gtk2/gtk/gtkdragsource.c
Alexander Mikhaylenko f63e6394ac dragsource: Use double coordinates for checking drag threshold
If multiple nested widgets have drag sources on them, both using bubble
phase, we need to reliably pick the inner one. Both of them will try to
start dragging, and we need to make sure there are no situations where the
outer widget starts drag earlier and cancels the inner one.

Currently, this can easily happen via integer rounding: start and current
coordinates passed into gtk_drag_check_threshold() are initially doubles
(other than in GtkNotebook and GtkIconView), and are casted to ints. Then
those rounded values are used to calculate deltas to compare to the drag
threshold, losing quite a lot of precision along the way, and often
resulting in the outer widget getting larger deltas.

To avoid it, just don't round it. Introduce a variant of the function that
operates on doubles: gtk_drag_check_threshold_double() and use it instead
of the original everywhere.
2021-01-29 12:01:34 +05:00

816 lines
24 KiB
C

/* GTK - The GIMP Toolkit
* Copyright (C) 1995-1999 Peter Mattis, Spencer Kimball and Josh MacDonald
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Modified by the GTK+ Team and others 1997-2000. See the AUTHORS
* file for a list of people on the GTK+ Team. See the ChangeLog
* files for a list of changes. These files are distributed with
* GTK+ at ftp://ftp.gtk.org/pub/gtk/.
*/
#include "config.h"
#include "gtkdragsourceprivate.h"
#include "gtkgesturedrag.h"
#include "gtkgesturesingleprivate.h"
#include "gtkimagedefinitionprivate.h"
#include "gtknative.h"
#include "gtkwidgetprivate.h"
#include "gtkintl.h"
#include "gtkimageprivate.h"
#include "gtkdragicon.h"
#include "gtkprivate.h"
#include "gtkmarshalers.h"
#include "gtkicontheme.h"
#include "gtkpicture.h"
#include "gtksettingsprivate.h"
#include "gtkgesturesingle.h"
/**
* SECTION:gtkdragsource
* @Short_description: Event controller to initiate DND operations
* @Title: GtkDragSource
*
* GtkDragSource is an auxiliary object that is used to initiate
* Drag-And-Drop operations. It can be set up with the necessary
* ingredients for a DND operation ahead of time. This includes
* the source for the data that is being transferred, in the form
* of a #GdkContentProvider, the desired action, and the icon to
* use during the drag operation. After setting it up, the drag
* source must be added to a widget as an event controller, using
* gtk_widget_add_controller().
*
* |[<!-- language="C" -->
* static void
* my_widget_init (MyWidget *self)
* {
* GtkDragSource *drag_source = gtk_drag_source_new ();
*
* g_signal_connect (drag_source, "prepare", G_CALLBACK (on_drag_prepare), self);
* g_signal_connect (drag_source, "drag-begin", G_CALLBACK (on_drag_begin), self);
*
* gtk_widget_add_controller (GTK_WIDGET (self), GTK_EVENT_CONTROLLER (drag_source));
* }
* ]|
*
* Setting up the content provider and icon ahead of time only
* makes sense when the data does not change. More commonly, you
* will want to set them up just in time. To do so, #GtkDragSource
* has #GtkDragSource::prepare and #GtkDragSource::drag-begin signals.
*
* The ::prepare signal is emitted before a drag is started, and
* can be used to set the content provider and actions that the
* drag should be started with.
*
* |[<!-- language="C" -->
* static GdkContentProvider *
* on_drag_prepare (GtkDragSource *source,
* double x,
* double y,
* MyWidget *self)
* {
* // This widget supports two types of content: GFile objects
* // and GdkPixbuf objects; GTK will handle the serialization
* // of these types automatically
* GFile *file = my_widget_get_file (self);
* GdkPixbuf *pixbuf = my_widget_get_pixbuf (self);
*
* return gdk_content_provider_new_union ((GdkContentProvider *[2]) {
* gdk_content_provider_new_typed (G_TYPE_FILE, file),
* gdk_content_provider_new_typed (GDK_TYPE_PIXBUF, pixbuf),
* }, 2);
* }
* ]|
*
* The ::drag-begin signal is emitted after the #GdkDrag object has
* been created, and can be used to set up the drag icon.
