+/* Reset the trackball to the default unrotated state,
+ plus an optional initial rotation.
+ */
+extern void gltrackball_reset (trackball_state *ts, float x, float y);
+
+/* A utility function for event-handler functions:
+ Handles the various motion and click events related to trackballs.
+ Returns True if the event was handled.
+ */
+extern Bool gltrackball_event_handler (XEvent *,
+ trackball_state *,
+ int window_width, int window_height,
+ Bool *button_down_p);
+
+#endif /* __GLTRACKBALL_H__ */