path: root/libXt/specs/CH07

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\&
.sp 1
.ce 3
\s+1\fBChapter 7\fP\s-1

\s+1\fBEvent Management\fP\s-1
.sp 2
.nr H1 7
.nr H2 0
.nr H3 0
.nr H4 0
.nr H5 0
.LP
.XS
Chapter 7 \(em Event Management
.XE
While Xlib allows the reading and processing of events anywhere in an application,
widgets in the \*(tk neither directly read events
nor grab the server or pointer.
Widgets register procedures that are to be called
when an event or class of events occurs in that widget.
.LP
A typical application consists of startup code followed by an event loop
that reads events and dispatches them by calling
the procedures that widgets have registered.
The default event loop provided by the \*(xI is
.PN XtAppMainLoop .
.LP
The event manager is a collection of functions to perform the following tasks:
.IP \(bu 5
Add or remove event sources other than X server events (in particular,
timer interrupts, file input, or POSIX signals).
.IP \(bu 5
Query the status of event sources.
.IP \(bu 5
Add or remove procedures to be called when an event occurs for a particular
widget.
.IP \(bu 5
Enable and
disable the dispatching of user-initiated events (keyboard and pointer events)
for a particular widget.
.IP \(bu 5
Constrain the dispatching of events to a cascade of pop-up widgets.
.IP \(bu 5
Register procedures to be called when specific events arrive.
.IP \(bu 5
Register procedures to be called when the \*(xI will block.
.IP \(bu 5
Enable safe operation in a multi-threaded environment.
.LP
Most widgets do not need to call any of the event handler functions explicitly.
The normal interface to X events is through the higher-level
translation manager,
which maps sequences of X events, with modifiers, into procedure calls.
Applications rarely use any of the event manager routines besides
.PN XtAppMainLoop .

.NH 2
Adding and Deleting Additional Event Sources
.XS
\fB\*(SN Adding and Deleting Additional Event Sources\fP
.XE
.LP
While most applications are driven only by X events,
some applications need to incorporate other sources of input 
into the \*(xI event-handling mechanism.
The event manager provides routines to integrate notification of timer events
and file data pending into this mechanism.
.LP
The next section describes functions that provide input gathering from files.
The application registers the files with the \*(xI read routine.
When input is pending on one of the files,
the registered callback procedures are invoked.

.NH 3
Adding and Removing Input Sources
.XS
\fB\*(SN Adding and Removing Input Sources\fP
.XE
.LP
To register a new file as an input source for a given application context, use
.PN XtAppAddInput .
.LP
.IN "XtAppAddInput" "" "@DEF@"
.sM
.FD 0
XtInputId XtAppAddInput(\fIapp_context\fP, \fIsource\fP, \fIcondition\fP, \
\fIproc\fP, \fIclient_data\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      int \fIsource\fP;
.br
      XtPointer \fIcondition\fP;
.br
      XtInputCallbackProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIsource\fP 1i
Specifies the source file descriptor on a POSIX-based system
or other operating-system-dependent device specification.
.IP \fIcondition\fP 1i
Specifies the mask that indicates a read, write, or exception condition
or some other operating-system-dependent condition.
.IP \fIproc\fP 1i
Specifies the procedure to be called when the condition is found.
.IP \fIclient_data\fP 1i
Specifies an argument passed to the specified procedure
when it is called.
.LP
.eM
The
.PN XtAppAddInput
function registers with the \*(xI read routine a new source of events,
which is usually file input but can also be file output.
Note that \fIfile\fP should be loosely interpreted to mean any sink 
or source of data.
.PN XtAppAddInput
also specifies the conditions under which the source can generate events.
When an event is pending on this source,
the callback procedure is called.
.LP
The legal values for the \fIcondition\fP argument are operating-system-dependent.
On a POSIX-based system,
\fIsource\fP is a file number and the condition is some union of the following:
.IN "XtInputReadMask" "" "@DEF@"
.IP \fBXtInputReadMask\fR 1.5i
Specifies that \fIproc\fP is to be called when \fIsource\fP has data to be read.
.IN "XtInputWriteMask" "" "@DEF@"
.IP \fBXtInputWriteMask\fR 1.5i
Specifies that \fIproc\fP is to be called when \fIsource\fP is ready
for writing.
.IN "XtInputExceptMask" "" "@DEF@"
.IP \fBXtInputExceptMask\fR 1.5i
Specifies that \fIproc\fP is to be called when \fIsource\fP has
exception data.
.LP
Callback procedure pointers used to handle file events are of
type
.PN XtInputCallbackProc .
.LP
.IN "XtInputCallbackProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtInputCallbackProc)(XtPointer, int*, XtInputId*);
.br
      XtPointer \fIclient_data\fP;
.br
      int *\fIsource\fP;
.br
      XtInputId *\fIid\fP;
.FN
.IP \fIclient_data\fP 1i
Passes the client data argument that was registered for this procedure in
.PN XtApp\%AddInput .
.IP \fIsource\fP 1i
Passes the source file descriptor generating the event.
.IP \fIid\fP 1i
Passes the id returned from the corresponding
.PN XtAppAddInput
call.
.LP
.eM
See Section 7.12 for information regarding the use of
.PN XtAppAddInput
in multiple threads.
.sp
.LP
To discontinue a source of input, use
.PN XtRemoveInput .
.LP
.IN "XtRemoveInput" "" "@DEF@"
.sM
.FD 0
void XtRemoveInput(\fIid\fP)
.br
      XtInputId \fIid\fP;
.FN
.IP \fIid\fP 1i
Specifies the id returned from the corresponding
.PN XtAppAddInput
call.
.LP
.eM
The
.PN XtRemoveInput
function causes the \*(xI read routine to stop watching for events
from the file source specified by \fIid\fP.
.LP
See Section 7.12 for information regarding the use of
.PN XtRemoveInput
in multiple threads.

.NH 3
Adding and Removing Blocking Notifications
.XS
\fB\*(SN Adding and Removing Blocking Notifications\fP
.XE
.LP
Occasionally it is desirable for an application to receive notification
when the \*(xI event manager detects no pending input from file sources
and no pending input from X server event sources and is about to block
in an operating system call.
.sp
.LP
To register a hook that is called immediately prior to event blocking, use
.PN XtAppAddBlockHook .
.LP
.IN "XtAppAddBlockHook" "" "@DEF@"
.sM
.FD 0
XtBlockHookId XtAppAddBlockHook(\fIapp_context\fP, \fIproc\fP, \
\fIclient_data\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtBlockHookProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIproc\fP 1i
Specifies the procedure to be called before blocking.
.IP \fIclient_data\fP 1i
Specifies an argument passed to the specified procedure when it is called.
.LP
.eM
The
.PN XtAppAddBlockHook 
function registers the specified procedure and returns an identifier for it.
The hook procedure \fIproc\fP is called at any time in the future when
the \*(xI are about to block pending some input.
.LP
The procedure pointers used to provide notification of event blocking
are of type
.PN XtBlockHookProc .
.LP
.IN "XtBlockHookProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtBlockHookProc)(XtPointer);
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIclient_data\fP 1i
Passes the client data argument that was registered for this procedure in
.PN XtApp\%AddBlockHook .
.LP
.eM
To discontinue the use of a procedure for blocking notification, use
.PN XtRemoveBlockHook .
.LP
.IN "XtRemoveBlockHook" "" "@DEF@"
.sM
.FD 0
void XtRemoveBlockHook(\fIid\fP)
.br
      XtBlockHookId \fIid\fP;
.FN
.IP \fIid\fP 1i
Specifies the identifier returned from the corresponding call to
.PN XtAppAddBlockHook .
.LP
.eM
The 
.PN XtRemoveBlockHook 
function removes the specified procedure from the list of procedures
that are called by the \*(xI read routine before blocking on event sources.

.NH 3
Adding and Removing Timeouts
.XS
\fB\*(SN Adding and Removing Timeouts\fP
.XE
.LP
The timeout facility notifies the application or the widget
through a callback procedure that a specified time interval has elapsed.
Timeout values are uniquely identified by an interval id.
.sp
.LP
To register a timeout callback, use
.PN XtAppAddTimeOut .
.LP
.IN "XtAppAddTimeOut" "" "@DEF@"
.sM
.FD 0
XtIntervalId XtAppAddTimeOut(\fIapp_context\fP, \fIinterval\fP, \fIproc\fP, \
\fIclient_data\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      unsigned long \fIinterval\fP;
.br
      XtTimerCallbackProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context for which the timer is to be set.
.IP \fIinterval\fP 1i
Specifies the time interval in milliseconds.
.IP \fIproc\fP 1i
Specifies the procedure to be called when the time expires.
.IP \fIclient_data\fP 1i
Specifies an argument passed to the specified procedure
when it is called.
.LP
.eM
The
.PN XtAppAddTimeOut
function creates a timeout and returns an identifier for it.
The timeout value is set to \fIinterval\fP.
The callback procedure \fIproc\fP is called when
.PN XtAppNextEvent
or
.PN XtAppProcessEvent
is next called after the time interval elapses,
and then the timeout is removed.
.LP
Callback procedure pointers used with timeouts are of
type
.PN XtTimerCallbackProc .
.LP
.IN "XtTimerCallbackProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtTimerCallbackProc)(XtPointer, XtIntervalId*);
.br
      XtPointer \fIclient_data\fP;
.br
      XtIntervalId *\fItimer\fP;
.FN
.IP \fIclient_data\fP 1i
Passes the client data argument that was registered for this procedure in
.PN XtApp\%AddTimeOut .
.IP \fItimer\fP 1i
Passes the id returned from the corresponding
.PN XtAppAddTimeOut
call.
.LP
.eM
See Section 7.12 for information regarding the use of
.PN XtAppAddTimeOut
in multiple threads.
.sp
.LP
To clear a timeout value, use
.PN XtRemoveTimeOut .
.LP
.IN "XtRemoveTimeOut" "" "@DEF@"
.sM
.FD 0
void XtRemoveTimeOut(\fItimer\fP)
.br
      XtIntervalId \fItimer\fP;
.FN
.IP \fItimer\fP 1i
Specifies the id for the timeout request to be cleared.
.LP
.eM
The
.PN XtRemoveTimeOut
function removes the pending timeout.
Note that timeouts are automatically removed once they trigger.
.LP
Please refer to Section 7.12 for information regarding the use of
.PN XtRemoveTimeOut
in multiple threads.

