xref: /xsrc/external/mit/libXt/dist/specs/CH07.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">

<chapter id='Event_Management'>
<title>Event Management</title>
<para>
While Xlib allows the reading and processing of events anywhere in an application,
widgets in the X Toolkit 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.
</para>

<para>
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 Intrinsics is
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>.
</para>

<para>
The event manager is a collection of functions to perform the following tasks:
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
Add or remove event sources other than X server events (in particular,
timer interrupts, file input, or POSIX signals).
    </para>
  </listitem>
  <listitem>
    <para>
Query the status of event sources.
    </para>
  </listitem>
  <listitem>
    <para>
Add or remove procedures to be called when an event occurs for a particular
widget.
    </para>
  </listitem>
  <listitem>
    <para>
Enable and
disable the dispatching of user-initiated events (keyboard and pointer events)
for a particular widget.
    </para>
  </listitem>
  <listitem>
    <para>
Constrain the dispatching of events to a cascade of pop-up widgets.
    </para>
  </listitem>
  <listitem>
    <para>
Register procedures to be called when specific events arrive.
    </para>
  </listitem>
  <listitem>
    <para>
Register procedures to be called when the Intrinsics will block.
    </para>
  </listitem>
  <listitem>
    <para>
Enable safe operation in a multi-threaded environment.
    </para>
  </listitem>
</itemizedlist>
<para>
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
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>.
</para>
<sect1 id="Adding_and_Deleting_Additional_Event_Sources">
<title>Adding and Deleting Additional Event Sources</title>
<para>
While most applications are driven only by X events,
some applications need to incorporate other sources of input
into the Intrinsics event-handling mechanism.
The event manager provides routines to integrate notification of timer events
and file data pending into this mechanism.
</para>

<para>
The next section describes functions that provide input gathering from files.
The application registers the files with the Intrinsics read routine.
When input is pending on one of the files,
the registered callback procedures are invoked.
</para>
<sect2 id="Adding_and_Removing_Input_Sources">
<title>Adding and Removing Input Sources</title>
<para>
To register a new file as an input source for a given application context, use
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppAddInput'>
<funcprototype>
<funcdef>XtInputId <function>XtAppAddInput</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>int <parameter>source</parameter></paramdef>
   <paramdef>XtPointer <parameter>condition</parameter></paramdef>
   <paramdef>XtInputCallbackProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>source</emphasis>
    </term>
    <listitem>
      <para>
Specifies the source file descriptor on a POSIX-based system
or other operating-system-dependent device specification.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>condition</emphasis>
    </term>
    <listitem>
      <para>
Specifies the mask that indicates a read, write, or exception condition
or some other operating-system-dependent condition.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called when the condition is found.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies an argument passed to the specified procedure
when it is called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>
function registers with the Intrinsics read routine a new source of events,
which is usually file input but can also be file output.
Note that <emphasis remap='I'>file</emphasis> should be loosely interpreted to mean any sink
or source of data.
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>
also specifies the conditions under which the source can generate events.
When an event is pending on this source,
the callback procedure is called.
</para>

<para>
The legal values for the <emphasis remap='I'>condition</emphasis> argument are operating-system-dependent.
On a POSIX-based system,
<emphasis remap='I'>source</emphasis> is a file number and the condition is some union of the following:
<variablelist>
  <varlistentry>
    <term>
      <emphasis role='strong'>XtInputReadMask</emphasis>
    </term>
    <listitem>
      <para>
Specifies that <emphasis remap='I'>proc</emphasis> is to be called when <emphasis remap='I'>source</emphasis> has data to be read.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis role='strong'>XtInputWriteMask</emphasis>
    </term>
    <listitem>
      <para>
Specifies that <emphasis remap='I'>proc</emphasis> is to be called when <emphasis remap='I'>source</emphasis> is ready
for writing.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis role='strong'>XtInputExceptMask</emphasis>
    </term>
    <listitem>
      <para>
Specifies that <emphasis remap='I'>proc</emphasis> is to be called when <emphasis remap='I'>source</emphasis> has
exception data.
    </para>
  </listitem>
  </varlistentry>
</variablelist>
</para>

<para>
Callback procedure pointers used to handle file events are of
type
<xref linkend='XtInputCallbackProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtInputCallbackProc'>
<funcprototype>
<funcdef>typedef void <function>(*XtInputCallbackProc)</function></funcdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>int *<parameter>source</parameter></paramdef>
   <paramdef>XtInputId *<parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Passes the client data argument that was registered for this procedure in
<function>XtAppAddInput</function>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>source</emphasis>
    </term>
    <listitem>
      <para>
Passes the source file descriptor generating the event.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Passes the id returned from the corresponding
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>
call.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
See <xref linkend='Using_the_Intrinsics_in_a_Multi_Threaded_Environment' />
for information regarding the use of
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>
in multiple threads.
</para>

<para>
To discontinue a source of input, use
<xref linkend='XtRemoveInput' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveInput'>
<funcprototype>
<funcdef>void <function>XtRemoveInput</function></funcdef>
   <paramdef>XtInputId <parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Specifies the id returned from the corresponding
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>
call.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveInput' xrefstyle='select: title'/>
function causes the Intrinsics read routine to stop watching for events
from the file source specified by <emphasis remap='I'>id</emphasis>.
</para>

<para>
See <xref linkend='Using_the_Intrinsics_in_a_Multi_Threaded_Environment' />
for information regarding the use of
<xref linkend='XtRemoveInput' xrefstyle='select: title'/>
in multiple threads.
</para>
</sect2>

<sect2 id="Adding_and_Removing_Blocking_Notifications">
<title>Adding and Removing Blocking Notifications</title>
<para>
Occasionally it is desirable for an application to receive notification
when the Intrinsics 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.
</para>

<para>
To register a hook that is called immediately prior to event blocking, use
<xref linkend='XtAppAddBlockHook' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppAddBlockHook'>
<funcprototype>
<funcdef>XtBlockHookId <function>XtAppAddBlockHook</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XtBlockHookProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called before blocking.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies an argument passed to the specified procedure when it is called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppAddBlockHook' xrefstyle='select: title'/>
function registers the specified procedure and returns an identifier for it.
The hook procedure <emphasis remap='I'>proc</emphasis> is called at any time in the future when
the Intrinsics are about to block pending some input.
</para>

<para>
The procedure pointers used to provide notification of event blocking
are of type
<xref linkend='XtBlockHookProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtBlockHookProc'>
<funcprototype>
<funcdef>typedef void *<function>XtBlockHookProc</function></funcdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Passes the client data argument that was registered for this procedure in
<function>XtAppAddBlockHook</function>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
To discontinue the use of a procedure for blocking notification, use
<xref linkend='XtRemoveBlockHook' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveBlockHook'>
<funcprototype>
<funcdef>void <function>XtRemoveBlockHook</function></funcdef>
   <paramdef>XtBlockHookId <parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Specifies the identifier returned from the corresponding call to
<xref linkend='XtAppAddBlockHook' xrefstyle='select: title'/>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveBlockHook' xrefstyle='select: title'/>
function removes the specified procedure from the list of procedures
that are called by the Intrinsics read routine before blocking on event sources.
</para>
</sect2>

<sect2 id="Adding_and_Removing_Timeouts">
<title>Adding and Removing Timeouts</title>
<para>
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.
</para>

<para>
To register a timeout callback, use
<xref linkend='XtAppAddTimeOut' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppAddTimeOut'>
<funcprototype>
<funcdef>XtIntervalId <function>XtAppAddTimeOut</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>unsigned long <parameter>interval</parameter></paramdef>
   <paramdef>XtTimerCallbackProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context for which the timer is to be set.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>interval</emphasis>
    </term>
    <listitem>
      <para>
Specifies the time interval in milliseconds.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called when the time expires.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies an argument passed to the specified procedure
when it is called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppAddTimeOut' xrefstyle='select: title'/>
function creates a timeout and returns an identifier for it.
The timeout value is set to <emphasis remap='I'>interval</emphasis>.
The callback procedure <emphasis remap='I'>proc</emphasis> is called when
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>
or
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
is next called after the time interval elapses,
and then the timeout is removed.
</para>