*
* |[<!-- language="C" -->
* static void
* on_drag_begin (GtkDragSource *source,
* GtkDrag *drag,
* MyWidget *self)
* {
* // Set the widget as the drag icon
* GdkPaintable *paintable = gtk_widget_paintable_new (GTK_WIDGET (self));
* gtk_drag_source_set_icon (source, paintable, 0, 0);
* g_object_unref (paintable);
* }
* ]|
*
* During the DND operation, GtkDragSource emits signals that
* can be used to obtain updates about the status of the operation,
* but it is not normally necessary to connect to any signals,
* except for one case: when the supported actions include
* %GDK_ACTION_MOVE, you need to listen for the
* #GtkDragSource::drag-end signal and delete the
* data after it has been transferred.
*/
struct _GtkDragSource
{
GtkGestureSingle parent_instance;
GdkContentProvider *content;
GdkDragAction actions;
GdkPaintable *paintable;
int hot_x;
int hot_y;
double start_x;
double start_y;
GdkDrag *drag;
};
struct _GtkDragSourceClass
{
GtkGestureSingleClass parent_class;
GdkContentProvider *(* prepare) (GtkDragSource *source,
double x,
double y);
};
enum {
PROP_CONTENT = 1,
PROP_ACTIONS,
NUM_PROPERTIES
};
static GParamSpec *properties[NUM_PROPERTIES];
enum {
PREPARE,
DRAG_BEGIN,
DRAG_END,
DRAG_CANCEL,
NUM_SIGNALS
};
static guint signals[NUM_SIGNALS];
static void gtk_drag_source_dnd_finished_cb (GdkDrag *drag,
GtkDragSource *source);
static void gtk_drag_source_cancel_cb (GdkDrag *drag,
GdkDragCancelReason reason,
GtkDragSource *source);
static GdkContentProvider *gtk_drag_source_prepare (GtkDragSource *source,
double x,
double y);
static void gtk_drag_source_drag_begin (GtkDragSource *source);
G_DEFINE_TYPE (GtkDragSource, gtk_drag_source, GTK_TYPE_GESTURE_SINGLE);
static void
gtk_drag_source_init (GtkDragSource *source)
{
source->actions = GDK_ACTION_COPY;
}
static void
gtk_drag_source_finalize (GObject *object)
{
GtkDragSource *source = GTK_DRAG_SOURCE (object);
g_clear_object (&source->content);
g_clear_object (&source->paintable);
G_OBJECT_CLASS (gtk_drag_source_parent_class)->finalize (object);
}
static void
gtk_drag_source_set_property (GObject *object,
guint prop_id,
const GValue *value,
GParamSpec *pspec)
{
GtkDragSource *source = GTK_DRAG_SOURCE (object);
switch (prop_id)
{
case PROP_CONTENT:
gtk_drag_source_set_content (source, g_value_get_object (value));
break;
case PROP_ACTIONS:
gtk_drag_source_set_actions (source, g_value_get_flags (value));
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
}
}
static void
gtk_drag_source_get_property (GObject *object,
guint prop_id,
GValue *value,
GParamSpec *pspec)
{
GtkDragSource *source = GTK_DRAG_SOURCE (object);
switch (prop_id)
{
case PROP_CONTENT:
g_value_set_object (value, gtk_drag_source_get_content (source));
break;
case PROP_ACTIONS:
g_value_set_flags (value, gtk_drag_source_get_actions (source));
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
}
}
static gboolean
gtk_drag_source_filter_event (GtkEventController *controller,
GdkEvent *event)
{
/* Let touchpad swipe events go through, only if they match n-points */
if (gdk_event_get_event_type (event) == GDK_TOUCHPAD_SWIPE)
{
guint n_points;
guint n_fingers;
g_object_get (G_OBJECT (controller), "n-points", &n_points, NULL);
n_fingers = gdk_touchpad_event_get_n_fingers (event);
if (n_fingers == n_points)
return FALSE;
else
return TRUE;
}
return GTK_EVENT_CONTROLLER_CLASS (gtk_drag_source_parent_class)->filter_event (controller, event);
