message: Only check for dependencies if we actually build MPI example apps
diff: option(OSPRAY_MODULE_MPI "MPI parallel device" OFF)
  -# Note: the MPI example viewer depends on tfn lib, so we must make sure that
  -# was built.
  -if (NOT TARGET ospray_tfn OR NOT TARGET ospray_imgui_util_sg
  - OR NOT TARGET ospray_imgui3d_sg)
  - message(FATAL_ERROR "ospray_tfn library is required for the MPI example app,"
  - " please set -DOSPRAY_APPS_EXAMPLEVIEWER=ON as well")
  -endif ()
  -
  if (OSPRAY_MODULE_MPI)
  option(OSPRAY_MODULE_MPI_APPS "MPI module viewer application"
  ${OSPRAY_APPS_EXAMPLEVIEWER})
  @@ -89,6 +81,14 @@ if (OSPRAY_MODULE_MPI)
  # Test apps
  ##############################################################
  if (OSPRAY_MODULE_MPI_APPS)
  + # Note: the MPI example viewer depends on tfn lib, so we must make sure that
  + # was built.
  + if (NOT TARGET ospray_tfn OR NOT TARGET ospray_imgui_util_sg
  + OR NOT TARGET ospray_imgui3d_sg)
  + message(FATAL_ERROR "ospray_tfn library is required for the MPI example app,"
  + " please set -DOSPRAY_APPS_EXAMPLEVIEWER=ON as well")
  + endif ()
  +
  add_subdirectory(apps)
  endif (OSPRAY_MODULE_MPI_APPS)
  