+ * @brief Unset a TDM buffer to a window object
+ * @details A TDM buffer will be applied when the output object
+ * of a layer object is committed.
+ * @param[in] hwc_window A window object
+ * @return #TDM_ERROR_NONE if success. Otherwise, error value.
+ *
+ * Implementation should return #TDM_ERROR_BUSY if #hwc_window can't
+ * be updated right now, this won't be interpreted like some critical
+ * error.
+ */
+ tdm_error (*hwc_window_unset_buffer)(tdm_hwc_window *hwc_window);
+
+ /**
+ * @brief Get a buffer which is set to a window object
+ * @details A TDM buffer will be applied when the output object
+ * of a layer object is committed.
+ * @param[in] hwc_window A window object
+ * @param[out] error #TDM_ERROR_NONE if success. Otherwise, error value.
+ * @return A buffer which is @b assigend to a window object
+ *
+ * Implementation should return #TDM_ERROR_BUSY if #hwc_window can't
+ * be updated right now, this won't be interpreted like some critical
+ * error.
+ */
+ tbm_surface_h (*hwc_window_get_buffer)(tdm_hwc_window *hwc_window,
+ tdm_error *error);
+
+ /**
+ * @brief Get a layer associated with a window object
+ * @param[in] hwc_window A window object
+ * @param[out] error #TDM_ERROR_NONE if success. Otherwise, error value.
+ * @return A layer which is @b assigend to a window object
+ * @remark
+ * A backend module @b SHOULD implement this function. The backend should
+ * return the tdm_layer assoicated with a hwc_window which must be assigend
+ * hw overlay.\n
+ */
+ tdm_layer *(*hwc_window_get_layer)(tdm_hwc_window *hwc_window,
+ tdm_error *error);
+
+ /**