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NAME

       XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProcessEvent,
       XtDispatchEvent, XtAppMainLoop - query and process events and input

SYNTAX

       void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);

       Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);

       XtInputMask XtAppPending(XtAppContext app_context);

       void XtAppProcessEvent(XtAppContext app_context, XtInputMask mask);

       Boolean XtDispatchEvent(XEvent *event);

       void XtAppMainLoop(XtAppContext app_context);

ARGUMENTS

       app_context
                 Specifies the application context that identifies the
                 application.

       event     Specifies a pointer to the event structure that is to be
                 dispatched to the appropriate event handler.

       event_return
                 Returns the event information to the specified event
                 structure.

       mask      Specifies what types of events to process.  The mask is the
                 bitwise inclusive OR of any combination of XtIMXEvent,
                 XtIMTimer, XtIMAlternateInput, and XtIMSignal.  As a
                 convenience, the X Toolkit defines the symbolic name XtIMAll
                 to be the bitwise inclusive OR of all event types.

DESCRIPTION

       If the X event queue is empty, XtAppNextEvent flushes the X output
       buffers of each Display in the application context and waits for an
       event while looking at the other input sources, timeout timeout values,
       and signal handlers and calling any callback procedures triggered by
       them.  This wait time can be used for background processing (see
       Section 7.8).

       If there is an event in the queue, XtAppPeekEvent fills in the event
       and returns a nonzero value. If no X input is on the queue,
       XtAppPeekEvent flushes the output buffer and blocks until input is
       available (possibly calling some timeout callbacks in the process).  If
       the input is an event, XtAppPeekEvent fills in the event and returns a
       nonzero value.  Otherwise, the input is for an alternate input source,
       and XtAppPeekEvent returns zero.

       The XtAppPending function returns a nonzero value if there are events
       pending from the X server, timer pending, or other input sources
       pending. The value returned is a bit mask that is the OR of XtIMXEvent,
       XtIMTimer, XtIMAlternateInput, and XtIMSignal (see XtAppProcessEvent).
       If there are no events pending, XtAppPending flushes the output buffer
       and returns zero.

       The XtAppProcessEvent function processes one timer, alternate input,
       signal source, or X event.  If there is nothing of the appropriate type
       to process, XtAppProcessEvent blocks until there is.  If there is more
       than one type of thing available to process, it is undefined which will
       get processed.  Usually, this procedure is not called by client
       applications (see XtAppMainLoop).  XtAppProcessEvent processes timer
       events by calling any appropriate timer callbacks, alternate input by
       calling any appropriate alternate input callbacks, signal source by
       calling any appropriate signal callbacks, and X events by calling
       XtDispatchEvent.

       When an X event is received, it is passed to XtDispatchEvent, which
       calls the appropriate event handlers and passes them the widget, the
       event, and client-specific data registered with each procedure.  If
       there are no handlers for that event registered, the event is ignored
       and the dispatcher simply returns.  The order in which the handlers are
       called is undefined.

       The XtDispatchEvent function sends those events to the event handler
       functions that have been previously registered with the dispatch
       routine.  XtDispatchEvent returns True if it dispatched the event to
       some handler and False if it found no handler to dispatch the event to.
       The most common use of XtDispatchEvent is to dispatch events acquired
       with the XtAppNextEvent procedure.  However, it also can be used to
       dispatch user-constructed events.  XtDispatchEvent also is responsible
       for implementing the grab semantics for XtAddGrab.

       The XtAppMainLoop function first reads the next incoming X event by
       calling XtAppNextEvent and then it dispatches the event to the
       appropriate registered procedure by calling XtDispatchEvent.  This
       constitutes the main loop of X Toolkit applications, and, as such, it
       does not return unless XtAppSetExitFlag is called.  Applications are
       expected to exit in response to some user action.  There is nothing
       special about XtAppMainLoop; it is simply an loop that calls
       XtAppNextEvent and then XtDispatchEvent, until XtAppGetExitFlag()
       returns true.

       Applications can provide their own version of this loop, which tests
       some global termination flag or tests that the number of top-level
       widgets is larger than zero before circling back to the call to
       XtAppNextEvent.

SEE ALSO

       X Toolkit Intrinsics - C Language Interface
       Xlib - C Language X Interface



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