.NH 3
Adding and Removing Signal Callbacks
.XS
\fB\*(SN Adding and Removing Signal Callbacks\fP
.XE
.LP
The signal facility notifies the application or the widget through a 
callback procedure that a signal or other external asynchronous event 
has occurred.  The registered callback procedures are uniquely identified 
by a signal id.
.sp
.LP
Prior to establishing a signal handler, the application or widget should
call
.PN XtAppAddSignal
and store the resulting identifier in a place accessible to the signal
handler.  When a signal arrives, the signal handler should call
.PN XtNoticeSignal
to notify the \*(xI that a signal has occured.  To register a signal 
callback use
.PN XtAppAddSignal .
.LP
.IN "XtAppAddSignal" "" "@DEF@"
.sM
.FD 0
XtSignalId XtAppAddSignal(\fIapp_context\fP, \fIproc\fP, \fIclient_data\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtSignalCallbackProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIproc\fP 1i
Specifies the procedure to be called when the signal is noticed.
.IP \fIclient_data\fP 1i
Specifies an argument passed to the specified procedure when it is called.
.LP
.eM
The callback procedure pointers used to handle signal events are of type
.PN XtSignalCallbackProc .
.LP
.IN "XtSignalCallbackProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtSignalCallbackProc)(XtPointer, XtSignalId*);
.br
	XtPointer \fIclient_data\fP;
.br
	XtSignalId *\fIid\fP;
.FN
.IP \fIclient_data\fP 1i
Passes the client data argument that was registered for this procedure in
.PN XtAppAddSignal .
.IP \fIid\fP 1i
Passes the id returned from the corresponding 
.PN XtAppAddSignal
call.
.LP
.eM
To notify the \*(xI that a signal has occured, use
.PN XtNoticeSignal .
.LP
.IN "XtNoticeSignal" "" "@DEF@"
.sp
.sM
.FD 0
void XtNoticeSignal(\fIid\fP)
.br
      XtSignalId \fIid\fP;
.FN
.IP \fIid\fP 1i
Specifies the id returned from the corresponding
.PN XtAppAddSignal
call.
.LP
.eM
On a POSIX-based system,
.PN XtNoticeSignal
is the only \*(xI function that can safely be called from a signal handler.
If 
.PN XtNoticeSignal
is invoked multiple times before the \*(xI are able to invoke the
registered callback, the callback is only called once.
Logically, the \*(xI maintain ``pending'' flag for each registered callback.
This flag is initially
.PN False
and is set to
.PN True
by
.PN XtNoticeSignal .
When 
.PN XtAppNextEvent
or
.PN XtAppProcessEvent
(with a mask including
.PN XtIMSignal )
is called, all registered callbacks with ``pending''
.PN True
are invoked and the flags are reset to
.PN False .
.LP
If the signal handler wants to track how many times the signal has been
raised, it can keep its own private counter.  Typically the handler would 
not do any other work; the callback does the actual processing for the 
signal. The \*(xI never block signals from being raised, so if a given 
signal can be raised multiple times before the \*(xI can invoke the 
callback for that signal, the callback must be designed to deal with 
this.  In another case, a signal might be raised just after the \*(xI
sets the pending flag to
.PN False
but before the callback can get control, in which case the pending flag
will still be
.PN True
after the callback returns, and the \*(xI will invoke the callback
again, even though all of the signal raises have been handled.  The
callback must also be prepared to handle this case.
.LP
To remove a registered signal callback, call
.PN XtRemoveSignal .
.LP
.IN "XtRemoveSignal" "" "@DEF@"
.sM
.FD 0
void XtRemoveSignal(\fIid\fP)
.br
      XtSignalId \fIid\fP;
.FN
.IP \fIid\fP 1i
Specifies the id returned by the corresponding call to
.PN XtAppAddSignal .
.LP
.eM
The client should typically disable the source of the signal before calling
.PN XtRemoveSignal .
If the signal could have been raised again before the source was disabled
and the client wants to process it, then after disabling the source but
before calling
.PN XtRemoveSignal
the client can test for signals with
.PN XtAppPending
and process them by calling
.PN XtAppProcessEvent
with the mask
.PN XtIMSignal .

.NH 2
Constraining Events to a Cascade of Widgets
.XS
\fB\*(SN Constraining Events to a Cascade of Widgets\fP
.XE
.LP
.IN "Grabbing Input"
.IN "Input Grabbing"
Modal widgets are widgets that, except for the input directed to them,
lock out user input to the application.
.LP
When a modal menu or modal dialog box is popped up using
.PN XtPopup ,
user events (keyboard and pointer events) that occur outside the modal
widget should be delivered to the modal widget or ignored.
In no case will user events be delivered to a widget outside
the modal widget.
.LP
Menus can pop up submenus, and dialog boxes can pop up further dialog
boxes to create a pop-up cascade.
In this case,
user events may be delivered to one of several modal widgets in the cascade.
.LP
Display-related events should be delivered outside the modal cascade so that
exposure events and the like keep the application's display up-to-date.
Any event that occurs within the cascade is delivered as usual.
The user events delivered to the most recent spring-loaded shell 
in the cascade when they occur outside the cascade are called remap events 
and are
.PN KeyPress ,
.PN KeyRelease ,
.PN ButtonPress ,
and
.PN ButtonRelease .
The user events ignored when they occur outside the cascade are
.PN MotionNotify
and
.PN EnterNotify .
All other events are delivered normally.
In particular, note that this is one
way in which widgets can receive
.PN LeaveNotify
events without first receiving
.PN EnterNotify
events; they should be prepared to deal with
this, typically by ignoring any unmatched
.PN LeaveNotify
events.
.LP
.PN XtPopup
uses the 
.PN XtAddGrab
and
.PN XtRemoveGrab
functions to constrain user events to a modal cascade 
and subsequently to remove a grab when the modal widget is popped down.

.sp
.LP
To constrain or redirect user input to a modal widget, use
.PN XtAddGrab .
.LP
.IN "XtAddGrab" "" "@DEF@"
.sM
.FD 0
void XtAddGrab(\fIw\fP, \fIexclusive\fP, \fIspring_loaded\fP)
.br
      Widget \fIw\fP;
.br
      Boolean \fIexclusive\fP;
.br
      Boolean \fIspring_loaded\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget to add to the modal cascade. \*(cI
.IP \fIexclusive\fP 1i
Specifies whether user events should be dispatched exclusively to this widget 
or also to previous widgets in the cascade.
.IP \fIspring_loaded\fP 1i
Specifies whether this widget was popped up because the user pressed
a pointer button.
.LP
.eM
The
.PN XtAddGrab
function appends the widget to the modal cascade
and checks that \fIexclusive\fP is 
.PN True 
if \fIspring_loaded\fP is 
.PN True .
If this condition is not met,
.PN XtAddGrab
generates a warning message.
.LP
The modal cascade is used by
.PN XtDispatchEvent
when it tries to dispatch a user event.
When at least one modal widget is in the widget cascade, 
.PN XtDispatchEvent
first determines if the event should be delivered.
It starts at the most recent cascade entry and follows the cascade up to and
including the most recent cascade entry added with the \fIexclusive\fP parameter
.PN True .
.LP
This subset of the modal cascade along with all descendants of these widgets
comprise the active subset.
User events that occur outside the widgets in this subset are ignored
or remapped.
Modal menus with submenus generally add a submenu widget to the cascade
with \fIexclusive\fP 
.PN False .
Modal dialog boxes that need to restrict user input to the most deeply nested
dialog box add a subdialog widget to the cascade with \fIexclusive\fP 
.PN True .
User events that occur within the active subset are delivered to the
appropriate widget, which is usually a child or further descendant of the modal
widget.
.LP
Regardless of where in the application they occur,
remap events are always delivered to the most recent widget in the active
subset of the cascade registered with \fIspring_loaded\fP 
.PN True ,
if any such widget exists.
If the event
occurred in the active subset of the cascade but outside the
spring-loaded widget, it is delivered normally before being
delivered also to the spring-loaded widget.
Regardless of where it is dispatched, the \*(xI do not modify
the contents of the event.
.sp
.LP
To remove the redirection of user input to a modal widget, use
.PN XtRemoveGrab .
.LP
.IN "XtRemoveGrab" "" "@DEF@"
.sM
.FD 0
void XtRemoveGrab(\fIw\fP)
.br
      Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget to remove from the modal cascade.
.LP
.eM
The
.PN XtRemoveGrab
function removes widgets from the modal cascade starting 
at the most recent widget up to and including the specified widget.
It issues a warning if the specified widget is not on the modal cascade.

.NH 3
Requesting Key and Button Grabs
.XS
\fB\*(SN Requesting Key and Button Grabs\fP
.XE
.LP
The \*(xI provide a set of key and button grab interfaces that
are parallel to those provided by Xlib and that allow the \*(xI
to modify event dispatching when necessary.  \*(tk applications and
widgets that need to passively grab keys or buttons or actively grab
the keyboard or pointer should use the
following \*(xI routines rather than the corresponding Xlib
routines.
.sp
.LP
To passively grab a single key of the keyboard, use
.PN XtGrabKey .
.LP
.IN "XtGrabKey" "" "@DEF@"
.sM
.FD 0
void XtGrabKey(\fIwidget\fP, \fIkeycode\fP, \fImodifiers\fP, \
\fIowner_events\fP, \fIpointer_mode\fP, \fIkeyboard_mode\fP)
.br
      Widget \fIwidget\fP;
.br
      KeyCode \fIkeycode\fP;
.br
      Modifiers \fImodifiers\fP;
.br
      Boolean \fIowner_events\fP;
.br
      int \fIpointer_mode\fP, \fIkeyboard_mode\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget in whose window the key is to be grabbed.  \*(cI
.sp 6p
.IP \fIkeycode\fP
.br
.ns
.IP \fImodifiers\fP
.br
.ns
.IP \fIowner_events\fP
.br
.ns
.IP \fIpointer_mode\fP
.br
.ns
.IP \fIkeyboard_mode\fP 1i
Specify arguments to
.PN XGrabKey ;
see Section 12.2 in \fI\*(xL\fP.
.LP
.eM
.PN XtGrabKey
calls
.PN XGrabKey
specifying the widget's window as the grab
window if the widget is realized.  The remaining arguments are exactly
as for
.PN XGrabKey .
If the widget is not realized, or is later unrealized, the call to
.PN XGrabKey
is performed (again) when
the widget is realized and its window becomes mapped.  In the future,
if
.PN XtDispatchEvent
is called with a
.PN KeyPress
event matching the specified keycode and modifiers (which may be
.PN AnyKey
or
.PN AnyModifier ,
respectively) for the
widget's window, the \*(xI will call
.PN XtUngrabKeyboard
with the timestamp from the
.PN KeyPress
event if either of the following conditions is true:
.IP \(bu 3
There is a modal cascade and the widget is not in
the active subset of the cascade and the keyboard was not previously
grabbed, or
.IP \(bu 3
.PN XFilterEvent
returns
.PN True .

