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.
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <math.h>
#include <string.h>
#include <stdio.h>
#include <gdk/gdkprivate.h>
#include <gtk/gtk.h>
#include <cairo-gobject.h>
#include "gailcanvas.h"
#include "gnome-canvas.h"
#include "gnome-canvas-i18n.h"
#include "gnome-canvas-util.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 gint  emit_event                       (GnomeCanvas *canvas, GdkEvent *event);

static guint item_signals[ITEM_LAST_SIGNAL];

G_DEFINE_TYPE (
    GnomeCanvasItem,
    gnome_canvas_item,
    G_TYPE_INITIALLY_UNOWNED)

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

    cairo_matrix_init_identity (&item->matrix);
}

/**
 * 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 property_id,
                                const GValue *value,
                                GParamSpec *pspec)
{
    GnomeCanvasItem *item;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (property_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, property_id, pspec);
        break;
    }
}

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

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

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

    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, property_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 dispose 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);

    if (GNOME_CANVAS_ITEM_GET_CLASS (item)->dispose)
        GNOME_CANVAS_ITEM_GET_CLASS (item)->dispose (item);

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

/* Update handler for canvas items */
static void
gnome_canvas_item_update (GnomeCanvasItem *item,
                          const cairo_matrix_t *matrix,
                          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;
}

/* 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;
}

/* Dispose handler for canvas items */
static void
gnome_canvas_item_dispose_item (GnomeCanvasItem *item)
{
    /* Placeholder so subclasses can safely chain up. */
}

/*
 * 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,
                                 const cairo_matrix_t *p2c,
                                 gint flags)
{
    gint child_flags;
    cairo_matrix_t i2c;

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

    /* Calculate actual item transformation matrix */

    cairo_matrix_multiply (&i2c, &item->matrix, p2c);

    /* 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, &i2c, 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 GnomeCanvasItem *
gnome_canvas_item_invoke_point (GnomeCanvasItem *item,
                                gdouble x,
                                gdouble y,
                                gint cx,
                                gint cy)
{
    cairo_matrix_t inverse;

    /* Calculate x & y in item local coordinates */
    inverse = item->matrix;
    if (cairo_matrix_invert (&inverse) != CAIRO_STATUS_SUCCESS)
        return NULL;

    cairo_matrix_transform_point (&inverse, &x, &y);

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

    return NULL;
}

/**
 * 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_transform:
 * @item: A canvas item.
 * @matrix: An affine transformation matrix.
 *
 * Combines the specified affine transformation matrix with the item's current
 * transformation.
 **/
void
gnome_canvas_item_transform (GnomeCanvasItem *item,
                             const cairo_matrix_t *matrix)
{
    cairo_matrix_t i2p;

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

    /* Calculate actual item transformation matrix */
    cairo_matrix_multiply (&i2p, matrix, &item->matrix);

    gnome_canvas_item_set_matrix (item, &i2p);
}

/**
 * gnome_canvas_item_set_matrix:
 * @item: A canvas item.
 * @matrix: An affine transformation matrix or %NULL for the identity matrix.
 *
 * Makes the item's affine transformation matrix be equal to the specified
 * matrix. NULL is treated as identity.
 **/
void
gnome_canvas_item_set_matrix (GnomeCanvasItem *item,
                              const cairo_matrix_t *matrix)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (matrix) {
        item->matrix = *matrix;
    } else {
        cairo_matrix_init_identity (&item->matrix);
    }

    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)
{
    cairo_matrix_t translate;

    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    cairo_matrix_init_translate (&translate, dx, dy);

    gnome_canvas_item_transform (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_return_if_fail (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_return_if_fail (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_return_if_fail (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_return_if_fail (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);
}

void
gnome_canvas_item_i2w_matrix (GnomeCanvasItem *item,
                              cairo_matrix_t *matrix)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (matrix != NULL);

    cairo_matrix_init_identity (matrix);

    while (item) {
        cairo_matrix_multiply (matrix, matrix, &item->matrix);

        item = item->parent;
    }
}

void
gnome_canvas_item_w2i_matrix (GnomeCanvasItem *item,
                              cairo_matrix_t *matrix)
{
    cairo_status_t status;

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

    gnome_canvas_item_i2w_matrix (item, matrix);
    status = cairo_matrix_invert (matrix);
    g_return_if_fail (status == CAIRO_STATUS_SUCCESS);
}

/**
 * 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)
{
    cairo_matrix_t matrix;

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

    gnome_canvas_item_w2i_matrix (item, &matrix);
    cairo_matrix_transform_point (&matrix, x, 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)
{
    cairo_matrix_t matrix;