}
static void
gtk_drag_source_begin (GtkGesture *gesture,
GdkEventSequence *sequence)
{
GtkDragSource *source = GTK_DRAG_SOURCE (gesture);
GdkEventSequence *current;
current = gtk_gesture_single_get_current_sequence (GTK_GESTURE_SINGLE (gesture));
gtk_gesture_get_point (gesture, current, &source->start_x, &source->start_y);
}
static void
gtk_drag_source_update (GtkGesture *gesture,
GdkEventSequence *sequence)
{
GtkDragSource *source = GTK_DRAG_SOURCE (gesture);
GtkWidget *widget;
double x, y;
if (!gtk_gesture_is_recognized (gesture))
return;
gtk_gesture_get_point (gesture, sequence, &x, &y);
widget = gtk_event_controller_get_widget (GTK_EVENT_CONTROLLER (gesture));
if (gtk_drag_check_threshold_double (widget, source->start_x, source->start_y, x, y))
{
gtk_drag_source_drag_begin (source);
}
}
static void
gtk_drag_source_class_init (GtkDragSourceClass *class)
{
GObjectClass *object_class = G_OBJECT_CLASS (class);
GtkEventControllerClass *controller_class = GTK_EVENT_CONTROLLER_CLASS (class);
GtkGestureClass *gesture_class = GTK_GESTURE_CLASS (class);
object_class->finalize = gtk_drag_source_finalize;
object_class->set_property = gtk_drag_source_set_property;
object_class->get_property = gtk_drag_source_get_property;
controller_class->filter_event = gtk_drag_source_filter_event;
gesture_class->begin = gtk_drag_source_begin;
gesture_class->update = gtk_drag_source_update;
gesture_class->end = NULL;
class->prepare = gtk_drag_source_prepare;
/**
* GtkDragSource:content:
*
* The data that is offered by drag operations from this source,
* in the form of a #GdkContentProvider.
*/
properties[PROP_CONTENT] =
g_param_spec_object ("content",
P_("Content"),
P_("The content provider for the dragged data"),
GDK_TYPE_CONTENT_PROVIDER,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_EXPLICIT_NOTIFY);
/**
* GtkDragSource:actions:
*
* The actions that are supported by drag operations from the source.
*
* Note that you must handle the #GtkDragSource::drag-end signal
* if the actions include %GDK_ACTION_MOVE.
*/
properties[PROP_ACTIONS] =
g_param_spec_flags ("actions",
P_("Actions"),
P_("Supported actions"),
GDK_TYPE_DRAG_ACTION, GDK_ACTION_COPY,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_EXPLICIT_NOTIFY);
g_object_class_install_properties (object_class, NUM_PROPERTIES, properties);
/**
* GtkDragSource::prepare:
* @source: the #GtkDragSource
* @x: the X coordinate of the drag starting point
* @y: the Y coordinate fo the drag starting point
*
* The ::prepare signal is emitted when a drag is about to be initiated.
* It returns the * #GdkContentProvider to use for the drag that is about
* to start. The default handler for this signal returns the value of
* the #GtkDragSource:content property, so if you set up that property
* ahead of time, you don't need to connect to this signal.
*
* Returns: (transfer full) (nullable): a #GdkContentProvider, or %NULL
*/
signals[PREPARE] =
g_signal_new (I_("prepare"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkDragSourceClass, prepare),
g_signal_accumulator_first_wins, NULL,
NULL,
GDK_TYPE_CONTENT_PROVIDER, 2,
G_TYPE_DOUBLE, G_TYPE_DOUBLE);
/**
* GtkDragSource::drag-begin:
* @source: the #GtkDragSource
* @drag: the #GdkDrag object
*
* The ::drag-begin signal is emitted on the drag source when a drag
* is started. It can be used to e.g. set a custom drag icon with
* gtk_drag_source_set_icon().