<para>
Callback procedure pointers used with timeouts are of
type
<xref linkend='XtTimerCallbackProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtTimerCallbackProc'>
<funcprototype>
<funcdef>typedef void *<function>XtTimerCallbackProc</function></funcdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XtIntervalId *<parameter>timer</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Passes the client data argument that was registered for this procedure in
<function>XtAppAddTimeOut</function>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>timer</emphasis>
    </term>
    <listitem>
      <para>
Passes the id returned from the corresponding
<xref linkend='XtAppAddTimeOut' xrefstyle='select: title'/>
call.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
See <xref linkend='Using_the_Intrinsics_in_a_Multi_Threaded_Environment' />
for information regarding the use of
<xref linkend='XtAppAddTimeOut' xrefstyle='select: title'/>
in multiple threads.
</para>

<para>
To clear a timeout value, use
<xref linkend='XtRemoveTimeOut' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveTimeOut'>
<funcprototype>
<funcdef>void <function>XtRemoveTimeOut</function></funcdef>
   <paramdef>XtIntervalId <parameter>timer</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>timer</emphasis>
    </term>
    <listitem>
      <para>
Specifies the id for the timeout request to be cleared.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveTimeOut' xrefstyle='select: title'/>
function removes the pending timeout.
Note that timeouts are automatically removed once they trigger.
</para>

<para>
Please refer to Section 7.12 for information regarding the use of
<xref linkend='XtRemoveTimeOut' xrefstyle='select: title'/>
in multiple threads.
</para>
</sect2>

<sect2 id="Adding_and_Removing_Signal_Callbacks">
<title>Adding and Removing Signal Callbacks</title>
<para>
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.
</para>

<para>
Prior to establishing a signal handler, the application or widget should
call
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>
and store the resulting identifier in a place accessible to the signal
handler.  When a signal arrives, the signal handler should call
<xref linkend='XtNoticeSignal' xrefstyle='select: title'/>
to notify the Intrinsics that a signal has occurred.  To register a signal
callback use
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppAddSignal'>
<funcprototype>
<funcdef>XtSignalId <function>XtAppAddSignal</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XtSignalCallbackProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called when the signal is noticed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies an argument passed to the specified procedure when it is called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The callback procedure pointers used to handle signal events are of type
<xref linkend='XtSignalCallbackProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtSignalCallbackProc'>
<funcprototype>
<funcdef>typedef void <function>(*XtSignalCallbackProc)</function></funcdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XtSignalId *<parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Passes the client data argument that was registered for this procedure in
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Passes the id returned from the corresponding
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>
call.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
To notify the Intrinsics that a signal has occurred, use
<xref linkend='XtNoticeSignal' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtNoticeSignal'>
<funcprototype>
<funcdef>void <function>XtNoticeSignal</function></funcdef>
   <paramdef>XtSignalId <parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Specifies the id returned from the corresponding
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>
call.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
On a POSIX-based system,
<xref linkend='XtNoticeSignal' xrefstyle='select: title'/>
is the only Intrinsics function that can safely be called from a signal handler.
If
<xref linkend='XtNoticeSignal' xrefstyle='select: title'/>
is invoked multiple times before the Intrinsics are able to invoke the
registered callback, the callback is only called once.
Logically, the Intrinsics maintain &ldquo;pending&rdquo; flag for each registered callback.
This flag is initially
<function>False</function>
and is set to
<function>True</function>
by
<xref linkend='XtNoticeSignal' xrefstyle='select: title'/>.
When
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>
or
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
(with a mask including
<function>XtIMSignal</function>)
is called, all registered callbacks with &ldquo;pending&rdquo;
<function>True</function>
are invoked and the flags are reset to
<function>False</function>.
</para>

<para>
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 Intrinsics never block signals from being raised, so if a given
signal can be raised multiple times before the Intrinsics 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 Intrinsics
sets the pending flag to
<function>False</function>
but before the callback can get control, in which case the pending flag
will still be
<function>True</function>
after the callback returns, and the Intrinsics 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.
</para>

<para>
To remove a registered signal callback, call
<xref linkend='XtRemoveSignal' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveSignal'>
<funcprototype>
<funcdef>void <function>XtRemoveSignal</function></funcdef>
   <paramdef>XtSignalId <parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Specifies the id returned by the corresponding call to
<xref linkend='XtAppAddSignal' xrefstyle='select: title'/>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The client should typically disable the source of the signal before calling
<xref linkend='XtRemoveSignal' xrefstyle='select: title'/>.
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
<xref linkend='XtRemoveSignal' xrefstyle='select: title'/>
the client can test for signals with
<xref linkend='XtAppPending' xrefstyle='select: title'/>
and process them by calling
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
with the mask
<function>XtIMSignal</function>.
</para>
</sect2>
</sect1>

<sect1 id="Constraining_Events_to_a_Cascade_of_Widgets">
<title>Constraining Events to a Cascade of Widgets</title>
<para>
Modal widgets are widgets that, except for the input directed to them,
lock out user input to the application.
</para>

<para>
When a modal menu or modal dialog box is popped up using
<xref linkend='XtPopup' xrefstyle='select: title'/>,
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.
</para>

<para>
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.
</para>

<para>
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
<function>KeyPress</function>,
<function>KeyRelease</function>,
<function>ButtonPress</function>,
and
<function>ButtonRelease</function>.
The user events ignored when they occur outside the cascade are
<function>MotionNotify</function>
and
<function>EnterNotify</function>.
All other events are delivered normally.
In particular, note that this is one
way in which widgets can receive
<function>LeaveNotify</function>
events without first receiving
<function>EnterNotify</function>
events; they should be prepared to deal with
this, typically by ignoring any unmatched
<function>LeaveNotify</function>
events.
</para>

<para>
<xref linkend='XtPopup' xrefstyle='select: title'/>
uses the
<xref linkend='XtAddGrab' xrefstyle='select: title'/>
and
<xref linkend='XtRemoveGrab' xrefstyle='select: title'/>
functions to constrain user events to a modal cascade
and subsequently to remove a grab when the modal widget is popped down.
</para>

<para>
To constrain or redirect user input to a modal widget, use
<xref linkend='XtAddGrab' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAddGrab'>
<funcprototype>
<funcdef>void <function>XtAddGrab</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Boolean <parameter>exclusive</parameter></paramdef>
   <paramdef>Boolean <parameter>spring_loaded</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to add to the modal cascade. Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>exclusive</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether user events should be dispatched exclusively to this widget
or also to previous widgets in the cascade.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>spring_loaded</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this widget was popped up because the user pressed
a pointer button.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAddGrab' xrefstyle='select: title'/>
function appends the widget to the modal cascade
and checks that <emphasis remap='I'>exclusive</emphasis> is
<function>True</function>
if <emphasis remap='I'>spring_loaded</emphasis> is
<function>True</function>.
If this condition is not met,
<xref linkend='XtAddGrab' xrefstyle='select: title'/>
generates a warning message.
</para>

<para>
The modal cascade is used by
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
when it tries to dispatch a user event.
When at least one modal widget is in the widget cascade,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
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 <emphasis remap='I'>exclusive</emphasis> parameter
<function>True</function>.
</para>

<para>
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 <emphasis remap='I'>exclusive</emphasis>
<function>False</function>.
Modal dialog boxes that need to restrict user input to the most deeply nested
dialog box add a subdialog widget to the cascade with <emphasis remap='I'>exclusive</emphasis>
<function>True</function>.
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.
</para>

