gtkgesture: Deprecate gtk_gesture_set_sequence_state()

We can abstract widgets about the specific ongoing sequences that
are triggering a GtkGesture. This used to be more necessary in
GTK3 world where complex widgets might have required handling
different events in different areas, but in GTK4 world that would
be done with multiple widgets.

This is no longer necessary to carry forward.

gtk/gtkgesture.c

@@ -69,7 +69,7 @@
  *
  * Within a widget, gestures can be grouped through [method@Gtk.Gesture.group].
  * Grouped gestures synchronize the state of sequences, so calling
- * [method@Gtk.Gesture.set_sequence_state] on one will effectively propagate
+ * [method@Gtk.Gesture.set_state] on one will effectively propagate
  * the state throughout the group.
  *
  * By default, all sequences start out in the %GTK_EVENT_SEQUENCE_NONE state,
@@ -99,7 +99,7 @@
  * again.
  *
  * Sequence states can't be changed freely.
- * See [method@Gtk.Gesture.set_sequence_state] to know about the possible
+ * See [method@Gtk.Gesture.set_state] to know about the possible
  * lifetimes of a `GdkEventSequence`.
  *
  * ## Touchpad gestures
@@ -519,7 +519,9 @@ _gtk_gesture_update_point (GtkGesture     *gesture,
       else
         state = gtk_gesture_get_group_state (gesture, sequence);
 
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
       gtk_gesture_set_sequence_state (gesture, sequence, state);
+G_GNUC_END_IGNORE_DEPRECATIONS
     }
 
   return TRUE;
@@ -1017,6 +1019,8 @@ gtk_gesture_get_sequence_state (GtkGesture       *gesture,
  *
  * Returns: %TRUE if @sequence is handled by @gesture,
  *   and the state is changed successfully
+ *
+ * Deprecated: 4.10. Use [method@Gtk.Gesture.set_state]
  */
 gboolean
 gtk_gesture_set_sequence_state (GtkGesture            *gesture,
@@ -1069,8 +1073,46 @@ gtk_gesture_set_sequence_state (GtkGesture            *gesture,
  * Sets the state of all sequences that @gesture is currently
  * interacting with.
  *
- * See [method@Gtk.Gesture.set_sequence_state] for more details
+ * Sequences start in state %GTK_EVENT_SEQUENCE_NONE, and whenever
- * on sequence states.
+ * they change state, they can never go back to that state. Likewise,
+ * sequences in state %GTK_EVENT_SEQUENCE_DENIED cannot turn back to
+ * a not denied state. With these rules, the lifetime of an event
+ * sequence is constrained to the next four:
+ *
+ * * None
+ * * None → Denied
+ * * None → Claimed
+ * * None → Claimed → Denied
+ *
+ * Note: Due to event handling ordering, it may be unsafe to set the
+ * state on another gesture within a [signal@Gtk.Gesture::begin] signal
+ * handler, as the callback might be executed before the other gesture
+ * knows about the sequence. A safe way to perform this could be:
+ *
+ * ```c
+ * static void
+ * first_gesture_begin_cb (GtkGesture       *first_gesture,
+ *                         GdkEventSequence *sequence,
+ *                         gpointer          user_data)
+ * {
+ *   gtk_gesture_set_state (first_gesture, GTK_EVENT_SEQUENCE_CLAIMED);
+ *   gtk_gesture_set_state (second_gesture, GTK_EVENT_SEQUENCE_DENIED);
+ * }
+ *
+ * static void
+ * second_gesture_begin_cb (GtkGesture       *second_gesture,
+ *                          GdkEventSequence *sequence,
+ *                          gpointer          user_data)
+ * {
+ *   if (gtk_gesture_get_sequence_state (first_gesture, sequence) == GTK_EVENT_SEQUENCE_CLAIMED)
+ *     gtk_gesture_set_state (second_gesture, GTK_EVENT_SEQUENCE_DENIED);
+ * }
+ * ```
+ *
+ * If both gestures are in the same group, just set the state on
+ * the gesture emitting the event, the sequence will be already
+ * be initialized to the group's global state when the second
+ * gesture processes the event.
  *
  * Returns: %TRUE if the state of at least one sequence
  *   was changed successfully
@@ -1090,8 +1132,10 @@ gtk_gesture_set_state (GtkGesture            *gesture,
   priv = gtk_gesture_get_instance_private (gesture);
   sequences = g_hash_table_get_keys (priv->points);
 
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
   for (l = sequences; l; l = l->next)
     handled |= gtk_gesture_set_sequence_state (gesture, l->data, state);
+G_GNUC_END_IGNORE_DEPRECATIONS
 
   g_list_free (sequences);
 

gtk/gtkgesture.h

@@ -51,7 +51,7 @@ GDK_AVAILABLE_IN_ALL
 GtkEventSequenceState
             gtk_gesture_get_sequence_state   (GtkGesture            *gesture,
                                               GdkEventSequence      *sequence);
-GDK_AVAILABLE_IN_ALL
+GDK_DEPRECATED_IN_4_10
 gboolean    gtk_gesture_set_sequence_state   (GtkGesture            *gesture,
                                               GdkEventSequence      *sequence,
                                               GtkEventSequenceState  state);

gtk/gtkwidget.c

@@ -2218,7 +2218,9 @@ _gtk_widget_set_sequence_state_internal (GtkWidget             *widget,
                gtk_gesture_get_sequence_state (gesture, sequence) != GTK_EVENT_SEQUENCE_CLAIMED)
         continue;
 
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
       retval = gtk_gesture_set_sequence_state (gesture, seq, gesture_state);
+G_GNUC_END_IGNORE_DEPRECATIONS
 
       if (retval || gesture == emitter)
         {