*/
signals[DRAG_BEGIN] =
g_signal_new (I_("drag-begin"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
0,
NULL, NULL,
NULL,
G_TYPE_NONE, 1,
GDK_TYPE_DRAG);
/**
* GtkDragSource::drag-end:
* @source: the #GtkDragSource
* @drag: the #GdkDrag object
* @delete_data: %TRUE if the drag was performing %GDK_ACTION_MOVE,
* and the data should be deleted
*
* The ::drag-end signal is emitted on the drag source when a drag is
* finished. A typical reason to connect to this signal is to undo
* things done in #GtkDragSource::prepare or #GtkDragSource::drag-begin.
*/
signals[DRAG_END] =
g_signal_new (I_("drag-end"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
0,
NULL, NULL,
NULL,
G_TYPE_NONE, 2,
GDK_TYPE_DRAG,
G_TYPE_BOOLEAN);
/**
* GtkDragSource::drag-cancel:
* @source: the #GtkDragSource
* @drag: the #GdkDrag object
* @reason: information on why the drag failed
*
* The ::drag-cancel signal is emitted on the drag source when a drag has
* failed. The signal handler may handle a failed drag operation based on
* the type of error. It should return %TRUE if the failure has been handled
* and the default "drag operation failed" animation should not be shown.
*
* Returns: %TRUE if the failed drag operation has been already handled
*/
signals[DRAG_CANCEL] =
g_signal_new (I_("drag-cancel"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
0,
_gtk_boolean_handled_accumulator, NULL,
_gtk_marshal_BOOLEAN__OBJECT_ENUM,
G_TYPE_BOOLEAN, 2,
GDK_TYPE_DRAG,
GDK_TYPE_DRAG_CANCEL_REASON);
}
static GdkContentProvider *
gtk_drag_source_prepare (GtkDragSource *source,
double x,
double y)
{
if (source->actions == 0)
return NULL;
if (source->content == NULL)
return NULL;
return g_object_ref (source->content);
}
static void
drag_end (GtkDragSource *source,
gboolean success)
{
gboolean delete_data;
g_signal_handlers_disconnect_by_func (source->drag, gtk_drag_source_dnd_finished_cb, source);
g_signal_handlers_disconnect_by_func (source->drag, gtk_drag_source_cancel_cb, source);
delete_data = success && gdk_drag_get_selected_action (source->drag) == GDK_ACTION_MOVE;
g_signal_emit (source, signals[DRAG_END], 0, source->drag, delete_data);
gdk_drag_drop_done (source->drag, success);
g_clear_object (&source->drag);
}
static void
gtk_drag_source_dnd_finished_cb (GdkDrag *drag,
GtkDragSource *source)
{
drag_end (source, TRUE);
}
static void
gtk_drag_source_cancel_cb (GdkDrag *drag,
GdkDragCancelReason reason,
GtkDragSource *source)
{
gboolean success = FALSE;
g_signal_emit (source, signals[DRAG_CANCEL], 0, source->drag, reason, &success);
drag_end (source, success);
}
static void
gtk_drag_source_ensure_icon (GtkDragSource *self,
GdkDrag *drag)
{
GdkContentProvider *provider;
GtkWidget *icon, *child;
GdkContentFormats *formats;
const GType *types;
gsize i, n_types;
icon = gtk_drag_icon_get_for_drag (drag);
/* If an icon has been set already, we don't need to set one. */
if (gtk_drag_icon_get_child (GTK_DRAG_ICON (icon)))
return;
if (self->paintable)
{
gtk_drag_icon_set_from_paintable (drag,
self->paintable,
self->hot_x,
self->hot_y);
return;
}
gdk_drag_set_hotspot (drag, -2, -2);
provider = gdk_drag_get_content (drag);
formats = gdk_content_provider_ref_formats (provider);
types = gdk_content_formats_get_gtypes (formats, &n_types);
for (i = 0; i < n_types; i++)
{
GValue value = G_VALUE_INIT;
g_value_init (&value, types[i]);
if (gdk_content_provider_get_value (provider, &value, NULL))
{
child = gtk_drag_icon_create_widget_for_value (&value);
if (child)
{
gtk_drag_icon_set_child (GTK_DRAG_ICON (icon), child);
