path: root/widgets/misc/e-canvas.c

/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) version 3.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with the program; if not, see <http://www.gnu.org/licenses/>
 *
 *
 * Authors:
 *      Chris Lahey <clahey@ximian.com>
 *
 * Copyright (C) 1999-2008 Novell, Inc. (www.novell.com)
 *
 */

#include <config.h>

#include <gtk/gtk.h>

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

#include "e-canvas.h"

#define d(x)

enum {
    REFLOW,
    LAST_SIGNAL
};

static guint signals[LAST_SIGNAL];

G_DEFINE_TYPE (
    ECanvas,
    e_canvas,
    GNOME_TYPE_CANVAS)

/* Emits an event for an item in the canvas, be it the current
 * item, grabbed item, or focused item, as appropriate. */
static gint
canvas_emit_event (GnomeCanvas *canvas,
                   GdkEvent *event)
{
    GdkEvent *ev;
    gint finished;
    GnomeCanvasItem *item;
    GnomeCanvasItem *parent;
    guint mask;

    /* 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;

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

    /* Perform checks for grabbed items */

    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;

            default:
                mask = 0;
                break;
        }

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

    /* Convert to world coordinates -- we have two cases because of
     * different 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;
    }

    /* 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 (item);

        g_signal_emit_by_name (item, "event", ev, &finished);

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

        item = parent;
    }

    gdk_event_free (ev);

    return finished;
}

/* This routine invokes the point method of the item.  The argument x, y
 * should be in the parent's item-relative coordinate system.  This routine
 * applies the inverse of the item's transform, maintaining the affine
 * invariant. */
#define HACKISH_AFFINE

static double
gnome_canvas_item_invoke_point (GnomeCanvasItem *item,
                                gdouble x,
                                gdouble y,
                                gint cx,
                                gint cy,
                                GnomeCanvasItem **actual_item)
{
#ifdef HACKISH_AFFINE
    gdouble i2w[6], w2c[6], i2c[6], c2i[6];
    ArtPoint c, i;
#endif

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

    return (* GNOME_CANVAS_ITEM_CLASS (G_OBJECT_GET_CLASS (item))->point) (
        item, x, y, cx, cy, actual_item);
}

/* Re-picks the current item in the canvas, based on the event's coordinates.
 * Also emits enter/leave events for items as appropriate.
 */
#define DISPLAY_X1(canvas) (GNOME_CANVAS (canvas)->layout.xoffset)
#define DISPLAY_Y1(canvas) (GNOME_CANVAS (canvas)->layout.yoffset)
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->scroll_x1 - canvas->zoom_xofs;
            y = canvas->pick_event.crossing.y + canvas->scroll_y1 - canvas->zoom_yofs;
        } else {
            x = canvas->pick_event.motion.x + canvas->scroll_x1 - canvas->zoom_xofs;
            y = canvas->pick_event.motion.y + canvas->scroll_y1 - canvas->zoom_yofs;
        }

        /* canvas pixel coords */

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

        /* world coords */

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

        /* find the closest item */

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

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

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

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

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

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

    /* new_current_item may have been set to NULL during
     * the call to canvas_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 = canvas_emit_event (canvas, &new_event);
    }

    return retval;
}

static void
canvas_style_set_recursive (GnomeCanvasItem *item,
                            GtkStyle *previous_style)
{
    guint signal_id = g_signal_lookup ("style_set", G_OBJECT_TYPE (item));
    if (signal_id >= 1) {
        GSignalQuery query;
        g_signal_query (signal_id, &query);
        if (query.return_type == G_TYPE_NONE &&
            query.n_params == 1 &&
            query.param_types[0] == GTK_TYPE_STYLE) {
            g_signal_emit (item, signal_id, 0, previous_style);
        }
    }

    if (GNOME_IS_CANVAS_GROUP (item) ) {
        GList *items = GNOME_CANVAS_GROUP (item)->item_list;
        for (; items; items = items->next)
            canvas_style_set_recursive (
                items->data, previous_style);
    }
}

static void
canvas_dispose (GObject *object)
{
    ECanvas *canvas = E_CANVAS (object);

