add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/backports/optional)
list(APPEND ASY_STATIC_LIBARIES OptionalBackport)
if (ENABLE_OPENGL)
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/backports/glew)
# using glew within the repo
list(APPEND ASY_STATIC_LIBARIES GLEW)
list(APPEND ASYMPTOTE_INCLUDES $<TARGET_PROPERTY:GLEW,INCLUDE_DIRECTORIES>)
endif()