cmake: add option to download voro

endif()

if(ENABLE_VORONOI)

  find_package(VORO REQUIRED) #some distros

  option(DOWNLOAD_VORO "Download voro++ (instead of using the system's one)" OFF)

  if(DOWNLOAD_VORO)

    include(ExternalProject)

    ExternalProject_Add(voro_build

      URL http://math.lbl.gov/voro++/download/dir/voro++-0.4.6.tar.gz

      URL_MD5 2338b824c3b7b25590e18e8df5d68af9

      CONFIGURE_COMMAND "" BUILD_IN_SOURCE 1 INSTALL_COMMAND "" 

      )

    ExternalProject_get_property(voro_build SOURCE_DIR)

    set(VORO_LIBRARIES ${SOURCE_DIR}/src/libvoro++.a)

    set(VORO_INCLUDE_DIRS ${SOURCE_DIR}/src)

    list(APPEND LAMMPS_DEPS voro_build)

  else()

    find_package(VORO)

    if(NOT VORO_FOUND)

      message(FATAL_ERROR "VORO not found, help CMake to find it by setting VORO_LIBRARY and VORO_INCLUDE_DIR, or set DOWNLOAD_VORO=ON to download it")

    endif()

  endif()

  include_directories(${VORO_INCLUDE_DIRS})

  list(APPEND LAMMPS_LINK_LIBS ${VORO_LIBRARIES})

endif()