    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_matrix (item, &matrix);
    cairo_matrix_transform_point (&matrix, x, y);
}

/**
 * gnome_canvas_item_i2c_matrix:
 * @item: A canvas item.
 * @matrix: Matrix to take the resulting transformation matrix (return value).
 *
 * Gets the affine transform that converts from item-relative coordinates to
 * canvas pixel coordinates.
 **/
void
gnome_canvas_item_i2c_matrix (GnomeCanvasItem *item,
                              cairo_matrix_t *matrix)
{
    cairo_matrix_t i2w, w2c;

    gnome_canvas_item_i2w_matrix (item, &i2w);
    gnome_canvas_w2c_matrix (item->canvas, &w2c);
    cairo_matrix_multiply (matrix, &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;

    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 */
    gnome_canvas_matrix_transform_rect (&item->matrix, &tx1, &ty1, &tx2, &ty2);

    /* 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_set_property (GObject               *object,
                        guint                  property_id,
                        const GValue          *value,
                        GParamSpec            *pspec);
static void gnome_canvas_group_get_property (GObject               *object,
                        guint                  property_id,
                        GValue                *value,
                        GParamSpec            *pspec);

static void gnome_canvas_group_dispose     (GnomeCanvasItem *object);

static void   gnome_canvas_group_update      (GnomeCanvasItem *item,
                                              const cairo_matrix_t *matrix,
                          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,
                          cairo_t *cr,
                          gint x, gint y,
                          gint width, gint height);
static GnomeCanvasItem *gnome_canvas_group_point (GnomeCanvasItem *item,
                          gdouble x, gdouble y,
                          gint cx, gint cy);
static void   gnome_canvas_group_bounds      (GnomeCanvasItem *item,
                          gdouble *x1, gdouble *y1,
                          gdouble *x2, gdouble *y2);

G_DEFINE_TYPE (
    GnomeCanvasGroup,
    gnome_canvas_group,
    GNOME_TYPE_CANVAS_ITEM)

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

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

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

    g_object_class_install_property
        (object_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
        (object_class, GROUP_PROP_Y,
         g_param_spec_double ("y",
                      "Y",
                      "Y",
                      -G_MAXDOUBLE, G_MAXDOUBLE, 0.0,
                      (G_PARAM_READABLE | G_PARAM_WRITABLE)));

    item_class->dispose = gnome_canvas_group_dispose;
    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->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)
{
}

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

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (property_id) {
    case GROUP_PROP_X:
        item->matrix.x0 = g_value_get_double (value);
        break;

    case GROUP_PROP_Y:
        item->matrix.y0 = g_value_get_double (value);
        break;

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

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

    g_return_if_fail (GNOME_IS_CANVAS_GROUP (gobject));

    item = GNOME_CANVAS_ITEM (gobject);

    switch (property_id) {
    case GROUP_PROP_X:
        g_value_set_double (value, item->matrix.x0);
        break;

    case GROUP_PROP_Y:
        g_value_set_double (value, item->matrix.y0);
        break;

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

/* Dispose handler for canvas groups */
static void
gnome_canvas_group_dispose (GnomeCanvasItem *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 (). */
        g_object_run_dispose (G_OBJECT (group->item_list->data));
    }

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_group_parent_class)->
        dispose (object);
}

/* Update handler for canvas groups */
static void
gnome_canvas_group_update (GnomeCanvasItem *item,
                           const cairo_matrix_t *i2c,
                           gint flags)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *i;
    gdouble x1, y1, x2, y2;

    group = GNOME_CANVAS_GROUP (item);

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_group_parent_class)->
        update (item, i2c, flags);

    x1 = G_MAXDOUBLE;
    y1 = G_MAXDOUBLE;
    x2 = -G_MAXDOUBLE;
    y2 = -G_MAXDOUBLE;

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

        gnome_canvas_item_invoke_update (i, i2c, flags);

        x1 = MIN (x1, i->x1);
        x2 = MAX (x2, i->x2);
        y1 = MIN (y1, i->y1);
        y2 = MAX (y2, i->y2);
    }
    if (x1 >= x2 || y1 >= y2) {
        item->x1 = item->x2 = item->y1 = item->y2 = 0;
    } else {
        item->x1 = x1;
        item->y1 = y1;
        item->x2 = x2;
        item->y2 = y2;
    }
}

/* 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);
    }

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_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);
    }

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_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);
    }

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_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);
    }

    GNOME_CANVAS_ITEM_CLASS (gnome_canvas_group_parent_class)->unmap (item);
}

/* Draw handler for canvas groups */
static void
gnome_canvas_group_draw (GnomeCanvasItem *item,
                         cairo_t *cr,
                         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))) {
            cairo_save (cr);