g_value_unset (&value);
gdk_content_formats_unref (formats);
return;
}
}
g_value_unset (&value);
}
gdk_content_formats_unref (formats);
child = gtk_image_new_from_icon_name ("text-x-generic");
gtk_image_set_icon_size (GTK_IMAGE (child), GTK_ICON_SIZE_LARGE);
gtk_drag_icon_set_child (GTK_DRAG_ICON (icon), child);
}
static void
gtk_drag_source_drag_begin (GtkDragSource *source)
{
GtkWidget *widget;
GdkDevice *device, *pointer;
GdkSeat *seat;
double x, y;
GtkNative *native;
GdkSurface *surface;
double px, py;
int dx, dy;
GdkContentProvider *content = NULL;
widget = gtk_event_controller_get_widget (GTK_EVENT_CONTROLLER (source));
device = gtk_gesture_get_device (GTK_GESTURE (source));
seat = gdk_device_get_seat (device);
if (device == gdk_seat_get_keyboard (seat))
pointer = gdk_seat_get_pointer (seat);
else
pointer = device;
native = gtk_widget_get_native (widget);
surface = gtk_native_get_surface (native);
gtk_widget_translate_coordinates (widget, GTK_WIDGET (native), source->start_x, source->start_y, &x, &y);
gdk_surface_get_device_position (surface, pointer, &px, &py, NULL);
dx = round (px - x);
dy = round (py - y);
g_signal_emit (source, signals[PREPARE], 0, source->start_x, source->start_y, &content);
if (!content)
return;
source->drag = gdk_drag_begin (surface, pointer, content, source->actions, dx, dy);
g_object_unref (content);
if (source->drag == NULL)
return;
gtk_widget_reset_controllers (widget);
g_signal_emit (source, signals[DRAG_BEGIN], 0, source->drag);
gtk_drag_source_ensure_icon (source, source->drag);
g_signal_connect (source->drag, "dnd-finished",
G_CALLBACK (gtk_drag_source_dnd_finished_cb), source);
g_signal_connect (source->drag, "cancel",
G_CALLBACK (gtk_drag_source_cancel_cb), source);
}
/**
* gtk_drag_source_new:
*
* Creates a new #GtkDragSource object.
*
* Returns: the new #GtkDragSource
*/
GtkDragSource *
gtk_drag_source_new (void)
{
return g_object_new (GTK_TYPE_DRAG_SOURCE, NULL);
}
/**
* gtk_drag_source_get_content:
* @source: a #GtkDragSource
*
* Gets the current content provider of a #GtkDragSource.
*
* Returns: (nullable) (transfer none): the #GdkContentProvider of @source
*/
GdkContentProvider *
gtk_drag_source_get_content (GtkDragSource *source)
{
g_return_val_if_fail (GTK_IS_DRAG_SOURCE (source), NULL);
return source->content;
}
/**
* gtk_drag_source_set_content:
* @source: a #GtkDragSource
* @content: (nullable): a #GdkContentProvider, or %NULL
*
* Sets a content provider on a #GtkDragSource.
*
* When the data is requested in the cause of a
* DND operation, it will be obtained from the
* content provider.
*
* This function can be called before a drag is started,
* or in a handler for the #GtkDragSource::prepare signal.
*
* You may consider setting the content provider back to
* %NULL in a #GtkDragSource::drag-end signal handler.
*/
void
gtk_drag_source_set_content (GtkDragSource *source,
GdkContentProvider *content)
{
g_return_if_fail (GTK_IS_DRAG_SOURCE (source));
if (!g_set_object (&source->content, content))
return;
g_object_notify_by_pspec (G_OBJECT (source), properties[PROP_CONTENT]);
}
/**
* gtk_drag_source_get_actions:
* @source: a #GtkDragSource
*
* Gets the actions that are currently set on the #GtkDragSource.
*
* Returns: the actions set on @source
*/
GdkDragAction
gtk_drag_source_get_actions (GtkDragSource *source)
{
g_return_val_if_fail (GTK_IS_DRAG_SOURCE (source), 0);
return source->actions;
}
/**
* gtk_drag_source_set_actions:
* @source: a #GtkDragSource
* @actions: the actions to offer
*
* Sets the actions on the #GtkDragSource.
