gdk: Add GdkEventSequence

GdkEventSequence is an opaque pointer type that is used
to identify sequences of touch events that belong together.

docs/reference/gdk/gdk3-sections.txt

@@ -790,6 +790,8 @@ gdk_event_get_root_coords
 gdk_event_get_scroll_direction
 gdk_event_get_state
 gdk_event_get_time
+GdkEventSequence
+gdk_event_get_event_sequence
 gdk_event_request_motions
 gdk_events_get_angle
 gdk_events_get_center

gdk/gdk.symbols

@@ -168,6 +168,7 @@ gdk_event_get_scroll_direction
 gdk_event_get_source_device
 gdk_event_get_state
 gdk_event_get_time
+gdk_event_get_event_sequence
 gdk_event_get_type
 gdk_event_handler_set
 gdk_event_mask_get_type

gdk/gdkevents.c

@@ -1684,6 +1684,27 @@ gdk_event_get_screen (const GdkEvent *event)
   return NULL;
 }
 
+/**
+ * gdk_event_get_event_sequence:
+ * @event: a #GdkEvent
+ *
+ * If @event if of type %GDK_TOUCH_BEGIN, %GDK_TOUCH_UPDATE,
+ * %GDK_TOUCH_END or %GDK_TOUCH_CANCEL, returns the #GdkEventSequence
+ * to which the event belongs. Otherwise, return %NULL.
+ *
+ * Returns: the event sequence that the event belongs to
+ *
+ * Since: 3.4
+ */
+GdkEventSequence *
+gdk_event_get_event_sequence (const GdkEvent *event)
+{
+  if (!event)
+    return NULL;
+
+  return NULL;
+}
+
 /**
  * gdk_set_show_events:
  * @show_events:  %TRUE to output event debugging information.

gdk/gdkevents.h

@@ -143,6 +143,8 @@ typedef struct _GdkEventWindowState GdkEventWindowState;
 typedef struct _GdkEventSetting     GdkEventSetting;
 typedef struct _GdkEventGrabBroken  GdkEventGrabBroken;
 
+typedef struct _GdkEventSequence    GdkEventSequence;
+
 typedef union  _GdkEvent	    GdkEvent;
 
 /**
@@ -1155,6 +1157,9 @@ void       gdk_event_set_screen         (GdkEvent        *event,
                                          GdkScreen       *screen);
 GdkScreen *gdk_event_get_screen         (const GdkEvent  *event);
 
+GDK_AVAILABLE_IN_3_4
+GdkEventSequence *gdk_event_get_event_sequence (const GdkEvent *event);
+
 void	  gdk_set_show_events		(gboolean	 show_events);
 gboolean  gdk_get_show_events		(void);