ViewerClasses USING [Viewer];

RETURNS[abort: BOOL ← FALSE] ;

abort will abort the event and the remaining EventProcs

{save, edit, destroy, create, close, open, grow, changeColumn, setInputFocus, killInputFocus} ;

There are two calls for each event: before anything happens and after everything (including the painting) is complete. The first call of a create occurs after the ViewerRec is NEW'ed but before the parameters are checked. Parameters can be changed if desired.

filter: REF ANY ← NIL, before: BOOL ← TRUE] RETURNS [EventRegistration] ;

Register a procedure that can be called before or after the specified event occurs. The filter can be a particular viewer, the atom for a class, or NIL. When before is TRUE the EventProc can abort the event. If the client wishes to unregister the procedure at some point, they should save the EventRegistration returned. N.B. - many of the EventProcs are called from within the Viewer tree write lock. If you attempt to perform a ViewerOps function that requires the write lock from within your EventProc then you will deadlock. Some of the events may additionally have acquired the paint lock. If you are concerned about deadlocks or if you plan to do anything time-consuming in an EventProc, consider forking a separate process so as not to adversely affect system performance.

Unregister an EventProc registered via RegisterEventProc.

RETURNS[abort: BOOL] ;

Window manager internal use only. Called once before and once after each event.