.sp
.LP
To cancel a passive key grab, use
.PN XtUngrabKey .
.LP
.IN "XtUngrabKey" "" "@DEF@"
.sM
.FD 0
void XtUngrabKey(\fIwidget\fP, \fIkeycode\fP\fI, modifiers\fP)
.br
      Widget \fIwidget\fP;
.br
      KeyCode \fIkeycode\fP;
.br
      Modifiers \fImodifiers\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget in whose window the key was grabbed.
.sp 6p
.IP \fIkeycode\fP
.br
.ns
.IP \fImodifiers\fP 1i
Specify arguments to
.PN XUngrabKey ;
see Section 12.2 in \fI\*(xL\fP.
.LP
.eM
The
.PN XtUngrabKey
procedure calls
.PN XUngrabKey
specifying the widget's
window as the ungrab window if the widget is realized.  The remaining
arguments are exactly as for
.PN XUngrabKey .
If the widget is not realized,
.PN XtUngrabKey
removes a deferred
.PN XtGrabKey
request, if any, for the specified widget, keycode, and modifiers.
.sp
.LP
To actively grab the keyboard, use
.PN XtGrabKeyboard .
.LP
.IN "XtGrabKeyboard" "" "@DEF@"
.sM
.FD 0
int XtGrabKeyboard(\fIwidget\fP, \fIowner_events\fP, \fIpointer_mode\fP, \
\fIkeyboard_mode\fP, \fItime\fP)
.br
      Widget \fIwidget\fP;
.br
      Boolean \fIowner_events\fP;
.br
      int \fIpointer_mode\fP, \fIkeyboard_mode\fP;
.br
      Time \fItime\fP;
.br
.FN
.IP \fIwidget\fP 1i
Specifies the widget for whose window the keyboard is to be grabbed.
\*(cI
.sp 6p
.IP \fIowner_events\fP
.br
.ns
.IP \fIpointer_mode\fP
.br
.ns
.IP \fIkeyboard_mode\fP
.br
.ns
.IP \fItime\fP 1i
Specify arguments to
.PN XGrabKeyboard ;
see Section 12.2 in \fI\*(xL\fP.
.LP
.eM
If the specified widget is realized,
.PN XtGrabKeyboard
calls
.PN XGrabKeyboard
specifying the widget's window as the grab window.  The remaining
arguments and return value are exactly as for
.PN XGrabKeyboard .
If the widget is not realized,
.PN XtGrabKeyboard
immediately returns
.PN GrabNotViewable .
No future automatic ungrab is implied by
.PN XtGrabKeyboard .
.sp
.LP
To cancel an active keyboard grab, use
.PN XtUngrabKeyboard .
.LP
.IN "XtUngrabKeyboard" "" "@DEF@"
.sM
.FD 0
void XtUngrabKeyboard(\fIwidget\fP, \fItime\fP)
.br
      Widget \fIwidget\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget that has the active keyboard grab.
.IP \fItime\fP 1i
Specifies the additional argument to
.PN XUngrabKeyboard ;
see Section 12.2 in \fI\*(xL\fP.
.LP
.eM
.PN XtUngrabKeyboard
calls
.PN XUngrabKeyboard
with the specified time.
.sp
.LP
To passively grab a single pointer button, use
.PN XtGrabButton .
.LP
.IN "XtGrabButton" "" "@DEF@"
.sM
.FD 0
void XtGrabButton(\fIwidget\fP, \fIbutton\fP, \fImodifiers\fP, \
\fIowner_events\fP, \fIevent_mask\fP, \fIpointer_mode\fP,
                  \fIkeyboard_mode\fP, \fIconfine_to\fP, \fIcursor\fP)
.br
      Widget \fIwidget\fP;
.br
      int \fIbutton\fP;
.br
      Modifiers \fImodifiers\fP;
.br
      Boolean \fIowner_events\fP;
.br
      unsigned int \fIevent_mask\fP;
.br
      int \fIpointer_mode\fP, \fIkeyboard_mode\fP;
.br
      Window \fIconfine_to\fP;
.br
      Cursor \fIcursor\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget in whose window the button is to be grabbed.  \*(cI
.sp 6p
.IP \fIbutton\fP
.br
.ns
.IP \fImodifiers\fP
.br
.ns
.IP \fIowner_events\fP
.br
.ns
.IP \fIevent_mask\fP
.br
.ns
.IP \fIpointer_mode\fP
.br
.ns
.IP \fIkeyboard_mode\fP
.br
.ns
.IP \fIconfine_to\fP
.br
.ns
.IP \fIcursor\fP 1i
Specify arguments to
.PN XGrabButton ;
see Section 12.1 in \fI\*(xL\fP.
.LP
.eM
.PN XtGrabButton
calls
.PN XGrabButton
specifying the widget's window as the
grab window if the widget is realized.  The remaining arguments are
exactly as for
.PN XGrabButton .
If the widget is not realized, or is later unrealized, the call to
.PN XGrabButton
is performed (again)
when the widget is realized and its window becomes mapped.  In the
future, if
.PN XtDispatchEvent
is called with a
.PN ButtonPress
event matching the specified button and modifiers (which may be
.PN AnyButton
or
.PN AnyModifier ,
respectively)
for the widget's window, the \*(xI will call
.PN XtUngrabPointer
with the timestamp from the
.PN ButtonPress
event if either of the following conditions is true:
.IP \(bu 3
There is a modal cascade and the
widget is not in the active subset of the cascade and the pointer was
not previously grabbed, or
.IP \(bu 3
.PN XFilterEvent
returns
.PN True .

.sp
.LP
To cancel a passive button grab, use
.PN XtUngrabButton .
.LP
.IN "XtUngrabButton" "" "@DEF@"
.sM
.FD 0
void XtUngrabButton(\fIwidget\fP, \fIbutton\fP, \fImodifiers\fP)
.br
      Widget \fIwidget\fP;
.br
      unsigned int \fIbutton\fP;
.br
      Modifiers \fImodifiers\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget in whose window the button was grabbed.
.IP \fIbutton\fP
.br
.ns
.IP \fImodifiers\fP 1i
Specify arguments to
.PN XUngrabButton ;
see Section 12.1 in \fI\*(xL\fP.
.LP
.eM
The
.PN XtUngrabButton
procedure calls
.PN XUngrabButton
specifying the
widget's window as the ungrab window if the widget is realized.  The
remaining arguments are exactly as for
.PN XUngrabButton .
If the widget is not realized,
.PN XtUngrabButton
removes a deferred
.PN XtGrabButton
request, if any, for the specified widget, button, and modifiers.
.sp
.LP
To actively grab the pointer, use
.PN XtGrabPointer .
.LP
.IN "XtGrabPointer" "" "@DEF@"
.sM
.FD 0
int XtGrabPointer(\fIwidget\fP, \fIowner_events\fP, \fIevent_mask\fP, \
\fIpointer_mode\fP, \fIkeyboard_mode\fP,
                  \fIconfine_to\fP, \fIcursor\fP, \fItime\fP)
.br
      Widget \fIwidget\fP;
.br
      Boolean \fIowner_events\fP;
.br
      unsigned int \fIevent_mask\fP;
.br
      int \fIpointer_mode\fP, \fIkeyboard_mode\fP;
.br
      Window \fIconfine_to\fP;
.br
      Cursor \fIcursor\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget for whose window the pointer is to be grabbed.  \*(cI
.sp 6p
.IP \fIowner_events\fP
.br
.ns
.IP \fIevent_mask\fP
.br
.ns
.IP \fIpointer_mode\fP
.br
.ns
.IP \fIkeyboard_mode\fP
.br
.ns
.IP \fIconfine_to\fP
.br
.ns
.IP \fIcursor\fP
.br
.ns
.IP \fItime\fP 1i
Specify arguments to
.PN XGrabPointer ;
see Section 12.1 in \fI\*(xL\fP.
.LP
.eM
If the specified widget is realized,
.PN XtGrabPointer
calls
.PN XGrabPointer ,
specifying the widget's window as the grab window.  The remaining
arguments and return value are exactly as for
.PN XGrabPointer .
If the widget is not realized,
.PN XtGrabPointer
immediately returns
.PN GrabNotViewable .
No future automatic ungrab is implied by
.PN XtGrabPointer .
.sp
.LP
To cancel an active pointer grab, use
.PN XtUngrabPointer .
.LP
.IN "XtUngrabPointer" "" "@DEF@"
.sM
.FD 0
void XtUngrabPointer(\fIwidget\fP, \fItime\fP)
.br
      Widget \fIwidget\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget that has the active pointer grab.
.IP \fItime\fP 1i
Specifies the time argument to
.PN XUngrabPointer ;
see Section 12.1 in \fI\*(xL\fP.
.LP
.eM
.PN XtUngrabPointer
calls
.PN XUngrabPointer
with the specified time.

.NH 2
Focusing Events on a Child
.XS
\fB\*(SN Focusing Events on a Child\fP
.XE
.LP
To redirect keyboard input to a normal descendant of a
widget without calling
.PN XSetInputFocus ,
use
.PN XtSetKeyboardFocus .
.LP
.IN "XtSetKeyboardFocus" "" "@DEF@"
.sM
.FD 0
void XtSetKeyboardFocus(\fIsubtree\fP\, \fIdescendant\fP)
.br
     Widget \fIsubtree\fP, \fIdescendant\fP;
.FN
.IP \fIsubtree\fP 1i
Specifies the subtree of the hierarchy for which the keyboard focus is 
to be set.  \*(cI
.IP \fIdescendant\fP 1i
Specifies either the normal (non-pop-up) descendant of \fIsubtree\fP to which
keyboard events are logically directed, or 
.PN None .
It is not an error to specify
.PN None
when no input focus was previously set.  \*(oI
.LP
.eM
.PN XtSetKeyboardFocus
causes
.PN XtDispatchEvent
to remap keyboard events occurring within the specified subtree
and dispatch them to the specified descendant widget or to an ancestor.
If the descendant's class is not a subclass of Core, the descendant is
replaced by its closest windowed ancestor.
.LP
When there is no modal cascade, keyboard events can be dispatched
to a widget in one of five ways.  Assume the server delivered the
event to the window for widget E (because of X input focus, key or
keyboard grabs, or pointer position).
.IP \(bu 3
If neither E nor any of E's ancestors have redirected the keyboard
focus, or if the event activated a grab for E as specified by a call
to
.PN XtGrabKey
with any value of \fIowner_events\fP, or
if the keyboard is actively grabbed by E with \fIowner_events\fP
.PN False
via
.PN XtGrabKeyboard
or
.PN XtGrabKey
on a previous key press, the event is dispatched to E.
.IP \(bu 3
Beginning with the ancestor of E closest to the root that has
redirected the keyboard focus or E if no such ancestor exists, if
the target of that focus redirection has in turn redirected the
keyboard focus, recursively follow this focus chain to find a widget
F that has not redirected focus.
.RS
.IP \- 3
If E is the final focus target widget F or a descendant of F, the
event is dispatched to E.
.IP \- 3
If E is not F, an ancestor of F, or a descendant of F, and the event
activated a grab for E as specified by a call to
.PN XtGrabKey
for E,
.PN XtUngrabKeyboard
is called.
.IP \- 3
If E is an ancestor of F, and the event is a key press, and either
.RS
.IP + 3
E has grabbed the key with
.PN XtGrabKey
and \fIowner_events\fP
.PN False ,
or
.IP + 3
E has grabbed the key with
.PN XtGrabKey
and \fIowner_events\fP
.PN True ,
and the coordinates of the event are outside the rectangle specified
by E's geometry,
.RE
then the event is dispatched to E.
.IP \- 3
Otherwise, define A as the closest common ancestor of E and F:
.RS
.IP + 3
If there is an active keyboard grab for any widget via either
.PN XtGrabKeyboard
or
.PN XtGrabKey
on a previous key press, or
if no widget between F and A (noninclusive) has grabbed
the key and modifier combination with
.PN XtGrabKey
and any value of \fIowner_events\fP, the event is dispatched to F.
.IP + 3
Else, the event is dispatched to the ancestor of F closest to A
that has grabbed the key and modifier combination with
.PN XtGrabKey .
.RE
.RE
.LP
When there is a modal cascade, if the final destination widget as
identified above is in the active subset of the cascade, the event is
dispatched; otherwise the event is remapped to a spring-loaded shell
or discarded.
Regardless of where it is dispatched, the \*(xI do not modify
the contents of the event.
.LP
When \fIsubtree\fP or one of its descendants acquires the X input focus
or the pointer moves into the subtree such that keyboard events would
now be delivered to the subtree, a
.PN FocusIn
event is generated for the descendant if
.PN FocusChange
events have been selected by the descendant.
Similarly, when \fIsubtree\fP loses the X input focus
or the keyboard focus for one of its ancestors, a
.PN FocusOut
event is generated for descendant if
.PN FocusChange
events have been selected by the descendant.
.sp
.LP
A widget tree may also actively manage the X server input focus.  To
do so, a widget class specifies an accept_focus procedure.
.LP
.IN "accept_focus procedure"
The accept_focus procedure pointer is of type
.PN XtAcceptFocusProc .
.LP
.IN "XtAcceptFocusProc" "" "@DEF@"
.sM
.FD 0
typedef Boolean (*XtAcceptFocusProc)(Widget, Time*);
.br
      Widget \fIw\fP;
.br
      Time *\fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.IP \fItime\fP 1i
Specifies the X time of the event causing the accept focus.
.LP
.eM
Widgets that need the input focus can call
.PN XSetInputFocus
explicitly, pursuant to the restrictions of the \fI\*(xC\fP.
To allow outside agents, such as the parent,
to cause a widget to take the input focus,
every widget exports an accept_focus procedure.
The widget returns a value indicating
whether it actually took the focus or not,
so that the parent can give the focus to another widget.
Widgets that need to know when they lose the input focus must use
the Xlib focus notification mechanism explicitly
(typically by specifying translations for
.PN FocusIn
and
.PN FocusOut
events).
Widgets classes that never want the input focus should set the
\fIaccept_focus\fP field to NULL.
.sp
.LP
To call a widget's accept_focus procedure, use
.PN XtCallAcceptFocus .
.LP
.IN "XtCallAcceptFocus" "" "@DEF@"
.sM
.FD 0
Boolean XtCallAcceptFocus(\fIw\fP, \fItime\fP)
.br
       Widget \fIw\fP;
.br
       Time *\fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.  \*(cI
.IP \fItime\fP 1i
Specifies the X time of the event that is causing the focus change.
.LP
.eM
The
.PN XtCallAcceptFocus
function calls the specified widget's accept_focus procedure,
passing it the specified widget and time, and returns what the accept_focus
procedure returns.
If \fIaccept_focus\fP is NULL,
.PN XtCallAcceptFocus
returns
.PN False .