*
* During a DND operation, the actions are offered
* to potential drop targets. If @actions include
* %GDK_ACTION_MOVE, you need to listen to the
* #GtkDragSource::drag-end signal and handle
* @delete_data being %TRUE.
*
* This function can be called before a drag is started,
* or in a handler for the #GtkDragSource::prepare signal.
*/
void
gtk_drag_source_set_actions (GtkDragSource *source,
GdkDragAction actions)
{
g_return_if_fail (GTK_IS_DRAG_SOURCE (source));
if (source->actions == actions)
return;
source->actions = actions;
g_object_notify_by_pspec (G_OBJECT (source), properties[PROP_ACTIONS]);
}
/**
* gtk_drag_source_set_icon:
* @source: a #GtkDragSource
* @paintable: (nullable): the #GdkPaintable to use as icon, or %NULL
* @hot_x: the hotspot X coordinate on the icon
* @hot_y: the hotspot Y coordinate on the icon
*
* Sets a paintable to use as icon during DND operations.
*
* The hotspot coordinates determine the point on the icon
* that gets aligned with the hotspot of the cursor.
*
* If @paintable is %NULL, a default icon is used.
*
* This function can be called before a drag is started, or in
* a #GtkDragSource::prepare or #GtkDragSource::drag-begin signal handler.
*/
void
gtk_drag_source_set_icon (GtkDragSource *source,
GdkPaintable *paintable,
int hot_x,
int hot_y)
{
g_return_if_fail (GTK_IS_DRAG_SOURCE (source));
g_set_object (&source->paintable, paintable);
source->hot_x = hot_x;
source->hot_y = hot_y;
}
/**
* gtk_drag_source_get_drag:
* @source: a #GtkDragSource
*
* Returns the underlying #GdkDrag object for an ongoing drag.
*
* Returns: (nullable) (transfer none): the #GdkDrag of the current drag operation, or %NULL
*/
GdkDrag *
gtk_drag_source_get_drag (GtkDragSource *source)
{
g_return_val_if_fail (GTK_IS_DRAG_SOURCE (source), NULL);
return source->drag;
}
/**
* gtk_drag_source_drag_cancel:
* @source: a #GtkDragSource
*
* Cancels a currently ongoing drag operation.
*/
void
gtk_drag_source_drag_cancel (GtkDragSource *source)
{
g_return_if_fail (GTK_IS_DRAG_SOURCE (source));
if (source->drag)
{
gboolean success = FALSE;
g_signal_emit (source, signals[DRAG_CANCEL], 0, source->drag, GDK_DRAG_CANCEL_ERROR, &success);
drag_end (source, FALSE);
}
}
/**
* gtk_drag_check_threshold: (method)
* @widget: a #GtkWidget
* @start_x: X coordinate of start of drag
* @start_y: Y coordinate of start of drag
* @current_x: current X coordinate
* @current_y: current Y coordinate
*
* Checks to see if a mouse drag starting at (@start_x, @start_y) and ending
* at (@current_x, @current_y) has passed the GTK drag threshold, and thus
* should trigger the beginning of a drag-and-drop operation.
*
* Returns: %TRUE if the drag threshold has been passed.
*/
gboolean
gtk_drag_check_threshold (GtkWidget *widget,
int start_x,
int start_y,
int current_x,
int current_y)
{
int drag_threshold;
g_return_val_if_fail (GTK_IS_WIDGET (widget), FALSE);
drag_threshold = gtk_settings_get_dnd_drag_threshold (gtk_widget_get_settings (widget));
return (ABS (current_x - start_x) > drag_threshold ||
ABS (current_y - start_y) > drag_threshold);
}
gboolean
gtk_drag_check_threshold_double (GtkWidget *widget,
double start_x,
double start_y,
double current_x,
double current_y)
{
int drag_threshold;
g_return_val_if_fail (GTK_IS_WIDGET (widget), FALSE);
drag_threshold = gtk_settings_get_dnd_drag_threshold (gtk_widget_get_settings (widget));
return (ABS (current_x - start_x) > drag_threshold ||
ABS (current_y - start_y) > drag_threshold);
}