glutTabletButtonFunc sets the special keyboard callback for the current window.
void glutTabletButtonFunc(void (*func)(int button, int state, int x, int y));
glutTabletButtonFunc sets the tablet button callback for the current window. The tablet button callback for a window is called when the window has tablet input focus (normally, when the mouse is in the window) and the user generates tablet button presses. The button parameter will be the button number (starting at one). The number of available tablet buttons can be determined with glutDeviceGet(GLUT_NUM_TABLET_BUTTONS). The state is either GLUT_UP or GLUT_DOWN indicating whether the callback was due to a release or press respectively. The x and y callback parameters indicate the window relative coordinates when the tablet button state changed.
Registering a tablet button callback when a tablet device is not available is ineffectual and not an error. In this case, no tablet button callbacks will be generated.
Passing NULL to glutTabletButtonFunc disables the generation of tablet button callbacks. When a new window is created, no tablet button callback is initially registered.