diff --git a/CMakeLists.txt b/CMakeLists.txt
index f00cece9b..5a948749a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,7 +17,38 @@ if(MSVC)
 endif(MSVC)
 
 option(USE_OPENMP "flag to use OpenMP for multithreading" ON)
+if(USE_OPENMP)
+    find_package(OpenMP)
+    if (OpenMP_CXX_FOUND)
+        message(STATUS "Building with OpenMP Multithreading.")
+    else()
+        message(STATUS "No OpenMP found, no multithreading.")
+    endif()
+endif()
 
+find_package(OpenGL)
+if(NOT OpenGL_FOUND)
+    message(WARNING "OpenGL not found, not compiling graphics programs.")
+else(NOT OpenGL_FOUND)
+    find_package(GLUT)
+    if(NOT GLUT_FOUND)
+        message(WARNING "GLUT not found, not compiling graphics programs.")
+    endif(NOT GLUT_FOUND)
+endif(NOT OpenGL_FOUND)
+    
+add_subdirectory(math)
+add_subdirectory(others)
+add_subdirectory(search)
+add_subdirectory(ciphers)
+add_subdirectory(strings)
+add_subdirectory(sorting)
+add_subdirectory(geometry)
+add_subdirectory(graphics)
+add_subdirectory(probability)
+add_subdirectory(data_structures)
+add_subdirectory(machine_learning)
+add_subdirectory(numerical_methods)
+    
 cmake_policy(SET CMP0054 NEW)
 cmake_policy(SET CMP0057 NEW)
 find_package(Doxygen OPTIONAL_COMPONENTS dot dia)
@@ -34,6 +65,7 @@ if(DOXYGEN_FOUND)
     set(DOXYGEN_STRIP_CODE_COMMENTS NO)
     set(DOXYGEN_EXT_LINKS_IN_WINDOW YES)
     set(DOXYGEN_BUILTIN_STL_SUPPORT YES)
+    set(DOXYGEN_ENABLE_PREPROCESSING YES)
     set(DOXYGEN_CLANG_ASSISTED_PARSING YES)
     set(DOXYGEN_FILE_PATTERNS *.cpp *.h *.hpp *.md)
     set(DOXYGEN_MATHJAX_EXTENSIONS  TeX/AMSmath TeX/AMSsymbols)
@@ -48,6 +80,12 @@ if(DOXYGEN_FOUND)
         set(DOXYGEN_INTERACTIVE_SVG YES)
         set(DOXYGEN_DOT_IMAGE_FORMAT "svg")
     endif()
+    if(OPENMP_FOUND)
+        set(DOXYGEN_PREDEFINED "_OPENMP=1")
+    endif()
+    if(GLUT_FOUND)
+        set(DOXYGEN_PREDEFINED ${DOXYGEN_PREDEFINED} "GLUT_FOUND=1")
+    endif()
 
     doxygen_add_docs(
         doc
@@ -56,28 +94,6 @@ if(DOXYGEN_FOUND)
     )
 endif()
 
-if(USE_OPENMP)
-    find_package(OpenMP)
-    if (OpenMP_CXX_FOUND)
-        message(STATUS "Building with OpenMP Multithreading.")
-    else()
-        message(STATUS "No OpenMP found, no multithreading.")
-    endif()
-endif()
-
-add_subdirectory(math)
-add_subdirectory(others)
-add_subdirectory(search)
-add_subdirectory(ciphers)
-add_subdirectory(strings)
-add_subdirectory(sorting)
-add_subdirectory(geometry)
-add_subdirectory(graphics)
-add_subdirectory(probability)
-add_subdirectory(data_structures)
-add_subdirectory(machine_learning)
-add_subdirectory(numerical_methods)
-
 set(CPACK_PROJECT_NAME ${PROJECT_NAME})
 set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
 include(CPack)
diff --git a/graphics/CMakeLists.txt b/graphics/CMakeLists.txt
index 12e60bd29..2e03a71ed 100644
--- a/graphics/CMakeLists.txt
+++ b/graphics/CMakeLists.txt
@@ -1,17 +1,6 @@
 # If necessary, use the RELATIVE flag, otherwise each source file may be listed
 # with full pathname. RELATIVE may makes it easier to extract an executable name
 # automatically.
-find_package(OpenGL)
-if(NOT OpenGL_FOUND)
-    message(WARNING "OpenGL not found, not compiling graphics programs.")
-
-else(NOT OpenGL_FOUND)
-    find_package(GLUT)
-    if(NOT GLUT_FOUND)
-        message(WARNING "GLUT not found, not compiling graphics programs.")
-    endif(NOT GLUT_FOUND)
-endif(NOT OpenGL_FOUND)
-
 file( GLOB APP_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.cpp )
 # file( GLOB APP_SOURCES ${CMAKE_SOURCE_DIR}/*.c )
 # AUX_SOURCE_DIRECTORY(${CMAKE_CURRENT_SOURCE_DIR} APP_SOURCES)
@@ -28,7 +17,7 @@ foreach( testsourcefile ${APP_SOURCES} )
         if(APPLE)
             target_compile_options(${testname} PUBLIC -Wno-deprecated)
         endif(APPLE)
-        target_compile_definitions(${testname} PUBLIC USE_GLUT)
+        target_compile_definitions(${testname} PUBLIC GLUT_FOUND)
         target_include_directories(${testname} PUBLIC ${GLUT_INCLUDE_DIRS})
         target_link_libraries(${testname} OpenGL::GL ${GLUT_LIBRARIES})
     endif(GLUT_FOUND)
diff --git a/graphics/spirograph.cpp b/graphics/spirograph.cpp
index adaad6d7b..59041b6d3 100644
--- a/graphics/spirograph.cpp
+++ b/graphics/spirograph.cpp
@@ -26,7 +26,10 @@
 #include <omp.h>
 #endif
 
-namespace {
+/**
+ * @namespace spirograph Functions related to spirograph.c
+ */
+namespace spirograph {
 /** Generate spirograph curve into arrays `x` and `y` such that the i^th point
  * in 2D is represented by `(x[i],y[i])`. The generating function is given by:
  * \f{eqnarray*}{
@@ -104,7 +107,7 @@ void test() {
     fp.close();
 }
 
-#ifdef USE_GLUT  // this is set by CMAKE automatically, if available
+#ifdef GLUT_FOUND  // this is set by CMAKE automatically, if available
 #ifdef __APPLE__
 #include <GLUT/glut.h>  // include path on Macs is different
 #else
@@ -211,21 +214,21 @@ void timer_cb(int t) {
     glutPostRedisplay();
 }
 #endif
-}  // namespace
+}  // namespace spirograph
 
 /** Main function */
 int main(int argc, char **argv) {
-#ifdef USE_GLUT
+#ifdef GLUT_FOUND
     glutInit(&argc, argv);
     glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
     glutCreateWindow("Spirograph");
     glutInitWindowSize(400, 400);
     // glutIdleFunc(glutPostRedisplay);
-    glutTimerFunc(25, timer_cb, 0);
-    glutDisplayFunc(test2);
+    glutTimerFunc(25, spirograph::timer_cb, 0);
+    glutDisplayFunc(spirograph::test2);
     glutMainLoop();
 #else
-    test();
+    spirograph::test();
 #endif
 
     return 0;