            GNOME_CANVAS_ITEM_GET_CLASS (child)->draw (
                child, cr, x, y, width, height);

            cairo_restore (cr);
        }
    }
}

/* Point handler for canvas groups */
static GnomeCanvasItem *
gnome_canvas_group_point (GnomeCanvasItem *item,
                          gdouble x,
                          gdouble y,
                          gint cx,
                          gint cy)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *child, *point_item;

    group = GNOME_CANVAS_GROUP (item);

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

        if ((child->x1 > cx) || (child->y1 > cy))
            continue;

        if ((child->x2 < cx) || (child->y2 < cy))
            continue;

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

        point_item = gnome_canvas_item_invoke_point (child, x, y, cx, cy);
        if (point_item)
            return point_item;
    }

    return NULL;
}

/* 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;
}

/* 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,
    LAST_SIGNAL
};

static void gnome_canvas_dispose             (GObject          *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_draw                (GtkWidget        *widget,
                          cairo_t          *cr);
static gint gnome_canvas_button              (GtkWidget        *widget,
                          GdkEventButton   *event);
static gint gnome_canvas_motion              (GtkWidget        *widget,
                          GdkEventMotion   *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,
                          cairo_t          *cr,
                          gint              x,
                          gint              y,
                          gint              width,
                          gint              height);

static guint canvas_signals[LAST_SIGNAL];

enum {
        PROP_0,
    PROP_FOCUSED_ITEM,
};

G_DEFINE_TYPE (
    GnomeCanvas,
    gnome_canvas,
    GTK_TYPE_LAYOUT)

static void
gnome_canvas_paint_rect (GnomeCanvas *canvas,
                         cairo_t *cr,
                         gint x0,
                         gint y0,
                         gint x1,
                         gint y1)
{
    GtkWidget *widget;
    GtkAllocation allocation;
    GtkScrollable *scrollable;
    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);

    scrollable = GTK_SCROLLABLE (canvas);
    hadjustment = gtk_scrollable_get_hadjustment (scrollable);
    vadjustment = gtk_scrollable_get_vadjustment (scrollable);

    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->draw_xofs = draw_x1;
    canvas->draw_yofs = draw_y1;

    cairo_save (cr);

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

    cairo_restore (cr);

    if (canvas->root->flags & GNOME_CANVAS_ITEM_VISIBLE) {
        cairo_save (cr);

        (* GNOME_CANVAS_ITEM_GET_CLASS (canvas->root)->draw) (
            canvas->root, cr,
            draw_x1, draw_y1,
            draw_width, draw_height);

        cairo_restore (cr);
    }
}

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

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

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

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

    object_class->set_property = gnome_canvas_set_property;
    object_class->get_property = gnome_canvas_get_property;
    object_class->dispose = gnome_canvas_dispose;

    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->draw = gnome_canvas_draw;
    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->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;

    class->draw_background = gnome_canvas_draw_background;
    class->request_update = gnome_canvas_request_update_real;

    g_object_class_install_property (object_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, NULL,
                  G_TYPE_NONE, 5, CAIRO_GOBJECT_TYPE_CONTEXT,
                  G_TYPE_INT, G_TYPE_INT, G_TYPE_INT, G_TYPE_INT);

    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_finalized (gpointer data,
                      GObject *gone_object)
{
    g_error ("Eeeek, root item %p of canvas %p was destroyed!", gone_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->idle_id = 0;

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

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

    gtk_scrollable_set_hadjustment (GTK_SCROLLABLE (canvas), NULL);
    gtk_scrollable_set_vadjustment (GTK_SCROLLABLE (canvas), NULL);

    /* 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);

    g_object_weak_ref (G_OBJECT (canvas->root), panic_root_finalized, 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)
{
    if (canvas->grabbed_item) {
        canvas->grabbed_item = NULL;
        gdk_pointer_ungrab (GDK_CURRENT_TIME);
    }

    remove_idle (canvas);
}

/* Dispose handler for GnomeCanvas */
static void
gnome_canvas_dispose (GObject *object)
{
    GnomeCanvas *canvas;

    g_return_if_fail (GNOME_IS_CANVAS (object));

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

    canvas = GNOME_CANVAS (object);

    if (canvas->root) {
        g_object_weak_unref (G_OBJECT (canvas->root), panic_root_finalized, canvas);
        g_object_unref (G_OBJECT (canvas->root));
        canvas->root = NULL;
    }

    shutdown_transients (canvas);

    /* Chain up to parent's dispose() method. */
    G_OBJECT_CLASS (gnome_canvas_parent_class)->dispose (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));
}

