NULL;
        item->canvas->need_repick = TRUE;
    }

    if (item->canvas && item == item->canvas->grabbed_item) {
        item->canvas->grabbed_item = NULL;
        gdk_pointer_ungrab (GDK_CURRENT_TIME);
    }

    if (item->canvas && item == item->canvas->focused_item)
        item->canvas->focused_item = NULL;

    /* Normal destroy stuff */

    if (item->flags & GNOME_CANVAS_ITEM_MAPPED)
        (* GNOME_CANVAS_ITEM_GET_CLASS (item)->unmap) (item);

    if (item->flags & GNOME_CANVAS_ITEM_REALIZED)
        (* GNOME_CANVAS_ITEM_GET_CLASS (item)->unrealize) (item);

    if (item->parent)
        group_remove (GNOME_CANVAS_GROUP (item->parent), item);

    g_free (item->xform);
    item->xform = NULL;

    G_OBJECT_CLASS (item_parent_class)->dispose (object);
    /* items should remove any reference to item->canvas after the
       first ::destroy */
    item->canvas = NULL;
}

/* Realize handler for canvas items */
static void
gnome_canvas_item_realize (GnomeCanvasItem *item)
{
    item->flags |= GNOME_CANVAS_ITEM_REALIZED;

    gnome_canvas_item_request_update (item);
}

/* Unrealize handler for canvas items */
static void
gnome_canvas_item_unrealize (GnomeCanvasItem *item)
{
    item->flags &= ~GNOME_CANVAS_ITEM_REALIZED;
}

/* Map handler for canvas items */
static void
gnome_canvas_item_map (GnomeCanvasItem *item)
{
    item->flags |= GNOME_CANVAS_ITEM_MAPPED;
}

/* Unmap handler for canvas items */
static void
gnome_canvas_item_unmap (GnomeCanvasItem *item)
{
    item->flags &= ~GNOME_CANVAS_ITEM_MAPPED;
}

/* Update handler for canvas items */
static void
gnome_canvas_item_update (GnomeCanvasItem *item,
                          gdouble *affine,
                          ArtSVP *clip_path,
                          gint flags)
{
    item->flags &= ~GNOME_CANVAS_ITEM_NEED_UPDATE;
    item->flags &= ~GNOME_CANVAS_ITEM_NEED_AFFINE;
    item->flags &= ~GNOME_CANVAS_ITEM_NEED_CLIP;
    item->flags &= ~GNOME_CANVAS_ITEM_NEED_VIS;
}

#define noHACKISH_AFFINE

/*
 * This routine invokes the update method of the item
 * Please notice, that we take parent to canvas pixel matrix as argument
 * unlike virtual method ::update, whose argument is item 2 canvas pixel
 * matrix
 *
 * I will try to force somewhat meaningful naming for affines (Lauris)
 * General naming rule is FROM2TO, where FROM and TO are abbreviations
 * So p2cpx is Parent2CanvasPixel and i2cpx is Item2CanvasPixel
 * I hope that this helps to keep track of what really happens
 *
 */

static void
gnome_canvas_item_invoke_update (GnomeCanvasItem *item,
                                 gdouble *p2cpx,
                                 ArtSVP *clip_path,
                                 gint flags)
{
    gint child_flags;
    gdouble i2cpx[6];

#ifdef HACKISH_AFFINE
    gdouble i2w[6], w2c[6], i2c[6];
#endif

    child_flags = flags;
    if (!(item->flags & GNOME_CANVAS_ITEM_VISIBLE))
        child_flags &= ~GNOME_CANVAS_UPDATE_IS_VISIBLE;

    /* Calculate actual item transformation matrix */

    if (item->xform) {
        if (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL) {
            /* Item has full affine */
            art_affine_multiply (i2cpx, item->xform, p2cpx);
        } else {
            /* Item has only translation */
            memcpy (i2cpx, p2cpx, 4 * sizeof (gdouble));
            i2cpx[4] = item->xform[0] * p2cpx[0] + item->xform[1] * p2cpx[2] + p2cpx[4];
            i2cpx[5] = item->xform[0] * p2cpx[1] + item->xform[1] * p2cpx[3] + p2cpx[5];
        }
    } else {
        /* Item has no matrix (i.e. identity) */
        memcpy (i2cpx, p2cpx, 6 * sizeof (gdouble));
    }

#ifdef HACKISH_AFFINE
    gnome_canvas_item_i2w_affine (item, i2w);
    gnome_canvas_w2c_affine (item->canvas, w2c);
    art_affine_multiply (i2c, i2w, w2c);
    /* invariant (doesn't hold now): child_affine == i2c */
    child_affine = i2c;
#endif

    /* apply object flags to child flags */

    child_flags &= ~GNOME_CANVAS_UPDATE_REQUESTED;

    if (item->flags & GNOME_CANVAS_ITEM_NEED_UPDATE)
        child_flags |= GNOME_CANVAS_UPDATE_REQUESTED;

    if (item->flags & GNOME_CANVAS_ITEM_NEED_AFFINE)
        child_flags |= GNOME_CANVAS_UPDATE_AFFINE;

    if (item->flags & GNOME_CANVAS_ITEM_NEED_CLIP)
        child_flags |= GNOME_CANVAS_UPDATE_CLIP;

    if (item->flags & GNOME_CANVAS_ITEM_NEED_VIS)
        child_flags |= GNOME_CANVAS_UPDATE_VISIBILITY;

    if (child_flags & GCI_UPDATE_MASK) {
        if (GNOME_CANVAS_ITEM_GET_CLASS (item)->update)
            GNOME_CANVAS_ITEM_GET_CLASS (item)->update (item, i2cpx, clip_path, child_flags);
    }
}

/*
 * This routine invokes the point method of the item.
 * The arguments x, y should be in the parent item local coordinates.
 *
 * This is potentially evil, as we are relying on matrix inversion (Lauris)
 */

static double
gnome_canvas_item_invoke_point (GnomeCanvasItem *item,
                                gdouble x,
                                gdouble y,
                                gint cx,
                                gint cy,
                                GnomeCanvasItem **actual_item)
{
    /* Calculate x & y in item local coordinates */

    if (item->xform) {
        if (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL) {
            gdouble p2i[6], t;
            /* Item has full affine */
            art_affine_invert (p2i, item->xform);
            t = x * p2i[0] + y * p2i[2] + p2i[4];
            y = x * p2i[1] + y * p2i[3] + p2i[5];
            x = t;
        } else {
            /* Item has only translation */
            x -= item->xform[0];
            y -= item->xform[1];
        }
    }

#ifdef HACKISH_AFFINE
    gdouble i2w[6], w2c[6], i2c[6], c2i[6];
    ArtPoint c, i;
#endif

#ifdef HACKISH_AFFINE
    gnome_canvas_item_i2w_affine (item, i2w);
    gnome_canvas_w2c_affine (item->canvas, w2c);
    art_affine_multiply (i2c, i2w, w2c);
    art_affine_invert (c2i, i2c);
    c.x = cx;
    c.y = cy;
    art_affine_point (&i, &c, c2i);
    x = i.x;
    y = i.y;
#endif

    if (GNOME_CANVAS_ITEM_GET_CLASS (item)->point)
        return GNOME_CANVAS_ITEM_GET_CLASS (item)->point (item, x, y, cx, cy, actual_item);

    return 1e18;
}

/**
 * gnome_canvas_item_set:
 * @item: A canvas item.
 * @first_arg_name: The list of object argument name/value pairs used to
 *                  configure the item.
 * @Varargs:
 *
 * Configures a canvas item.  The arguments in the item are set to the
 * specified values, and the item is repainted as appropriate.
 **/
void
gnome_canvas_item_set (GnomeCanvasItem *item, const gchar *first_arg_name, ...)
{
    va_list args;

    va_start (args, first_arg_name);
    gnome_canvas_item_set_valist (item, first_arg_name, args);
    va_end (args);
}

/**
 * gnome_canvas_item_set_valist:
 * @item: A canvas item.
 * @first_arg_name: The name of the first argument used to configure the item.
 * @args: The list of object argument name/value pairs used to configure the item.
 *
 * Configures a canvas item.  The arguments in the item are set to the specified
 * values, and the item is repainted as appropriate.
 **/
void
gnome_canvas_item_set_valist (GnomeCanvasItem *item,
                              const gchar *first_arg_name,
                              va_list args)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    g_object_set_valist (G_OBJECT (item), first_arg_name, args);

    item->canvas->need_repick = TRUE;
}

/**
 * gnome_canvas_item_affine_relative:
 * @item: A canvas item.
 * @affine: An affine transformation matrix.
 *
 * Combines the specified affine transformation matrix with the item's current
 * transformation. NULL affine is not allowed.
 **/
#define GCIAR_EPSILON 1e-6
void
gnome_canvas_item_affine_relative (GnomeCanvasItem *item, const gdouble affine[6])
{
    gdouble i2p[6];

    g_return_if_fail (item != NULL);
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (affine != NULL);

    /* Calculate actual item transformation matrix */

    if (item->xform) {
        if (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL) {
            /* Item has full affine */
            art_affine_multiply (i2p, affine, item->xform);
        } else {
            /* Item has only translation */
            memcpy (i2p, affine, 6 * sizeof (gdouble));
            i2p[4] += item->xform[0];
            i2p[5] += item->xform[1];
        }
    } else {
        /* Item has no matrix (i.e. identity) */
        memcpy (i2p, affine, 6 * sizeof (gdouble));
    }

    gnome_canvas_item_affine_absolute (item, i2p);
}

/**
 * gnome_canvas_item_affine_absolute:
 * @item: A canvas item.
 * @affine: An affine transformation matrix.
 *
 * Makes the item's affine transformation matrix be equal to the specified
 * matrix. NULL affine is treated as identity.
 **/
void
gnome_canvas_item_affine_absolute (GnomeCanvasItem *item, const gdouble i2p[6])
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (i2p &&
        (fabs (i2p[0] - 1.0) < GCI_EPSILON) &&
        (fabs (i2p[1] - 0.0) < GCI_EPSILON) &&
        (fabs (i2p[2] - 0.0) < GCI_EPSILON) &&
        (fabs (i2p[3] - 1.0) < GCI_EPSILON) &&
        (fabs (i2p[4] - 0.0) < GCI_EPSILON) &&
        (fabs (i2p[5] - 0.0) < GCI_EPSILON)) {
        /* We are identity */
        i2p = NULL;
    }

    if (i2p) {
        if (item->xform && !(item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL)) {
            /* We do not want to deal with translation-only affines */
            g_free (item->xform);
            item->xform = NULL;
        }
        if (!item->xform) item->xform = g_new (gdouble, 6);
        memcpy (item->xform, i2p, 6 * sizeof (gdouble));
        item->flags |= GNOME_CANVAS_ITEM_AFFINE_FULL;
    } else {
        if (item->xform) {
            g_free (item->xform);
            item->xform = NULL;
        }
    }

    if (!(item->flags & GNOME_CANVAS_ITEM_NEED_AFFINE)) {
        /* Request update */
        item->flags |= GNOME_CANVAS_ITEM_NEED_AFFINE;
        gnome_canvas_item_request_update (item);
    }

    item->canvas->need_repick = TRUE;
}

/**
 * gnome_canvas_item_move:
 * @item: A canvas item.
 * @dx: Horizontal offset.
 * @dy: Vertical offset.
 *
 * Moves a canvas item by creating an affine transformation matrix for
 * translation by using the specified values. This happens in item
 * local coordinate system, so if you have nontrivial transform, it
 * most probably does not do, what you want.
 **/
void
gnome_canvas_item_move (GnomeCanvasItem *item, gdouble dx, gdouble dy)
{
    gdouble translate[6];

    g_return_if_fail (item != NULL);
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    art_affine_translate (translate, dx, dy);

    gnome_canvas_item_affine_relative (item, translate);
}

/* Convenience function to reorder items in a group's child list.  This puts the
 * specified link after the "before" link. Returns TRUE if the list was changed.
 */
static gboolean
put_item_after (GList *link, GList *before)
{
    GnomeCanvasGroup *parent;
    GList *old_before, *old_after;
    GList *after;

    parent = GNOME_CANVAS_GROUP (GNOME_CANVAS_ITEM (link->data)->parent);

    if (before)
        after = before->next;
    else
        after = parent->item_list;

    if (before == link || after == link)
        return FALSE;

    /* Unlink */

    old_before = link->prev;
    old_after = link->next;

    if (old_before)
        old_before->next = old_after;
    else
        parent->item_list = old_after;

    if (old_after)
        old_after->prev = old_before;
    else
        parent->item_list_end = old_before;

    /* Relink */

    link->prev = before;
    if (before)
        before->next = link;
    else
        parent->item_list = link;

    link->next = after;
    if (after)
        after->prev = link;
    else
        parent->item_list_end = link;

    return TRUE;
}

/**
 * gnome_canvas_item_raise:
 * @item: A canvas item.
 * @positions: Number of steps to raise the item.
 *
 * Raises the item in its parent's stack by the specified number of positions.
 * If the number of positions is greater than the distance to the top of the
 * stack, then the item is put at the top.
 **/
void
gnome_canvas_item_raise (GnomeCanvasItem *item, gint positions)
{
    GList *link, *before;
    GnomeCanvasGroup *parent;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (positions >= 0);

    if (!item->parent || positions == 0)
        return;

    parent = GNOME_CANVAS_GROUP (item->parent);
    link = g_list_find (parent->item_list, item);
    g_assert (link != NULL);

    for (before = link; positions && before; positions--)
        before = before->next;

    if (!before)
        before = parent->item_list_end;

    if (put_item_after (link, before)) {
        redraw_if_visible (item);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_lower:
 * @item: A canvas item.
 * @positions: Number of steps to lower the item.
 *
 * Lowers the item in its parent's stack by the specified number of positions.
 * If the number of positions is greater than the distance to the bottom of the
 * stack, then the item is put at the bottom.
 **/
void
gnome_canvas_item_lower (GnomeCanvasItem *item, gint positions)
{
    GList *link, *before;
    GnomeCanvasGroup *parent;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (positions >= 1);

    if (!item->parent || positions == 0)
        return;

    parent = GNOME_CANVAS_GROUP (item->parent);
    link = g_list_find (parent->item_list, item);
    g_assert (link != NULL);

    if (link->prev)
        for (before = link->prev; positions && before; positions--)
            before = before->prev;
    else
        before = NULL;

    if (put_item_after (link, before)) {
        redraw_if_visible (item);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_raise_to_top:
 * @item: A canvas item.
 *
 * Raises an item to the top of its parent's stack.
 **/
void
gnome_canvas_item_raise_to_top (GnomeCanvasItem *item)
{
    GList *link;
    GnomeCanvasGroup *parent;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (!item->parent)
        return;

    parent = GNOME_CANVAS_GROUP (item->parent);
    link = g_list_find (parent->item_list, item);
    g_assert (link != NULL);

    if (put_item_after (link, parent->item_list_end)) {
        redraw_if_visible (item);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_lower_to_bottom:
 * @item: A canvas item.
 *
 * Lowers an item to the bottom of its parent's stack.
 **/
void
gnome_canvas_item_lower_to_bottom (GnomeCanvasItem *item)
{
    GList *link;
    GnomeCanvasGroup *parent;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (!item->parent)
        return;

    parent = GNOME_CANVAS_GROUP (item->parent);
    link = g_list_find (parent->item_list, item);
    g_assert (link != NULL);

    if (put_item_after (link, NULL)) {
        redraw_if_visible (item);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_show:
 * @item: A canvas item.
 *
 * Shows a canvas item.  If the item was already shown, then no action is taken.
 **/
void
gnome_canvas_item_show (GnomeCanvasItem *item)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (!(item->flags & GNOME_CANVAS_ITEM_VISIBLE)) {
        item->flags |= GNOME_CANVAS_ITEM_VISIBLE;
        gnome_canvas_request_redraw (
            item->canvas, item->x1, item->y1,
            item->x2 + 1, item->y2 + 1);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_hide:
 * @item: A canvas item.
 *
 * Hides a canvas item.  If the item was already hidden, then no action is
 * taken.
 **/
void
gnome_canvas_item_hide (GnomeCanvasItem *item)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (item->flags & GNOME_CANVAS_ITEM_VISIBLE) {
        item->flags &= ~GNOME_CANVAS_ITEM_VISIBLE;
        gnome_canvas_request_redraw (
            item->canvas, item->x1, item->y1,
            item->x2 + 1, item->y2 + 1);
        item->canvas->need_repick = TRUE;
    }
}

