configure OpenGL on CMake in Mac OS

IF(APPLE)
INCLUDE_DIRECTORIES ( /System/Library/Frameworks )
FIND_LIBRARY(COCOA_LIBRARY Cocoa)
FIND_LIBRARY(GLUT_LIBRARY GLUT )
FIND_LIBRARY(OpenGL_LIBRARY OpenGL )
MARK_AS_ADVANCED (COCOA_LIBRARY
GLUT_LIBRARY
OpenGL_LIBRARY)
SET(EXTRA_LIBS ${COCOA_LIBRARY} ${GLUT_LIBRARY} ${OpenGL_LIBRARY} -lpng)
ENDIF (APPLE)