/* 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 */

    GTK_WIDGET_CLASS (gnome_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 */

    GTK_WIDGET_CLASS (gnome_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 */

    GTK_WIDGET_CLASS (gnome_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_SCROLL_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 */

    (* 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);

    GTK_WIDGET_CLASS (gnome_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;
    GtkAllocation allocation;
    GtkScrollable *scrollable;
    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);

    scrollable = GTK_SCROLLABLE (canvas);
    hadjustment = gtk_scrollable_get_hadjustment (scrollable);
    vadjustment = gtk_scrollable_get_vadjustment (scrollable);

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

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

    scroll_width =
        floor ((canvas->scroll_x2 - canvas->scroll_x1) + 0.5);
    scroll_height =
        floor ((canvas->scroll_y2 - canvas->scroll_y1) + 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;
        canvas->zoom_xofs = (canvas_width - scroll_width) / 2;
        scroll_width = canvas_width;
    } 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;
        canvas->zoom_yofs = (canvas_height - scroll_height) / 2;
        scroll_height = canvas_height;
    } 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)
{
    GtkScrollable *scrollable;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;

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

    GTK_WIDGET_CLASS (gnome_canvas_parent_class)->
        size_allocate (widget, allocation);

    scrollable = GTK_SCROLLABLE (widget);
    hadjustment = gtk_scrollable_get_hadjustment (scrollable);
    vadjustment = gtk_scrollable_get_vadjustment (scrollable);

    /* 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));
}

static gboolean
gnome_canvas_draw (GtkWidget *widget,
                   cairo_t *cr)
{
    GnomeCanvas *canvas = GNOME_CANVAS (widget);
    cairo_rectangle_int_t rect;
    GtkLayout *layout;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    layout = GTK_LAYOUT (canvas);
    hadjustment = gtk_scrollable_get_hadjustment (GTK_SCROLLABLE (layout));
    vadjustment = gtk_scrollable_get_vadjustment (GTK_SCROLLABLE (layout));

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

    gdk_cairo_get_clip_rectangle (cr, &rect);

    if (canvas->need_update) {
        cairo_matrix_t w2c;

        /* We start updating root with w2c matrix */
        gnome_canvas_w2c_matrix (canvas, &w2c);

        gnome_canvas_item_invoke_update (canvas->root, &w2c, 0);

        canvas->need_update = FALSE;
    }

    cairo_save (cr);
    cairo_translate (cr,
             -canvas->zoom_xofs + rect.x,
             -canvas->zoom_yofs + rect.y);

    rect.x += hadjustment_value;
    rect.y += vadjustment_value;

    /* No pending updates, draw exposed area immediately */
    gnome_canvas_paint_rect (canvas, cr,
                 rect.x, rect.y,
                 rect.x + rect.width,
                 rect.y + rect.height);
    cairo_restore (cr);

    /* And call expose on parent container class */
    GTK_WIDGET_CLASS (gnome_canvas_parent_class)->draw (widget, cr);

    return FALSE;
}

/* 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;
        y = canvas->scroll_y1 + y;

        /* find the closest item */

        if (canvas->root->flags & GNOME_CANVAS_ITEM_VISIBLE)
            canvas->new_current_item =
                gnome_canvas_item_invoke_point (
                canvas->root, x, y, cx, cy);
        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_warn_if_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 (gnome_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_warn_if_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;

    /* XXX Detect and disregard synthesized crossing events generated
     *     by synth_crossing() in gtkwidget.c.  The pointer coordinates
     *     are invalid and pick_current_item() relies on them. */
    if (event->x == 0 && event->y == 0 &&
        event->x_root == 0 && event->y_root == 0)
        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;
}

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

    style = gtk_widget_get_style (GTK_WIDGET (canvas));

    cairo_save (cr);
    gdk_cairo_set_source_color (cr, &style->bg[GTK_STATE_NORMAL]);
    cairo_paint (cr);
    cairo_restore (cr);
}

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

update_again:
    if (canvas->need_update) {
        cairo_matrix_t w2c;

        /* We start updating root with w2c matrix */
        gnome_canvas_w2c_matrix (canvas, &w2c);

        gnome_canvas_item_invoke_update (canvas->root, &w2c, 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;
    }
}

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

    canvas = GNOME_CANVAS (data);

    do_update (canvas);

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

    return FALSE;
}

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

    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)
{
    GtkScrollable *scrollable;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;
    gdouble wxofs, wyofs;
    gint xofs, yofs;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    scrollable = GTK_SCROLLABLE (canvas);
    hadjustment = gtk_scrollable_get_hadjustment (scrollable);
    vadjustment = gtk_scrollable_get_vadjustment (scrollable);