/**
 * gnome_canvas_item_grab:
 * @item: A canvas item.
 * @event_mask: Mask of events that will be sent to this item.
 * @cursor: If non-NULL, the cursor that will be used while the grab is active.
 * @etime: The timestamp required for grabbing the mouse, or GDK_CURRENT_TIME.
 *
 * Specifies that all events that match the specified event mask should be sent
 * to the specified item, and also grabs the mouse by calling
 * gdk_pointer_grab().  The event mask is also used when grabbing the pointer.
 * If @cursor is not NULL, then that cursor is used while the grab is active.
 * The @etime parameter is the timestamp required for grabbing the mouse.
 *
 * Return value: If an item was already grabbed, it returns
 * %GDK_GRAB_ALREADY_GRABBED.  If the specified item was hidden by calling
 * gnome_canvas_item_hide(), then it returns %GDK_GRAB_NOT_VIEWABLE.  Else,
 * it returns the result of calling gdk_pointer_grab().
 **/
gint
gnome_canvas_item_grab (GnomeCanvasItem *item,
                        guint event_mask,
                        GdkCursor *cursor,
                        guint32 etime)
{
    GtkLayout *layout;
    GdkWindow *bin_window;
    gint retval;

    g_return_val_if_fail (
        GNOME_IS_CANVAS_ITEM (item), GDK_GRAB_NOT_VIEWABLE);
    g_return_val_if_fail (
        gtk_widget_get_mapped (GTK_WIDGET (item->canvas)),
        GDK_GRAB_NOT_VIEWABLE);

    if (item->canvas->grabbed_item)
        return GDK_GRAB_ALREADY_GRABBED;

    if (!(item->flags & GNOME_CANVAS_ITEM_VISIBLE))
        return GDK_GRAB_NOT_VIEWABLE;

    layout = GTK_LAYOUT (item->canvas);
    bin_window = gtk_layout_get_bin_window (layout);

    retval = gdk_pointer_grab (bin_window,
                   FALSE,
                   event_mask,
                   NULL,
                   cursor,
                   etime);

    if (retval != GDK_GRAB_SUCCESS)
        return retval;

    item->canvas->grabbed_item = item;
    item->canvas->grabbed_event_mask = event_mask;
    item->canvas->current_item = item; /* So that events go to the grabbed item */

    return retval;
}

/**
 * gnome_canvas_item_ungrab:
 * @item: A canvas item that holds a grab.
 * @etime: The timestamp for ungrabbing the mouse.
 *
 * Ungrabs the item, which must have been grabbed in the canvas, and ungrabs the
 * mouse.
 **/
void
gnome_canvas_item_ungrab (GnomeCanvasItem *item, guint32 etime)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (item->canvas->grabbed_item != item)
        return;

    item->canvas->grabbed_item = NULL;

    gdk_pointer_ungrab (etime);
}

/**
 * gnome_canvas_item_i2w_affine:
 * @item: A canvas item
 * @affine: An affine transformation matrix (return value).
 *
 * Gets the affine transform that converts from the item's coordinate system to
 * world coordinates.
 **/
void
gnome_canvas_item_i2w_affine (GnomeCanvasItem *item, gdouble affine[6])
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (affine != NULL);

    art_affine_identity (affine);

    while (item) {
        if (item->xform != NULL) {
            if (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL) {
                art_affine_multiply (affine, affine, item->xform);
            } else {
                affine[4] += item->xform[0];
                affine[5] += item->xform[1];
            }
        }

        item = item->parent;
    }
}

/**
 * gnome_canvas_item_w2i:
 * @item: A canvas item.
 * @x: X coordinate to convert (input/output value).
 * @y: Y coordinate to convert (input/output value).
 *
 * Converts a coordinate pair from world coordinates to item-relative
 * coordinates.
 **/
void
gnome_canvas_item_w2i (GnomeCanvasItem *item, gdouble *x, gdouble *y)
{
    gdouble affine[6], inv[6];
    ArtPoint w, i;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (x != NULL);
    g_return_if_fail (y != NULL);

    gnome_canvas_item_i2w_affine (item, affine);
    art_affine_invert (inv, affine);
    w.x = *x;
    w.y = *y;
    art_affine_point (&i, &w, inv);
    *x = i.x;
    *y = i.y;
}

/**
 * gnome_canvas_item_i2w:
 * @item: A canvas item.
 * @x: X coordinate to convert (input/output value).
 * @y: Y coordinate to convert (input/output value).
 *
 * Converts a coordinate pair from item-relative coordinates to world
 * coordinates.
 **/
void
gnome_canvas_item_i2w (GnomeCanvasItem *item, gdouble *x, gdouble *y)
{
    gdouble affine[6];
    ArtPoint w, i;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (x != NULL);
    g_return_if_fail (y != NULL);

    gnome_canvas_item_i2w_affine (item, affine);
    i.x = *x;
    i.y = *y;
    art_affine_point (&w, &i, affine);
    *x = w.x;
    *y = w.y;
}

/**
 * gnome_canvas_item_i2c_affine:
 * @item: A canvas item.
 * @affine: An affine transformation matrix (return value).
 *
 * Gets the affine transform that converts from item-relative coordinates to
 * canvas pixel coordinates.
 **/
void
gnome_canvas_item_i2c_affine (GnomeCanvasItem *item, gdouble affine[6])
{
    gdouble i2w[6], w2c[6];

    gnome_canvas_item_i2w_affine (item, i2w);
    gnome_canvas_w2c_affine (item->canvas, w2c);
    art_affine_multiply (affine, i2w, w2c);
}

/* Returns whether the item is an inferior of or is equal to the parent. */
static gint
is_descendant (GnomeCanvasItem *item, GnomeCanvasItem *parent)
{
    for (; item; item = item->parent)
        if (item == parent)
            return TRUE;

    return FALSE;
}

/**
 * gnome_canvas_item_reparent:
 * @item: A canvas item.
 * @new_group: A canvas group.
 *
 * Changes the parent of the specified item to be the new group.  The item keeps
 * its group-relative coordinates as for its old parent, so the item may change
 * its absolute position within the canvas.
 **/
void
gnome_canvas_item_reparent (GnomeCanvasItem *item, GnomeCanvasGroup *new_group)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (GNOME_IS_CANVAS_GROUP (new_group));

    /* Both items need to be in the same canvas */
    g_return_if_fail (item->canvas == GNOME_CANVAS_ITEM (new_group)->canvas);

    /* The group cannot be an inferior of the item or be the item itself --
     * this also takes care of the case where the item is the root item of
     * the canvas.  */
    g_return_if_fail (!is_descendant (GNOME_CANVAS_ITEM (new_group), item));

    /* Everything is ok, now actually reparent the item */

    g_object_ref (G_OBJECT (item)); /* protect it from the unref in group_remove */

    redraw_if_visible (item);

    group_remove (GNOME_CANVAS_GROUP (item->parent), item);
    item->parent = GNOME_CANVAS_ITEM (new_group);
    group_add (new_group, item);

    /* Redraw and repick */

    redraw_if_visible (item);
    item->canvas->need_repick = TRUE;

    g_object_unref (G_OBJECT (item));
}

/**
 * gnome_canvas_item_grab_focus:
 * @item: A canvas item.
 *
 * Makes the specified item take the keyboard focus, so all keyboard events will
 * be sent to it.  If the canvas widget itself did not have the focus, it grabs
 * it as well.
 **/
void
gnome_canvas_item_grab_focus (GnomeCanvasItem *item)
{
    GnomeCanvasItem *focused_item;
    GdkEvent ev;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (gtk_widget_get_can_focus (GTK_WIDGET (item->canvas)));

    focused_item = item->canvas->focused_item;

    if (focused_item) {
        GtkLayout *layout;
        GdkWindow *bin_window;

        layout = GTK_LAYOUT (item->canvas);
        bin_window = gtk_layout_get_bin_window (layout);

        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = bin_window;
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = FALSE;

        emit_event (item->canvas, &ev);
    }

    item->canvas->focused_item = item;
    gtk_widget_grab_focus (GTK_WIDGET (item->canvas));

    if (focused_item) {
        GtkLayout *layout;
        GdkWindow *bin_window;

        layout = GTK_LAYOUT (item->canvas);
        bin_window = gtk_layout_get_bin_window (layout);

        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = bin_window;
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = TRUE;

        emit_event (item->canvas, &ev);
    }
}

/**
 * gnome_canvas_item_get_bounds:
 * @item: A canvas item.
 * @x1: Leftmost edge of the bounding box (return value).
 * @y1: Upper edge of the bounding box (return value).
 * @x2: Rightmost edge of the bounding box (return value).
 * @y2: Lower edge of the bounding box (return value).
 *
 * Queries the bounding box of a canvas item.  The bounds are returned in the
 * coordinate system of the item's parent.
 **/
void
gnome_canvas_item_get_bounds (GnomeCanvasItem *item,
                              gdouble *x1,
                              gdouble *y1,
                              gdouble *x2,
                              gdouble *y2)
{
    gdouble tx1, ty1, tx2, ty2;
    ArtPoint p1, p2, p3, p4;
    ArtPoint q1, q2, q3, q4;
    gdouble min_x1, min_y1, min_x2, min_y2;
    gdouble max_x1, max_y1, max_x2, max_y2;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    tx1 = ty1 = tx2 = ty2 = 0.0;

    /* Get the item's bounds in its coordinate system */

    if (GNOME_CANVAS_ITEM_GET_CLASS (item)->bounds)
        (* GNOME_CANVAS_ITEM_GET_CLASS (item)->bounds) (item, &tx1, &ty1, &tx2, &ty2);

    /* Make the bounds relative to the item's parent coordinate system */

    if (item->xform && (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL)) {
        p1.x = p2.x = tx1;
        p1.y = p4.y = ty1;
        p3.x = p4.x = tx2;
        p2.y = p3.y = ty2;

        art_affine_point (&q1, &p1, item->xform);
        art_affine_point (&q2, &p2, item->xform);
        art_affine_point (&q3, &p3, item->xform);
        art_affine_point (&q4, &p4, item->xform);

        if (q1.x < q2.x) {
            min_x1 = q1.x;
            max_x1 = q2.x;
        } else {
            min_x1 = q2.x;
            max_x1 = q1.x;
        }

        if (q1.y < q2.y) {
            min_y1 = q1.y;
            max_y1 = q2.y;
        } else {
            min_y1 = q2.y;
            max_y1 = q1.y;
        }

        if (q3.x < q4.x) {
            min_x2 = q3.x;
            max_x2 = q4.x;
        } else {
            min_x2 = q4.x;
            max_x2 = q3.x;
        }

        if (q3.y < q4.y) {
            min_y2 = q3.y;
            max_y2 = q4.y;
        } else {
            min_y2 = q4.y;
            max_y2 = q3.y;
        }

        tx1 = MIN (min_x1, min_x2);
        ty1 = MIN (min_y1, min_y2);
        tx2 = MAX (max_x1, max_x2);
        ty2 = MAX (max_y1, max_y2);
    } else if (item->xform) {
        tx1 += item->xform[0];
        ty1 += item->xform[1];
        tx2 += item->xform[0];
        ty2 += item->xform[1];
    }

    /* Return the values */

    if (x1)
        *x1 = tx1;

    if (y1)
        *y1 = ty1;

    if (x2)
        *x2 = tx2;

    if (y2)
        *y2 = ty2;
}

/**
 * gnome_canvas_item_request_update
 * @item: A canvas item.
 *
 * To be used only by item implementations.  Requests that the canvas queue an
 * update for the specified item.
 **/
void
gnome_canvas_item_request_update (GnomeCanvasItem *item)
{
    if (item->flags & GNOME_CANVAS_ITEM_NEED_UPDATE)
        return;

    item->flags |= GNOME_CANVAS_ITEM_NEED_UPDATE;

    if (item->parent != NULL) {
        /* Recurse up the tree */
        gnome_canvas_item_request_update (item->parent);
    } else {
        /* Have reached the top of the tree, make sure the update call gets scheduled. */
        gnome_canvas_request_update (item->canvas);
    }
}

/*** GnomeCanvasGroup ***/

enum {
    GROUP_PROP_0,
    GROUP_PROP_X,
    GROUP_PROP_Y
};

static void gnome_canvas_group_class_init  (GnomeCanvasGroupClass *class);
static void gnome_canvas_group_init        (GnomeCanvasGroup      *group);
static void gnome_canvas_group_set_property(GObject               *object,
                        guint                  param_id,
                        const GValue          *value,
                        GParamSpec            *pspec);
static void gnome_canvas_group_get_property(GObject               *object,
                        guint                  param_id,
                        GValue                *value,
                        GParamSpec            *pspec);

static void gnome_canvas_group_destroy     (GtkObject             *object);

static void   gnome_canvas_group_update      (GnomeCanvasItem *item, gdouble *affine,
                          ArtSVP *clip_path, gint flags);
static void   gnome_canvas_group_realize     (GnomeCanvasItem *item);
static void   gnome_canvas_group_unrealize   (GnomeCanvasItem *item);
static void   gnome_canvas_group_map         (GnomeCanvasItem *item);
static void   gnome_canvas_group_unmap       (GnomeCanvasItem *item);
static void   gnome_canvas_group_draw        (GnomeCanvasItem *item,
                          GdkDrawable *drawable,
                          gint x, gint y,
                          gint width, gint height);
static gdouble gnome_canvas_group_point       (GnomeCanvasItem *item,
                          gdouble x, gdouble y,
                          gint cx, gint cy,
                          GnomeCanvasItem **actual_item);
static void   gnome_canvas_group_bounds      (GnomeCanvasItem *item,
                          gdouble *x1, gdouble *y1,
                          gdouble *x2, gdouble *y2);
static void   gnome_canvas_group_render      (GnomeCanvasItem *item,
                          GnomeCanvasBuf *buf);

static GnomeCanvasItemClass *group_parent_class;

