MACRO(USE_ARTOOLKIT)
  IF ((NOT ARTOOLKIT_FOUND) AND (${ARGC} LESS 1))
    USING_MESSAGE("Skipping because of missing ARTOOLKIT")
    RETURN()
  ENDIF((NOT ARTOOLKIT_FOUND) AND (${ARGC} LESS 1))
  IF(NOT ARTOOLKIT_USED AND ARTOOLKIT_FOUND)
    SET(ARTOOLKIT_USED TRUE)
    ADD_DEFINITIONS(-DHAVE_AR)
    INCLUDE_DIRECTORIES(SYSTEM ${ARTOOLKIT_INCLUDE_DIR})
    SET(EXTRA_LIBS ${EXTRA_LIBS} ${ARTOOLKIT_LIBRARIES})
  ENDIF()
ENDMACRO(USE_ARTOOLKIT)