/tmp/ccC9EXQy.o: In function `circle(float, float, float)':
stavros.cpp:(.text+0x7d): undefined reference to `glColor3f'
stavros.cpp:(.text+0x87): undefined reference to `glBegin'
stavros.cpp:(.text+0x121): undefined reference to `glVertex2f'
stavros.cpp:(.text+0x130): undefined reference to `glEnd'
/tmp/ccC9EXQy.o: In function `main':
stavros.cpp:(.text.startup+0x5c): undefined reference to `sf::VideoMode::VideoMode(unsigned int, unsigned int, unsigned int)'
stavros.cpp:(.text.startup+0x8b): undefined reference to `sf::Window::Window(sf::VideoMode, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned long, sf::WindowSettings const&)'
stavros.cpp:(.text.startup+0xa7): undefined reference to `sf::Window::SetFramerateLimit(unsigned int)'
stavros.cpp:(.text.startup+0xb4): undefined reference to `sf::Clock::Clock()'
stavros.cpp:(.text.startup+0xbe): undefined reference to `glMatrixMode'
stavros.cpp:(.text.startup+0xc3): undefined reference to `glLoadIdentity'
stavros.cpp:(.text.startup+0xec): undefined reference to `glOrtho'
stavros.cpp:(.text.startup+0xf6): undefined reference to `glDisable'
stavros.cpp:(.text.startup+0x100): undefined reference to `glMatrixMode'
stavros.cpp:(.text.startup+0x105): undefined reference to `glLoadIdentity'
stavros.cpp:(.text.startup+0x116): undefined reference to `glClearColor'
stavros.cpp:(.text.startup+0x25b): undefined reference to `sf::Window::SetActive(bool) const'
stavros.cpp:(.text.startup+0x265): undefined reference to `glClear'
stavros.cpp:(.text.startup+0x26f): undefined reference to `glBegin'
stavros.cpp:(.text.startup+0x282): undefined reference to `glColor3f'
stavros.cpp:(.text.startup+0x292): undefined reference to `glVertex2f'
stavros.cpp:(.text.startup+0x2a2): undefined reference to `glVertex2f'
stavros.cpp:(.text.startup+0x2b2): undefined reference to `glVertex2f'
stavros.cpp:(.text.startup+0x2c2): undefined reference to `glVertex2f'
stavros.cpp:(.text.startup+0x2c7): undefined reference to `glEnd'
stavros.cpp:(.text.startup+0x2d1): undefined reference to `glBegin'
stavros.cpp:(.text.startup+0x304): undefined reference to `glColor3f'
stavros.cpp:(.text.startup+0x323): undefined reference to `glVertex2f'
stavros.cpp:(.text.startup+0x335): undefined reference to `glEnd'
stavros.cpp:(.text.startup+0x342): undefined reference to `sf::Clock::GetElapsedTime() const'
stavros.cpp:(.text.startup+0x39a): undefined reference to `sf::Window::Display()'
stavros.cpp:(.text.startup+0x3a4): undefined reference to `sf::Window::IsOpened() const'
stavros.cpp:(.text.startup+0x3be): undefined reference to `sf::Window::GetEvent(sf::Event&)'
stavros.cpp:(.text.startup+0x467): undefined reference to `glViewport'
stavros.cpp:(.text.startup+0x476): undefined reference to `sf::Window::Close()'
stavros.cpp:(.text.startup+0x4a1): undefined reference to `sf::Window::Close()'
stavros.cpp:(.text.startup+0x4c3): undefined reference to `glViewport'
stavros.cpp:(.text.startup+0x591): undefined reference to `glViewport'
stavros.cpp:(.text.startup+0x5ec): undefined reference to `sf::Window::~Window()'
stavros.cpp:(.text.startup+0x63c): undefined reference to `sf::Window::~Window()'
collect2: ld returned 1 exit status