<para>
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 <emphasis remap='I'>spring_loaded</emphasis>
<function>True</function>,
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 Intrinsics do not modify
the contents of the event.
</para>

<para>
To remove the redirection of user input to a modal widget, use
<xref linkend='XtRemoveGrab' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveGrab'>
<funcprototype>
<funcdef>void <function>XtRemoveGrab</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to remove from the modal cascade.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveGrab' xrefstyle='select: title'/>
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.
</para>
<sect2 id="Requesting_Key_and_Button_Grabs">
<title>Requesting Key and Button Grabs</title>
<para>
The Intrinsics provide a set of key and button grab interfaces that
are parallel to those provided by Xlib and that allow the Intrinsics
to modify event dispatching when necessary.  X Toolkit applications and
widgets that need to passively grab keys or buttons or actively grab
the keyboard or pointer should use the
following Intrinsics routines rather than the corresponding Xlib
routines.
</para>

<para>
To passively grab a single key of the keyboard, use
<xref linkend='XtGrabKey' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGrabKey'>
<funcprototype>
<funcdef>void <function>XtGrabKey</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>KeyCode <parameter>keycode</parameter></paramdef>
   <paramdef>Modifiers <parameter>modifiers</parameter></paramdef>
   <paramdef>Boolean <parameter>owner_events</parameter></paramdef>
   <paramdef>int <parameter>pointer_mode</parameter></paramdef>
   <paramdef>int <parameter>keyboard_mode</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget in whose window the key is to be grabbed.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>keycode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>modifiers</emphasis>
    </term>
    <term>
      <emphasis remap='I'>owner_events</emphasis>
    </term>
    <term>
      <emphasis remap='I'>pointer_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>keyboard_mode</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XGrabKey</function>;
see <olink targetdoc='libX11' targetptr='Keyboard_Grabbing'>Section 12.2</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.

    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
calls
<function>XGrabKey</function>
specifying the widget's window as the grab
window if the widget is realized.  The remaining arguments are exactly
as for
<function>XGrabKey</function>.
If the widget is not realized, or is later unrealized, the call to
<function>XGrabKey</function>
is performed (again) when
the widget is realized and its window becomes mapped.  In the future,
if
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
is called with a
<function>KeyPress</function>
event matching the specified keycode and modifiers (which may be
<function>AnyKey</function>
or
<function>AnyModifier</function>,
respectively) for the
widget's window, the Intrinsics will call
<xref linkend='XtUngrabKeyboard' xrefstyle='select: title'/>
with the timestamp from the
<function>KeyPress</function>
event if either of the following conditions is true:
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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
    </para>
  </listitem>
  <listitem>
    <para>
<function>XFilterEvent</function>
returns
<function>True</function>.
    </para>
  </listitem>
</itemizedlist>
<para>
To cancel a passive key grab, use
<xref linkend='XtUngrabKey' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtUngrabKey'>
<funcprototype>
<funcdef>void <function>XtUngrabKey</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>KeyCode <parameter>keycode</parameter></paramdef>
   <paramdef>Modifiers <parameter>modifiers</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget in whose window the key was grabbed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>keycode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>modifiers</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XUngrabKey</function>;
see <olink targetdoc='libX11' targetptr='Keyboard_Grabbing'>Section 12.2</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtUngrabKey' xrefstyle='select: title'/>
procedure calls
<function>XUngrabKey</function>
specifying the widget's
window as the ungrab window if the widget is realized.  The remaining
arguments are exactly as for
<function>XUngrabKey</function>.
If the widget is not realized,
<xref linkend='XtUngrabKey' xrefstyle='select: title'/>
removes a deferred
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
request, if any, for the specified widget, keycode, and modifiers.
</para>

<para>
To actively grab the keyboard, use
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGrabKeyboard'>
<funcprototype>
<funcdef>int <function>XtGrabKeyboard</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>Boolean <parameter>owner_events</parameter></paramdef>
   <paramdef>int <parameter>pointer_mode</parameter></paramdef>
   <paramdef>int <parameter>keyboard_mode</parameter></paramdef>
   <paramdef>Time <parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for whose window the keyboard is to be grabbed.
Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>owner_events</emphasis>
    </term>
    <term>
      <emphasis remap='I'>pointer_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>keyboard_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XGrabKeyboard</function>;
see <olink targetdoc='libX11' targetptr='Keyboard_Grabbing'>Section 12.2</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
If the specified widget is realized,
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>
calls
<function>XGrabKeyboard</function>
specifying the widget's window as the grab window.  The remaining
arguments and return value are exactly as for
<function>XGrabKeyboard</function>.
If the widget is not realized,
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>
immediately returns
<function>GrabNotViewable</function>.
No future automatic ungrab is implied by
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>.
</para>

<para>
To cancel an active keyboard grab, use
<xref linkend='XtUngrabKeyboard' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtUngrabKeyboard'>
<funcprototype>
<funcdef>void <function>XtUngrabKeyboard</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>Time <parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget that has the active keyboard grab.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specifies the additional argument to
<function>XUngrabKeyboard</function>;
see <olink targetdoc='libX11' targetptr='Keyboard_Grabbing'>Section 12.2</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtUngrabKeyboard' xrefstyle='select: title'/>
calls
<function>XUngrabKeyboard</function>
with the specified time.
</para>

<para>
To passively grab a single pointer button, use
<xref linkend='XtGrabButton' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGrabButton'>
<funcprototype>
<funcdef>void <function>XtGrabButton</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>int <parameter>button</parameter></paramdef>
   <paramdef>Modifiers <parameter>modifiers</parameter></paramdef>
   <paramdef>Boolean <parameter>owner_events</parameter></paramdef>
   <paramdef>unsigned int <parameter>event_mask</parameter></paramdef>
   <paramdef>int <parameter>pointer_mode</parameter></paramdef>
   <paramdef>int <parameter>keyboard_mode</parameter></paramdef>
   <paramdef>Window <parameter>confine_to</parameter></paramdef>
   <paramdef>Cursor <parameter>cursor</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget in whose window the button is to be grabbed.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>button</emphasis>
    </term>
    <term>
      <emphasis remap='I'>modifiers</emphasis>
    </term>
    <term>
      <emphasis remap='I'>owner_events</emphasis>
    </term>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <term>
      <emphasis remap='I'>pointer_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>keyboard_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>confine_to</emphasis>
    </term>
    <term>
      <emphasis remap='I'>cursor</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XGrabButton</function>;
see <olink targetdoc='libX11' targetptr='Pointer_Grabbing'>Section 12.1</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtGrabButton' xrefstyle='select: title'/>
calls
<function>XGrabButton</function>
specifying the widget's window as the
grab window if the widget is realized.  The remaining arguments are
exactly as for
<function>XGrabButton</function>.
If the widget is not realized, or is later unrealized, the call to
<function>XGrabButton</function>
is performed (again)
when the widget is realized and its window becomes mapped.  In the
future, if
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
is called with a
<function>ButtonPress</function>
event matching the specified button and modifiers (which may be
<function>AnyButton</function>
or
<function>AnyModifier</function>,
respectively)
for the widget's window, the Intrinsics will call
<xref linkend='XtUngrabPointer' xrefstyle='select: title'/>
with the timestamp from the
<function>ButtonPress</function>
event if either of the following conditions is true:
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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
    </para>
  </listitem>
  <listitem>
    <para>
<function>XFilterEvent</function>
returns
<function>True</function>.
    </para>
  </listitem>
</itemizedlist>
<para>
To cancel a passive button grab, use
<xref linkend='XtUngrabButton' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtUngrabButton'>
<funcprototype>
<funcdef>void <function>XtUngrabButton</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>unsigned int <parameter>button</parameter></paramdef>
   <paramdef>Modifiers <parameter>modifiers</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget in whose window the button was grabbed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>button</emphasis>
    </term>
    <term>
      <emphasis remap='I'>modifiers</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XUngrabButton</function>;
see <olink targetdoc='libX11' targetptr='Pointer_Grabbing'>Section 12.1</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtUngrabButton' xrefstyle='select: title'/>
procedure calls
<function>XUngrabButton</function>
specifying the
widget's window as the ungrab window if the widget is realized.  The
remaining arguments are exactly as for
<function>XUngrabButton</function>.
If the widget is not realized,
<xref linkend='XtUngrabButton' xrefstyle='select: title'/>
removes a deferred
<xref linkend='XtGrabButton' xrefstyle='select: title'/>
request, if any, for the specified widget, button, and modifiers.
</para>