/**
 * gnome_canvas_group_get_type:
 *
 * Registers the &GnomeCanvasGroup class if necessary, and returns the type ID
 * associated to it.
 *
 * Return value:  The type ID of the &GnomeCanvasGroup class.
 **/
GType
gnome_canvas_group_get_type (void)
{
    static GType canvas_group_type;

    if (!canvas_group_type) {
        const GTypeInfo object_info = {
            sizeof (GnomeCanvasGroupClass),
            (GBaseInitFunc) NULL,
            (GBaseFinalizeFunc) NULL,
            (GClassInitFunc) gnome_canvas_group_class_init,
            (GClassFinalizeFunc) NULL,
            NULL,           /* class_data */
            sizeof (GnomeCanvasGroup),
            0,          /* n_preallocs */
            (GInstanceInitFunc) gnome_canvas_group_init,
            NULL            /* value_table */
        };

        canvas_group_type = g_type_register_static (
            GNOME_TYPE_CANVAS_ITEM, "GnomeCanvasGroup",
            &object_info, 0);
    }

    return canvas_group_type;
}

/* Class initialization function for GnomeCanvasGroupClass */
static void
gnome_canvas_group_class_init (GnomeCanvasGroupClass *class)
{
    GObjectClass *gobject_class;
    GtkObjectClass *object_class;
    GnomeCanvasItemClass *item_class;

    gobject_class = (GObjectClass *) class;
    object_class = (GtkObjectClass *) class;
    item_class = (GnomeCanvasItemClass *) class;

    group_parent_class = g_type_class_peek_parent (class);

    gobject_class->set_property = gnome_canvas_group_set_property;
    gobject_class->get_property = gnome_canvas_group_get_property;

    g_object_class_install_property
        (gobject_class, GROUP_PROP_X,
         g_param_spec_double ("x",
                      "X",
                      "X",
                      -G_MAXDOUBLE, G_MAXDOUBLE, 0.0,
                      (G_PARAM_READABLE | G_PARAM_WRITABLE)));
    g_object_class_install_property
        (gobject_class, GROUP_PROP_Y,
         g_param_spec_double ("y",
                      "Y",
                      "Y",
                      -G_MAXDOUBLE, G_MAXDOUBLE, 0.0,
                      (G_PARAM_READABLE | G_PARAM_WRITABLE)));

    object_class->destroy = gnome_canvas_group_destroy;

    item_class->update = gnome_canvas_group_update;
    item_class->realize = gnome_canvas_group_realize;
    item_class->unrealize = gnome_canvas_group_unrealize;
    item_class->map = gnome_canvas_group_map;
    item_class->unmap = gnome_canvas_group_unmap;
    item_class->draw = gnome_canvas_group_draw;
    item_class->render = gnome_canvas_group_render;
    item_class->point = gnome_canvas_group_point;
    item_class->bounds = gnome_canvas_group_bounds;
}

/* Object initialization function for GnomeCanvasGroup */
static void
gnome_canvas_group_init (GnomeCanvasGroup *group)
{
#if 0
    group->xpos = 0.0;
    group->ypos = 0.0;
#endif
}

/* Translate handler for canvas groups */
static gdouble *
gnome_canvas_ensure_translate (GnomeCanvasItem *item)
{
    if (item->xform == NULL) {
        item->flags &= ~GNOME_CANVAS_ITEM_AFFINE_FULL;
        item->xform = g_new (double, 2);
        item->xform[0] = 0.0;
        item->xform[1] = 0.0;
        return item->xform;
    } else if (item->flags & GNOME_CANVAS_ITEM_AFFINE_FULL) {
        return item->xform + 4;
    } else {
        return item->xform;
    }
}

/* Set_property handler for canvas groups */
static void
gnome_canvas_group_set_property (GObject *gobject, guint param_id,
                 const GValue *value, GParamSpec *pspec)
{
    GnomeCanvasItem *item;
    gdouble *xlat;

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (param_id) {
    case GROUP_PROP_X:
        xlat = gnome_canvas_ensure_translate (item);
        xlat[0] = g_value_get_double (value);
        break;

    case GROUP_PROP_Y:
        xlat = gnome_canvas_ensure_translate (item);
        xlat[1] = g_value_get_double (value);
        break;

    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, param_id, pspec);
        break;
    }
}

/* Get_property handler for canvas groups */
static void
gnome_canvas_group_get_property (GObject *gobject, guint param_id,
                 GValue *value, GParamSpec *pspec)
{
    GnomeCanvasItem *item;

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (param_id) {
    case GROUP_PROP_X:
        if (item->xform == NULL)
            g_value_set_double (value, 0);
        else if (GNOME_CANVAS_ITEM (gobject)->flags & GNOME_CANVAS_ITEM_AFFINE_FULL)
            g_value_set_double (value, item->xform[4]);
        else
            g_value_set_double (value, item->xform[0]);
        break;

    case GROUP_PROP_Y:
        if (item->xform == NULL)
            g_value_set_double (value, 0);
        else if (GNOME_CANVAS_ITEM (gobject)->flags & GNOME_CANVAS_ITEM_AFFINE_FULL)
            g_value_set_double (value, item->xform[5]);
        else
            g_value_set_double (value, item->xform[1]);
        break;

    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, param_id, pspec);
        break;
    }
}

/* Destroy handler for canvas groups */
static void
gnome_canvas_group_destroy (GtkObject *object)
{
    GnomeCanvasGroup *group;

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (object));

    group = GNOME_CANVAS_GROUP (object);

    while (group->item_list) {
        // child is unref'ed by the child's group_remove().
        gtk_object_destroy (GTK_OBJECT (group->item_list->data));
    }

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

/* Update handler for canvas groups */
static void
gnome_canvas_group_update (GnomeCanvasItem *item,
                           gdouble *affine,
                           ArtSVP *clip_path,
                           gint flags)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;
    ArtDRect bbox, child_bbox;

    group = GNOME_CANVAS_GROUP (item);

    (* group_parent_class->update) (item, affine, clip_path, flags);

    bbox.x0 = 0;
    bbox.y0 = 0;
    bbox.x1 = 0;
    bbox.y1 = 0;

    for (list = group->item_list; list; list = list->next) {
        i = list->data;

        gnome_canvas_item_invoke_update (i, affine, clip_path, flags);

        child_bbox.x0 = i->x1;
        child_bbox.y0 = i->y1;
        child_bbox.x1 = i->x2;
        child_bbox.y1 = i->y2;
        art_drect_union (&bbox, &bbox, &child_bbox);
    }
    item->x1 = bbox.x0;
    item->y1 = bbox.y0;
    item->x2 = bbox.x1;
    item->y2 = bbox.y1;
}

/* Realize handler for canvas groups */
static void
gnome_canvas_group_realize (GnomeCanvasItem *item)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        i = list->data;

        if (!(i->flags & GNOME_CANVAS_ITEM_REALIZED))
            (* GNOME_CANVAS_ITEM_GET_CLASS (i)->realize) (i);
    }

    (* group_parent_class->realize) (item);
}

/* Unrealize handler for canvas groups */
static void
gnome_canvas_group_unrealize (GnomeCanvasItem *item)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        i = list->data;

        if (i->flags & GNOME_CANVAS_ITEM_REALIZED)
            (* GNOME_CANVAS_ITEM_GET_CLASS (i)->unrealize) (i);
    }

    (* group_parent_class->unrealize) (item);
}

/* Map handler for canvas groups */
static void
gnome_canvas_group_map (GnomeCanvasItem *item)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        i = list->data;

        if (!(i->flags & GNOME_CANVAS_ITEM_MAPPED))
            (* GNOME_CANVAS_ITEM_GET_CLASS (i)->map) (i);
    }

    (* group_parent_class->map) (item);
}

/* Unmap handler for canvas groups */
static void
gnome_canvas_group_unmap (GnomeCanvasItem *item)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        i = list->data;

        if (i->flags & GNOME_CANVAS_ITEM_MAPPED)
            (* GNOME_CANVAS_ITEM_GET_CLASS (i)->unmap) (i);
    }

    (* group_parent_class->unmap) (item);
}

/* Draw handler for canvas groups */
static void
gnome_canvas_group_draw (GnomeCanvasItem *item, GdkDrawable *drawable,
             gint x, gint y, gint width, gint height)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *child = NULL;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        child = list->data;

        if (((child->flags & GNOME_CANVAS_ITEM_VISIBLE)
             && ((child->x1 < (x + width))
             && (child->y1 < (y + height))
             && (child->x2 > x)
             && (child->y2 > y)))
            || ((child->flags & GNOME_CANVAS_ITEM_ALWAYS_REDRAW)
            && (child->x1 < child->canvas->redraw_x2)
            && (child->y1 < child->canvas->redraw_y2)
            && (child->x2 > child->canvas->redraw_x1)
            && (child->y2 > child->canvas->redraw_y2)))
            if (GNOME_CANVAS_ITEM_GET_CLASS (child)->draw)
                (* GNOME_CANVAS_ITEM_GET_CLASS (child)->draw) (
                    child, drawable, x, y, width, height);
    }
}

/* Point handler for canvas groups */
static double
gnome_canvas_group_point (GnomeCanvasItem *item,
                          gdouble x,
                          gdouble y,
                          gint cx,
                          gint cy,
                          GnomeCanvasItem **actual_item)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *child, *point_item;
    gint x1, y1, x2, y2;
    gdouble gx, gy;
    gdouble dist, best;
    gint has_point;

    group = GNOME_CANVAS_GROUP (item);

    x1 = cx - item->canvas->close_enough;
    y1 = cy - item->canvas->close_enough;
    x2 = cx + item->canvas->close_enough;
    y2 = cy + item->canvas->close_enough;

    best = 0.0;
    *actual_item = NULL;

    gx = x;
    gy = y;

    dist = 0.0; /* keep gcc happy */

    for (list = group->item_list; list; list = list->next) {
        child = list->data;

        if ((child->x1 > x2) || (child->y1 > y2) || (child->x2 < x1) || (child->y2 < y1))
            continue;

        point_item = NULL; /* cater for incomplete item implementations */

        if ((child->flags & GNOME_CANVAS_ITEM_VISIBLE)
            && GNOME_CANVAS_ITEM_GET_CLASS (child)->point) {
            dist = gnome_canvas_item_invoke_point (child, gx, gy, cx, cy, &point_item);
            has_point = TRUE;
        } else
            has_point = FALSE;

        if (has_point
            && point_item
            && ((gint) (dist * item->canvas->pixels_per_unit + 0.5)
            <= item->canvas->close_enough)) {
            best = dist;
            *actual_item = point_item;
        }
    }

    return best;
}

/* Bounds handler for canvas groups */
static void
gnome_canvas_group_bounds (GnomeCanvasItem *item,
                           gdouble *x1,
                           gdouble *y1,
                           gdouble *x2,
                           gdouble *y2)
{
    GnomeCanvasGroup *group;
    GnomeCanvasItem *child;
    GList *list;
    gdouble tx1, ty1, tx2, ty2;
    gdouble minx, miny, maxx, maxy;
    gint set;

    group = GNOME_CANVAS_GROUP (item);

    /* Get the bounds of the first visible item */

    child = NULL; /* Unnecessary but eliminates a warning. */

    set = FALSE;

    for (list = group->item_list; list; list = list->next) {
        child = list->data;

        if (child->flags & GNOME_CANVAS_ITEM_VISIBLE) {
            set = TRUE;
            gnome_canvas_item_get_bounds (child, &minx, &miny, &maxx, &maxy);
            break;
        }
    }

    /* If there were no visible items, return an empty bounding box */

    if (!set) {
        *x1 = *y1 = *x2 = *y2 = 0.0;
        return;
    }

    /* Now we can grow the bounds using the rest of the items */

    list = list->next;

    for (; list; list = list->next) {
        child = list->data;

        if (!(child->flags & GNOME_CANVAS_ITEM_VISIBLE))
            continue;

        gnome_canvas_item_get_bounds (child, &tx1, &ty1, &tx2, &ty2);

        if (tx1 < minx)
            minx = tx1;

        if (ty1 < miny)
            miny = ty1;

        if (tx2 > maxx)
            maxx = tx2;

        if (ty2 > maxy)
            maxy = ty2;
    }

    *x1 = minx;
    *y1 = miny;
    *x2 = maxx;
    *y2 = maxy;
}

/* Render handler for canvas groups */
static void
gnome_canvas_group_render (GnomeCanvasItem *item, GnomeCanvasBuf *buf)
{
    GnomeCanvasGroup *group;
    GnomeCanvasItem *child;
    GList *list;

    group = GNOME_CANVAS_GROUP (item);

    for (list = group->item_list; list; list = list->next) {
        child = list->data;

        if (((child->flags & GNOME_CANVAS_ITEM_VISIBLE)
             && ((child->x1 < buf->rect.x1)
             && (child->y1 < buf->rect.y1)
             && (child->x2 > buf->rect.x0)
             && (child->y2 > buf->rect.y0)))
            || ((child->flags & GNOME_CANVAS_ITEM_ALWAYS_REDRAW)
            && (child->x1 < child->canvas->redraw_x2)
            && (child->y1 < child->canvas->redraw_y2)
            && (child->x2 > child->canvas->redraw_x1)
            && (child->y2 > child->canvas->redraw_y2)))
            if (GNOME_CANVAS_ITEM_GET_CLASS (child)->render)
                (* GNOME_CANVAS_ITEM_GET_CLASS (child)->render) (
                    child, buf);
    }
}

