Added find_package for OpenGL in CMake (#771)

CMakeLists.txt

@@ -386,6 +386,8 @@ if (UNIX OR APPLE)
 
   # 3D
   if (WITH_3D_RENDERER)
+    # OpenGL
+	find_package(OpenGL REQUIRED)
     # GLUT
     find_package(GLUT REQUIRED)
   endif (WITH_3D_RENDERER)
@@ -404,7 +406,7 @@ if (UNIX OR APPLE)
   if (WITH_3D_ADAM_MODEL)
     if (NOT WITH_3D_RENDERER)
       message(FATAL_ERROR "WITH_3D_RENDERER is required if WITH_3D_ADAM_MODEL is enabled.")
-    endif (WITH_3D_RENDERER)
+    endif (NOT WITH_3D_RENDERER)
     find_package(PkgConfig)
     pkg_check_modules(EIGEN3 REQUIRED eigen3)
     # Others: sudo apt-get install libglm-dev
@@ -816,7 +818,7 @@ if (WITH_3D_ADAM_MODEL)
   include_directories(${EIGEN3_INCLUDE_DIRS})
   include_directories(${IGL_INCLUDE_DIRS})
   include_directories(${LIBIGL_INCLUDE_DIRS})
-  include_directories(${OPENGL_INCLUDE_DIRS} ${GLUT_INCLUDE_DIRS} ${GLEW_INCLUDE_DIRS})
+  include_directories(${OPENGL_INCLUDE_DIR} ${GLUT_INCLUDE_DIRS} ${GLEW_INCLUDE_DIRS})
 endif (WITH_3D_ADAM_MODEL)
 # Windows includes
 if (WIN32)
@@ -861,7 +863,7 @@ if (WITH_3D_ADAM_MODEL)
       ${OPENGL_LIBRARIES} ${GLUT_LIBRARY} ${GLEW_LIBRARY} ${FREE_IMAGE_LIBRARY})
 endif (WITH_3D_ADAM_MODEL)
 if (WITH_3D_RENDERER)
-  set(OpenPose_3rdparty_libraries ${OpenPose_3rdparty_libraries} ${GLUT_LIBRARY})
+  set(OpenPose_3rdparty_libraries ${OpenPose_3rdparty_libraries} ${OPENGL_LIBRARIES} ${GLUT_LIBRARY})
 endif (WITH_3D_RENDERER)
 if (WITH_CERES)
   set(OpenPose_3rdparty_libraries ${OpenPose_3rdparty_libraries} ${CERES_LIBRARIES})