<para>
To actively grab the pointer, use
<xref linkend='XtGrabPointer' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGrabPointer'>
<funcprototype>
<funcdef>int <function>XtGrabPointer</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>Boolean <parameter>owner_events</parameter></paramdef>
   <paramdef>unsigned int <parameter>event_mask</parameter></paramdef>
   <paramdef>int <parameter>pointer_mode</parameter></paramdef>
   <paramdef>int <parameter>keyboard_mode</parameter></paramdef>
   <paramdef>Window <parameter>confine_to</parameter></paramdef>
   <paramdef>Cursor <parameter>cursor</parameter></paramdef>
   <paramdef>Time <parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for whose window the pointer is to be grabbed.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>owner_events</emphasis>
    </term>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <term>
      <emphasis remap='I'>pointer_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>keyboard_mode</emphasis>
    </term>
    <term>
      <emphasis remap='I'>confine_to</emphasis>
    </term>
    <term>
      <emphasis remap='I'>cursor</emphasis>
    </term>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specify arguments to
<function>XGrabPointer</function>;
see <olink targetdoc='libX11' targetptr='Pointer_Grabbing'>Section 12.1</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
If the specified widget is realized,
<xref linkend='XtGrabPointer' xrefstyle='select: title'/>
calls
<function>XGrabPointer</function>,
specifying the widget's window as the grab window.  The remaining
arguments and return value are exactly as for
<function>XGrabPointer</function>.
If the widget is not realized,
<xref linkend='XtGrabPointer' xrefstyle='select: title'/>
immediately returns
<function>GrabNotViewable</function>.
No future automatic ungrab is implied by
<xref linkend='XtGrabPointer' xrefstyle='select: title'/>.
</para>

<para>
To cancel an active pointer grab, use
<xref linkend='XtUngrabPointer' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtUngrabPointer'>
<funcprototype>
<funcdef>void <function>XtUngrabPointer</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>Time <parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget that has the active pointer grab.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specifies the time argument to
<function>XUngrabPointer</function>;
see <olink targetdoc='libX11' targetptr='Pointer_Grabbing'>Section 12.1</olink>
in <olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtUngrabPointer' xrefstyle='select: title'/>
calls
<function>XUngrabPointer</function>
with the specified time.
</para>
</sect2>
</sect1>

<sect1 id="Focusing_Events_on_a_Child">
<title>Focusing Events on a Child</title>
<para>
To redirect keyboard input to a normal descendant of a
widget without calling
<function>XSetInputFocus</function>,
use
<xref linkend='XtSetKeyboardFocus' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtSetKeyboardFocus'>
<funcprototype>
<funcdef>void <function>XtSetKeyboardFocus</function></funcdef>
   <paramdef>Widget <parameter>subtree</parameter></paramdef>
   <paramdef>Widget <parameter>descendent</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>subtree</emphasis>
    </term>
    <listitem>
      <para>
Specifies the subtree of the hierarchy for which the keyboard focus is
to be set.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>descendant</emphasis>
    </term>
    <listitem>
      <para>
Specifies either the normal (non-pop-up) descendant of <emphasis remap='I'>subtree</emphasis> to which
keyboard events are logically directed, or
<function>None</function>.
It is not an error to specify
<function>None</function>
when no input focus was previously set.  Must be of class Object or any subclass thereof.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtSetKeyboardFocus' xrefstyle='select: title'/>
causes
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
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.
</para>

<para>
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).
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
with any value of <emphasis remap='I'>owner_events</emphasis>, or
if the keyboard is actively grabbed by E with <emphasis remap='I'>owner_events</emphasis>
<function>False</function>
via
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>
or
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
on a previous key press, the event is dispatched to E.
    </para>
  </listitem>
  <listitem>
    <para>
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.
    </para>
  </listitem>
  <listitem>
    <itemizedlist spacing='compact'>
      <listitem>
        <para>
If E is the final focus target widget F or a descendant of F, the
event is dispatched to E.
        </para>
      </listitem>
      <listitem>
        <para>
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
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
for E,
<xref linkend='XtUngrabKeyboard' xrefstyle='select: title'/>
is called.
        </para>
      </listitem>
      <listitem>
        <para>
If E is an ancestor of F, and the event is a key press, and either
        </para>
        <itemizedlist spacing='compact'>
          <listitem>
            <para>
E has grabbed the key with
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
and <emphasis remap='I'>owner_events</emphasis>
<function>False</function>,
or
            </para>
          </listitem>
          <listitem>
            <para>
E has grabbed the key with
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
and <emphasis remap='I'>owner_events</emphasis>
<function>True</function>,
and the coordinates of the event are outside the rectangle specified
by E's geometry,
then the event is dispatched to E.
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
Otherwise, define A as the closest common ancestor of E and F:
        </para>
        <itemizedlist spacing='compact'>
          <listitem>
            <para>
If there is an active keyboard grab for any widget via either
<xref linkend='XtGrabKeyboard' xrefstyle='select: title'/>
or
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
on a previous key press, or
if no widget between F and A (noninclusive) has grabbed
the key and modifier combination with
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
and any value of <emphasis remap='I'>owner_events</emphasis>, the event is dispatched to F.
            </para>
          </listitem>
          <listitem>
            <para>
Else, the event is dispatched to the ancestor of F closest to A
that has grabbed the key and modifier combination with
<xref linkend='XtGrabKey' xrefstyle='select: title'/>.
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
    </itemizedlist>
  </listitem>
</itemizedlist>
<para>
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 Intrinsics do not modify
the contents of the event.
</para>

<para>
When <emphasis remap='I'>subtree</emphasis> 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
<function>FocusIn</function>
event is generated for the descendant if
<function>FocusChange</function>
events have been selected by the descendant.
Similarly, when <emphasis remap='I'>subtree</emphasis> loses the X input focus
or the keyboard focus for one of its ancestors, a
<function>FocusOut</function>
event is generated for descendant if
<function>FocusChange</function>
events have been selected by the descendant.
</para>

<para>
A widget tree may also actively manage the X server input focus.  To
do so, a widget class specifies an accept_focus procedure.
</para>

<para>
The accept_focus procedure pointer is of type
<xref linkend='XtAcceptFocusProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAcceptFocusProc'>
<funcprototype>
<funcdef>typedef Boolean *<function>XtAcceptFocusProc</function></funcdef>

   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Time *<parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specifies the X time of the event causing the accept focus.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
Widgets that need the input focus can call
<function>XSetInputFocus</function>
explicitly, pursuant to the restrictions of the <emphasis remap='I'>Inter-Client Communication Conventions Manual</emphasis>.
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
<function>FocusIn</function>
and
<function>FocusOut</function>
events).
Widgets classes that never want the input focus should set the
<emphasis remap='I'>accept_focus</emphasis> field to NULL.
</para>

