libobs: Add functions to defer scene item update

Allows the ability to defer updating the item transform until all
functions have been executed.

libobs/obs-scene.c

@@ -293,6 +293,9 @@ static void update_item_transform(struct obs_scene_item *item)
 	struct calldata params;
 	uint8_t         stack[128];
 
+	if (os_atomic_load_long(&item->defer_update) > 0)
+		return;
+
 	vec2_zero(&base_origin);
 	vec2_zero(&origin);
 
@@ -1573,3 +1576,20 @@ void obs_scene_atomic_update(obs_scene_t *scene,
 	full_unlock(scene);
 	obs_scene_release(scene);
 }
+
+void obs_sceneitem_defer_update_begin(obs_sceneitem_t *item)
+{
+	if (!obs_ptr_valid(item, "obs_sceneitem_defer_update_begin"))
+		return;
+
+	os_atomic_inc_long(&item->defer_update);
+}
+
+void obs_sceneitem_defer_update_end(obs_sceneitem_t *item)
+{
+	if (!obs_ptr_valid(item, "obs_sceneitem_defer_update_end"))
+		return;
+
+	if (os_atomic_dec_long(&item->defer_update) == 0)
+		update_item_transform(item);
+}

libobs/obs-scene.h

@@ -35,6 +35,7 @@ struct obs_scene_item {
 	struct obs_scene      *parent;
 	struct obs_source     *source;
 	volatile long         active_refs;
+	volatile long         defer_update;
 	bool                  user_visible;
 	bool                  visible;
 	bool                  selected;

libobs/obs.h

@@ -1237,6 +1237,9 @@ EXPORT void obs_sceneitem_get_box_transform(const obs_sceneitem_t *item,
 EXPORT bool obs_sceneitem_visible(const obs_sceneitem_t *item);
 EXPORT bool obs_sceneitem_set_visible(obs_sceneitem_t *item, bool visible);
 
+EXPORT void obs_sceneitem_defer_update_begin(obs_sceneitem_t *item);
+EXPORT void obs_sceneitem_defer_update_end(obs_sceneitem_t *item);
+
 
 /* ------------------------------------------------------------------------- */
 /* Outputs */