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

    if (canvas->grab_cancelled_check_id)
        g_source_remove (canvas->grab_cancelled_check_id);
    canvas->grab_cancelled_check_id = 0;

    if (canvas->toplevel) {
        if (canvas->visibility_notify_id)
            g_signal_handler_disconnect (canvas->toplevel,
                             canvas->visibility_notify_id);
        canvas->visibility_notify_id = 0;

        g_object_unref (canvas->toplevel);
        canvas->toplevel = NULL;
    }

    if (canvas->im_context) {
        g_object_unref (canvas->im_context);
        canvas->im_context = NULL;
    }

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

static void
canvas_realize (GtkWidget *widget)
{
    ECanvas *ecanvas = E_CANVAS (widget);
    GdkWindow *window;

    /* Chain up to parent's realize() method. */
    GTK_WIDGET_CLASS (e_canvas_parent_class)->realize (widget);

    window = gtk_layout_get_bin_window (GTK_LAYOUT (widget));
    gdk_window_set_back_pixmap (window, NULL, FALSE);

    window = gtk_widget_get_window (widget);
    gtk_im_context_set_client_window (ecanvas->im_context, window);
}

static void
canvas_unrealize (GtkWidget *widget)
{
    ECanvas * ecanvas = E_CANVAS (widget);

    if (ecanvas->idle_id) {
        g_source_remove (ecanvas->idle_id);
        ecanvas->idle_id = 0;
    }

    gtk_im_context_set_client_window (ecanvas->im_context, NULL);

    /* Chain up to parent's unrealize() method. */
    GTK_WIDGET_CLASS (e_canvas_parent_class)->unrealize (widget);
}

static void
canvas_style_set (GtkWidget *widget,
                  GtkStyle *previous_style)
{
    canvas_style_set_recursive (
        GNOME_CANVAS_ITEM (gnome_canvas_root (
        GNOME_CANVAS (widget))), previous_style);
}

static gint
canvas_button_event (GtkWidget *widget,
                     GdkEventButton *event)
{
    GnomeCanvas *canvas;
    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);
    bin_window = gtk_layout_get_bin_window (GTK_LAYOUT (canvas));

    d(g_print ("button %d, event type %d, grabbed=%p, current=%p\n",
           event->button,
           event->type,
           canvas->grabbed_item,
           canvas->current_item));

        /* 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 = canvas_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 = canvas_emit_event (canvas, (GdkEvent *) event);
            event->state ^= mask;
            canvas->state = event->state;
            pick_current_item (canvas, (GdkEvent *) event);
            event->state ^= mask;
            break;

        default:
            g_return_val_if_reached (0);
    }

    return retval;
}

static gint
canvas_key_event (GtkWidget *widget,
                  GdkEventKey *event)
{
    GnomeCanvas *canvas;
    GdkEvent full_event;

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

    canvas = GNOME_CANVAS (widget);

    full_event.key = *event;

    return canvas_emit_event (canvas, &full_event);
}

static gint
canvas_focus_in_event (GtkWidget *widget,
                       GdkEventFocus *event)
{
    GnomeCanvas *canvas;
    ECanvas *ecanvas;
    GdkEvent full_event;

    canvas = GNOME_CANVAS (widget);
    ecanvas = E_CANVAS (widget);

    /* 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

    gtk_im_context_focus_in (ecanvas->im_context);

    if (canvas->focused_item) {
        full_event.focus_change = *event;
        return canvas_emit_event (canvas, &full_event);
    } else {
        return FALSE;
    }
}

static gint
canvas_focus_out_event (GtkWidget *widget,
                        GdkEventFocus *event)
{
    GnomeCanvas *canvas;
    ECanvas *ecanvas;
    GdkEvent full_event;

    canvas = GNOME_CANVAS (widget);
    ecanvas = E_CANVAS (widget);