/* Adds an item to a group */
static void
group_add (GnomeCanvasGroup *group, GnomeCanvasItem *item)
{
    g_object_ref_sink (G_OBJECT (item));

    if (!group->item_list) {
        group->item_list = g_list_append (group->item_list, item);
        group->item_list_end = group->item_list;
    } else
        group->item_list_end = g_list_append (group->item_list_end, item)->next;

    if (group->item.flags & GNOME_CANVAS_ITEM_REALIZED)
        (* GNOME_CANVAS_ITEM_GET_CLASS (item)->realize) (item);

    if (group->item.flags & GNOME_CANVAS_ITEM_MAPPED)
        (* GNOME_CANVAS_ITEM_GET_CLASS (item)->map) (item);

    g_object_notify (G_OBJECT (item), "parent");
}

/* Removes an item from a group */
static void
group_remove (GnomeCanvasGroup *group, GnomeCanvasItem *item)
{
    GList *children;

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (group));
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    for (children = group->item_list; children; children = children->next)
        if (children->data == item) {
            if (item->flags & GNOME_CANVAS_ITEM_MAPPED)
                (* GNOME_CANVAS_ITEM_GET_CLASS (item)->unmap) (item);

            if (item->flags & GNOME_CANVAS_ITEM_REALIZED)
                (* GNOME_CANVAS_ITEM_GET_CLASS (item)->unrealize) (item);

            /* Unparent the child */

            item->parent = NULL;
            g_object_unref (G_OBJECT (item));

            /* Remove it from the list */

            if (children == group->item_list_end)
                group->item_list_end = children->prev;

            group->item_list = g_list_remove_link (group->item_list, children);
            g_list_free (children);
            break;
        }
}

/*** GnomeCanvas ***/

enum {
    DRAW_BACKGROUND,
    RENDER_BACKGROUND,
    LAST_SIGNAL
};

static void gnome_canvas_class_init          (GnomeCanvasClass *class);
static void gnome_canvas_init                (GnomeCanvas      *canvas);
static void gnome_canvas_destroy             (GtkObject        *object);
static void gnome_canvas_map                 (GtkWidget        *widget);
static void gnome_canvas_unmap               (GtkWidget        *widget);
static void gnome_canvas_realize             (GtkWidget        *widget);
static void gnome_canvas_unrealize           (GtkWidget        *widget);
static void gnome_canvas_size_allocate       (GtkWidget        *widget,
                          GtkAllocation    *allocation);
static gint gnome_canvas_button              (GtkWidget        *widget,
                          GdkEventButton   *event);
static gint gnome_canvas_motion              (GtkWidget        *widget,
                          GdkEventMotion   *event);
static gint gnome_canvas_expose              (GtkWidget        *widget,
                          GdkEventExpose   *event);
static gboolean gnome_canvas_key             (GtkWidget        *widget,
                          GdkEventKey      *event);
static gint gnome_canvas_crossing            (GtkWidget        *widget,
                          GdkEventCrossing *event);
static gint gnome_canvas_focus_in            (GtkWidget        *widget,
                          GdkEventFocus    *event);
static gint gnome_canvas_focus_out           (GtkWidget        *widget,
                          GdkEventFocus    *event);
static void gnome_canvas_request_update_real (GnomeCanvas      *canvas);
static void gnome_canvas_draw_background     (GnomeCanvas      *canvas,
                          GdkDrawable      *drawable,
                          gint               x,
                          gint               y,
                          gint               width,
                          gint               height);

static GtkLayoutClass *canvas_parent_class;

static guint canvas_signals[LAST_SIGNAL];

enum {
    PROP_AA = 1,
    PROP_FOCUSED_ITEM
};

/**
 * gnome_canvas_get_type:
 *
 * Registers the &GnomeCanvas class if necessary, and returns the type ID
 * associated to it.
 *
 * Return value:  The type ID of the &GnomeCanvas class.
 **/
GType
gnome_canvas_get_type (void)
{
    static GType canvas_type;

    if (!canvas_type) {
        const GTypeInfo object_info = {
            sizeof (GnomeCanvasClass),
            (GBaseInitFunc) NULL,
            (GBaseFinalizeFunc) NULL,
            (GClassInitFunc) gnome_canvas_class_init,
            (GClassFinalizeFunc) NULL,
            NULL,           /* class_data */
            sizeof (GnomeCanvas),
            0,          /* n_preallocs */
            (GInstanceInitFunc) gnome_canvas_init,
            NULL            /* value_table */
        };

        canvas_type = g_type_register_static (GTK_TYPE_LAYOUT, "GnomeCanvas",
                              &object_info, 0);
    }

    return canvas_type;
}

static void
gnome_canvas_get_property (GObject    *object,
               guint       prop_id,
               GValue     *value,
               GParamSpec *pspec)
{
    switch (prop_id) {
    case PROP_AA:
        g_value_set_boolean (value, GNOME_CANVAS (object)->aa);
        break;
    case PROP_FOCUSED_ITEM:
        g_value_set_object (value, GNOME_CANVAS (object)->focused_item);
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
}

static void
gnome_canvas_set_property (GObject      *object,
               guint         prop_id,
               const GValue *value,
               GParamSpec   *pspec)
{
    switch (prop_id) {
    case PROP_AA:
        GNOME_CANVAS (object)->aa = g_value_get_boolean (value);
        break;
    case PROP_FOCUSED_ITEM:
        GNOME_CANVAS (object)->focused_item = g_value_get_object (value);
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
}

/* Class initialization function for GnomeCanvasClass */
static void
gnome_canvas_class_init (GnomeCanvasClass *klass)
{
    GObjectClass   *gobject_class;
    GtkObjectClass *object_class;
    GtkWidgetClass *widget_class;

    gobject_class = (GObjectClass *)klass;
    object_class  = (GtkObjectClass *) klass;
    widget_class  = (GtkWidgetClass *) klass;

    canvas_parent_class = g_type_class_peek_parent (klass);

    gobject_class->set_property = gnome_canvas_set_property;
    gobject_class->get_property = gnome_canvas_get_property;

    object_class->destroy = gnome_canvas_destroy;

    widget_class->map = gnome_canvas_map;
    widget_class->unmap = gnome_canvas_unmap;
    widget_class->realize = gnome_canvas_realize;
    widget_class->unrealize = gnome_canvas_unrealize;
    widget_class->size_allocate = gnome_canvas_size_allocate;
    widget_class->button_press_event = gnome_canvas_button;
    widget_class->button_release_event = gnome_canvas_button;
    widget_class->motion_notify_event = gnome_canvas_motion;
    widget_class->expose_event = gnome_canvas_expose;
    widget_class->key_press_event = gnome_canvas_key;
    widget_class->key_release_event = gnome_canvas_key;
    widget_class->enter_notify_event = gnome_canvas_crossing;
    widget_class->leave_notify_event = gnome_canvas_crossing;
    widget_class->focus_in_event = gnome_canvas_focus_in;
    widget_class->focus_out_event = gnome_canvas_focus_out;

    klass->draw_background = gnome_canvas_draw_background;
    klass->render_background = NULL;
    klass->request_update = gnome_canvas_request_update_real;

    g_object_class_install_property (G_OBJECT_CLASS (object_class),
                     PROP_AA,
                     g_param_spec_boolean ("aa",
                                   "Antialiased",
                                   "The antialiasing mode of the canvas.",
                                   FALSE,
                                   G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY));

    g_object_class_install_property (gobject_class, PROP_FOCUSED_ITEM,
                     g_param_spec_object ("focused_item", NULL, NULL,
                     GNOME_TYPE_CANVAS_ITEM,
                     (G_PARAM_READABLE | G_PARAM_WRITABLE)));

    canvas_signals[DRAW_BACKGROUND] =
        g_signal_new ("draw_background",
                  G_TYPE_FROM_CLASS (object_class),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GnomeCanvasClass, draw_background),
                  NULL, NULL,
                  gnome_canvas_marshal_VOID__OBJECT_INT_INT_INT_INT,
                  G_TYPE_NONE, 5, GDK_TYPE_DRAWABLE,
                  G_TYPE_INT, G_TYPE_INT, G_TYPE_INT, G_TYPE_INT);
    canvas_signals[RENDER_BACKGROUND] =
        g_signal_new ("render_background",
                  G_TYPE_FROM_CLASS (object_class),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GnomeCanvasClass, render_background),
                  NULL, NULL,
                  g_cclosure_marshal_VOID__POINTER,
                  G_TYPE_NONE, 1, G_TYPE_POINTER);

    gail_canvas_init();
}

/* Callback used when the root item of a canvas is destroyed.  The user should
 * never ever do this, so we panic if this happens.
 */
G_GNUC_NORETURN static void
panic_root_destroyed (GtkObject *object, gpointer data)
{
    g_error ("Eeeek, root item %p of canvas %p was destroyed!", object, data);
}

/* Object initialization function for GnomeCanvas */
static void
gnome_canvas_init (GnomeCanvas *canvas)
{
    GtkLayout *layout;
    guint layout_width, layout_height;

    layout = GTK_LAYOUT (canvas);
    gtk_layout_get_size (layout, &layout_width, &layout_height);

    gtk_widget_set_can_focus (GTK_WIDGET (canvas), TRUE);

    canvas->need_update = FALSE;
    canvas->need_redraw = FALSE;
    canvas->redraw_area = NULL;
    canvas->idle_id = 0;

    canvas->scroll_x1 = 0.0;
    canvas->scroll_y1 = 0.0;
    canvas->scroll_x2 = layout_width;
    canvas->scroll_y2 = layout_height;

    canvas->pixels_per_unit = 1.0;

    canvas->pick_event.type = GDK_LEAVE_NOTIFY;
    canvas->pick_event.crossing.x = 0;
    canvas->pick_event.crossing.y = 0;

    canvas->dither = GDK_RGB_DITHER_MAX;

    /* This may not be what people want, but it is set to be turned on by
     * default to have the same initial behavior as the canvas in GNOME 1.4.
     */
    canvas->center_scroll_region = TRUE;

    gtk_layout_set_hadjustment (GTK_LAYOUT (canvas), NULL);
    gtk_layout_set_vadjustment (GTK_LAYOUT (canvas), NULL);

    /* Disable the gtk+ gdouble buffering since the canvas uses it's own. */
    gtk_widget_set_double_buffered (GTK_WIDGET (canvas), FALSE);

    /* Create the root item as a special case */

    canvas->root = GNOME_CANVAS_ITEM (
        g_object_new (gnome_canvas_group_get_type (), NULL));
    canvas->root->canvas = canvas;

    g_object_ref_sink (canvas->root);

    canvas->root_destroy_id = g_signal_connect (canvas->root, "destroy",
                            G_CALLBACK (panic_root_destroyed),
                            canvas);

    canvas->need_repick = TRUE;
}

/* Convenience function to remove the idle handler of a canvas */
static void
remove_idle (GnomeCanvas *canvas)
{
    if (canvas->idle_id == 0)
        return;

    g_source_remove (canvas->idle_id);
    canvas->idle_id = 0;
}

/* Removes the transient state of the canvas (idle handler, grabs). */
static void
shutdown_transients (GnomeCanvas *canvas)
{
    /* We turn off the need_redraw flag, since if the canvas is mapped again
     * it will request a redraw anyways.  We do not turn off the need_update
     * flag, though, because updates are not queued when the canvas remaps
     * itself.
     */
    if (canvas->need_redraw) {
        canvas->need_redraw = FALSE;
        art_uta_free (canvas->redraw_area);
        canvas->redraw_area = NULL;
        canvas->redraw_x1 = 0;
        canvas->redraw_y1 = 0;
        canvas->redraw_x2 = 0;
        canvas->redraw_y2 = 0;
    }

    if (canvas->grabbed_item) {
        canvas->grabbed_item = NULL;
        gdk_pointer_ungrab (GDK_CURRENT_TIME);
    }

    remove_idle (canvas);
}

/* Destroy handler for GnomeCanvas */
static void
gnome_canvas_destroy (GtkObject *object)
{
    GnomeCanvas *canvas;

    g_return_if_fail (GNOME_IS_CANVAS (object));

    /* remember, destroy can be run multiple times! */

    canvas = GNOME_CANVAS (object);

    if (canvas->root_destroy_id) {
        g_signal_handler_disconnect (canvas->root, canvas->root_destroy_id);
        canvas->root_destroy_id = 0;
    }
    if (canvas->root) {
        gtk_object_destroy (GTK_OBJECT (canvas->root));
        g_object_unref (G_OBJECT (canvas->root));
        canvas->root = NULL;
    }

    shutdown_transients (canvas);

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

/**
 * gnome_canvas_new:
 *
 * Creates a new empty canvas in non-antialiased mode.
 *
 * Return value: A newly-created canvas.
 **/
GtkWidget *
gnome_canvas_new (void)
{
    return GTK_WIDGET (g_object_new (gnome_canvas_get_type (), NULL));
}

/**
 * gnome_canvas_new_aa:
 *
 * Creates a new empty canvas in antialiased mode.
 *
 * Return value: A newly-created antialiased canvas.
 **/
GtkWidget *
gnome_canvas_new_aa (void)
{
    return GTK_WIDGET (g_object_new (GNOME_TYPE_CANVAS,
                     "aa", TRUE,
                     NULL));
}

/* Map handler for the canvas */
static void
gnome_canvas_map (GtkWidget *widget)
{
    GnomeCanvas *canvas;

    g_return_if_fail (GNOME_IS_CANVAS (widget));

    /* Normal widget mapping stuff */

    if (GTK_WIDGET_CLASS (canvas_parent_class)->map)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->map) (widget);

    canvas = GNOME_CANVAS (widget);

    if (canvas->need_update)
        add_idle (canvas);

    /* Map items */

    if (GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->map)
        (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->map) (canvas->root);
}

/* Unmap handler for the canvas */
static void
gnome_canvas_unmap (GtkWidget *widget)
{
    GnomeCanvas *canvas;

    g_return_if_fail (GNOME_IS_CANVAS (widget));

    canvas = GNOME_CANVAS (widget);

    shutdown_transients (canvas);

    /* Unmap items */

    if (GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->unmap)
        (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->unmap) (canvas->root);

    /* Normal widget unmapping stuff */

    if (GTK_WIDGET_CLASS (canvas_parent_class)->unmap)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->unmap) (widget);
}

/* Realize handler for the canvas */
static void
gnome_canvas_realize (GtkWidget *widget)
{
    GnomeCanvas *canvas;
    GtkLayout *layout;
    GdkWindow *bin_window;

    g_return_if_fail (GNOME_IS_CANVAS (widget));

    /* Normal widget realization stuff */

    if (GTK_WIDGET_CLASS (canvas_parent_class)->realize)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->realize) (widget);

    canvas = GNOME_CANVAS (widget);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);

    gdk_window_set_events (bin_window,
                   (gdk_window_get_events (bin_window)
                 | GDK_EXPOSURE_MASK
                 | GDK_BUTTON_PRESS_MASK
                 | GDK_BUTTON_RELEASE_MASK
                 | GDK_POINTER_MOTION_MASK
                 | GDK_KEY_PRESS_MASK
                 | GDK_KEY_RELEASE_MASK
                 | GDK_ENTER_NOTIFY_MASK
                 | GDK_LEAVE_NOTIFY_MASK
                 | GDK_FOCUS_CHANGE_MASK));