<para>
To call a widget's accept_focus procedure, use
<xref linkend='XtCallAcceptFocus' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtCallAcceptFocus'>
<funcprototype>
<funcdef>Boolean <function>XtCallAcceptFocus</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Time *<parameter>time</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>time</emphasis>
    </term>
    <listitem>
      <para>
Specifies the X time of the event that is causing the focus change.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtCallAcceptFocus' xrefstyle='select: title'/>
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 <emphasis remap='I'>accept_focus</emphasis> is NULL,
<xref linkend='XtCallAcceptFocus' xrefstyle='select: title'/>
returns
<function>False</function>.
</para>
<sect2 id="Events_for_Drawables_That_Are_Not_a_Widget_s_Window">
<title>Events for Drawables That Are Not a Widget's Window</title>
<para>
Sometimes an application must handle events for drawables that are not
associated with widgets in its widget tree.  Examples include handling
<function>GraphicsExpose</function>
and
<function>NoExpose</function>
events on Pixmaps, and handling
<function>PropertyNotify</function>
events on the root window.
</para>

<para>
To register a drawable with the Intrinsics event dispatching, use
<xref linkend='XtRegisterDrawable' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRegisterDrawable'>
<funcprototype>
<funcdef>void <function>XtRegisterDrawable</function></funcdef>
   <paramdef>Display *<parameter>display</parameter></paramdef>
   <paramdef>Drawable <parameter>drawable</parameter></paramdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the drawable's display.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>drawable</emphasis>
    </term>
    <listitem>
      <para>
Specifies the drawable to register.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to register the drawable for.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtRegisterDrawable' xrefstyle='select: title'/>
associates the specified drawable with the specified widget
so that future calls to
<xref linkend='XtWindowToWidget' xrefstyle='select: title'/>
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.
</para>

<para>
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
<xref linkend='XtRegisterDrawable' xrefstyle='select: title'/>
are undefined.
</para>

<para>
To unregister a drawable with the Intrinsics event dispatching, use
<xref linkend='XtUnregisterDrawable' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtUnregisterDrawable'>
<funcprototype>
<funcdef>void <function>XtUnregisterDrawable</function></funcdef>
   <paramdef>Display *<parameter>display</parameter></paramdef>
   <paramdef>Drawable <parameter>drawable</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the drawable's display.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>drawable</emphasis>
    </term>
    <listitem>
      <para>
Specifies the drawable to unregister.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtUnregisterDrawable' xrefstyle='select: title'/>
removes an association created with
<xref linkend='XtRegisterDrawable' xrefstyle='select: title'/>.
If the drawable is the window of a widget in the client's widget tree
the results of calling
<xref linkend='XtUnregisterDrawable' xrefstyle='select: title'/>
are undefined.
</para>
</sect2>
</sect1>

<sect1 id="Querying_Event_Sources">
<title>Querying Event Sources</title>
<para>
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 Intrinsics equivalents of the
<function>XPending</function>,
<function>XPeekEvent</function>,
and
<function>XNextEvent</function>
Xlib calls.
</para>

<para>
To determine if there are any events on the input queue for a given application,
use
<xref linkend='XtAppPending' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppPending'>
<funcprototype>
<funcdef>XtInputMask <function>XtAppPending</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application to check.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppPending' xrefstyle='select: title'/>
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
<function>XtIMXEvent</function>,
<function>XtIMTimer</function>,
<function>XtIMAlternateInput</function>,
and
<function>XtIMSignal</function>
(see
<function>XtAppProcessEvent ).</function>
If there are no events pending,
<xref linkend='XtAppPending' xrefstyle='select: title'/>
flushes the output buffers of each Display in the application context
and returns zero.
</para>

<para>
To return the event from the head of a given application's input queue
without removing input from the queue, use
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppPeekEvent'>
<funcprototype>
<funcdef>Boolean <function>XtAppPeekEvent</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XEvent *<parameter>event_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the event information to the specified event structure.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
If there is an X event in the queue,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>
copies it into <emphasis remap='I'>event_return</emphasis> and returns
<function>True</function>.
If no X input is on the queue,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>
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,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>
fills in <emphasis remap='I'>event_return</emphasis> and returns
<function>True</function>.
Otherwise, the input is for an input source
registered with
<xref linkend='XtAppAddInput' xrefstyle='select: title'/>,
and
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>
returns
<function>False</function>.
The sample implementations provides XtAppPeekEvent as described.  Timeout callbacks
are called while blocking for input.  If some input for an input source is
available,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>
will return
<function>True</function>
without returning an event.
</para>

<para>
To remove and return the event
from the head of a given application's X event queue,
use
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppNextEvent'>
<funcprototype>
<funcdef>void <function>XtAppNextEvent</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XEvent *<parameter>event_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_return</emphasis>
    </term>
    <listitem>
      <para>
Returns the event information to the specified event structure.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
If the X event queue is empty,
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>
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 <xref linkend='Adding_Background_Work_Procedures' />.
</para>
</sect1>

<sect1 id="Dispatching_Events">
<title>Dispatching Events</title>
<para>
The Intrinsics provide functions that dispatch events
to widgets or other application code.
Every client interested in X events on a widget uses
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
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 <xref linkend='Translation_Management' />.
</para>

<para>
Applications that need direct control of the processing of different types
of input should use
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppProcessEvent'>
<funcprototype>
<funcdef>void <function>XtAppProcessEvent</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XtInputMask <parameter>mask</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the
application for which to process input.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies what types of events to process.
The mask is the bitwise inclusive OR of any combination of
<function>XtIMXEvent</function>,
<function>XtIMTimer</function>,
<function>XtIMAlternateInput</function>,
and
<function>XtIMSignal</function>.
As a convenience,
<filename class="headerfile">Intrinsic.h</filename>
defines the symbolic name
<function>XtIMAll</function>
to be the bitwise inclusive OR of these four event types.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
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
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
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
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>.
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
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
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>.
</para>

<para>
When an X event is received,
it is passed to
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>,
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.
</para>

<para>
To dispatch an event returned by
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>,
retrieved directly from the Xlib queue, or synthetically constructed,
to any registered event filters or event handlers, call
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtDispatchEvent'>
<funcprototype>
<funcdef>Boolean <function>XtDispatchEvent</function></funcdef>
   <paramdef>XEvent *<parameter>event</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>event</emphasis>
    </term>
    <listitem>
      <para>
Specifies a pointer to the event structure to be dispatched
to the appropriate event handlers.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
function first calls
<function>XFilterEvent</function>
with the <emphasis remap='I'>event</emphasis> and the window of the widget to which the
Intrinsics intend to dispatch the event, or the event window if
the Intrinsics would not dispatch the event to any handlers.
If
<function>XFilterEvent</function>
returns
<function>True</function>
and the event activated a server grab as identified
by a previous call to
<xref linkend='XtGrabKey' xrefstyle='select: title'/>
or
<xref linkend='XtGrabButton' xrefstyle='select: title'/>,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
calls
<xref linkend='XtUngrabKeyboard' xrefstyle='select: title'/>
or
<xref linkend='XtUngrabPointer' xrefstyle='select: title'/>
with the timestamp from the event and immediately returns
<function>True</function>.
If
<function>XFilterEvent</function>
returns
<function>True</function>
and a grab was not activated,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
just immediately returns
<function>True</function>.
Otherwise,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
sends the event to the event handler functions that
have been previously registered with the dispatch routine.
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
returns
<function>True</function>
if
<function>XFilterEvent</function>
returned
<function>True</function>,
or if the event was dispatched to some handler, and
<function>False</function>
if it found no handler to which to dispatch the event.
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
records the last timestamp in any event that
contains a timestamp (see
<function>XtLastTimestampProcessed</function>),
regardless of whether it was filtered or dispatched.
If a modal cascade is active with <emphasis remap='I'>spring_loaded</emphasis>
<function>True</function>,
and if the event is a remap event as defined by
<xref linkend='XtAddGrab' xrefstyle='select: title'/>,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
may dispatch the event a second time.  If it does so,
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
will call
<function>XFilterEvent</function>
again with the window of the spring-loaded widget prior to the second
dispatch, and if
<function>XFilterEvent</function>
returns
<function>True</function>,
the second dispatch will not be performed.
</para>
</sect1>