.NH 3
Events for Drawables That Are Not a Widget's Window
.XS 
\fB\*(SN Events for Drawables That Are Not a Widget's Window\fP
.XE
.LP
Sometimes an application must handle events for drawables that are not
associated with widgets in its widget tree.  Examples include handling
.PN GraphicsExpose
and
.PN NoExpose
events on Pixmaps, and handling 
.PN PropertyNotify
events on the root window.
.LP
To register a drawable with the \*(xI event dispatching, use
.PN XtRegisterDrawable .
.LP
.IN "XtRegisterDrawable" "" "@DEF@"
.sM
.FD 0
void XtRegisterDrawable(\fIdisplay\fP, \fIdrawable\fP, \fIwidget\fP)
.br
      Display *\fIdisplay\fP;
.br
      Drawable \fIdrawable\fP;
.br
      Widget \fIwidget\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the drawable's display.
.IP \fIdrawable\fP 1i
Specifies the drawable to register.
.IP \fIwidget\fP 1i
Specifies the widget to register the drawable for.
.LP
.eM
.PN XtRegisterDrawable
associates the specified drawable with the specified widget
so that future calls to
.PN XtWindowToWidget
with the drawable will return the widget.
The default event dispatcher will dispatch future events that
arrive for the drawable to the widget in the same manner as
events that contain the widget's window.
.LP
If the drawable is already registered with another widget, or if the
drawable is the window of a widget in the client's widget tree, the
results of calling
.PN XtRegisterDrawable
are undefined.

.LP
To unregister a drawable with the Intrinsics event dispatching, use
.PN XtUnregisterDrawable .
.LP
.IN "XtUnregisterDrawable" "" "@DEF@"
.sM
.FD 0
void XtUnregisterDrawable(\fIdisplay\fP, \fIdrawable\fP)
.br
      Display *\fIdisplay\fP;
.br
      Drawable \fIdrawable\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the drawable's display.
.IP \fIdrawable\fP 1i
Specifies the drawable to unregister.
.LP
.eM
.PN XtUnregisterDrawable
removes an association created with 
.PN XtRegisterDrawable .  
If the drawable is the window of a widget in the client's widget tree
the results of calling 
.PN XtUnregisterDrawable
are undefined.

.NH 2
Querying Event Sources
.XS
\fB\*(SN Querying Event Sources\fP
.XE
.LP
The event manager provides several functions to examine and read events
(including file and timer events) that are in the queue.
The next three functions are \*(xI equivalents of the
.PN XPending ,
.PN XPeekEvent ,
and
.PN XNextEvent
Xlib calls.
.sp
.LP
.IN "Events"
To determine if there are any events on the input queue for a given application,
use
.PN XtAppPending .
.LP
.IN "XtAppPending" "" "@DEF@"
.sM
.FD 0
XtInputMask XtAppPending(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application to check.
.LP
.eM
The
.PN XtAppPending
function returns a nonzero value if there are
events pending from the X server, timer pending, other input sources
pending, or signal sources pending.  The
value returned is a bit mask that is the OR of
.PN XtIMXEvent ,
.PN XtIMTimer ,
.PN XtIMAlternateInput ,
and 
.PN XtIMSignal 
(see
.PN XtAppProcessEvent ).
If there are no events pending, 
.PN XtAppPending
flushes the output buffers of each Display in the application context
and returns zero.
.sp
.LP
To return the event from the head of a given application's input queue
without removing input from the queue, use
.PN XtAppPeekEvent .
.LP
.IN "XtAppPeekEvent" "" "@DEF@"
.sM
.FD 0
Boolean XtAppPeekEvent(\fIapp_context\fP, \fIevent_return\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XEvent *\fIevent_return\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIevent_return\fP 1i
Returns the event information to the specified event structure.
.LP
.eM
If there is an X event in the queue,
.PN XtAppPeekEvent
copies it into \fIevent_return\fP and returns
.PN True .
If no X input is on the queue,
.PN XtAppPeekEvent
flushes the output buffers of each Display in the application context
and blocks until some input is available
(possibly calling some timeout callbacks in the interim).
If the next available input is an X event,
.PN XtAppPeekEvent
fills in \fIevent_return\fP and returns
.PN True .
Otherwise, the input is for an input source
registered with
.PN XtAppAddInput ,
and
.PN XtAppPeekEvent
returns
.PN False .
.FS
The sample implementations provides XtAppPeekEvent as described.  Timeout callbacks
are called while blocking for input.  If some input for an input source is
available, 
.PN XtAppPeekEvent
will return 
.PN True
without returning an event.
.FE
.sp
.LP
To remove and return the event
from the head of a given application's X event queue,
use
.PN XtAppNextEvent .
.LP
.IN "XtAppNextEvent" "" "@DEF@"
.sM
.FD 0
void XtAppNextEvent(\fIapp_context\fP, \fIevent_return\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XEvent *\fIevent_return\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIevent_return\fP 1i
Returns the event information to the specified event structure.
.LP
.eM
If the X event queue is empty,
.PN XtAppNextEvent
flushes the X output buffers of each Display in the application context
and waits for an X event while looking at the other input sources
and timeout values and calling any callback procedures triggered by them.
This wait time can be used for background processing;
see Section 7.8.

.NH 2
Dispatching Events
.XS
\fB\*(SN Dispatching Events\fP
.XE
.LP
The \*(xI provide functions that dispatch events
to widgets or other application code.
Every client interested in X events on a widget uses
.PN XtAddEventHandler
to register which events it is
interested in and a procedure (event handler) to be called
when the event happens in that window.
The translation manager automatically registers event handlers for widgets
that use translation tables; see Chapter 10.
.sp
.LP
Applications that need direct control of the processing of different types
of input should use
.PN XtAppProcessEvent .
.LP
.IN "XtAppProcessEvent" "" "@DEF@"
.sM
.FD 0
void XtAppProcessEvent(\fIapp_context\fP, \fImask\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtInputMask \fImask\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the
application for which to process input.
.IP \fImask\fP 1i
Specifies what types of events to process.
The mask is the bitwise inclusive OR of any combination of
.PN XtIMXEvent ,
.PN XtIMTimer ,
.PN XtIMAlternateInput ,
and
.PN XtIMSignal .
As a convenience,
.PN Intrinsic.h
defines the symbolic name
.PN XtIMAll
to be the bitwise inclusive OR of these four event types.
.LP
.eM
The
.PN XtAppProcessEvent
function processes one timer, input source, signal source, or X event.
If there is no event or input of the appropriate type to process, then
.PN XtAppProcessEvent
blocks until there is.
If there is more than one type of input available to process,
it is undefined which will get processed.
Usually, this procedure is not called by client applications; see
.PN XtAppMainLoop .
.PN XtAppProcessEvent
processes timer events by calling any appropriate timer callbacks,
input sources by calling any appropriate input callbacks, 
signal source by calling any appropriate signal callbacks,
and X events by
calling
.PN XtDispatchEvent .
.LP
When an X event is received,
it is passed to
.PN XtDispatchEvent ,
which calls the appropriate event handlers
and passes them the widget, the event, and client-specific data
registered with each procedure.
If no handlers for that event are registered,
the event is ignored and the dispatcher simply returns.

.sp
.LP
To dispatch an event returned by
.PN XtAppNextEvent ,
retrieved directly from the Xlib queue, or synthetically constructed,
to any registered event filters or event handlers, call
.PN XtDispatchEvent .
.LP
.IN "XtDispatchEvent" "" "@DEF@"
.sM
.FD 0
Boolean XtDispatchEvent(\fIevent\fP)
.br
      XEvent *\fIevent\fP;
.FN
.IP \fIevent\fP 1i
Specifies a pointer to the event structure to be dispatched
to the appropriate event handlers.
.LP
.eM
The
.PN XtDispatchEvent
function first calls
.PN XFilterEvent
with the \fIevent\fP and the window of the widget to which the
\*(xI intend to dispatch the event, or the event window if
the \*(xI would not dispatch the event to any handlers.
If
.PN XFilterEvent
returns
.PN True
and the event activated a server grab as identified
by a previous call to
.PN XtGrabKey
or
.PN XtGrabButton ,
.PN XtDispatchEvent
calls
.PN XtUngrabKeyboard
or
.PN XtUngrabPointer
with the timestamp from the event and immediately returns
.PN True .
If
.PN XFilterEvent
returns
.PN True
and a grab was not activated,
.PN XtDispatchEvent
just immediately returns
.PN True .
Otherwise,
.PN XtDispatchEvent
sends the event to the event handler functions that
have been previously registered with the dispatch routine.
.PN XtDispatchEvent
returns 
.PN True
if
.PN XFilterEvent
returned
.PN True ,
or if the event was dispatched to some handler, and
.PN False
if it found no handler to which to dispatch the event.
.PN XtDispatchEvent
records the last timestamp in any event that
contains a timestamp (see
.PN XtLastTimestampProcessed ),
regardless of whether it was filtered or dispatched.
If a modal cascade is active with \fIspring_loaded\fP
.PN True ,
and if the event is a remap event as defined by
.PN XtAddGrab ,
.PN XtDispatchEvent
may dispatch the event a second time.  If it does so,
.PN XtDispatchEvent
will call
.PN XFilterEvent
again with the window of the spring-loaded widget prior to the second
dispatch, and if
.PN XFilterEvent
returns
.PN True ,
the second dispatch will not be performed.

.NH 2
The Application Input Loop
.XS
\fB\*(SN The Application Input Loop\fP
.XE
.LP
To process all input from a given application in a continuous loop,
use the convenience procedure
.PN XtAppMainLoop .
.LP
.IN "XtAppMainLoop" "" "@DEF@"
.sM
.FD 0
void XtAppMainLoop(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.LP
.eM
The
.PN XtAppMainLoop
function first reads the next incoming X event by calling
.PN XtAppNextEvent 
and then dispatches the event to the appropriate registered procedure 
by calling
.PN XtDispatchEvent .
This constitutes the main loop of \*(tk applications.
There is nothing special about
.PN XtAppMainLoop ;
it simply calls
.PN XtAppNextEvent
and then
.PN XtDispatchEvent
in a conditional loop.
At the bottom of the loop, it checks to see if the specified
application context's destroy flag is set.
If the flag is set, the loop breaks.
The whole loop is enclosed between a matching
.PN XtAppLock
and 
.PN XtAppUnlock .
.LP
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
.PN XtAppNextEvent .