    /* Create our own temporary pixmap gc and realize all the items */

    canvas->pixmap_gc = gdk_gc_new (bin_window);

    (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->realize) (canvas->root);
}

/* Unrealize handler for the canvas */
static void
gnome_canvas_unrealize (GtkWidget *widget)
{
    GnomeCanvas *canvas;

    g_return_if_fail (GNOME_IS_CANVAS (widget));

    canvas = GNOME_CANVAS (widget);

    shutdown_transients (canvas);

    /* Unrealize items and parent widget */

    (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->unrealize) (canvas->root);

    g_object_unref (canvas->pixmap_gc);
    canvas->pixmap_gc = NULL;

    if (GTK_WIDGET_CLASS (canvas_parent_class)->unrealize)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->unrealize) (widget);
}

/* Handles scrolling of the canvas.  Adjusts the scrolling and zooming offset to
 * keep as much as possible of the canvas scrolling region in view.
 */
static void
scroll_to (GnomeCanvas *canvas, gint cx, gint cy)
{
    GtkWidget *widget;
    GtkLayout *layout;
    GtkAllocation allocation;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    guint layout_width, layout_height;
    gint scroll_width, scroll_height;
    gint right_limit, bottom_limit;
    gint old_zoom_xofs, old_zoom_yofs;
    gint canvas_width, canvas_height;

    widget = GTK_WIDGET (canvas);
    gtk_widget_get_allocation (widget, &allocation);

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);
    gtk_layout_get_size (layout, &layout_width, &layout_height);

    canvas_width = allocation.width;
    canvas_height = allocation.height;

    scroll_width =
        floor ((canvas->scroll_x2 - canvas->scroll_x1) *
        canvas->pixels_per_unit + 0.5);
    scroll_height =
        floor ((canvas->scroll_y2 - canvas->scroll_y1) *
        canvas->pixels_per_unit + 0.5);

    right_limit = scroll_width - canvas_width;
    bottom_limit = scroll_height - canvas_height;

    old_zoom_xofs = canvas->zoom_xofs;
    old_zoom_yofs = canvas->zoom_yofs;

    if (right_limit < 0) {
        cx = 0;

        if (canvas->center_scroll_region) {
            canvas->zoom_xofs = (canvas_width - scroll_width) / 2;
            scroll_width = canvas_width;
        } else
            canvas->zoom_xofs = 0;
    } else if (cx < 0) {
        cx = 0;
        canvas->zoom_xofs = 0;
    } else if (cx > right_limit) {
        cx = right_limit;
        canvas->zoom_xofs = 0;
    } else
        canvas->zoom_xofs = 0;

    if (bottom_limit < 0) {
        cy = 0;

        if (canvas->center_scroll_region) {
            canvas->zoom_yofs = (canvas_height - scroll_height) / 2;
            scroll_height = canvas_height;
        } else
            canvas->zoom_yofs = 0;
    } else if (cy < 0) {
        cy = 0;
        canvas->zoom_yofs = 0;
    } else if (cy > bottom_limit) {
        cy = bottom_limit;
        canvas->zoom_yofs = 0;
    } else
        canvas->zoom_yofs = 0;

    if ((canvas->zoom_xofs != old_zoom_xofs) || (canvas->zoom_yofs != old_zoom_yofs)) {
        /* This can only occur, if either canvas size or widget size changes */
        /* So I think we can request full redraw here */
        /* The reason is, that coverage UTA will be invalidated by offset change */
        /* fixme: Strictly this is not correct - we have to remove our own idle (Lauris) */
        /* More stuff - we have to mark root as needing fresh affine (Lauris) */
        if (!(canvas->root->flags & GNOME_CANVAS_ITEM_NEED_AFFINE)) {
            canvas->root->flags |= GNOME_CANVAS_ITEM_NEED_AFFINE;
            gnome_canvas_request_update (canvas);
        }
        gtk_widget_queue_draw (GTK_WIDGET (canvas));
    }

    if (hadjustment)
        gtk_adjustment_set_value (hadjustment, cx);

    if (vadjustment)
        gtk_adjustment_set_value (vadjustment, cy);

    if ((scroll_width != (gint) layout_width)
        || (scroll_height != (gint) layout_height))
        gtk_layout_set_size (GTK_LAYOUT (canvas), scroll_width, scroll_height);
}

/* Size allocation handler for the canvas */
static void
gnome_canvas_size_allocate (GtkWidget *widget, GtkAllocation *allocation)
{
    GtkLayout *layout;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;

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

    if (GTK_WIDGET_CLASS (canvas_parent_class)->size_allocate)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->size_allocate) (widget, allocation);

    layout = GTK_LAYOUT (widget);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    /* Recenter the view, if appropriate */

    g_object_freeze_notify (G_OBJECT (hadjustment));
    g_object_freeze_notify (G_OBJECT (vadjustment));

    gtk_adjustment_set_page_size (hadjustment, allocation->width);
    gtk_adjustment_set_page_increment (hadjustment, allocation->width / 2);

    gtk_adjustment_set_page_size (vadjustment, allocation->height);
    gtk_adjustment_set_page_increment (vadjustment, allocation->height / 2);

    scroll_to (GNOME_CANVAS (widget),
           gtk_adjustment_get_value (hadjustment),
           gtk_adjustment_get_value (vadjustment));

    g_object_thaw_notify (G_OBJECT (hadjustment));
    g_object_thaw_notify (G_OBJECT (vadjustment));
}

/* Emits an event for an item in the canvas, be it the current item, grabbed
 * item, or focused item, as appropriate.
 */

static gint
emit_event (GnomeCanvas *canvas, GdkEvent *event)
{
    GdkEvent *ev;
    gint finished;
    GnomeCanvasItem *item;
    GnomeCanvasItem *parent;
    guint mask;

    /* Perform checks for grabbed items */

    if (canvas->grabbed_item &&
        !is_descendant (canvas->current_item, canvas->grabbed_item)) {
        /* I think this warning is annoying and I don't know what it's for
         * so I'll disable it for now.
         */
/*                g_warning ("emit_event() returning FALSE!\n");*/
        return FALSE;
        }

    if (canvas->grabbed_item) {
        switch (event->type) {
        case GDK_ENTER_NOTIFY:
            mask = GDK_ENTER_NOTIFY_MASK;
            break;

        case GDK_LEAVE_NOTIFY:
            mask = GDK_LEAVE_NOTIFY_MASK;
            break;

        case GDK_MOTION_NOTIFY:
            mask = GDK_POINTER_MOTION_MASK;
            break;

        case GDK_BUTTON_PRESS:
        case GDK_2BUTTON_PRESS:
        case GDK_3BUTTON_PRESS:
            mask = GDK_BUTTON_PRESS_MASK;
            break;

        case GDK_BUTTON_RELEASE:
            mask = GDK_BUTTON_RELEASE_MASK;
            break;

        case GDK_KEY_PRESS:
            mask = GDK_KEY_PRESS_MASK;
            break;

        case GDK_KEY_RELEASE:
            mask = GDK_KEY_RELEASE_MASK;
            break;

        case GDK_SCROLL:
            mask = GDK_SCROLL_MASK;
            break;

        default:
            mask = 0;
            break;
        }

        if (!(mask & canvas->grabbed_event_mask))
            return FALSE;
    }

    /* Convert to world coordinates -- we have two cases because of diferent
     * offsets of the fields in the event structures.
     */

    ev = gdk_event_copy (event);

    switch (ev->type)
        {
    case GDK_ENTER_NOTIFY:
    case GDK_LEAVE_NOTIFY:
        gnome_canvas_window_to_world (canvas,
                          ev->crossing.x, ev->crossing.y,
                          &ev->crossing.x, &ev->crossing.y);
        break;

    case GDK_MOTION_NOTIFY:
    case GDK_BUTTON_PRESS:
    case GDK_2BUTTON_PRESS:
    case GDK_3BUTTON_PRESS:
    case GDK_BUTTON_RELEASE:
                gnome_canvas_window_to_world (canvas,
                                              ev->motion.x, ev->motion.y,
                                              &ev->motion.x, &ev->motion.y);
                break;

    default:
        break;
    }

    /* Choose where we send the event */

    item = canvas->current_item;

    if (canvas->focused_item
        && ((event->type == GDK_KEY_PRESS) ||
        (event->type == GDK_KEY_RELEASE) ||
        (event->type == GDK_FOCUS_CHANGE)))
        item = canvas->focused_item;

    /* The event is propagated up the hierarchy (for if someone connected to
     * a group instead of a leaf event), and emission is stopped if a
     * handler returns TRUE, just like for GtkWidget events.
     */

    finished = FALSE;

    while (item && !finished) {
        g_object_ref (G_OBJECT (item));

        g_signal_emit (item, item_signals[ITEM_EVENT], 0,
                   ev, &finished);

        parent = item->parent;
        g_object_unref (G_OBJECT (item));

        item = parent;
    }

    gdk_event_free (ev);

    return finished;
}

/* Re-picks the current item in the canvas, based on the event's coordinates.
 * Also emits enter/leave events for items as appropriate.
 */
static gint
pick_current_item (GnomeCanvas *canvas, GdkEvent *event)
{
    gint button_down;
    gdouble x, y;
    gint cx, cy;
    gint retval;

    retval = FALSE;

    /* If a button is down, we'll perform enter and leave events on the
     * current item, but not enter on any other item.  This is more or less
     * like X pointer grabbing for canvas items.
     */
    button_down = canvas->state & (GDK_BUTTON1_MASK
                       | GDK_BUTTON2_MASK
                       | GDK_BUTTON3_MASK
                       | GDK_BUTTON4_MASK
                       | GDK_BUTTON5_MASK);
    if (!button_down)
        canvas->left_grabbed_item = FALSE;

    /* Save the event in the canvas.  This is used to synthesize enter and
     * leave events in case the current item changes.  It is also used to
     * re-pick the current item if the current one gets deleted.  Also,
     * synthesize an enter event.
     */
    if (event != &canvas->pick_event) {
        if ((event->type == GDK_MOTION_NOTIFY) || (event->type == GDK_BUTTON_RELEASE)) {
            /* these fields have the same offsets in both types of events */

            canvas->pick_event.crossing.type       = GDK_ENTER_NOTIFY;
            canvas->pick_event.crossing.window     = event->motion.window;
            canvas->pick_event.crossing.send_event = event->motion.send_event;
            canvas->pick_event.crossing.subwindow  = NULL;
            canvas->pick_event.crossing.x          = event->motion.x;
            canvas->pick_event.crossing.y          = event->motion.y;
            canvas->pick_event.crossing.mode       = GDK_CROSSING_NORMAL;
            canvas->pick_event.crossing.detail     = GDK_NOTIFY_NONLINEAR;
            canvas->pick_event.crossing.focus      = FALSE;
            canvas->pick_event.crossing.state      = event->motion.state;

            /* these fields don't have the same offsets in both types of events */

            if (event->type == GDK_MOTION_NOTIFY) {
                canvas->pick_event.crossing.x_root = event->motion.x_root;
                canvas->pick_event.crossing.y_root = event->motion.y_root;
            } else {
                canvas->pick_event.crossing.x_root = event->button.x_root;
                canvas->pick_event.crossing.y_root = event->button.y_root;
            }
        } else
            canvas->pick_event = *event;
    }

    /* Don't do anything else if this is a recursive call */

    if (canvas->in_repick)
        return retval;

    /* LeaveNotify means that there is no current item, so we don't look for one */

    if (canvas->pick_event.type != GDK_LEAVE_NOTIFY) {
        /* these fields don't have the same offsets in both types of events */

        if (canvas->pick_event.type == GDK_ENTER_NOTIFY) {
            x = canvas->pick_event.crossing.x - canvas->zoom_xofs;
            y = canvas->pick_event.crossing.y - canvas->zoom_yofs;
        } else {
            x = canvas->pick_event.motion.x - canvas->zoom_xofs;
            y = canvas->pick_event.motion.y - canvas->zoom_yofs;
        }

        /* canvas pixel coords */

        cx = (gint) (x + 0.5);
        cy = (gint) (y + 0.5);

        /* world coords */

        x = canvas->scroll_x1 + x / canvas->pixels_per_unit;
        y = canvas->scroll_y1 + y / canvas->pixels_per_unit;

        /* find the closest item */

        if (canvas->root->flags & GNOME_CANVAS_ITEM_VISIBLE)
            gnome_canvas_item_invoke_point (canvas->root, x, y, cx, cy,
                            &canvas->new_current_item);
        else
            canvas->new_current_item = NULL;
    } else
        canvas->new_current_item = NULL;

    if ((canvas->new_current_item == canvas->current_item) && !canvas->left_grabbed_item)
        return retval; /* current item did not change */

    /* Synthesize events for old and new current items */

    if ((canvas->new_current_item != canvas->current_item)
        && (canvas->current_item != NULL)
        && !canvas->left_grabbed_item) {
        GdkEvent new_event;

        new_event = canvas->pick_event;
        new_event.type = GDK_LEAVE_NOTIFY;

        new_event.crossing.detail = GDK_NOTIFY_ANCESTOR;
        new_event.crossing.subwindow = NULL;
        canvas->in_repick = TRUE;
        retval = emit_event (canvas, &new_event);
        canvas->in_repick = FALSE;
    }

    /* new_current_item may have been set to NULL during the call to emit_event() above */

    if ((canvas->new_current_item != canvas->current_item) && button_down) {
        canvas->left_grabbed_item = TRUE;
        return retval;
    }

    /* Handle the rest of cases */

    canvas->left_grabbed_item = FALSE;
    canvas->current_item = canvas->new_current_item;

    if (canvas->current_item != NULL) {
        GdkEvent new_event;

        new_event = canvas->pick_event;
        new_event.type = GDK_ENTER_NOTIFY;
        new_event.crossing.detail = GDK_NOTIFY_ANCESTOR;
        new_event.crossing.subwindow = NULL;
        retval = emit_event (canvas, &new_event);
    }

    return retval;
}

/* Button event handler for the canvas */
static gint
gnome_canvas_button (GtkWidget *widget, GdkEventButton *event)
{
    GnomeCanvas *canvas;
    GtkLayout *layout;
    GdkWindow *bin_window;
    gint mask;
    gint retval;

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

    retval = FALSE;

    canvas = GNOME_CANVAS (widget);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);