<sect1 id="The_Application_Input_Loop">
<title>The Application Input Loop</title>
<para>
To process all input from a given application in a continuous loop,
use the convenience procedure
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppMainLoop'>
<funcprototype>
<funcdef>void <function>XtAppMainLoop</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The <xref linkend='XtAppMainLoop' xrefstyle='select: title'/>
function processes events using
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>,
varying the <emphasis remap='I'>mask parameter</emphasis>
and using <xref linkend='XtAppPending' xrefstyle='select: title'/>
to ensure that it has a chance to handle events of all types,
i.e., X events, timer events, input events and signal sources.
This constitutes the main loop of X Toolkit applications.
There is nothing special about
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>;
it simply processes events 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
<xref linkend='XtAppLock' xrefstyle='select: title'/>
and
<xref linkend='XtAppUnlock' xrefstyle='select: title'/>.
</para>

<para>
Applications can provide their own version of this loop,
which tests some global termination flag or tests that the number
of top-level widgets is larger than zero before
circling back for the next event.
</para>

<para>
The design of 
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>
has changed since Release 6.
Originally it looped over calls to
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>,
and
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>,
but because the latter returns only after an X event
(not for timers, signals, inputs),
it was modified to allow any type of event to break out of the loop.
</para>
</sect1>

<sect1 id="Setting_and_Checking_the_Sensitivity_State_of_a_Widget">
<title>Setting and Checking the Sensitivity State of a Widget</title>
<para>
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.
</para>

<para>
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
<function>KeyPress</function>,
<function>KeyRelease</function>,
<function>ButtonPress</function>,
<function>ButtonRelease</function>,
<function>MotionNotify</function>,
<function>EnterNotify</function>,
<function>LeaveNotify</function>,
<function>FocusIn</function>,
or
<function>FocusOut</function>.
</para>

<para>
A widget can be insensitive because its <emphasis remap='I'>sensitive</emphasis> field is
<function>False</function>
or because one of its ancestors is insensitive and thus the widget's
<emphasis remap='I'>ancestor_sensitive</emphasis> field also is
<function>False</function>.
A widget can but does not need to distinguish these two cases visually.
</para>

<note>
<para>
Pop-up shells will have
<emphasis remap='I'>ancestor_sensitive</emphasis>
<function>False</function>
if the parent was insensitive when the shell
was created.  Since
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
on the parent will not
modify the resource of the pop-up child, clients are advised to include
a resource specification of the form
&ldquo;*TransientShell.ancestorSensitive: True&rdquo;
in the application defaults resource file or to
otherwise ensure that the parent is
sensitive when creating pop-up shells.
</para>
</note>

<para>
To set the sensitivity state of a widget, use
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtSetSensitive'>
<funcprototype>
<funcdef>void <function>XtSetSensitive</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>Boolean <parameter>sensitive</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class RectObj or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>sensitive</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether the widget should receive
keyboard, pointer, and focus events.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
function first calls
<xref linkend='XtSetValues' xrefstyle='select: title'/>
on the current widget with an argument list specifying the
XtNsensitive resource and the new value.
If <emphasis remap='I'>sensitive</emphasis> is
<function>False</function>
and the widget's class is a subclass of
Composite,
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
recursively propagates the new value
down the child tree by calling
<xref linkend='XtSetValues' xrefstyle='select: title'/>
on each child to set <emphasis remap='I'>ancestor_sensitive</emphasis> to
<function>False</function>.
If <emphasis remap='I'>sensitive</emphasis> is
<function>True</function>
and the widget's class is a subclass of
Composite
and the widget's <emphasis remap='I'>ancestor_sensitive</emphasis> field is
<function>True</function>,
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
sets the <emphasis remap='I'>ancestor_sensitive</emphasis> of each child to
<function>True</function>
and then recursively calls
<xref linkend='XtSetValues' xrefstyle='select: title'/>
on each normal descendant that is now sensitive to set
<emphasis remap='I'>ancestor_sensitive</emphasis> to
<function>True</function>.
</para>

<para>
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
calls
<xref linkend='XtSetValues' xrefstyle='select: title'/>
to change the <emphasis remap='I'>sensitive</emphasis> and <emphasis remap='I'>ancestor_sensitive</emphasis> 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).
</para>

<para>
<xref linkend='XtSetSensitive' xrefstyle='select: title'/>
maintains the invariant that, if the parent has either <emphasis remap='I'>sensitive</emphasis>
or <emphasis remap='I'>ancestor_sensitive</emphasis>
<function>False</function>,
then all children have <emphasis remap='I'>ancestor_sensitive</emphasis>
<function>False</function>.
</para>

<para>
To check the current sensitivity state of a widget,
use
<xref linkend='XtIsSensitive' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtIsSensitive'>
<funcprototype>
<funcdef>Boolean <function>XtIsSensitive</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the object.  Must be of class Object or any subclass thereof.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtIsSensitive' xrefstyle='select: title'/>
function returns
<function>True</function>
or
<function>False</function>
to indicate whether user input events are being dispatched.
If object's class is a subclass of RectObj and
both <emphasis remap='I'>sensitive</emphasis> and <emphasis remap='I'>ancestor_sensitive</emphasis> are
<function>True</function>,
<xref linkend='XtIsSensitive' xrefstyle='select: title'/>
returns
<function>True</function>;
otherwise, it returns
<function>False</function>.
</para>
</sect1>

<sect1 id="Adding_Background_Work_Procedures">
<title>Adding Background Work Procedures</title>
<para>
The Intrinsics 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
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>
or
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>.
Work procedure pointers are of type
<xref linkend='XtWorkProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtWorkProc'>
<funcprototype>
<funcdef>typedef Boolean <function>(*XtWorkProc)</function></funcdef>

   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Passes the client data specified when the work procedure was registered.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
This procedure should return
<function>True</function>
when it is done to indicate that it
should be removed.
If the procedure returns
<function>False</function>,
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.
</para>

<para>
To register a work procedure for a given application, use
<xref linkend='XtAppAddWorkProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppAddWorkProc'>
<funcprototype>
<funcdef>XtWorkProcId <function>XtAppAddWorkProc</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
   <paramdef>XtWorkProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that identifies the application.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called when the application is idle.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the argument passed to the specified procedure
when it is called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAppAddWorkProc' xrefstyle='select: title'/>
function adds the specified work procedure for the application identified
by <emphasis remap='I'>app_context</emphasis>
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.
</para>

<para>
To remove a work procedure, either return
<function>True</function>
from the procedure when it is called or use
<xref linkend='XtRemoveWorkProc' xrefstyle='select: title'/>
outside of the procedure.
</para>

<funcsynopsis id='XtRemoveWorkProc'>
<funcprototype>
<funcdef>void <function>XtRemoveWorkProc</function></funcdef>
   <paramdef>XtWorkProcId <parameter>id</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>id</emphasis>
    </term>
    <listitem>
      <para>
Specifies which work procedure to remove.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveWorkProc' xrefstyle='select: title'/>
function explicitly removes the specified background work procedure.
</para>
</sect1>

<sect1 id="X_Event_Filters">
<title>X Event Filters</title>
<para>
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.
</para>
<sect2 id="Pointer_Motion_Compression">
<title>Pointer Motion Compression</title>
<para>
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 <emphasis remap='I'>compress_motion</emphasis> should be
<function>True</function>.
When a request for an event would return a motion event,
the Intrinsics 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.
</para>
</sect2>

<sect2 id="Enter_Leave_Compression">
<title>Enter/Leave Compression</title>
<para>
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 <emphasis remap='I'>compress_enterleave</emphasis> should be
<function>True</function>.
These enter and leave events are not delivered to the client
if they are found together in the input queue.
</para>
</sect2>

<sect2 id="Exposure_Compression">
<title>Exposure Compression</title>
<para>
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.
</para>

