events: Add platform-data to allocated Events

Events allocated by Clutter should have a pointer to platform-specific
data; this would allow backends to add separate structures for holding
ancillary data, whilst retaining the ClutterEvent structure for use on
the stack.

In theory, for Clutter 2.x we might just want to drop Event and use an
opaque structure, or a typed data structure inheriting from
GTypeInstance instead.

clutter/clutter-event.c

@@ -43,6 +43,52 @@
  * be synthesized by Clutter itself or by the application code.
  */
 
+typedef struct _ClutterEventPrivate {
+  ClutterEvent base;
+
+  gpointer platform_data;
+} ClutterEventPrivate;
+
+static GHashTable *all_events = NULL;
+
+static gboolean
+is_event_allocated (const ClutterEvent *event)
+{
+  if (all_events == NULL)
+    return FALSE;
+
+  return g_hash_table_lookup (all_events, event) != NULL;
+}
+
+/*
+ * _clutter_event_get_platform_data:
+ * @event: a #ClutterEvent
+ *
+ * Retrieves the pointer to platform-specific data inside an event
+ *
+ * Return value: a pointer to platform-specific data
+ *
+ * Since: 1.4
+ */
+gpointer
+_clutter_event_get_platform_data (const ClutterEvent *event)
+{
+  if (!is_event_allocated (event))
+    return NULL;
+
+  return ((ClutterEventPrivate *) event)->platform_data;
+}
+
+void
+_clutter_event_set_platform_data (ClutterEvent *event,
+                                  gpointer      data)
+{
+  if (!is_event_allocated (event))
+    return;
+
+  ((ClutterEventPrivate *) event)->platform_data = data;
+}
+
 /**
  * clutter_event_type:
  * @event: a #ClutterEvent
@@ -606,10 +652,18 @@ ClutterEvent *
 clutter_event_new (ClutterEventType type)
 {
   ClutterEvent *new_event;
+  ClutterEventPrivate *priv;
 
-  new_event = g_slice_new0 (ClutterEvent);
+  priv = g_slice_new0 (ClutterEventPrivate);
+
+  new_event = (ClutterEvent *) priv;
   new_event->type = new_event->any.type = type;
 
+  if (all_events == NULL)
+    all_events = g_hash_table_new (NULL, NULL);
+
+  g_hash_table_replace (all_events, priv, GUINT_TO_POINTER (1));
+
   return new_event;
 }
 
@@ -631,6 +685,11 @@ clutter_event_copy (ClutterEvent *event)
   new_event = clutter_event_new (CLUTTER_NOTHING);
   *new_event = *event;
 
+  if (is_event_allocated (event))
+    _clutter_backend_copy_event_data (clutter_get_default_backend (),
+                                      event,
+                                      new_event);
+
   return new_event;
 }
 
@@ -644,7 +703,12 @@ void
 clutter_event_free (ClutterEvent *event)
 {
   if (G_LIKELY (event != NULL))
-    g_slice_free (ClutterEvent, event);
+    {
+      _clutter_backend_free_event_data (clutter_get_default_backend (), event);
+
+      g_hash_table_remove (all_events, event);
+      g_slice_free (ClutterEventPrivate, (ClutterEventPrivate *) event);
+    }
 }
 
 /**