NAME

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

SYNTAX

       #include <X11/Intrinsic.h>

       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 processes events using XtAppProcessEvent, varying the mask
       parameter and using XtAppPending to ensure that it has a chance to handle events of all
       types, i.e., X events, timer events, input events and signal sources.  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 processes
       events 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 for the next event.

SEE ALSO

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