    /* 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

    gtk_im_context_focus_out (ecanvas->im_context);

    if (canvas->focused_item) {
        full_event.focus_change = *event;
        return canvas_emit_event (canvas, &full_event);
    } else {
        return FALSE;
    }
}

static void
e_canvas_class_init (ECanvasClass *class)
{
    GObjectClass *object_class;
    GtkWidgetClass *widget_class;

    object_class = G_OBJECT_CLASS (class);
    object_class->dispose = canvas_dispose;

    widget_class = GTK_WIDGET_CLASS (class);
    widget_class->realize = canvas_realize;
    widget_class->unrealize = canvas_unrealize;
    widget_class->style_set = canvas_style_set;
    widget_class->button_press_event = canvas_button_event;
    widget_class->button_release_event = canvas_button_event;
    widget_class->key_press_event = canvas_key_event;
    widget_class->key_release_event = canvas_key_event;
    widget_class->focus_in_event = canvas_focus_in_event;
    widget_class->focus_out_event = canvas_focus_out_event;

    signals[REFLOW] = g_signal_new (
        "reflow",
        G_OBJECT_CLASS_TYPE (object_class),
        G_SIGNAL_RUN_LAST,
        G_STRUCT_OFFSET (ECanvasClass, reflow),
        NULL, NULL,
        g_cclosure_marshal_VOID__VOID,
        G_TYPE_NONE, 0);
}

static void
e_canvas_init (ECanvas *canvas)
{
    canvas->im_context = gtk_im_multicontext_new ();
}

GtkWidget *
e_canvas_new (void)
{
    return g_object_new (E_TYPE_CANVAS, NULL);
}

/**
 * e_canvas_item_grab_focus:
 * @item: A canvas item.
 * @widget_too: Whether or not to grab the widget-level focus too
 *
 * 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 and @widget_too is %TRUE, it grabs that focus as well.
 **/
void
e_canvas_item_grab_focus (GnomeCanvasItem *item,
                          gboolean widget_too)
{
    GnomeCanvasItem *focused_item;
    GdkWindow *bin_window;
    GdkEvent ev;

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

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

    focused_item = item->canvas->focused_item;

    if (focused_item) {
        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = bin_window;
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = FALSE;

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

    item->canvas->focused_item = item;

    if (widget_too && !gtk_widget_has_focus (GTK_WIDGET (item->canvas))) {
        gtk_widget_grab_focus (GTK_WIDGET (item->canvas));
    }

    if (item) {
        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = bin_window;
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = TRUE;

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

static void
e_canvas_item_invoke_reflow (GnomeCanvasItem *item,
                             gint flags)
{
    GnomeCanvasGroup *group;
    GList *list;
    GnomeCanvasItem *child;

    if (GNOME_IS_CANVAS_GROUP (item)) {
        group = GNOME_CANVAS_GROUP (item);
        for (list = group->item_list; list; list = list->next) {
            child = GNOME_CANVAS_ITEM (list->data);
            if (child->flags & E_CANVAS_ITEM_DESCENDENT_NEEDS_REFLOW)
                e_canvas_item_invoke_reflow (child, flags);
        }
    }

    if (item->flags & E_CANVAS_ITEM_NEEDS_REFLOW) {
        ECanvasItemReflowFunc func;
        func = (ECanvasItemReflowFunc)
            g_object_get_data (G_OBJECT (item),
                       "ECanvasItem::reflow_callback");
        if (func)
            func (item, flags);
    }

    item->flags &= ~E_CANVAS_ITEM_NEEDS_REFLOW;
    item->flags &= ~E_CANVAS_ITEM_DESCENDENT_NEEDS_REFLOW;
}

static void
do_reflow (ECanvas *canvas)
{
    if (GNOME_CANVAS (canvas)->root->flags & E_CANVAS_ITEM_DESCENDENT_NEEDS_REFLOW)
        e_canvas_item_invoke_reflow (GNOME_CANVAS (canvas)->root, 0);
}

/* Idle handler for the e-canvas.  It deals with pending reflows. */
static gint
idle_handler (gpointer data)
{
    ECanvas *canvas;

    GDK_THREADS_ENTER ();

    canvas = E_CANVAS (data);
    do_reflow (canvas);

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

    g_signal_emit (canvas, signals[REFLOW], 0);