    /*
     * dispatch normally regardless of the event's window if an item has
     * has a pointer grab in effect
     */
    if (!canvas->grabbed_item && event->window != bin_window)
        return retval;

    switch (event->button) {
    case 1:
        mask = GDK_BUTTON1_MASK;
        break;
    case 2:
        mask = GDK_BUTTON2_MASK;
        break;
    case 3:
        mask = GDK_BUTTON3_MASK;
        break;
    case 4:
        mask = GDK_BUTTON4_MASK;
        break;
    case 5:
        mask = GDK_BUTTON5_MASK;
        break;
    default:
        mask = 0;
    }

    switch (event->type) {
    case GDK_BUTTON_PRESS:
    case GDK_2BUTTON_PRESS:
    case GDK_3BUTTON_PRESS:
        /* Pick the current item as if the button were not pressed, and
         * then process the event.
         */
        canvas->state = event->state;
        pick_current_item (canvas, (GdkEvent *) event);
        canvas->state ^= mask;
        retval = emit_event (canvas, (GdkEvent *) event);
        break;

    case GDK_BUTTON_RELEASE:
        /* Process the event as if the button were pressed, then repick
         * after the button has been released
         */
        canvas->state = event->state;
        retval = emit_event (canvas, (GdkEvent *) event);
        event->state ^= mask;
        canvas->state = event->state;
        pick_current_item (canvas, (GdkEvent *) event);
        event->state ^= mask;
        break;

    default:
        g_assert_not_reached ();
    }

    return retval;
}

/* Motion event handler for the canvas */
static gint
gnome_canvas_motion (GtkWidget *widget, GdkEventMotion *event)
{
    GnomeCanvas *canvas;
    GtkLayout *layout;
    GdkWindow *bin_window;

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

    canvas = GNOME_CANVAS (widget);

    layout = GTK_LAYOUT (widget);
    bin_window = gtk_layout_get_bin_window (layout);

    if (event->window != bin_window)
        return FALSE;

    canvas->state = event->state;
    pick_current_item (canvas, (GdkEvent *) event);
    return emit_event (canvas, (GdkEvent *) event);
}

/* Key event handler for the canvas */
static gboolean
gnome_canvas_key (GtkWidget *widget, GdkEventKey *event)
{
    GnomeCanvas *canvas;

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

    canvas = GNOME_CANVAS (widget);

    if (!emit_event (canvas, (GdkEvent *) event)) {
        GtkWidgetClass *widget_class;

        widget_class = GTK_WIDGET_CLASS (canvas_parent_class);

        if (event->type == GDK_KEY_PRESS) {
            if (widget_class->key_press_event)
                return (* widget_class->key_press_event) (widget, event);
        } else if (event->type == GDK_KEY_RELEASE) {
            if (widget_class->key_release_event)
                return (* widget_class->key_release_event) (widget, event);
        } else
            g_assert_not_reached ();

        return FALSE;
    } else
        return TRUE;
}

/* Crossing event handler for the canvas */
static gint
gnome_canvas_crossing (GtkWidget *widget, GdkEventCrossing *event)
{
    GnomeCanvas *canvas;
    GtkLayout *layout;
    GdkWindow *bin_window;

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

    canvas = GNOME_CANVAS (widget);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);

    if (event->window != bin_window)
        return FALSE;

    canvas->state = event->state;
    return pick_current_item (canvas, (GdkEvent *) event);
}

/* Focus in handler for the canvas */
static gint
gnome_canvas_focus_in (GtkWidget *widget, GdkEventFocus *event)
{
    GnomeCanvas *canvas;

    /* XXX Can't access flags directly anymore, but is it really needed?
     *     If so, could we call gtk_widget_send_focus_change() instead? */
#if 0
    GTK_WIDGET_SET_FLAGS (widget, GTK_HAS_FOCUS);
#endif

    canvas = GNOME_CANVAS (widget);

    if (canvas->focused_item)
        return emit_event (canvas, (GdkEvent *) event);
    else
        return FALSE;
}

/* Focus out handler for the canvas */
static gint
gnome_canvas_focus_out (GtkWidget *widget, GdkEventFocus *event)
{
    GnomeCanvas *canvas;

    /* XXX Can't access flags directly anymore, but is it really needed?
     *     If so, could we call gtk_widget_send_focus_change() instead? */
#if 0
    GTK_WIDGET_UNSET_FLAGS (widget, GTK_HAS_FOCUS);
#endif

    canvas = GNOME_CANVAS (widget);

    if (canvas->focused_item)
        return emit_event (canvas, (GdkEvent *) event);
    else
        return FALSE;
}

#define REDRAW_QUANTUM_SIZE 512

static void
gnome_canvas_paint_rect (GnomeCanvas *canvas, gint x0, gint y0, gint x1, gint y1)
{
    GtkWidget *widget;
    GtkLayout *layout;
    GdkWindow *bin_window;
    GtkAllocation allocation;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gint draw_x1, draw_y1;
    gint draw_x2, draw_y2;
    gint draw_width, draw_height;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    g_return_if_fail (!canvas->need_update);

    widget = GTK_WIDGET (canvas);
    gtk_widget_get_allocation (widget, &allocation);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    hadjustment_value = gtk_adjustment_get_value (hadjustment);
    vadjustment_value = gtk_adjustment_get_value (vadjustment);

    draw_x1 = MAX (x0, hadjustment_value - canvas->zoom_xofs);
    draw_y1 = MAX (y0, vadjustment_value - canvas->zoom_yofs);
    draw_x2 = MIN (draw_x1 + allocation.width, x1);
    draw_y2 = MIN (draw_y1 + allocation.height, y1);

    draw_width = draw_x2 - draw_x1;
    draw_height = draw_y2 - draw_y1;

    if (draw_width < 1 || draw_height < 1)
        return;

    canvas->redraw_x1 = draw_x1;
    canvas->redraw_y1 = draw_y1;
    canvas->redraw_x2 = draw_x2;
    canvas->redraw_y2 = draw_y2;
    canvas->draw_xofs = draw_x1;
    canvas->draw_yofs = draw_y1;

    if (canvas->aa) {
        GnomeCanvasBuf buf;
        guchar *px;
        GdkColor *color;
        GtkStyle *style;

        px = g_new (guchar, draw_width * 3 * draw_height);

        buf.buf = px;
        buf.buf_rowstride = draw_width * 3;
        buf.rect.x0 = draw_x1;
        buf.rect.y0 = draw_y1;
        buf.rect.x1 = draw_x2;
        buf.rect.y1 = draw_y2;
        style = gtk_widget_get_style (widget);
        color = &style->bg[GTK_STATE_NORMAL];
        buf.bg_color =
            (((color->red & 0xff00) << 8) |
            (color->green & 0xff00) | (color->blue >> 8));
        buf.is_bg = 1;
        buf.is_buf = 0;

        g_signal_emit (G_OBJECT (canvas), canvas_signals[RENDER_BACKGROUND], 0, &buf);

        if (canvas->root->flags & GNOME_CANVAS_ITEM_VISIBLE)
            (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->render) (canvas->root, &buf);

        if (buf.is_bg) {
            gdk_gc_set_rgb_fg_color (canvas->pixmap_gc, color);
            gdk_draw_rectangle (bin_window,
                        canvas->pixmap_gc,
                        TRUE,
                        (draw_x1 + canvas->zoom_xofs),
                        (draw_y1 + canvas->zoom_yofs),
                        draw_width, draw_height);
        } else {
            gdk_draw_rgb_image_dithalign (bin_window,
                              canvas->pixmap_gc,
                              (draw_x1 + canvas->zoom_xofs),
                              (draw_y1 + canvas->zoom_yofs),
                              draw_width, draw_height,
                              canvas->dither,
                              buf.buf,
                              buf.buf_rowstride,
                              draw_x1, draw_y1);
        }

        g_free (px);
    } else {
        GdkPixmap *pixmap;
        GdkVisual *visual;
        gint depth;

        visual = gtk_widget_get_visual (widget);
        depth = gdk_visual_get_depth (visual);

        pixmap = gdk_pixmap_new (bin_window,
                     draw_width, draw_height, depth);

        g_signal_emit (G_OBJECT (canvas), canvas_signals[DRAW_BACKGROUND], 0, pixmap,
                   draw_x1, draw_y1, draw_width, draw_height);

        if (canvas->root->flags & GNOME_CANVAS_ITEM_VISIBLE)
            (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->draw) (
                canvas->root, pixmap,
                draw_x1, draw_y1,
                draw_width, draw_height);

        /* Copy the pixmap to the window and clean up */

        gdk_draw_drawable (bin_window,
                   canvas->pixmap_gc,
                   pixmap,
                   0, 0,
                   draw_x1 + canvas->zoom_xofs,
                   draw_y1 + canvas->zoom_yofs,
                   draw_width, draw_height);

        g_object_unref (pixmap);
    }
}

/* Expose handler for the canvas */
static gint
gnome_canvas_expose (GtkWidget *widget, GdkEventExpose *event)
{
    GnomeCanvas *canvas;
    GtkLayout *layout;
    GdkWindow *bin_window;
    GdkRectangle *rects;
    gint n_rects;
    gint i;

    canvas = GNOME_CANVAS (widget);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);

    if (!gtk_widget_is_drawable (widget) || (event->window != bin_window))
        return FALSE;

#ifdef VERBOSE
    g_print ("Expose\n");
#endif

    gdk_region_get_rectangles (event->region, &rects, &n_rects);

    for (i = 0; i < n_rects; i++) {
        ArtIRect rect;

        rect.x0 = rects[i].x - canvas->zoom_xofs;
        rect.y0 = rects[i].y - canvas->zoom_yofs;
        rect.x1 = rects[i].x + rects[i].width - canvas->zoom_xofs;
        rect.y1 = rects[i].y + rects[i].height - canvas->zoom_yofs;

        if (canvas->need_update || canvas->need_redraw) {
            ArtUta *uta;

            /* Update or drawing is scheduled, so just mark exposed area as dirty */
            uta = art_uta_from_irect (&rect);
            gnome_canvas_request_redraw_uta (canvas, uta);
        } else {
            /* No pending updates, draw exposed area immediately */
            gnome_canvas_paint_rect (canvas, rect.x0, rect.y0, rect.x1, rect.y1);

            /* And call expose on parent container class */
            if (GTK_WIDGET_CLASS (canvas_parent_class)->expose_event)
                (* GTK_WIDGET_CLASS (canvas_parent_class)->expose_event) (
                    widget, event);
        }
    }

    g_free (rects);

    return FALSE;
}

/* Repaints the areas in the canvas that need it */
static void
paint (GnomeCanvas *canvas)
{
    GtkWidget *widget;
    GtkLayout *layout;
    GdkWindow *bin_window;
    GtkAllocation allocation;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    ArtIRect *rects;
    gint n_rects, i;
    ArtIRect visible_rect;
    GdkRegion *region;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    widget = GTK_WIDGET (canvas);
    gtk_widget_get_allocation (widget, &allocation);

    layout = GTK_LAYOUT (canvas);
    bin_window = gtk_layout_get_bin_window (layout);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    hadjustment_value = gtk_adjustment_get_value (hadjustment);
    vadjustment_value = gtk_adjustment_get_value (vadjustment);

    /* Extract big rectangles from the microtile array */

    rects = art_rect_list_from_uta (canvas->redraw_area,
                    REDRAW_QUANTUM_SIZE, REDRAW_QUANTUM_SIZE,
                    &n_rects);

    art_uta_free (canvas->redraw_area);
    canvas->redraw_area = NULL;
    canvas->need_redraw = FALSE;

    /* Turn those rectangles into a GdkRegion for exposing */

    visible_rect.x0 = hadjustment_value - canvas->zoom_xofs;
    visible_rect.y0 = vadjustment_value - canvas->zoom_yofs;
    visible_rect.x1 = visible_rect.x0 + allocation.width;
    visible_rect.y1 = visible_rect.y0 + allocation.height;

    region = gdk_region_new ();

    for (i = 0; i < n_rects; i++) {
        ArtIRect clipped;

        art_irect_intersect (&clipped, &visible_rect, rects + i);
        if (!art_irect_empty (&clipped)) {
            GdkRectangle gdkrect;

            gdkrect.x = clipped.x0 + canvas->zoom_xofs;
            gdkrect.y = clipped.y0 + canvas->zoom_yofs;
            gdkrect.width = clipped.x1 - clipped.x0;
            gdkrect.height = clipped.y1 - clipped.y0;

            region = gdk_region_rectangle (&gdkrect);
            gdk_window_invalidate_region (bin_window, region, FALSE);
            gdk_region_destroy (region);
        }
    }

    art_free (rects);

    canvas->redraw_x1 = 0;
    canvas->redraw_y1 = 0;
    canvas->redraw_x2 = 0;
    canvas->redraw_y2 = 0;
}

static void
gnome_canvas_draw_background (GnomeCanvas *canvas, GdkDrawable *drawable,
                  gint x, gint y, gint width, gint height)
{
    GtkStyle *style;

    style = gtk_widget_get_style (GTK_WIDGET (canvas));

    /* By default, we use the style background. */
    gdk_gc_set_foreground (canvas->pixmap_gc,
                   &style->bg[GTK_STATE_NORMAL]);
    gdk_draw_rectangle (drawable,
                canvas->pixmap_gc,
                TRUE,
                0, 0,
                width, height);
}

static void
do_update (GnomeCanvas *canvas)
{
    /* Cause the update if necessary */

update_again:
    if (canvas->need_update) {
        gdouble w2cpx[6];

        /* We start updating root with w2cpx affine */
        w2cpx[0] = canvas->pixels_per_unit;
        w2cpx[1] = 0.0;
        w2cpx[2] = 0.0;
        w2cpx[3] = canvas->pixels_per_unit;
        w2cpx[4] = -canvas->scroll_x1 * canvas->pixels_per_unit;
        w2cpx[5] = -canvas->scroll_y1 * canvas->pixels_per_unit;

        gnome_canvas_item_invoke_update (canvas->root, w2cpx, NULL, 0);

        canvas->need_update = FALSE;
    }

    /* Pick new current item */

    while (canvas->need_repick) {
        canvas->need_repick = FALSE;
        pick_current_item (canvas, &canvas->pick_event);
    }

    /* it is possible that during picking we emitted an event in which
       the user then called some function which then requested update
       of something.  Without this we'd be left in a state where
       need_update would have been left TRUE and the canvas would have
       been left unpainted. */
    if (canvas->need_update) {
        goto update_again;
    }

    /* Paint if able to */

    if (gtk_widget_is_drawable (GTK_WIDGET (canvas)) && canvas->need_redraw)
        paint (canvas);
}

/* Idle handler for the canvas.  It deals with pending updates and redraws. */
static gboolean
idle_handler (gpointer data)
{
    GnomeCanvas *canvas;

    GDK_THREADS_ENTER ();

    canvas = GNOME_CANVAS (data);

    do_update (canvas);

    /* Reset idle id */
    canvas->idle_id = 0;