.NH 2
Setting and Checking the Sensitivity State of a Widget
.XS
\fB\*(SN Setting and Checking the Sensitivity State of a Widget\fP
.XE
.LP
Many widgets have a mode in which they assume a different appearance
(for example, are grayed out or stippled), do not respond to user events,
and become dormant.
.LP
When dormant,
a widget is considered to be insensitive.
If a widget is insensitive,
the event manager does not dispatch any events to the widget
with an event type of
.PN KeyPress ,
.PN KeyRelease ,
.PN ButtonPress ,
.PN ButtonRelease ,
.PN MotionNotify ,
.PN EnterNotify ,
.PN LeaveNotify ,
.PN FocusIn ,
or
.PN FocusOut .
.LP
A widget can be insensitive because its \fIsensitive\fP field is
.PN False
or because one of its ancestors is insensitive and thus the widget's
\fIancestor_sensitive\fP field also is 
.PN False .
A widget can but does not need to distinguish these two cases visually.
.NT
Pop-up shells will have
\fIancestor_sensitive\fP
.PN False
if the parent was insensitive when the shell
was created.  Since
.PN XtSetSensitive
on the parent will not
modify the resource of the pop-up child, clients are advised to include
a resource specification of the form
``*TransientShell.ancestorSensitive: True''
in the application defaults resource file or to
otherwise ensure that the parent is
sensitive when creating pop-up shells.
.NE
.sp
.LP
To set the sensitivity state of a widget, use
.PN XtSetSensitive .
.LP
.IN "XtSetSensitive" "" "@DEF@"
.sM
.FD 0
void XtSetSensitive(\fIw\fP, \fIsensitive\fP)
.br
      Widget \fIw\fP;
.br
      Boolean \fIsensitive\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.  \*(rI
.IP \fIsensitive\fP 1i
Specifies whether the widget should receive
keyboard, pointer, and focus events.
.LP
.eM
The
.PN XtSetSensitive
function first calls
.PN XtSetValues
on the current widget with an argument list specifying the
XtNsensitive resource and the new value.
If \fIsensitive\fP is
.PN False
and the widget's class is a subclass of
Composite,
.PN XtSetSensitive
recursively propagates the new value
down the child tree by calling
.PN XtSetValues
on each child to set \fIancestor_sensitive\fP to
.PN False .
If \fIsensitive\fP is
.PN True
and the widget's class is a subclass of
Composite
and the widget's \fIancestor_sensitive\fP field is
.PN True ,
.PN XtSetSensitive
sets the \fIancestor_sensitive\fP of each child to
.PN True
and then recursively calls
.PN XtSetValues
on each normal descendant that is now sensitive to set
\fIancestor_sensitive\fP to
.PN True .
.LP
.PN XtSetSensitive
calls
.PN XtSetValues
to change the \fIsensitive\fP and \fIancestor_sensitive\fP fields
of each affected widget.
Therefore, when one of these changes,
the widget's set_values procedure should
take whatever display actions are needed
(for example, graying out or stippling the widget).
.LP
.PN XtSetSensitive
maintains the invariant that, if the parent has either \fIsensitive\fP 
or \fIancestor_sensitive\fP 
.PN False ,
then all children have \fIancestor_sensitive\fP 
.PN False .
.sp
.LP
To check the current sensitivity state of a widget,
use
.PN XtIsSensitive .
.LP
.IN "XtIsSensitive" "" "@DEF@"
.sM
.FD 0
Boolean XtIsSensitive(\fIw\fP)
.br
     Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the object.  \*(oI
.LP
.eM
The
.PN XtIsSensitive
function returns 
.PN True 
or 
.PN False 
to indicate whether user input events are being dispatched.
If object's class is a subclass of RectObj and
both \fIsensitive\fP and \fIancestor_sensitive\fP are 
.PN True ,
.PN XtIsSensitive
returns 
.PN True ;
otherwise, it returns 
.PN False .

.NH 2
Adding Background Work Procedures
.XS
\fB\*(SN Adding Background Work Procedures\fP
.XE
.LP
The \*(xI have some limited support for background processing.
Because most applications spend most of their time waiting for input, 
you can register an idle-time work procedure
that is called when the toolkit would otherwise block in
.PN XtAppNextEvent
or
.PN XtAppProcessEvent .
Work procedure pointers are of type
.PN XtWorkProc .
.LP
.IN "XtWorkProc" "" "@DEF@"
.sM
.FD 0
typedef Boolean (*XtWorkProc)(XtPointer);
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIclient_data\fP 1i
Passes the client data specified when the work procedure was registered.
.LP
.eM
This procedure should return
.PN True
when it is done to indicate that it
should be removed.
If the procedure returns
.PN False ,
it will remain registered and called again when the
application is next idle.
Work procedures should be very judicious about how much they do. 
If they run for more than a small part of a second,
interactive feel is likely to suffer.
.sp
.LP
To register a work procedure for a given application, use
.PN XtAppAddWorkProc .
.LP
.IN "XtAppAddWorkProc" "" "@DEF@"
.sM
.FD 0
XtWorkProcId XtAppAddWorkProc(\fIapp_context\fP, \fIproc\fP, \fIclient_data\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtWorkProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that identifies the application.
.IP \fIproc\fP 1i
Specifies the procedure to be called when the application is idle.
.IP \fIclient_data\fP 1i
Specifies the argument passed to the specified procedure
when it is called.
.LP
.eM
The
.PN XtAppAddWorkProc
function adds the specified work procedure for the application identified
by \fIapp_context\fP
and returns an opaque unique identifier for this work procedure.
Multiple work procedures can be registered,
and the most recently added one is always the one that is called.
However, if a work procedure adds another work procedure, 
the newly added one has lower priority than the current one.
.sp
.LP
To remove a work procedure, either return 
.PN True 
from the procedure when it is called or use
.PN XtRemoveWorkProc
outside of the procedure.
.LP
.IN "XtRemoveWorkProc" "" "@DEF@"
.sM
.FD 0
void XtRemoveWorkProc(\fIid\fP)
.br
      XtWorkProcId \fIid\fP;
.FN
.IP \fIid\fP 1i
Specifies which work procedure to remove.
.LP
.eM
The
.PN XtRemoveWorkProc
function explicitly removes the specified background work procedure.

.NH 2
X Event Filters
.XS
\*(SN X Event Filters
.XE
.LP
The event manager provides filters that can be applied to
specific X events.
The filters, which screen out events that are redundant or are temporarily
unwanted, handle
pointer motion compression,
enter/leave compression, and
exposure compression.

.NH 3
Pointer Motion Compression
.XS
\*(SN Pointer Motion Compression
.XE
.LP
Widgets can have a hard time keeping up with a rapid stream of
pointer motion events.  Furthermore,
they usually do not care about every motion event.  To throw out
redundant motion events, the widget class field \fIcompress_motion\fP should be
.PN True .
.IN "compress_motion field"
When a request for an event would return a motion event,
the \*(xI check if there are any other motion events
for the same widget immediately
following the current one and, if so, skip all but the last of them.

.NH 3
Enter/Leave Compression
.XS
\*(SN Enter/Leave Compression
.XE
.LP
To throw out pairs of enter and leave events that have no intervening events,
as can happen when the user moves the pointer across a widget 
without stopping in it,
the widget class field \fIcompress_enterleave\fP should be 
.PN True .
.IN "compress_enterleave field"
These enter and leave events are not delivered to the client
if they are found together in the input queue.

.NH 3
Exposure Compression
.XS
\*(SN Exposure Compression
.XE
.LP
.IN "compress_expose field"
Many widgets prefer to process a series of exposure events as a
single expose region rather than as individual rectangles.  Widgets
with complex displays might use the expose region as a clip list
in a graphics context, and widgets with simple displays might
ignore the region entirely and redisplay their whole window or
might get the bounding box from the region and redisplay only that
rectangle.
.LP
In either case, these widgets do not care about getting partial exposure events.
The \fIcompress_exposure\fP field in the widget class
structure specifies the type and number of exposure events that are
dispatched to the widget's expose procedure.  This field must be
initialized to one of the following values:
.sp
.sM
.Ds 0
.TA 3i
.ta 3i
#define XtExposeNoCompress	((XtEnum)False)
#define XtExposeCompressSeries	((XtEnum)True)
#define XtExposeCompressMultiple	<implementation-defined>
#define XtExposeCompressMaximal	<implementation-defined>
.De
.LP
.eM
optionally ORed with any combination of the following flags (all with
implementation-defined values):
.PN XtExposeGraphicsExpose ,
.PN XtExposeGraphicsExposeMerged ,
.PN XtExposeNoExpose ,
and
.PN XtExposeNoRegion .

.LP
If the \fIcompress_exposure\fP field in the widget class structure does not
specify
.PN XtExposeNoCompress ,
the event manager calls the widget's expose procedure only
once for a series of exposure events.
In this case, all
.PN Expose
or
.PN GraphicsExpose
events are accumulated into a region.
When the final event is received,
the event manager replaces the rectangle in the event with the
bounding box for the region
and calls the widget's expose procedure,
passing the modified exposure event and (unless 
.PN XtExposeNoRegion
is specified) the region.
For more information on regions, see Section 16.5 in \fI\*(xL\fP.)
.LP
The values have the following interpretation:
.sp
.LP
.PN XtExposeNoCompress
.IN "XtExposeNoCompress" "" "@DEF@"
.IP
No exposure compression is performed; every selected event is
individually dispatched to the expose procedure with a \fIregion\fP
argument of NULL.
.sp
.LP
.PN XtExposeCompressSeries
.IN "XtExposeCompressSeries" "" "@DEF@"
.IP
Each series of exposure events is coalesced into a single event,
which is dispatched
when an exposure event with count equal to zero is reached.
.sp
.LP
.PN XtExposeCompressMultiple
.IN "XtExposeCompressMultiple" "" "@DEF@"
.IP
Consecutive series of exposure events are coalesced into a single
event, which is dispatched
when an exposure event with count equal to zero is reached and either
the event queue is empty or the next event is not an exposure event
for the same widget.
.sp
.LP
.PN XtExposeCompressMaximal
.IN "XtExposeCompressMaximal" "" "@DEF"
.IP
All expose series currently in the queue for the widget
are coalesced into a single
event without regard to intervening nonexposure events.  If a
partial series is in the end of the queue, the \*(xI will
block until the end of the series is received.
.sp
.LP
The additional flags have the following meaning:
.sp
.LP
.PN XtExposeGraphicsExpose
.IN "XtExposeGraphicsExpose" "" "@DEF@"
.IP
Specifies that
.PN GraphicsExpose
events are also to be dispatched to
the expose procedure.
.PN GraphicsExpose
events are compressed, if specified, in the same manner as
.PN Expose
events.
.sp
.LP
.PN XtExposeGraphicsExposeMerged
.IN "XtExposeGraphicsExposeMerged" "" "@DEF@"
.IP
Specifies in the case of
.PN XtExposeCompressMultiple
and
.PN XtExposeCompressMaximal
that series of
.PN GraphicsExpose
and
.PN Expose
events are to be compressed together, with the final event type
determining the type of the event passed to the expose procedure.
If this flag is not set, then only series of the same event type
as the event at the head of the queue are coalesced.  This flag
also implies
.PN XtExposeGraphicsExpose .
.sp
.LP
.PN XtExposeNoExpose
.IN "XtExposeNoExpose" "" "@DEF@"
.IP
Specifies that
.PN NoExpose
events are also to be dispatched to the expose procedure.
.PN NoExpose
events are never coalesced with
other exposure events or with each other.
.sp
.LP
.PN XtExposeNoRegion
.IN "XtExposeNoRegion" "" "@DEF"
.IP
Specifies that the final region argument passed to the expose
procedure is NULL.  The rectangle in the event will still
contain bounding box information for the entire series of
compressed exposure events.  This option saves processing time when the
region is not needed by the widget.