<para>
In either case, these widgets do not care about getting partial exposure events.
The <emphasis remap='I'>compress_exposure</emphasis> 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:
</para>

<programlisting>
#define XtExposeNoCompress              ((XtEnum)False)
#define XtExposeCompressSeries          ((XtEnum)True)
#define XtExposeCompressMultiple        &lt;implementation-defined&gt;
#define XtExposeCompressMaximal         &lt;implementation-defined&gt;
</programlisting>

<para>
optionally ORed with any combination of the following flags (all with
implementation-defined values):
<function>XtExposeGraphicsExpose</function>,
<function>XtExposeGraphicsExposeMerged</function>,
<function>XtExposeNoExpose</function>,
and
<function>XtExposeNoRegion</function>.
</para>

<para>
If the <emphasis remap='I'>compress_exposure</emphasis> field in the widget class structure does not
specify
<function>XtExposeNoCompress</function>,
the event manager calls the widget's expose procedure only
once for a series of exposure events.
In this case, all
<function>Expose</function>
or
<function>GraphicsExpose</function>
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
<function>XtExposeNoRegion</function>
is specified) the region.
For more information on regions, see
<olink targetdoc='libX11' targetptr='Manipulating_Regions'>Section 16.5</olink> in
<olink targetdoc='libX11' targetptr='libX11'>Xlib &mdash; C Language X Interface</olink>.
</para>

<para>
The values have the following interpretation:
</para>

<para>
<function>XtExposeNoCompress</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
No exposure compression is performed; every selected event is
individually dispatched to the expose procedure with a <emphasis remap='I'>region</emphasis>
argument of NULL.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeCompressSeries</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeCompressMultiple</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeCompressMaximal</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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 Intrinsics will
block until the end of the series is received.
    </para>
  </listitem>
</itemizedlist>
<para>
The additional flags have the following meaning:
</para>

<para>
<function>XtExposeGraphicsExpose</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
Specifies that
<function>GraphicsExpose</function>
events are also to be dispatched to
the expose procedure.
<function>GraphicsExpose</function>
events are compressed, if specified, in the same manner as
<function>Expose</function>
events.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeGraphicsExposeMerged</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
Specifies in the case of
<function>XtExposeCompressMultiple</function>
and
<function>XtExposeCompressMaximal</function>
that series of
<function>GraphicsExpose</function>
and
<function>Expose</function>
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
<function>XtExposeGraphicsExpose</function>.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeNoExpose</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
Specifies that
<function>NoExpose</function>
events are also to be dispatched to the expose procedure.
<function>NoExpose</function>
events are never coalesced with
other exposure events or with each other.
    </para>
  </listitem>
</itemizedlist>
<para>
<function>XtExposeNoRegion</function>
</para>
<itemizedlist spacing='compact'>
  <listitem>
    <para>
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.
    </para>
  </listitem>
</itemizedlist>
</sect2>
</sect1>

<sect1 id="Widget_Exposure_and_Visibility">
<title>Widget Exposure and Visibility</title>
<para>
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.
</para>

<sect2 id="Redisplay_of_a_Widget_The_expose_Procedure">
<title>Redisplay of a Widget: The expose Procedure</title>
<para>
The expose procedure pointer in a widget class is of type
<xref linkend='XtExposeProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtExposeProc'>
<funcprototype>
<funcdef>typedef void <function>(*XtExposeProc)</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XEvent *<parameter>event</parameter></paramdef>
   <paramdef>Region <parameter>region</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget instance requiring redisplay.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event</emphasis>
    </term>
    <listitem>
      <para>
Specifies the exposure event giving the rectangle requiring redisplay.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>region</emphasis>
    </term>
    <listitem>
      <para>
Specifies the union of all rectangles in this exposure sequence.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
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 <emphasis remap='I'>expose</emphasis> field.
Many composite widgets serve only as containers for their children
and have no expose procedure.
</para>

<note>
<para>
If the <emphasis remap='I'>expose</emphasis> procedure is NULL,
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/>
fills in a default bit gravity of
<function>NorthWestGravity</function>
before it calls the widget's realize procedure.
</para>
</note>

<para>
If the widget's <emphasis remap='I'>compress_exposure</emphasis> class field specifies
<function>XtExposeNoCompress</function>
or
<function>XtExposeNoRegion</function>,
or if the event type is
<function>NoExpose</function>
(see <xref linkend='Exposure_Compression' />),
<emphasis remap='I'>region</emphasis> is NULL.  If
<function>XtExposeNoCompress</function>
is not specified and the event type is not
<function>NoExpose</function>,
the event is the final event in the compressed series
but <emphasis remap='I'>x</emphasis>, <emphasis remap='I'>y</emphasis>, <emphasis remap='I'>width</emphasis>, and <emphasis remap='I'>height</emphasis> contain
the bounding box for all the compressed events.
The region is created and destroyed by the Intrinsics, but
the widget is permitted to modify the region contents.
</para>

<para>
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.
</para>

<para>
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
</para>
<programlisting>
Boolean         invert;
Boolean         highlight;
Dimension       highlight_width;
</programlisting>
<para>
Label would have <emphasis remap='I'>invert</emphasis> and <emphasis remap='I'>highlight</emphasis> always
<function>False</function>
and <emphasis remap='I'>highlight_width</emphasis> zero.
Pushbutton would dynamically set <emphasis remap='I'>highlight</emphasis> and <emphasis remap='I'>highlight_width</emphasis>,
but it would leave <emphasis remap='I'>invert</emphasis> always
<function>False</function>.
Finally, Toggle would dynamically set all three.
In this case,
the expose procedures for Pushbutton and Toggle inherit
their superclass's expose procedure;
see <xref linkend='Inheritance_of_Superclass_Operations' />.
</para>
</sect2>

<sect2 id="Widget_Visibility">
<title>Widget Visibility</title>
<para>
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.
</para>

<para>
The <emphasis remap='I'>visible</emphasis> 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
<function>True</function>
by the time an
exposure
event is processed if any part of the widget is visible,
but is
<function>False</function>
if the widget is fully obscured.
</para>

<para>
Widgets can use or ignore the <emphasis remap='I'>visible</emphasis> hint.
If they ignore it,
they should have <emphasis remap='I'>visible_interest</emphasis> in their widget class record set
<function>False</function>.
In such cases,
the <emphasis remap='I'>visible</emphasis> field is initialized
<function>True</function>
and never changes.
If <emphasis remap='I'>visible_interest</emphasis> is
<function>True</function>,
the event manager asks for
<function>VisibilityNotify</function>
events for the widget and sets <emphasis remap='I'>visible</emphasis> to
<function>True</function>
on
<function>VisibilityUnobscured</function>
or
<function>VisibilityPartiallyObscured</function>
events and
<function>False</function>
on
<function>VisibilityFullyObscured</function>
events.
</para>
</sect2>
</sect1>

<sect1 id="X_Event_Handlers">
<title>X Event Handlers</title>
<para>
Event handlers are procedures called when specified events
occur in a widget.
Most widgets need not use event handlers explicitly.
Instead, they use the Intrinsics translation manager.
Event handler procedure pointers are of the type
<xref linkend='XtEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtEventHandler'>
<funcprototype>
<funcdef>typedef void <function>(*XtEventHandler)</function></funcdef>

   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XEvent *<parameter>event</parameter></paramdef>
   <paramdef>Boolean *<parameter>continue_to_dispatch</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which the event arrived.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies any client-specific information registered with the event handler.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event</emphasis>
    </term>
    <listitem>
      <para>
Specifies the triggering event.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>continue_to_dispatch</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether the remaining event
handlers registered for the current event
should be called.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
After receiving an event and before calling any event handlers, the
Boolean pointed to by <emphasis remap='I'>continue_to_dispatch</emphasis> is initialized to
<function>True</function>.
When an event handler is called, it may decide that further processing
of the event is not desirable and may store
<function>False</function>
in this Boolean, in
which case any handlers remaining to be called for the event are
ignored.
</para>