    GDK_THREADS_LEAVE ();

    return FALSE;
}

/* Convenience function to add an idle handler to a canvas */
static void
add_idle (GnomeCanvas *canvas)
{
    g_assert (canvas->need_update || canvas->need_redraw);

    if (!canvas->idle_id)
        canvas->idle_id = g_idle_add_full (CANVAS_IDLE_PRIORITY,
                           idle_handler,
                           canvas,
                           NULL);

/*  canvas->idle_id = gtk_idle_add (idle_handler, canvas); */
}

/**
 * gnome_canvas_root:
 * @canvas: A canvas.
 *
 * Queries the root group of a canvas.
 *
 * Return value: The root group of the specified canvas.
 **/
GnomeCanvasGroup *
gnome_canvas_root (GnomeCanvas *canvas)
{
    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), NULL);

    return GNOME_CANVAS_GROUP (canvas->root);
}

/**
 * gnome_canvas_set_scroll_region:
 * @canvas: A canvas.
 * @x1: Leftmost limit of the scrolling region.
 * @y1: Upper limit of the scrolling region.
 * @x2: Rightmost limit of the scrolling region.
 * @y2: Lower limit of the scrolling region.
 *
 * Sets the scrolling region of a canvas to the specified rectangle.  The canvas
 * will then be able to scroll only within this region.  The view of the canvas
 * is adjusted as appropriate to display as much of the new region as possible.
 **/
void
gnome_canvas_set_scroll_region (GnomeCanvas *canvas,
                                gdouble x1,
                                gdouble y1,
                                gdouble x2,
                                gdouble y2)
{
    GtkLayout *layout;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;
    gdouble wxofs, wyofs;
    gint xofs, yofs;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    hadjustment_value = gtk_adjustment_get_value (hadjustment);
    vadjustment_value = gtk_adjustment_get_value (vadjustment);

    /*
     * Set the new scrolling region.  If possible, do not move the visible contents of the
     * canvas.
     */

    gnome_canvas_c2w (canvas,
              hadjustment_value + canvas->zoom_xofs,
              vadjustment_value + canvas->zoom_yofs,
              /*canvas->zoom_xofs,
              canvas->zoom_yofs,*/
              &wxofs, &wyofs);

    canvas->scroll_x1 = x1;
    canvas->scroll_y1 = y1;
    canvas->scroll_x2 = x2;
    canvas->scroll_y2 = y2;

    gnome_canvas_w2c (canvas, wxofs, wyofs, &xofs, &yofs);

    scroll_to (canvas, xofs, yofs);

    canvas->need_repick = TRUE;
#if 0
    /* todo: should be requesting update */
    (* GNOME_CANVAS_ITEM_CLASS (canvas->root->object.klass)->update) (
        canvas->root, NULL, NULL, 0);
#endif
}

/**
 * gnome_canvas_get_scroll_region:
 * @canvas: A canvas.
 * @x1: Leftmost limit of the scrolling region (return value).
 * @y1: Upper limit of the scrolling region (return value).
 * @x2: Rightmost limit of the scrolling region (return value).
 * @y2: Lower limit of the scrolling region (return value).
 *
 * Queries the scrolling region of a canvas.
 **/
void
gnome_canvas_get_scroll_region (GnomeCanvas *canvas,
                                gdouble *x1,
                                gdouble *y1,
                                gdouble *x2,
                                gdouble *y2)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    if (x1)
        *x1 = canvas->scroll_x1;

    if (y1)
        *y1 = canvas->scroll_y1;

    if (x2)
        *x2 = canvas->scroll_x2;

    if (y2)
        *y2 = canvas->scroll_y2;
}

/**
 * gnome_canvas_set_center_scroll_region:
 * @canvas: A canvas.
 * @center_scroll_region: Whether to center the scrolling region in the canvas
 * window when it is smaller than the canvas' allocation.
 *
 * When the scrolling region of the canvas is smaller than the canvas window,
 * e.g.  the allocation of the canvas, it can be either centered on the window
 * or simply made to be on the upper-left corner on the window.  This function
 * lets you configure this property.
 **/
void
gnome_canvas_set_center_scroll_region (GnomeCanvas *canvas,
                                       gboolean center_scroll_region)
{
    GtkLayout *layout;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    hadjustment_value = gtk_adjustment_get_value (hadjustment);
    vadjustment_value = gtk_adjustment_get_value (vadjustment);

    canvas->center_scroll_region = center_scroll_region != 0;

    scroll_to (canvas, hadjustment_value, vadjustment_value);
}

/**
 * gnome_canvas_get_center_scroll_region:
 * @canvas: A canvas.
 *
 * Returns whether the canvas is set to center the scrolling region in the window
 * if the former is smaller than the canvas' allocation.
 *
 * Return value: Whether the scroll region is being centered in the canvas window.
 **/
gboolean
gnome_canvas_get_center_scroll_region (GnomeCanvas *canvas)
{
    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), FALSE);

    return canvas->center_scroll_region ? TRUE : FALSE;
}

/**
 * gnome_canvas_set_pixels_per_unit:
 * @canvas: A canvas.
 * @n: The number of pixels that correspond to one canvas unit.
 *
 * Sets the zooming factor of a canvas by specifying the number of pixels that
 * correspond to one canvas unit.
 *
 * The anchor point for zooming, i.e. the point that stays fixed and all others
 * zoom inwards or outwards from it, depends on whether the canvas is set to
 * center the scrolling region or not.  You can control this using the
 * gnome_canvas_set_center_scroll_region() function.  If the canvas is set to
 * center the scroll region, then the center of the canvas window is used as the
 * anchor point for zooming.  Otherwise, the upper-left corner of the canvas
 * window is used as the anchor point.
 **/
void
gnome_canvas_set_pixels_per_unit (GnomeCanvas *canvas, gdouble n)
{
    GtkLayout *layout;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble ax, ay;
    gint x1, y1;
    gint anchor_x, anchor_y;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (n > GNOME_CANVAS_EPSILON);

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    if (canvas->center_scroll_region) {
        GtkAllocation allocation;

        gtk_widget_get_allocation (GTK_WIDGET (canvas), &allocation);

        anchor_x = allocation.width / 2;
        anchor_y = allocation.height / 2;
    } else
        anchor_x = anchor_y = 0;

    /* Find the coordinates of the anchor point in units. */
    if (hadjustment) {
        gdouble value = gtk_adjustment_get_value (hadjustment);
        ax = (value + anchor_x) / canvas->pixels_per_unit +
            canvas->scroll_x1 + canvas->zoom_xofs;
    } else {
        ax = (0.0 + anchor_x) / canvas->pixels_per_unit +
            canvas->scroll_x1 + canvas->zoom_xofs;
    }
    if (vadjustment) {
        gdouble value = gtk_adjustment_get_value (vadjustment);
        ay = (value + anchor_y) / canvas->pixels_per_unit +
            canvas->scroll_y1 + canvas->zoom_yofs;
    } else {
        ay = (0.0 + anchor_y) / canvas->pixels_per_unit +
            canvas->scroll_y1 + canvas->zoom_yofs;
    }

    /* Now calculate the new offset of the upper left corner. */
    x1 = ((ax - canvas->scroll_x1) * n) - anchor_x;
    y1 = ((ay - canvas->scroll_y1) * n) - anchor_y;

    canvas->pixels_per_unit = n;

    scroll_to (canvas, x1, y1);

    if (!(canvas->root->flags & GNOME_CANVAS_ITEM_NEED_AFFINE)) {
        canvas->root->flags |= GNOME_CANVAS_ITEM_NEED_AFFINE;
        gnome_canvas_request_update (canvas);
    }

    canvas->need_repick = TRUE;
}

/**
 * gnome_canvas_scroll_to:
 * @canvas: A canvas.
 * @cx: Horizontal scrolling offset in canvas pixel units.
 * @cy: Vertical scrolling offset in canvas pixel units.
 *
 * Makes a canvas scroll to the specified offsets, given in canvas pixel units.
 * The canvas will adjust the view so that it is not outside the scrolling
 * region.  This function is typically not used, as it is better to hook
 * scrollbars to the canvas layout's scrolling adjusments.
 **/
void
gnome_canvas_scroll_to (GnomeCanvas *canvas, gint cx, gint cy)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    scroll_to (canvas, cx, cy);
}

/**
 * gnome_canvas_get_scroll_offsets:
 * @canvas: A canvas.
 * @cx: Horizontal scrolling offset (return value).
 * @cy: Vertical scrolling offset (return value).
 *
 * Queries the scrolling offsets of a canvas.  The values are returned in canvas
 * pixel units.
 **/
void
gnome_canvas_get_scroll_offsets (GnomeCanvas *canvas, gint *cx, gint *cy)
{
    GtkLayout *layout;
    GtkAdjustment *adjustment;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    layout = GTK_LAYOUT (canvas);

    if (cx) {
        adjustment = gtk_layout_get_hadjustment (layout);
        *cx = (gint) gtk_adjustment_get_value (adjustment);
    }

    if (cy) {
        adjustment = gtk_layout_get_vadjustment (layout);
        *cy = (gint) gtk_adjustment_get_value (adjustment);
    }
}

/**
 * gnome_canvas_update_now:
 * @canvas: A canvas.
 *
 * Forces an immediate update and redraw of a canvas.  If the canvas does not
 * have any pending update or redraw requests, then no action is taken.  This is
 * typically only used by applications that need explicit control of when the
 * display is updated, like games.  It is not needed by normal applications.
 */
void
gnome_canvas_update_now (GnomeCanvas *canvas)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    if (!(canvas->need_update || canvas->need_redraw)) {
        g_assert (canvas->idle_id == 0);
        g_assert (canvas->redraw_area == NULL);
        return;
    }

    remove_idle (canvas);
    do_update (canvas);
}

/**
 * gnome_canvas_get_item_at:
 * @canvas: A canvas.
 * @x: X position in world coordinates.
 * @y: Y position in world coordinates.
 *
 * Looks for the item that is under the specified position, which must be
 * specified in world coordinates.
 *
 * Return value: The sought item, or NULL if no item is at the specified
 * coordinates.
 **/
GnomeCanvasItem *
gnome_canvas_get_item_at (GnomeCanvas *canvas, gdouble x, gdouble y)
{
    GnomeCanvasItem *item;
    gdouble dist;
    gint cx, cy;

    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), NULL);

    gnome_canvas_w2c (canvas, x, y, &cx, &cy);

    dist = gnome_canvas_item_invoke_point (canvas->root, x, y, cx, cy, &item);
    if ((gint) (dist * canvas->pixels_per_unit + 0.5) <= canvas->close_enough)
        return item;
    else
        return NULL;
}

/* Queues an update of the canvas */
static void
gnome_canvas_request_update (GnomeCanvas *canvas)
{
    GNOME_CANVAS_GET_CLASS (canvas)->request_update (canvas);
}

static void
gnome_canvas_request_update_real (GnomeCanvas *canvas)
{
    if (canvas->need_update)
        return;

    canvas->need_update = TRUE;
    if (gtk_widget_get_mapped ((GtkWidget *) canvas))
        add_idle (canvas);
}

/* Computes the union of two microtile arrays while clipping the result to the
 * specified rectangle.  Any of the specified utas can be NULL, in which case it
 * is taken to be an empty region.
 */
static ArtUta *
uta_union_clip (ArtUta *uta1, ArtUta *uta2, ArtIRect *clip)
{
    ArtUta *uta;
    ArtUtaBbox *utiles;
    gint clip_x1, clip_y1, clip_x2, clip_y2;
    gint union_x1, union_y1, union_x2, union_y2;
    gint new_x1, new_y1, new_x2, new_y2;
    gint x, y;
    gint ofs, ofs1, ofs2;

    g_assert (clip != NULL);

    /* Compute the tile indices for the clipping rectangle */

    clip_x1 = clip->x0 >> ART_UTILE_SHIFT;
    clip_y1 = clip->y0 >> ART_UTILE_SHIFT;
    clip_x2 = (clip->x1 >> ART_UTILE_SHIFT) + 1;
    clip_y2 = (clip->y1 >> ART_UTILE_SHIFT) + 1;

    /* Get the union of the bounds of both utas */

    if (!uta1) {
        if (!uta2)
            return art_uta_new (clip_x1, clip_y1, clip_x1 + 1, clip_y1 + 1);

        union_x1 = uta2->x0;
        union_y1 = uta2->y0;
        union_x2 = uta2->x0 + uta2->width;
        union_y2 = uta2->y0 + uta2->height;
    } else {
        if (!uta2) {
            union_x1 = uta1->x0;
            union_y1 = uta1->y0;
            union_x2 = uta1->x0 + uta1->width;
            union_y2 = uta1->y0 + uta1->height;
        } else {
            union_x1 = MIN (uta1->x0, uta2->x0);
            union_y1 = MIN (uta1->y0, uta2->y0);
            union_x2 = MAX (uta1->x0 + uta1->width, uta2->x0 + uta2->width);
            union_y2 = MAX (uta1->y0 + uta1->height, uta2->y0 + uta2->height);
        }
    }

    /* Clip the union of the bounds */

    new_x1 = MAX (clip_x1, union_x1);
    new_y1 = MAX (clip_y1, union_y1);
    new_x2 = MIN (clip_x2, union_x2);
    new_y2 = MIN (clip_y2, union_y2);

    if (new_x1 >= new_x2 || new_y1 >= new_y2)
        return art_uta_new (clip_x1, clip_y1, clip_x1 + 1, clip_y1 + 1);

    /* Make the new clipped union */

    uta = art_new (ArtUta, 1);
    uta->x0 = new_x1;
    uta->y0 = new_y1;
    uta->width = new_x2 - new_x1;
    uta->height = new_y2 - new_y1;
    uta->utiles = utiles = art_new (ArtUtaBbox, uta->width * uta->height);

    ofs = 0;
    ofs1 = ofs2 = 0;

    for (y = new_y1; y < new_y2; y++) {
        if (uta1)
            ofs1 = (y - uta1->y0) * uta1->width + new_x1 - uta1->x0;

        if (uta2)
            ofs2 = (y - uta2->y0) * uta2->width + new_x1 - uta2->x0;

        for (x = new_x1; x < new_x2; x++) {
            ArtUtaBbox bb1, bb2, bb;

            if (!uta1
                || x < uta1->x0 || y < uta1->y0
                || x >= uta1->x0 + uta1->width || y >= uta1->y0 + uta1->height)
                bb1 = 0;
            else
                bb1 = uta1->utiles[ofs1];

            if (!uta2
                || x < uta2->x0 || y < uta2->y0
                || x >= uta2->x0 + uta2->width || y >= uta2->y0 + uta2->height)
                bb2 = 0;
            else
                bb2 = uta2->utiles[ofs2];

            if (bb1 == 0)
                bb = bb2;
            else if (bb2 == 0)
                bb = bb1;
            else
                bb = ART_UTA_BBOX_CONS (MIN (ART_UTA_BBOX_X0 (bb1),
                                 ART_UTA_BBOX_X0 (bb2)),
                            MIN (ART_UTA_BBOX_Y0 (bb1),
                                 ART_UTA_BBOX_Y0 (bb2)),
                            MAX (ART_UTA_BBOX_X1 (bb1),
                                 ART_UTA_BBOX_X1 (bb2)),
                            MAX (ART_UTA_BBOX_Y1 (bb1),
                                 ART_UTA_BBOX_Y1 (bb2)));

            utiles[ofs] = bb;

            ofs++;
            ofs1++;
            ofs2++;
        }
    }

    return uta;
}

static inline void
get_visible_region (GnomeCanvas *canvas, ArtIRect *visible)
{
    GtkLayout *layout;
    GtkAllocation allocation;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    gtk_widget_get_allocation (GTK_WIDGET (canvas), &allocation);