    GDK_THREADS_LEAVE ();

    return FALSE;
}

/* Convenience function to add an idle handler to a canvas */
static void
add_idle (ECanvas *canvas)
{
    if (canvas->idle_id != 0)
        return;

    canvas->idle_id = g_idle_add_full (
        G_PRIORITY_HIGH_IDLE, idle_handler, (gpointer) canvas, NULL);
}

static void
e_canvas_item_descendent_needs_reflow (GnomeCanvasItem *item)
{
    if (item->flags & E_CANVAS_ITEM_DESCENDENT_NEEDS_REFLOW)
        return;

    item->flags |= E_CANVAS_ITEM_DESCENDENT_NEEDS_REFLOW;
    if (item->parent)
        e_canvas_item_descendent_needs_reflow (item->parent);
}

void
e_canvas_item_request_reflow (GnomeCanvasItem *item)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (item->flags & GNOME_CANVAS_ITEM_REALIZED) {
        item->flags |= E_CANVAS_ITEM_NEEDS_REFLOW;
        e_canvas_item_descendent_needs_reflow (item);
        add_idle (E_CANVAS (item->canvas));
    }
}

void
e_canvas_item_request_parent_reflow (GnomeCanvasItem *item)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    e_canvas_item_request_reflow (item->parent);
}

void
e_canvas_item_set_reflow_callback (GnomeCanvasItem *item,
                                   ECanvasItemReflowFunc func)
{
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));
    g_return_if_fail (func != NULL);

    g_object_set_data (
        G_OBJECT(item), "ECanvasItem::reflow_callback",
        (gpointer) func);
}

static gboolean
grab_cancelled_check (gpointer data)
{
    ECanvas *canvas = data;

    if (GNOME_CANVAS (canvas)->grabbed_item == NULL) {
        canvas->grab_cancelled_cb = NULL;
        canvas->grab_cancelled_check_id = 0;
        canvas->grab_cancelled_time = 0;
        canvas->grab_cancelled_data = NULL;
        return FALSE;
    }

    if (gtk_grab_get_current ()) {
        gnome_canvas_item_ungrab (
            GNOME_CANVAS (canvas)->grabbed_item,
            canvas->grab_cancelled_time);
        if (canvas->grab_cancelled_cb)
            canvas->grab_cancelled_cb (
                canvas, GNOME_CANVAS (canvas)->grabbed_item,
                canvas->grab_cancelled_data);
        canvas->grab_cancelled_cb = NULL;
        canvas->grab_cancelled_check_id = 0;
        canvas->grab_cancelled_time = 0;
        canvas->grab_cancelled_data = NULL;
        return FALSE;
    }
    return TRUE;
}

gint
e_canvas_item_grab (ECanvas *canvas,
                    GnomeCanvasItem *item,
                    guint event_mask,
                    GdkCursor *cursor,
                    guint32 etime,
                    ECanvasItemGrabCancelled cancelled_cb,
                    gpointer cancelled_data)
{
    gint ret_val;

    g_return_val_if_fail (E_IS_CANVAS (canvas), -1);
    g_return_val_if_fail (GNOME_IS_CANVAS_ITEM (item), -1);

    if (gtk_grab_get_current ())
        return GDK_GRAB_ALREADY_GRABBED;

    ret_val = gnome_canvas_item_grab (
        item, event_mask, cursor, etime);
    if (ret_val == GDK_GRAB_SUCCESS) {
        canvas->grab_cancelled_cb = cancelled_cb;
        canvas->grab_cancelled_check_id = g_timeout_add_full (
            G_PRIORITY_LOW, 100,
            grab_cancelled_check, canvas, NULL);
        canvas->grab_cancelled_time = etime;
        canvas->grab_cancelled_data = cancelled_data;
    }

    return ret_val;
}

void
e_canvas_item_ungrab (ECanvas *canvas,
                      GnomeCanvasItem *item,
                      guint32 etime)
{
    g_return_if_fail (E_IS_CANVAS (canvas));
    g_return_if_fail (GNOME_IS_CANVAS_ITEM (item));

    if (canvas->grab_cancelled_check_id) {
        g_source_remove (canvas->grab_cancelled_check_id);
        canvas->grab_cancelled_cb = NULL;
        canvas->grab_cancelled_check_id = 0;
        canvas->grab_cancelled_time = 0;
        canvas->grab_cancelled_data = NULL;
        gnome_canvas_item_ungrab (item, etime);
    }
}