Add API to install an event filter

This adds clutter_event_add/remove_filter which adds a callback
function which will receive all Clutter events just before the event
signal is emitted for them. The event filter will be invoked
regardless of any grabs or captures. This will be used by Mutter which
wants to access the events at a lower level then the event bubbling
mechanism. It needs to see all mouse motion events even if there is a
grab in place.

https://bugzilla.gnome.org/show_bug.cgi?id=707560

1 files changed, 106 insertions, 0 deletions

diff --git a/clutter/clutter-event.c b/clutter/clutter-event.c
index 03655f6c3..06870c61d 100644
--- a/clutter/clutter-event.c
+++ b/clutter/clutter-event.c
@@ -64,6 +64,15 @@ typedef struct _ClutterEventPrivate {
   guint is_pointer_emulated : 1;
 } ClutterEventPrivate;
 
+typedef struct _ClutterEventFilter {
+  int id;
+
+  ClutterStage *stage;
+  ClutterEventFilterFunc func;
+  GDestroyNotify notify;
+  gpointer user_data;
+} ClutterEventFilter;
+
 static GHashTable *all_events = NULL;
 
 G_DEFINE_BOXED_TYPE (ClutterEvent, clutter_event,
@@ -1720,3 +1729,100 @@ clutter_event_is_pointer_emulated (const ClutterEvent *event)
 
   return ((ClutterEventPrivate *) event)->is_pointer_emulated;
 }
+
+gboolean
+_clutter_event_process_filters (ClutterEvent *event)
+{
+  ClutterMainContext *context = _clutter_context_get_default ();
+  GList *l, *next;
+
+  /* Event filters are handled in order from least recently added to
+   * most recently added */
+
+  for (l = context->event_filters; l; l = next)
+    {
+      ClutterEventFilter *event_filter = l->data;
+
+      next = l->next;
+
+      if (event_filter->stage && event_filter->stage != event->any.stage)
+        continue;
+
+      if (event_filter->func (event, event_filter->user_data) == CLUTTER_EVENT_STOP)
+        return CLUTTER_EVENT_STOP;
+    }
+
+  return CLUTTER_EVENT_PROPAGATE;
+}
+
+/**
+ * clutter_event_add_filter:
+ * @stage: (allow-none): The #ClutterStage to capture events for
+ * @func: The callback function which will be passed all events.
+ * @notify: A #GDestroyNotify
+ * @user_data: A data pointer to pass to the function.
+ *
+ * Adds a function which will be called for all events that Clutter
+ * processes. The function will be called before any signals are
+ * emitted for the event and it will take precedence over any grabs.
+ *
+ * Return value: an identifier for the event filter, to be used
+ *   with clutter_event_remove_filter().
+ *
+ * Since: 1.18
+ */
+guint
+clutter_event_add_filter (ClutterStage          *stage,
+                          ClutterEventFilterFunc func,
+                          GDestroyNotify         notify,
+                          gpointer               user_data)
+{
+  ClutterMainContext *context = _clutter_context_get_default ();
+  ClutterEventFilter *event_filter = g_slice_new (ClutterEventFilter);
+  static guint event_filter_id = 0;
+
+  event_filter->stage = stage;
+  event_filter->id = ++event_filter_id;
+  event_filter->func = func;
+  event_filter->notify = notify;
+  event_filter->user_data = user_data;
+
+  /* The event filters are kept in order from least recently added to
+   * most recently added so we must add it to the end */
+  context->event_filters = g_list_append (context->event_filters, event_filter);
+
+  return event_filter->id;
+}
+
+/**
+ * clutter_event_remove_filter:
+ * @id: The ID of the event filter, as returned from clutter_event_add_filter()
+ *
+ * Removes an event filter that was previously added with
+ * clutter_event_add_filter().
+ *
+ * Since: 1.18
+ */
+void
+clutter_event_remove_filter (guint id)
+{
+  ClutterMainContext *context = _clutter_context_get_default ();
+  GList *l;
+
+  for (l = context->event_filters; l; l = l->next)
+    {
+      ClutterEventFilter *event_filter = l->data;
+
+      if (event_filter->id == id)
+        {
+          if (event_filter->notify)
+            event_filter->notify (event_filter->user_data);
+
+          context->event_filters = g_list_delete_link (context->event_filters, l);
+          g_slice_free (ClutterEventFilter, event_filter);
+          return;
+        }
+    }
+
+  g_warning ("No event filter found for id: %d\n", id);
+}