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_layout_get_hadjustment (layout);
    vadjustment = gtk_layout_get_vadjustment (layout);

    hadjustment_value = gtk_adjustment_get_value (hadjustment);
    vadjustment_value = gtk_adjustment_get_value (vadjustment);

    visible->x0 = hadjustment_value - canvas->zoom_xofs;
    visible->y0 = vadjustment_value - canvas->zoom_yofs;
    visible->x1 = visible->x0 + allocation.width;
    visible->y1 = visible->y0 + allocation.height;
}

/**
 * gnome_canvas_request_redraw_uta:
 * @canvas: A canvas.
 * @uta: Microtile array that specifies the area to be redrawn.  It will
 * be freed by this function, so the argument you pass will be invalid
 * after you call this function.
 *
 * Informs a canvas that the specified area, given as a microtile array, needs
 * to be repainted.  To be used only by item implementations.
 **/
void
gnome_canvas_request_redraw_uta (GnomeCanvas *canvas,
                                 ArtUta      *uta)
{
    ArtIRect visible;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (uta != NULL);

    if (!gtk_widget_is_drawable (GTK_WIDGET (canvas))) {
        art_uta_free (uta);
        return;
    }

    get_visible_region (canvas, &visible);

    if (canvas->need_redraw) {
        ArtUta *new_uta;

        g_assert (canvas->redraw_area != NULL);
        /* ALEX: This can fail if e.g. redraw_uta is called by an item
           update function and we're called from update_now -> do_update
           because update_now sets idle_id == 0. There is also some way
           to get it from the expose handler (see bug #102811).
           g_assert (canvas->idle_id != 0);  */

        new_uta = uta_union_clip (canvas->redraw_area, uta, &visible);
        art_uta_free (canvas->redraw_area);
        art_uta_free (uta);
        canvas->redraw_area = new_uta;
        if (canvas->idle_id == 0)
            add_idle (canvas);
    } else {
        ArtUta *new_uta;

        g_assert (canvas->redraw_area == NULL);

        new_uta = uta_union_clip (uta, NULL, &visible);
        art_uta_free (uta);
        canvas->redraw_area = new_uta;

        canvas->need_redraw = TRUE;
        add_idle (canvas);
    }
}

/**
 * gnome_canvas_request_redraw:
 * @canvas: A canvas.
 * @x1: Leftmost coordinate of the rectangle to be redrawn.
 * @y1: Upper coordinate of the rectangle to be redrawn.
 * @x2: Rightmost coordinate of the rectangle to be redrawn, plus 1.
 * @y2: Lower coordinate of the rectangle to be redrawn, plus 1.
 *
 * Convenience function that informs a canvas that the specified rectangle needs
 * to be repainted.  This function converts the rectangle to a microtile array
 * and feeds it to gnome_canvas_request_redraw_uta().  The rectangle includes
 * @x1 and @y1, but not @x2 and @y2.  To be used only by item implementations.
 **/
void
gnome_canvas_request_redraw (GnomeCanvas *canvas, gint x1, gint y1, gint x2, gint y2)
{
    ArtUta *uta;
    ArtIRect bbox;
    ArtIRect visible;
    ArtIRect clip;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    if (!gtk_widget_is_drawable (GTK_WIDGET (canvas)) || (x1 >= x2) || (y1 >= y2))
        return;

    bbox.x0 = x1;
    bbox.y0 = y1;
    bbox.x1 = x2;
    bbox.y1 = y2;

    get_visible_region (canvas, &visible);

    art_irect_intersect (&clip, &bbox, &visible);

    if (!art_irect_empty (&clip)) {
        uta = art_uta_from_irect (&clip);
        gnome_canvas_request_redraw_uta (canvas, uta);
    }
}

/**
 * gnome_canvas_w2c_affine:
 * @canvas: A canvas.
 * @affine: An affine transformation matrix (return value).
 *
 * Gets the affine transform that converts from world coordinates to canvas
 * pixel coordinates.
 **/
void
gnome_canvas_w2c_affine (GnomeCanvas *canvas, gdouble affine[6])
{
    gdouble zooom;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (affine != NULL);

    zooom = canvas->pixels_per_unit;

    affine[0] = zooom;
    affine[1] = 0;
    affine[2] = 0;
    affine[3] = zooom;
    affine[4] = -canvas->scroll_x1 * zooom;
    affine[5] = -canvas->scroll_y1 * zooom;
}

/**
 * gnome_canvas_w2c:
 * @canvas: A canvas.
 * @wx: World X coordinate.
 * @wy: World Y coordinate.
 * @cx: X pixel coordinate (return value).
 * @cy: Y pixel coordinate (return value).
 *
 * Converts world coordinates into canvas pixel coordinates.
 **/
void
gnome_canvas_w2c (GnomeCanvas *canvas, gdouble wx, gdouble wy, gint *cx, gint *cy)
{
    gdouble affine[6];
    ArtPoint w, c;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    gnome_canvas_w2c_affine (canvas, affine);
    w.x = wx;
    w.y = wy;
    art_affine_point (&c, &w, affine);
    if (cx)
        *cx = floor (c.x + 0.5);
    if (cy)
        *cy = floor (c.y + 0.5);
}

/**
 * gnome_canvas_w2c_d:
 * @canvas: A canvas.
 * @wx: World X coordinate.
 * @wy: World Y coordinate.
 * @cx: X pixel coordinate (return value).
 * @cy: Y pixel coordinate (return value).
 *
 * Converts world coordinates into canvas pixel coordinates.  This
 * version returns coordinates in floating point coordinates, for
 * greater precision.
 **/
void
gnome_canvas_w2c_d (GnomeCanvas *canvas,
                    gdouble wx,
                    gdouble wy,
                    gdouble *cx,
                    gdouble *cy)
{
    gdouble affine[6];
    ArtPoint w, c;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    gnome_canvas_w2c_affine (canvas, affine);
    w.x = wx;
    w.y = wy;
    art_affine_point (&c, &w, affine);
    if (cx)
        *cx = c.x;
    if (cy)
        *cy = c.y;
}

/**
 * gnome_canvas_c2w:
 * @canvas: A canvas.
 * @cx: Canvas pixel X coordinate.
 * @cy: Canvas pixel Y coordinate.
 * @wx: X world coordinate (return value).
 * @wy: Y world coordinate (return value).
 *
 * Converts canvas pixel coordinates to world coordinates.
 **/
void
gnome_canvas_c2w (GnomeCanvas *canvas, gint cx, gint cy, gdouble *wx, gdouble *wy)
{
    gdouble affine[6], inv[6];
    ArtPoint w, c;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    gnome_canvas_w2c_affine (canvas, affine);
    art_affine_invert (inv, affine);
    c.x = cx;
    c.y = cy;
    art_affine_point (&w, &c, inv);
    if (wx)
        *wx = w.x;
    if (wy)
        *wy = w.y;
}

/**
 * gnome_canvas_window_to_world:
 * @canvas: A canvas.
 * @winx: Window-relative X coordinate.
 * @winy: Window-relative Y coordinate.
 * @worldx: X world coordinate (return value).
 * @worldy: Y world coordinate (return value).
 *
 * Converts window-relative coordinates into world coordinates.  You can use
 * this when you need to convert mouse coordinates into world coordinates, for
 * example.
 **/
void
gnome_canvas_window_to_world (GnomeCanvas *canvas, gdouble winx, gdouble winy,
                  gdouble *worldx, gdouble *worldy)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    if (worldx)
        *worldx = canvas->scroll_x1 + ((winx - canvas->zoom_xofs)
                           / canvas->pixels_per_unit);

    if (worldy)
        *worldy = canvas->scroll_y1 + ((winy - canvas->zoom_yofs)
                           / canvas->pixels_per_unit);
}

/**
 * gnome_canvas_world_to_window:
 * @canvas: A canvas.
 * @worldx: World X coordinate.
 * @worldy: World Y coordinate.
 * @winx: X window-relative coordinate.
 * @winy: Y window-relative coordinate.
 *
 * Converts world coordinates into window-relative coordinates.
 **/
void
gnome_canvas_world_to_window (GnomeCanvas *canvas, gdouble worldx, gdouble worldy,
                  gdouble *winx, gdouble *winy)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    if (winx)
        *winx = (canvas->pixels_per_unit)*(worldx - canvas->scroll_x1) + canvas->zoom_xofs;

    if (winy)
        *winy = (canvas->pixels_per_unit)*(worldy - canvas->scroll_y1) + canvas->zoom_yofs;
}

/**
 * gnome_canvas_get_color:
 * @canvas: A canvas.
 * @spec: X color specification, or NULL for "transparent".
 * @color: Returns the allocated color.
 *
 * Allocates a color based on the specified X color specification.  As a
 * convenience to item implementations, it returns TRUE if the color was
 * allocated, or FALSE if the specification was NULL.  A NULL color
 * specification is considered as "transparent" by the canvas.
 *
 * Return value: TRUE if @spec is non-NULL and the color is allocated.  If @spec
 * is NULL, then returns FALSE.
 **/
gint
gnome_canvas_get_color (GnomeCanvas *canvas, const gchar *spec, GdkColor *color)
{
    GdkColormap *colormap;

    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), FALSE);
    g_return_val_if_fail (color != NULL, FALSE);

    if (!spec) {
        color->pixel = 0;
        color->red = 0;
        color->green = 0;
        color->blue = 0;
        return FALSE;
    }

    gdk_color_parse (spec, color);

    colormap = gtk_widget_get_colormap (GTK_WIDGET (canvas));

    gdk_rgb_find_color (colormap, color);

    return TRUE;
}

/**
 * gnome_canvas_get_color_pixel:
 * @canvas: A canvas.
 * @rgba: RGBA color specification.
 *
 * Allocates a color from the RGBA value passed into this function.  The alpha
 * opacity value is discarded, since normal X colors do not support it.
 *
 * Return value: Allocated pixel value corresponding to the specified color.
 **/
gulong
gnome_canvas_get_color_pixel (GnomeCanvas *canvas, guint rgba)
{
    GdkColormap *colormap;
    GdkColor color;

    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), 0);

    color.red = ((rgba & 0xff000000) >> 16) + ((rgba & 0xff000000) >> 24);
    color.green = ((rgba & 0x00ff0000) >> 8) + ((rgba & 0x00ff0000) >> 16);
    color.blue = (rgba & 0x0000ff00) + ((rgba & 0x0000ff00) >> 8);
    color.pixel = 0;

    colormap = gtk_widget_get_colormap (GTK_WIDGET (canvas));

    gdk_rgb_find_color (colormap, &color);

    return color.pixel;
}

/**
 * gnome_canvas_set_stipple_origin:
 * @canvas: A canvas.
 * @gc: GC on which to set the stipple origin.
 *
 * Sets the stipple origin of the specified GC as is appropriate for the canvas,
 * so that it will be aligned with other stipple patterns used by canvas items.
 * This is typically only needed by item implementations.
 **/
void
gnome_canvas_set_stipple_origin (GnomeCanvas *canvas, GdkGC *gc)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (GDK_IS_GC (gc));

    gdk_gc_set_ts_origin (gc, -canvas->draw_xofs, -canvas->draw_yofs);
}

/**
 * gnome_canvas_set_dither:
 * @canvas: A canvas.
 * @dither: Type of dithering used to render an antialiased canvas.
 *
 * Controls dithered rendering for antialiased canvases. The value of
 * dither should be #GDK_RGB_DITHER_NONE, #GDK_RGB_DITHER_NORMAL, or
 * #GDK_RGB_DITHER_MAX. The default canvas setting is
 * #GDK_RGB_DITHER_NORMAL.
 **/
void
gnome_canvas_set_dither (GnomeCanvas *canvas, GdkRgbDither dither)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    canvas->dither = dither;
}

/**
 * gnome_canvas_get_dither:
 * @canvas: A canvas.
 *
 * Returns the type of dithering used to render an antialiased canvas.
 *
 * Return value: The dither setting.
 **/
GdkRgbDither
gnome_canvas_get_dither (GnomeCanvas *canvas)
{
    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), GDK_RGB_DITHER_NONE);

    return canvas->dither;
}

static gboolean
boolean_handled_accumulator (GSignalInvocationHint *ihint,
                 GValue                *return_accu,
                 const GValue          *handler_return,
                 gpointer               dummy)
{
    gboolean continue_emission;
    gboolean signal_handled;

    signal_handled = g_value_get_boolean (handler_return);
    g_value_set_boolean (return_accu, signal_handled);
    continue_emission = !signal_handled;

    return continue_emission;
}

/* Class initialization function for GnomeCanvasItemClass */
static void
gnome_canvas_item_class_init (GnomeCanvasItemClass *class)
{
    GObjectClass *gobject_class;

    gobject_class = (GObjectClass *) class;

    item_parent_class = g_type_class_peek_parent (class);

    gobject_class->set_property = gnome_canvas_item_set_property;
    gobject_class->get_property = gnome_canvas_item_get_property;

    g_object_class_install_property
        (gobject_class, ITEM_PROP_PARENT,
         g_param_spec_object ("parent", NULL, NULL,
                      GNOME_TYPE_CANVAS_ITEM,
                      (G_PARAM_READABLE | G_PARAM_WRITABLE)));

    item_signals[ITEM_EVENT] =
        g_signal_new ("event",
                  G_TYPE_FROM_CLASS (class),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GnomeCanvasItemClass, event),
                  boolean_handled_accumulator, NULL,
                  gnome_canvas_marshal_BOOLEAN__BOXED,
                  G_TYPE_BOOLEAN, 1,
                  GDK_TYPE_EVENT | G_SIGNAL_TYPE_STATIC_SCOPE);

    gobject_class->dispose = gnome_canvas_item_dispose;

    class->realize = gnome_canvas_item_realize;
    class->unrealize = gnome_canvas_item_unrealize;
    class->map = gnome_canvas_item_map;
    class->unmap = gnome_canvas_item_unmap;
    class->update = gnome_canvas_item_update;
}