    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.class)->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_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)
{
    GtkAdjustment *adjustment;
    GtkScrollable *scrollable;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    scrollable = GTK_SCROLLABLE (canvas);

    if (cx) {
        adjustment = gtk_scrollable_get_hadjustment (scrollable);
        *cx = (gint) gtk_adjustment_get_value (adjustment);
    }

    if (cy) {
        adjustment = gtk_scrollable_get_vadjustment (scrollable);
        *cy = (gint) gtk_adjustment_get_value (adjustment);
    }
}

/**
 * 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)
{
    gint cx, cy;

    g_return_val_if_fail (GNOME_IS_CANVAS (canvas), NULL);

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

    return gnome_canvas_item_invoke_point (canvas->root, x, y, cx, cy);
}

/* 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);
}

static inline void
get_visible_rect (GnomeCanvas *canvas,
                  GdkRectangle *visible)
{
    GtkAllocation allocation;
    GtkScrollable *scrollable;
    GtkAdjustment *hadjustment;
    GtkAdjustment *vadjustment;
    gdouble hadjustment_value;
    gdouble vadjustment_value;

    gtk_widget_get_allocation (GTK_WIDGET (canvas), &allocation);

    scrollable = GTK_SCROLLABLE (canvas);
    hadjustment = gtk_scrollable_get_hadjustment (scrollable);
    vadjustment = gtk_scrollable_get_vadjustment (scrollable);

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

    visible->x = hadjustment_value - canvas->zoom_xofs;
    visible->y = vadjustment_value - canvas->zoom_yofs;
    visible->width = allocation.width;
    visible->height = allocation.height;
}

/**
 * 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.  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)
{
    GdkRectangle area, clip;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

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

    area.x = x1;
    area.y = y1;
    area.width = x2 - x1 + 1;
    area.height = y2 - y1 + 1;

    get_visible_rect (canvas, &clip);
    if (!gdk_rectangle_intersect (&area, &clip, &area))
        return;

    gdk_window_invalidate_rect (gtk_layout_get_bin_window (GTK_LAYOUT (canvas)),
                    &area, FALSE);
}

/**
 * gnome_canvas_w2c_matrix:
 * @canvas: A canvas.
 * @matrix: (out): matrix to initialize
 *
 * Gets the transformtion matrix that converts from world coordinates to canvas
 * pixel coordinates.
 **/
void
gnome_canvas_w2c_matrix (GnomeCanvas *canvas,
                         cairo_matrix_t *matrix)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (matrix != NULL);

    cairo_matrix_init_translate (
        matrix, -canvas->scroll_x1, -canvas->scroll_y1);
}

/**
 * gnome_canvas_c2w_matrix:
 * @canvas: A canvas.
 * @matrix: (out): matrix to initialize
 *
 * Gets the transformtion matrix that converts from canvas pixel coordinates to
 * world coordinates.
 **/
void
gnome_canvas_c2w_matrix (GnomeCanvas *canvas,
                         cairo_matrix_t *matrix)
{
    g_return_if_fail (GNOME_IS_CANVAS (canvas));
    g_return_if_fail (matrix != NULL);

    cairo_matrix_init_translate (
        matrix, canvas->scroll_x1, canvas->scroll_y1);
}

/**
 * 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)
{
    cairo_matrix_t w2c;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    gnome_canvas_w2c_matrix (canvas, &w2c);
    cairo_matrix_transform_point (&w2c, &wx, &wy);

    if (cx)
        *cx = floor (wx + 0.5);
    if (cy)
        *cy = floor (wy + 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)
{
    cairo_matrix_t w2c;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    gnome_canvas_w2c_matrix (canvas, &w2c);
    cairo_matrix_transform_point (&w2c, &wx, &wy);

    if (cx)
        *cx = wx;
    if (cy)
        *cy = wy;
}

/**
 * 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)
{
    cairo_matrix_t c2w;
    gdouble x, y;

    g_return_if_fail (GNOME_IS_CANVAS (canvas));

    x = cx;
    y = cy;
    gnome_canvas_c2w_matrix (canvas, &c2w);
    cairo_matrix_transform_point (&c2w, &x, &y);

    if (wx)
        *wx = x;
    if (wy)
        *wy = 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);

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

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

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

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;

    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, NULL,
                  G_TYPE_BOOLEAN, 1,
                  GDK_TYPE_EVENT | G_SIGNAL_TYPE_STATIC_SCOPE);

    gobject_class->dispose = gnome_canvas_item_dispose;

    class->update = gnome_canvas_item_update;
    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->dispose = gnome_canvas_item_dispose_item;
}