-OPTION(CLITK_BUILD_VV "Build vv the 4D visualizer (requires VTK and QT)" ON)
-IF (CLITK_BUILD_VV)
- ADD_SUBDIRECTORY(${CLITK_SOURCE_DIR}/vv ${PROJECT_BINARY_DIR}/vv)
-ENDIF(CLITK_BUILD_VV)
+option(CLITK_BUILD_VV "Build vv the 4D visualizer (requires VTK and QT)" ON)
+
+if(CLITK_BUILD_VV)
+ set(vv_QT_VERSION "4" CACHE STRING "Expected Qt version")
+ set_property(CACHE vv_QT_VERSION PROPERTY STRINGS 4 5)
+ if(NOT (vv_QT_VERSION VERSION_EQUAL "4" OR vv_QT_VERSION VERSION_EQUAL "5"))
+ message(FATAL_ERROR "Expected value for vv_QT_VERSION is either '4' or '5'")
+ endif()
+
+ add_subdirectory(${CLITK_SOURCE_DIR}/vv ${PROJECT_BINARY_DIR}/vv)
+endif(CLITK_BUILD_VV)