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