glutForceJoystickFunc forces the current window's joystick callback to be called, reporting the latest joystick state.
The joystick callback is called either due to polling of the joystick at the uniform timer interval set by glutJoystickFunc's pollInterval (specified in milliseconds) or in response to calling glutForceJoystickFunc. If the pollInterval is non-positive, no joystick polling is performed and the GLUT application must frequently (usually from an idle callback) call glutForceJoystickFunc.
The joystick callback will be called once (if one exists) for each time glutForceJoystickFunc is called. The callback is called from glutJoystickFunc. That is, when glutJoystickFunc returns, the callback will have already happened.
The current implementation of GLUT for X11 supports the joystick API, but not actual joystick input. A future implementation of GLUT for X11 may add joystick support.
The current implementation of GLUT for Win32 supports the joystick API and joystick input, but does so through the dated joySetCapture and joyGetPosEx Win32 Multimedia API. The current GLUT joystick support for Win32 has all the limitations of the Win32 Multimedia API joystick support. A future implementation of GLUT for Win32 may use DirectInput.