.NH 2
Widget Exposure and Visibility
.XS
\*(SN Widget Exposure and Visibility
.XE
.LP
Every primitive widget and some composite widgets display data on the screen
by means of direct Xlib calls.
Widgets cannot simply write to the screen and forget what they have done.
They must keep enough state to redisplay the window or parts
of it if a portion is obscured and then reexposed.

.NH 3
Redisplay of a Widget: The expose Procedure
.XS
\*(SN Redisplay of a Widget: The expose Procedure
.XE
.IN "expose procedure"
.LP
The expose procedure pointer in a widget class is of type
.PN XtExposeProc .
.LP
.IN "XtExposeProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtExposeProc)(Widget, XEvent*, Region);
.br
      Widget \fIw\fP;
.br
      XEvent *\fIevent\fP;
.br
      Region \fIregion\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget instance requiring redisplay.
.IP \fIevent\fP 1i
Specifies the exposure event giving the rectangle requiring redisplay.
.IP \fIregion\fP 1i
Specifies the union of all rectangles in this exposure sequence.
.LP
.eM
The redisplay of a widget upon exposure is the responsibility of the
expose procedure in the widget's class record.
If a widget has no display semantics,
it can specify NULL for the \fIexpose\fP field.
Many composite widgets serve only as containers for their children
and have no expose procedure.
.NT
If the \fIexpose\fP procedure is NULL,
.PN XtRealizeWidget
fills in a default bit gravity of
.PN NorthWestGravity
before it calls the widget's realize procedure.
.NE
.LP
If the widget's \fIcompress_exposure\fP class field specifies
.PN XtExposeNoCompress
or 
.PN XtExposeNoRegion ,
or if the event type is
.PN NoExpose
(see Section 7.9.3),
\fIregion\fP is NULL.  If
.PN XtExposeNoCompress
is not specified and the event type is not
.PN NoExpose ,
the event is the final event in the compressed series
but \fIx\fP, \fIy\fP, \fIwidth\fP, and \fIheight\fP contain
the bounding box for all the compressed events.
The region is created and destroyed by the \*(xI, but
the widget is permitted to modify the region contents.
.LP
A small simple widget (for example, Label) can ignore the bounding box
information in the event and redisplay the entire window.
A more complicated widget (for example, Text) can use the bounding box
information to minimize the amount of calculation and redisplay it does.
A very complex widget uses the region as a clip list in a GC and
ignores the event information.
The expose procedure is not chained and is therefore
responsible for exposure of all superclass data
as well as its own.
.LP
However,
it often is possible to anticipate the display needs of several levels
of subclassing.
For example, rather than implement separate display procedures for
the widgets Label, Pushbutton, and Toggle,
you could write a single display routine in Label that uses display state
fields like
.LP
.DS
Boolean invert;
Boolean highlight;
Dimension highlight_width;
.DE
Label would have \fIinvert\fP and \fIhighlight\fP always 
.PN False
and \fIhighlight_width\fP zero.
Pushbutton would dynamically set \fIhighlight\fP and \fIhighlight_width\fP, 
but it would leave \fIinvert\fP always 
.PN False .
Finally, Toggle would dynamically set all three.
In this case,
the expose procedures for Pushbutton and Toggle inherit
their superclass's expose procedure;
see Section 1.6.10.

.NH 3
Widget Visibility
.XS
\*(SN Widget Visibility
.XE
.LP
Some widgets may use substantial computing resources to produce the
data they will display.
However, this effort is wasted if the widget is not actually visible
on the screen, that is, if the widget is obscured by another application 
or is iconified.
.LP
.IN "Visibility"
The \fIvisible\fP field in the
core
widget structure provides a hint to the widget that it need not compute
display data.
This field is guaranteed to be
.PN True
by the time an
exposure
event is processed if any part of the widget is visible,
but is
.PN False 
if the widget is fully obscured.
.LP
Widgets can use or ignore the \fIvisible\fP hint.
If they ignore it,
they should have \fIvisible_interest\fP in their widget class record set 
.PN False .
In such cases,
the \fIvisible\fP field is initialized 
.PN True 
and never changes.
If \fIvisible_interest\fP is 
.PN True ,
the event manager asks for
.PN VisibilityNotify
events for the widget and sets \fIvisible\fP to
.PN True
on
.PN VisibilityUnobscured
or
.PN VisibilityPartiallyObscured
.IN VisibilityNotify
events and
.PN False
on
.PN VisibilityFullyObscured
events.

.NH 2
X Event Handlers
.XS
\*(SN X Event Handlers
.XE
.LP
Event handlers are procedures called when specified events
occur in a widget.
Most widgets need not use event handlers explicitly.
Instead, they use the \*(xI translation manager.
Event handler procedure pointers are of the type
.PN XtEventHandler .
.LP
.IN "XtEventHandler" "" "@DEF@"
.sM
.FD 0
typedef void (*XtEventHandler)(Widget, XtPointer, XEvent*, Boolean*);
.br
      Widget \fIw\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XEvent *\fIevent\fP;
.br
      Boolean *\fIcontinue_to_dispatch\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which the event arrived.
.IP \fIclient_data\fP 1i
Specifies any client-specific information registered with the event handler.
.IP \fIevent\fP 1i
Specifies the triggering event.
.IP \fIcontinue_to_dispatch\fP 1i
Specifies whether the remaining event
handlers registered for the current event
should be called.
.LP
.eM
After receiving an event and before calling any event handlers, the
Boolean pointed to by \fIcontinue_to_dispatch\fP is initialized to
.PN True .
When an event handler is called, it may decide that further processing
of the event is not desirable and may store
.PN False
in this Boolean, in
which case any handlers remaining to be called for the event are
ignored.
.LP
The circumstances under which the \*(xI may add event handlers
to a widget are currently implementation-dependent.  Clients must
therefore be aware that storing
.PN False
into the \fIcontinue_to_dispatch\fP argument can lead to portability problems.

.NH 3
Event Handlers That Select Events
.XS
\*(SN Event Handlers That Select Events
.XE
.LP
To register an event handler procedure with the dispatch mechanism, use
.PN XtAddEventHandler .
.LP
.IN "XtAddEventHandler" "" "@DEF@"
.sM
.FD 0
void XtAddEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this event handler is being registered.  \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to call this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
called on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be called.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the event handler.
.LP
.eM
The
.PN XtAddEventHandler
function registers a procedure with the dispatch mechanism that is
to be called when an event that matches the mask occurs on the specified
widget.
Each widget has a single registered event handler list, which will
contain any procedure/client_data pair exactly once regardless of
the manner in which it is registered.
If the procedure is already registered with the same \fIclient_data\fP
value,
the specified mask augments the existing mask.
If the widget is realized,
.PN XtAddEventHandler
calls
.PN XSelectInput ,
if necessary.
The order in which this procedure is called relative to other handlers
registered for the same event is not defined.
.sp
.LP
To remove a previously registered event handler, use
.PN XtRemoveEventHandler .
.LP
.IN "XtRemoveEventHandler" "" "@DEF@"
.sM
.FD 0
void XtRemoveEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this procedure is registered.  \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to unregister this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
removed on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be removed.
.IP \fIclient_data\fP 1i
Specifies the registered client data.
.LP
.eM
The
.PN XtRemoveEventHandler
function unregisters an event handler registered with
.PN XtAddEventHandler
or
.PN XtInsertEventHandler
for the specified events.
The request is ignored if \fIclient_data\fP does not match the value given
when the handler was registered.
If the widget is realized and no other event handler requires the event,
.PN XtRemoveEventHandler
calls
.PN XSelectInput .
If the specified procedure has not been registered 
or if it has been registered with a different value of \fIclient_data\fP,
.PN XtRemoveEventHandler
returns without reporting an error.
.LP
To stop a procedure registered with
.PN XtAddEventHandler
or
.PN XtInsertEventHandler
from receiving all selected events, call
.PN XtRemoveEventHandler
with an \fIevent_mask\fP of
.PN XtAllEvents
and \fInonmaskable\fP 
.PN True .
The procedure will continue to receive any events
that have been specified in calls to
.PN XtAddRawEventHandler
or
.PN XtInsertRawEventHandler .
.sp
.LP
To register an event handler procedure that receives events before or
after all previously registered event handlers, use
.PN XtInsertEventHandler .
.LP
.IN "XtListPosition" "" "@DEF@"
.IN "XtInsertEventHandler" "" "@DEF@"
.sM
.Ds 0
typedef enum {XtListHead, XtListTail} XtListPosition;
.De
.LP
.FD 0
void XtInsertEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP, \fIposition\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtListPosition \fIposition\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this event handler is being registered. \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to call this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
called on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be called.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the client's event handler.
.IP \fIposition\fP 1i
Specifies when the event handler is to be called
relative to other previously registered handlers.
.LP
.eM
.PN XtInsertEventHandler
is identical to
.PN XtAddEventHandler
with the additional \fIposition\fP argument.  If \fIposition\fP is
.PN XtListHead ,
the event
handler is registered so that it is called before any event
handlers that were previously registered for the same widget.  If
\fIposition\fP is
.PN XtListTail ,
the event handler is registered to be called
after any previously registered event handlers.  If the procedure is
already registered with the same \fIclient_data\fP value, the specified mask
augments the existing mask and the procedure is repositioned in
the list.

