US Patent 7818755 Window server event taps

Methods, devices and an associated application programming interface are described that permits a user to register event tap routines (“ETRs”) with an application such as, for example, a window server application. Event tap routines permit events such as human interface device events to be processed at multiple points and in a manner not provided during normal window server operations. Event tap routines may effect passive or active event responses. Passive ETRs may merely record the occurrence of an event or the time between successive events without modifying or altering the event's processing sequence within a window server. Active ETRs, on the other hand, effect some programmatic response to an event. For example, active ETRs may modify the state of an event, delete the event, create one or more additional events or cause the event to be processed “out of sequence” by the window server application.