Doxygen: explicit cmake option, more corrections

- Correct log message for directory of generated doxygen doc
- Correct path for image
- Skip to build libraries if not requested

doc/CMakeLists.txt

@@ -1,15 +1,13 @@
+add_boolean_option(GENERATE_DOXYGEN False "Generate source code doc using doxygen")
 
-find_package(Doxygen QUIET)
+if(GENERATE_DOXYGEN)
+  find_package(Doxygen REQUIRED)
 
-if(DOXYGEN_FOUND)
   configure_file(Doxyfile ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
   add_custom_target(doc
     ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
     COMMENT "Generating API documentation with Doxygen" VERBATIM
-    )
+  )
 else()
-  add_custom_target(doc
-    message(FATAL_ERROR "required to generate doxygen documentation but doxygen not installed")
-    )
-endif(DOXYGEN_FOUND)
-
+  message(STATUS "No Doxygen documentation requested")
+endif()

doc/Doxyfile

@@ -51,14 +51,14 @@ PROJECT_BRIEF          = "Full experimental OpenSource LTE and NR implementation
 # pixels and the maximum width should not exceed 200 pixels. Doxygen will copy
 # the logo to the output directory.
 
-PROJECT_LOGO           = images/oai_logo.png
+PROJECT_LOGO           = @CMAKE_SOURCE_DIR@/doc/oai_logo.png
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute) path
 # into which the generated documentation will be written. If a relative path is
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = GeneratedDoc
+#OUTPUT_DIRECTORY       = .
 
 # If the CREATE_SUBDIRS tag is set to YES then doxygen will create 4096 sub-
 # directories (in 2 levels) under the output directory of each output format and