.NH 3
Event Handlers That Do Not Select Events
.XS
\*(SN Event Handlers That Do Not Select Events
.XE
.LP
On occasion,
clients need to register an event handler procedure with the
dispatch mechanism without explicitly
causing the X server to select for that event.
To do this, use
.PN XtAddRawEventHandler .
.LP
.IN "XtAddRawEventHandler" "" "@DEF@"
.sM
.FD 0
void XtAddRawEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this event handler is being registered. \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to call this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
called on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be called.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the client's event handler.
.LP
.eM
The
.PN XtAddRawEventHandler
function is similar to
.PN XtAddEventHandler 
except that it does not affect the widget's event mask and never causes an
.PN XSelectInput
for its events.
Note that the widget might already have those mask bits set
because of other nonraw event handlers registered on it.
If the procedure is already registered with the same \fIclient_data\fP,
the specified mask augments the existing mask.
The order in which this procedure is called relative to other handlers
registered for the same event is not defined.
.sp
.LP
To remove a previously registered raw event handler, use
.PN XtRemoveRawEventHandler .
.LP
.IN "XtRemoveRawEventHandler" "" "@DEF@"
.sM
.FD 0
void XtRemoveRawEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this procedure is registered.  \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to unregister this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
removed on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be registered.
.IP \fIclient_data\fP 1i
Specifies the registered client data.
.LP
.eM
The
.PN XtRemoveRawEventHandler
function unregisters an event handler registered with
.PN XtAddRawEventHandler
or
.PN XtInsertRawEventHandler
for the specified events without changing
the window event mask.
The request is ignored if \fIclient_data\fP does not match the value given
when the handler was registered.
If the specified procedure has not been registered 
or if it has been registered with a different value of \fIclient_data\fP,
.PN XtRemoveRawEventHandler
returns without reporting an error.
.LP
To stop a procedure
registered with
.PN XtAddRawEventHandler
or
.PN XtInsertRawEventHandler
from receiving all nonselected events, call
.PN XtRemoveRawEventHandler
with an \fIevent_mask\fP of
.PN XtAllEvents
and \fInonmaskable\fP
.PN True .
The procedure
will continue to receive any events that have been specified in calls to
.PN XtAddEventHandler
or
.PN XtInsertEventHandler .
.sp
.LP
To register an event handler procedure that receives events before or
after all previously registered event handlers without selecting for
the events, use
.PN XtInsertRawEventHandler .
.LP
.IN "XtInsertRawEventHandler" "" "@DEF@"
.sM
.FD 0
void XtInsertRawEventHandler(\fIw\fP, \fIevent_mask\fP, \fInonmaskable\fP, \
\fIproc\fP, \fIclient_data\fP, \fIposition\fP)
.br
      Widget \fIw\fP;
.br
      EventMask \fIevent_mask\fP;
.br
      Boolean \fInonmaskable\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtListPosition \fIposition\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget for which this event handler is being registered. \*(cI
.IP \fIevent_mask\fP 1i
Specifies the event mask for which to call this procedure.
.IP \fInonmaskable\fP 1i
Specifies whether this procedure should be 
called on the nonmaskable events
.Pn ( GraphicsExpose ,
.PN NoExpose ,
.PN SelectionClear ,
.PN SelectionRequest ,
.PN SelectionNotify ,
.PN ClientMessage ,
and
.PN MappingNotify ).
.IP \fIproc\fP 1i
Specifies the procedure to be registered.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the client's event handler.
.IP \fIposition\fP 1i
Specifies when the event handler is to be called
relative to other previously registered handlers.
.LP
.eM
The
.PN XtInsertRawEventHandler
function is similar to
.PN XtInsertEventHandler
except that it does not modify the widget's event
mask and never causes an
.PN XSelectInput
for the specified events.  If
the procedure is already registered with the same \fIclient_data\fP
value, the
specified mask augments the existing mask and the procedure is
repositioned in the list.

.NH 3
Current Event Mask
.XS
\*(SN Current Event Mask
.XE
.LP
To retrieve the event mask for a given widget, use
.PN XtBuildEventMask .
.LP
.IN "XtBuildEventMask" "" "@DEF@"
.sM
.FD 0
EventMask XtBuildEventMask(\fIw\fP)
.br
      Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.  \*(cI
.LP
.eM
The
.PN XtBuildEventMask
function returns the event mask representing the logical OR
of all event masks for event handlers registered on the widget with
.PN XtAddEventHandler
and
.PN XtInsertEventHandler
and all event translations, including accelerators,
installed on the widget.
This is the same event mask stored into the 
.PN XSetWindowAttributes
structure by
.PN XtRealizeWidget
and sent to the server when event handlers and translations are installed or
removed on the realized widget.

.NH 3
Event Handlers for X11 Protocol Extensions
.XS
\fB\*(SN Event Handlers for X11 Protocol Extensions\fP
.XE
.LP
To register an event handler procedure with the \*(xI dispatch
mechanism according to an event type, use 
.PN XtInsertEventTypeHandler .
.LP
.IN "XtInsertEventTypeHandler" "" "@DEF"
.sM
.FD 0
void XtInsertEventTypeHandler(\fIwidget\fP, \fIevent_type\fP, \
\fIselect_data\fP, \fIproc\fP, \fIclient_data\fP, \fIposition\fP)
.br
      Widget \fIwidget\fP;
.br
      int \fIevent_type\fP;
.br
      XtPointer \fIselect_data\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtListPosition \fIposition\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget for which this event handler is being registered.  \*(cI
.IP \fIevent_type\fP 1i
Specifies the event type for which to call this event handler.
.IP \fIselect_data\fP 1i
Specifies data used to request events of the specified type from the server,
or NULL.
.IP \fIproc\fP 1i
Specifies the event handler to be called.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the event handler.
.IP \fIposition\fP 1i
Specifies when the event handler is to be called relative to other
previously registered handlers.
.LP
.eM
.PN XtInsertEventTypeHandler
registers a procedure with the
dispatch mechanism that is to be called when an event that matches the
specified \fIevent_type\fP is dispatched to the specified \fIwidget\fP.  
.LP
If \fIevent_type\fP specifies one of the core X protocol events, then
\fIselect_data\fP must be a pointer to a value of type 
.PN EventMask ,
indicating
the event mask to be used to select for the desired event.  This event
mask is included in the value returned by 
.PN XtBuildEventMask .
If the widget is realized,
.PN XtInsertEventTypeHandler 
calls 
.PN XSelectInput
if necessary.  Specifying NULL for \fIselect_data\fP is equivalent to
specifying a pointer to an event mask containing 0.  This is similar
to the 
.PN XtInsertRawEventHandler
function.  
.LP
If \fIevent_type\fP specifies an extension event type, then the semantics of
the data pointed to by \fIselect_data\fP are defined by the extension
selector registered for the specified event type.
.LP
In either case the \*(xI are not required to copy the data
pointed to by \fIselect_data\fP, so the caller must ensure that it remains
valid as long as the event handler remains registered with this value
of \fIselect_data\fP.
.LP
The \fIposition\fP argument allows the client to control the order of
invocation of event handlers registered for the same event type.  If
the client does not care about the order, it should normally specify
.PN XtListTail ,
which registers this event handler after any previously
registered handlers for this event type.
.LP
Each widget has a single registered event handler list, which will
contain any procedure/client_data pair exactly once if it is
registered with 
.PN XtInsertEventTypeHandler ,
regardless of the manner
in which it is registered and regardless of the value(s)
of \fIselect_data\fP.  If the procedure is already registered with the
same \fIclient_data\fP value, the specified mask augments the existing
mask and the procedure is repositioned in the list.
.sp
.LP
To remove an event handler registered with 
.PN XtInsertEventTypeHandler ,
use
.PN XtRemoveEventTypeHandler .
.LP
.IN "XtRemoveEventTypeHandler" "" "@DEF"
.sM
.FD 0
void XtRemoveEventTypeHandler(\fIwidget\fP, \fIevent_type\fP, \
\fIselect_data\fP, \fIproc\fP, \fIclient_data\fP)
.br
      Widget \fIwidget\fP;
.br
      int \fIevent_type\fP;
.br
      XtPointer \fIselect_data\fP;
.br
      XtEventHandler \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget for which the event handler was registered.  \*(cI
.IP \fIevent_type\fP 1i
Specifies the event type for which the handler was registered.
.IP \fIselect_data\fP 1i
Specifies data used to deselect events of the specified type 
from the server, or NULL.
.IP \fIproc\fP 1i
Specifies the event handler to be removed.
.IP \fIclient_data\fP 1i
Specifies the additional client data with which the procedure was registered.
.LP
.eM
The
.PN XtRemoveEventTypeHandler
function unregisters an event handler
registered with
.PN XtInsertEventTypeHandler
for the specified event type.
The request is ignored if \fIclient_data\fP does not match the value given
when the handler was registered.
.LP
If \fIevent_type\fP specifies one of the core X protocol events,
\fIselect_data\fP must be a pointer to a value of type 
.PN EventMask, indicating the event
mask to be used to deselect for the appropriate event.  If the widget
is realized, 
.PN XtRemoveEventTypeHandler
calls
.PN XSelectInput
if necessary.
Specifying NULL for \fIselect_data\fP is equivalent to specifying a pointer
to an event mask containing 0.  This is similar to the
.PN XtRemoveRawEventHandler
function.
.LP
If \fIevent_type\fP specifies an extension event type, then the semantics of
the data pointed to by \fIselect_data\fP are defined by the extension
selector registered for the specified event type.
.sp
.LP
To register a procedure to select extension events for a widget, use
.PN XtRegisterExtensionSelector .
.LP
.IN "XtRegisterExtensionSelector" "" "@DEF@"
.sM
.FD 0
void XtRegisterExtensionSelector(\fIdisplay\fP, \fImin_event_type\fP, \
\fImax_event_type\fP, \fIproc\fP,
                                                     \fIclient_data\fP)
.br
      Display \fI*display\fP;
.br
      int \fImin_event_type\fP;
.br
      int \fImax_event_type\fP;
.br
      XtExtensionSelectProc \fIproc\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIdisplay\fP 1.5i
Specifies the display for which the extension selector is to be registered.
.IP \fImin_event_type\fP
.IP \fImax_event_type\fP 1.5i
Specifies the range of event types for the extension.
.IP \fIproc\fP 1.5i
Specifies the extension selector procedure.
.IP \fIclient_data\fP 1.5i
Specifies additional data to be passed to the extension selector.
.LP
.eM
The
.PN XtRegisterExtensionSelector
function registers a procedure to arrange 
for the delivery of extension events to widgets.
.LP
If \fImin_event_type\fP and \fImax_event_type\fP match the parameters
to a previous call to
.PN XtRegisterExtensionSelector
for the same \fIdisplay\fP, then \fIproc\fP and \fIclient_data\fP
replace the previously
registered values.  If the range specified by \fImin_event_type\fP
and \fImax_event_type\fP overlaps the range of the parameters to a
previous call for the same display in any other way, an error results.
.LP
When a widget is realized, 
after the \fIcore.realize\fP method is called,
the \*(xI check to see if any event
handler specifies an event type within the range of a registered
extension selector.  If so, the \*(xI call each such selector.
If an event type handler is added or removed, the \*(xI check to
see if the event type falls within the range of a registered extension
selector, and if it does, calls the selector.  In either case the \*(xI
pass a list of all the widget's event types that are within the
selector's range.  The corresponding select data are also passed.  The
selector is responsible for enabling the delivery of extension events
required by the widget.
.sp
.LP
An extension selector is of type
.PN XtExtensionSelectProc .
.LP
.IN "XtExtensionSelectProc" "" "@DEF"
.sM
.FD 0
typedef void (*XtExtensionSelectProc)(Widget, int *, XtPointer *, int, \
XtPointer);
.br
      Widget \fIwidget\fP;
.br
      int *\fIevent_types\fP;
.br
      XtPointer *\fIselect_data\fP;
.br
      int \fIcount\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget that is being realized or is having
an event handler added or removed.
.IP \fIevent_types\fP 1i
Specifies a list of event types that the widget has
registered event handlers for.
.IP \fIselect_data\fP 1i
Specifies a list of the select_data parameters specified in
.PN XtInsertEventTypeHandler .
.IP \fIcount\fP 1i
Specifies the number of entries in the \fIevent_types\fP and \fIselect_data\fP
lists.
.IP \fIclient_data\fP 1i
Specifies the additional client data with which the procedure was registered.
.LP
.eM
The \fIevent_types\fP and \fIselect_data\fP lists will always have the
same number of elements, specified by \fIcount\fP.  
Each event type/select data pair represents one call to
.PN XtInsertEventTypeHandler .
.sp
.LP
To register a procedure to dispatch events of a specific type within
.PN XtDispatchEvent ,
use
.PN XtSetEventDispatcher .
.LP
.IN "XtSetEventDispatcher" "" "@DEF@"
.sM
.FD 0
XtEventDispatchProc XtSetEventDispatcher(\fIdisplay\fP, \fIevent_type\fP, \
\fIproc\fP)
.br
      Display *\fIdisplay\fP;
.br
      int \fIevent_type\fP;
.br
      XtEventDispatchProc \fIproc\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the display for which the event dispatcher is to be registered.
.IP \fIevent_type\fP 1i
Specifies the event type for which the dispatcher should be invoked.
.IP \fIproc\fP 1i
Specifies the event dispatcher procedure.
.LP
.eM
The 
.PN XtSetEventDispatcher
function registers the event dispatcher procedure specified by \fIproc\fP
for events with the type \fIevent_type\fP.  The previously registered
dispatcher (or the default dispatcher if there was no previously registered
dispatcher) is returned.  If \fIproc\fP is NULL, the default procedure is
restored for the specified type.
.LP
In the future, when
.PN XtDispatchEvent
is called with an event type of \fIevent_type\fP, the specified \fIproc\fP
(or the default dispatcher) is invoked to determine a widget
to which to dispatch the event. 
.LP
The default dispatcher handles the \*(xI modal cascade and keyboard
focus mechanisms, handles the semantics of \fIcompress_enterleave\fP
and \fIcompress_motion\fP, and discards all extension events.
.sp
.LP
An event dispatcher procedure pointer is of type
.PN XtEventDispatchProc .
.LP
.IN "XtEventDispatchProc" "" "@DEF@"
.sM
.FD 0
typedef Boolean (*XtEventDispatchProc)(XEvent*)
.br
      XEvent *\fIevent\fP;
.FN
.IP \fIevent\fP 1i
Passes the event to be dispatched.
.LP
.eM
The event dispatcher procedure should determine whether this event is of
a type that should be dispatched to a widget.  
.LP
If the event should be dispatched to a widget, the event dispatcher
procedure should determine the appropriate widget to receive the
event, call 
.PN XFilterEvent
with the window of this widget, or
.PN None
if the event is to be discarded, and if
.PN XFilterEvent
returns
.PN False ,
dispatch the event to the widget using
.PN XtDispatchEventToWidget .
The procedure should return
.PN True
if either
.PN XFilterEvent
or
.PN XtDispatchEventToWidget
returned
.PN True
and
.PN False
otherwise.
.LP
If the event should not be dispatched to a widget, the event
dispatcher procedure should attempt to dispatch the event elsewhere as
appropriate and return
.PN True
if it successfully dispatched the event and
.PN False
otherwise.
.sp
.LP
Some dispatchers for extension events may wish to forward events
according to the Intrinsics' keyboard focus mechanism.  To determine
which widget is the end result of keyboard event forwarding, use
.PN XtGetKeyboardFocusWidget .
.LP
.IN "XtGetKeyboardFocusWidget" "" "@DEF@"
.sM
.FD 0
Widget XtGetKeyboardFocusWidget(\fIwidget\fP)
.br
      Widget \fIwidget\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget to get forwarding information for.
.LP
.eM
The
.PN XtGetKeyboardFocusWidget 
function returns the widget that would be the end result of keyboard
event forwarding for a keyboard event for the specified widget.
.sp
.LP
To dispatch an event to a specified widget, use
.PN XtDispatchEventToWidget .
.LP
.IN "XtDispatchEventToWidget" "" "@DEF@"
.sM
.FD 0
Boolean XtDispatchEventToWidget(\fIwidget\fP, \fIevent\fP)
.br
      Widget \fIwidget\fP;
.br
      XEvent *\fIevent\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget to which to dispatch the event.
.IP \fIevent\fP 1i
Specifies a pointer to the event to be dispatched.
.LP
.eM
The 
.PN XtDispatchEventToWidget
function scans the list of registered event handlers for the
specified widget and calls each handler that has been registered
for the specified event type, subject to the \fIcontinue_to_dispatch\fP
value returned by each handler.
The \*(xI behave as if event handlers were registered at the head
of the list for
.PN Expose ,
.PN NoExpose ,
.PN GraphicsExpose ,
and
.PN VisibilityNotify
events to invoke the widget's expose procedure according to the exposure
compression rules and to update the widget's \fIvisible\fP field
if \fIvisible_interest\fP is
.PN True .
These internal event handlers never set \fIcontinue_to_dispatch\fP to
.PN False .
.LP
.PN XtDispatchEventToWidget
returns
.PN True
if any event handler was called and
.PN False
otherwise.

