glutSpaceballButtonFunc  - sets the Spaceball button call-
       back for the current window.

SYNTAX

       void glutSpaceballButtonFunc(void (*func)(int button, int state));

ARGUMENTS

       func      The new spaceball button callback function.

DESCRIPTION

       glutSpaceballButtonFunc sets the Spaceball button callback
       for  the current window. The Spaceball button callback for
       a window is called when the  window  has  Spaceball  input
       focus  (normally, when the mouse is in the window) and the
       user generates Spaceball button presses. The button param-
       eter will be the button number (starting at one). The num-
       ber of available Spaceball buttons can be determined  with
       glutDeviceGet(GLUT_NUM_SPACEBALL_BUTTONS).  The  state  is
       either GLUT_UP or GLUT_DOWN indicating whether  the  call-
       back was due to a release or press respectively.

       Registering  a  Spaceball button callback when a Spaceball
       device is not available is ineffectual and not  an  error.
       In this case, no Spaceball button callbacks will be gener-
       ated.

       Passing NULL to glutSpaceballButtonFunc disables the  gen-
       eration  of  Spaceball button callbacks. When a new window
       is created, no Spaceball button callback is initially reg-
       istered.

SEE ALSO

       glutSpaceballMotionFunc, glutSpaceballRotateFunc, glutMouseFunc,
       glutButtonBoxFunc, glutTabletButtonFunc, glutJoystickFunc,
       glutDeviceGet

AUTHOR

       Mark J. Kilgard (mjk@nvidia.com)