.NH 2
Using the \*(xI in a Multi-Threaded Environment
.XS
\*(SN Using the \*(xI in a Multi-Threaded Environment
.XE
.LP
The \*(xI may be used in environments that offer multiple threads
of execution within the context of a single process.  A multi-threaded 
application using the \*(xI must explicitly initialize the toolkit 
for mutually exclusive access by calling
.PN XtToolkitThreadInitialize .

.NH 3
Initializing a Multi-Threaded \*(xI Application
.XS
\fB\*(SN Initializing a Multi-Threaded \*(xI Application\fP
.XE
.LP
To test and initialize \*(xI support for mutually exclusive thread
access, call
.PN XtToolkitThreadInitialize .
.LP
.IN "XtToolkitThreadInitialize" "" "@DEF@"
.sM
.FD 0
Boolean XtToolkitThreadInitialize()
.FN
.LP
.eM
.PN XtToolkitThreadInitialize
returns \fBTrue\fP if the \*(xI support mutually exclusive thread 
access, otherwise it returns \fBFalse\fP. \fBXtToolkitThreadInitialize\fP
must be called before
.PN XtCreateApplicationContext ,
.PN XtAppInitialize ,
.PN XtOpenApplication ,
or
.PN XtSetLanguageProc
is called. \fBXtToolkitThreadInitialize\fP may be called more than once;
however, the application writer must ensure that it is not called 
simultaneously by two or more threads.

.NH 3
Locking \*(tk Data Structures
.XS
\fB\*(SN Locking \*(tk Data Structures\fP
.XE
.LP
The \*(xI employs two levels of locking: application context and
process.  Locking an application context ensures mutually exclusive
access by a thread to the state associated with the application context,
including all displays and widgets associated with it.  Locking a
process ensures mutually exclusive access by a thread to \*(xI process
global data.
.LP
A client may acquire a lock multiple times and the effect is cumulative.
The client must ensure that the lock is released an equal number of times in
order for the lock to be acquired by another thread.
.LP
Most application writers will have little need to use locking as the
\*(xI performs the necessary locking internally.
Resource converters are an exception.
They require the application context or process to be locked
before the application can safely call them directly, for example:
.LP
.KS
.Ds
.TA .5i 2i
.ta .5i 2i
	...
	XtAppLock(app_context);
	XtCvtStringToPixel(dpy, args, num_args, fromVal, toVal, closure_ret);
	XtAppUnlock(app_context);
	...
.De
.KE
.LP
When the application relies upon
.PN XtConvertAndStore
or a converter to provide the storage for the results of a
conversion, the application should acquire the process lock before
calling out and hold the lock until the results have been copied.
.LP
Application writers who write their own
utility functions, such as one which retrieves the being_destroyed field from
a widget instance, must lock the application context before accessing
widget internal data.  For example:
.LP
.KS
.Ds
.TA .5i 2i
.ta .5i 2i
#include <X11/CoreP.h>
Boolean BeingDestroyed (widget)
	Widget widget;
{
	Boolean ret;
	XtAppLock(XtWidgetToApplicationContext(widget));
	ret = widget->core.being_destroyed;
	XtAppUnlock(XtWidgetToApplicationContext(widget));
	return ret;
}
.De
.KE
A client that wishes to atomically call two or more \*(xI functions 
must lock the application context.  For example:
.LP
.KS
.Ds
.TA .5i 2i
.ta .5i 2i
	...
	XtAppLock(XtWidgetToApplicationContext(widget));
	XtUnmanageChild (widget1);
	XtManageChild (widget2);
	XtAppUnlock(XtWidgetToApplicationContext(widget));
	...
.De
.KE

.NH 4
Locking the Application Context
.XS
\fB\*(SN Locking the Application Context\fP
.XE
.LP
To ensure mutual exclusion of application context, display, or 
widget internal state, use
.PN XtAppLock.
.LP
.IN "XtAppLock" "" "@DEF@"
.sM
.FD 0
void XtAppLock(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context to lock.
.LP
.eM
\fBXtAppLock\fP blocks until it is able to acquire the lock.  Locking the 
application context also ensures that only the thread holding the lock 
makes Xlib calls from within Xt.  An application that makes its own
direct Xlib calls must either lock the application context around every 
call or enable thread locking in Xlib.
.LP
To unlock a locked application context, use
.PN XtAppUnlock.
.LP
.IN "XtAppUnlock" "" "@DEF@"
.sM
.FD 0
void XtAppUnlock(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context that was previously locked.
.LP
.eM

.NH 4
Locking the Process
.XS
\*(SN Locking the Process
.XE
.LP
To ensure mutual exclusion of \*(tk process global data, a
widget writer must use
.PN XtProcessLock.
.LP
.IN "XtProcessLock" "" "@DEF@"
.sM
.FD 0
void XtProcessLock()
.FN
.LP
.eM
\fBXtProcessLock\fP blocks until it is able to acquire the lock.
Widget writers may use XtProcessLock to guarantee mutually exclusive 
access to widget static data.
.LP
To unlock a locked process, use
.PN XtProcessUnlock .
.LP
.IN "XtProcessUnlock" "" "@DEF@"
.sM
.FD 0
void XtProcessUnlock()
.FN
.LP
.eM
To lock both an application context and the process at the same 
time, call
.PN XtAppLock
first and then
.PN XtProcessLock .
To release both locks, call
.PN XtProcessUnlock
first and then
.PN XtAppUnlock .
The order is important to avoid deadlock.

.NH 3
Event Management in a Multi-Threaded Environment
.XS
\fB\*(SN Event Management in a Multi-Threaded Environment\fP
.XE
.LP
In a nonthreaded environment an application writer could reasonably
assume that it is safe to exit the application from a quit callback. 
This assumption may no longer hold true in a multi-threaded environment; 
therefore it is desirable to provide a mechanism to terminate an
event-processing loop without necessarily terminating its thread.
.LP
To indicate that the event loop should terminate after the current 
event dispatch has completed, use
.PN XtAppSetExitFlag .
.LP
.IN "XtAppSetExitFlag" "" "@DEF@"
.sM
.FD 0
void XtAppSetExitFlag(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.LP
.eM
.PN XtAppMainLoop
tests the value of the flag and will return if the flag is \fBTrue\fP.
.LP
Application writers who implement their own main loop may test the 
value of the exit flag with
.PN XtAppGetExitFlag .
.LP
.IN "XtAppGetExitFlag" "" "@DEF@"
.sM
.FD 0
Boolean XtAppGetExitFlag(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.LP
.eM
.PN XtAppGetExitFlag
will normally return \fBFalse\fP, indicating that event processing
may continue.  When
.PN XtAppGetExitFlag
returns \fBTrue\fP, the loop must terminate and return to the caller,
which might then destroy the application context.
.LP
Application writers should be aware that, if a thread is blocked in 
.PN XtAppNextEvent , 
.PN XtAppPeekEvent , 
or 
.PN XtAppProcessEvent
and another thread in the same application context opens a new display, 
adds an alternate input, or a timeout, any new source(s) will not 
normally be "noticed" by the blocked thread.  Any new sources are
"noticed" the next time one of these functions is called.
.LP
The \*(xI manage access to events on a last-in, first-out basis.  If 
multiple threads in the same application context block in
.PN XtAppNextEvent , 
.PN XtAppPeekEvent , 
or 
.PN XtAppProcessEvent ,
the last thread to call one of these functions is the first
thread to return.
.bp