<para>
The circumstances under which the Intrinsics may add event handlers
to a widget are currently implementation-dependent.  Clients must
therefore be aware that storing
<function>False</function>
into the <emphasis remap='I'>continue_to_dispatch</emphasis> argument can lead to portability problems.
</para>
<sect2 id="Event_Handlers_That_Select_Events">
<title>Event Handlers That Select Events</title>
<para>
To register an event handler procedure with the dispatch mechanism, use
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAddEventHandler'>
<funcprototype>
<funcdef>void <function>XtAddEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this event handler is being registered.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to call this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
called on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the event handler.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
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 <emphasis remap='I'>client_data</emphasis>
value,
the specified mask augments the existing mask.
If the widget is realized,
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
calls
<function>XSelectInput</function>,
if necessary.
The order in which this procedure is called relative to other handlers
registered for the same event is not defined.
</para>

<para>
To remove a previously registered event handler, use
<xref linkend='XtRemoveEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveEventHandler'>
<funcprototype>
<funcdef>void <function>XtRemoveEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this procedure is registered.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to unregister this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
removed on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be removed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the registered client data.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveEventHandler' xrefstyle='select: title'/>
function unregisters an event handler registered with
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>
for the specified events.
The request is ignored if <emphasis remap='I'>client_data</emphasis> does not match the value given
when the handler was registered.
If the widget is realized and no other event handler requires the event,
<xref linkend='XtRemoveEventHandler' xrefstyle='select: title'/>
calls
<function>XSelectInput</function>.
If the specified procedure has not been registered
or if it has been registered with a different value of <emphasis remap='I'>client_data</emphasis>,
<xref linkend='XtRemoveEventHandler' xrefstyle='select: title'/>
returns without reporting an error.
</para>

<para>
To stop a procedure registered with
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>
from receiving all selected events, call
<xref linkend='XtRemoveEventHandler' xrefstyle='select: title'/>
with an <emphasis remap='I'>event_mask</emphasis> of
<function>XtAllEvents</function>
and <emphasis remap='I'>nonmaskable</emphasis>
<function>True</function>.
The procedure will continue to receive any events
that have been specified in calls to
<xref linkend='XtAddRawEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>.
</para>

<para>
To register an event handler procedure that receives events before or
after all previously registered event handlers, use
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>.
</para>
<programlisting>
typedef enum {XtListHead, XtListTail} XtListPosition;
</programlisting>

<funcsynopsis id='XtInsertEventHandler'>
<funcprototype>
<funcdef>void <function>XtInsertEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XtListPosition <parameter>position</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to call this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
called on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the client's event handler.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>position</emphasis>
    </term>
    <listitem>
      <para>
Specifies when the event handler is to be called
relative to other previously registered handlers.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>
is identical to
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
with the additional <emphasis remap='I'>position</emphasis> argument.  If <emphasis remap='I'>position</emphasis> is
<function>XtListHead</function>,
the event
handler is registered so that it is called before any event
handlers that were previously registered for the same widget.  If
<emphasis remap='I'>position</emphasis> is
<function>XtListTail</function>,
the event handler is registered to be called
after any previously registered event handlers.  If the procedure is
already registered with the same <emphasis remap='I'>client_data</emphasis> value, the specified mask
augments the existing mask and the procedure is repositioned in
the list.
</para>
</sect2>

<sect2 id="Event_Handlers_That_Do_Not_Select_Events">
<title>Event Handlers That Do Not Select Events</title>
<para>
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
<xref linkend='XtAddRawEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAddRawEventHandler'>
<funcprototype>
<funcdef>void <function>XtAddRawEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to call this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
called on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be called.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the client's event handler.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtAddRawEventHandler' xrefstyle='select: title'/>
function is similar to
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
except that it does not affect the widget's event mask and never causes an
<function>XSelectInput</function>
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 <emphasis remap='I'>client_data</emphasis>,
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.
</para>

<para>
To remove a previously registered raw event handler, use
<xref linkend='XtRemoveRawEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveRawEventHandler'>
<funcprototype>
<funcdef>void <function>XtRemoveRawEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this procedure is registered.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to unregister this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
removed on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the registered client data.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveRawEventHandler' xrefstyle='select: title'/>
function unregisters an event handler registered with
<xref linkend='XtAddRawEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>
for the specified events without changing
the window event mask.
The request is ignored if <emphasis remap='I'>client_data</emphasis> 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 <emphasis remap='I'>client_data</emphasis>,
<xref linkend='XtRemoveRawEventHandler' xrefstyle='select: title'/>
returns without reporting an error.
</para>

<para>
To stop a procedure
registered with
<xref linkend='XtAddRawEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>
from receiving all nonselected events, call
<xref linkend='XtRemoveRawEventHandler' xrefstyle='select: title'/>
with an <emphasis remap='I'>event_mask</emphasis> of
<function>XtAllEvents</function>
and <emphasis remap='I'>nonmaskable</emphasis>
<function>True</function>.
The procedure
will continue to receive any events that have been specified in calls to
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
or
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>.
</para>

<para>
To register an event handler procedure that receives events before or
after all previously registered event handlers without selecting for
the events, use
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtInsertRawEventHandler'>
<funcprototype>
<funcdef>void <function>XtInsertRawEventHandler</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
   <paramdef>EventMask <parameter>event_mask</parameter></paramdef>
   <paramdef>Boolean <parameter>nonmaskable</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XtListPosition <parameter>position</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_mask</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event mask for which to call this procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>nonmaskable</emphasis>
    </term>
    <listitem>
      <para>
Specifies whether this procedure should be
called on the nonmaskable events
<function>( GraphicsExpose</function>,
<function>NoExpose</function>,
<function>SelectionClear</function>,
<function>SelectionRequest</function>,
<function>SelectionNotify</function>,
<function>ClientMessage</function>,
and
<function>MappingNotify ).</function>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the procedure to be registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the client's event handler.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>position</emphasis>
    </term>
    <listitem>
      <para>
Specifies when the event handler is to be called
relative to other previously registered handlers.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>
function is similar to
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>
except that it does not modify the widget's event
mask and never causes an
<function>XSelectInput</function>
for the specified events.  If
the procedure is already registered with the same <emphasis remap='I'>client_data</emphasis>
value, the
specified mask augments the existing mask and the procedure is
repositioned in the list.
</para>
</sect2>

<sect2 id="Current_Event_Mask">
<title>Current Event Mask</title>
<para>
To retrieve the event mask for a given widget, use
<xref linkend='XtBuildEventMask' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtBuildEventMask'>
<funcprototype>
<funcdef>EventMask <function>XtBuildEventMask</function></funcdef>
   <paramdef>Widget <parameter>w</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>w</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget.  Must be of class Core or any subclass thereof.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtBuildEventMask' xrefstyle='select: title'/>
function returns the event mask representing the logical OR
of all event masks for event handlers registered on the widget with
<xref linkend='XtAddEventHandler' xrefstyle='select: title'/>
and
<xref linkend='XtInsertEventHandler' xrefstyle='select: title'/>
and all event translations, including accelerators,
installed on the widget.
This is the same event mask stored into the
<function>XSetWindowAttributes</function>
structure by
<xref linkend='XtRealizeWidget' xrefstyle='select: title'/>
and sent to the server when event handlers and translations are installed or
removed on the realized widget.
</para>
</sect2>

<sect2 id="Event_Handlers_for_X_Protocol_Extensions">
<title>Event Handlers for X11 Protocol Extensions</title>
<para>
To register an event handler procedure with the Intrinsics dispatch
mechanism according to an event type, use
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtInsertEventTypeHandler'>
<funcprototype>
<funcdef>void <function>XtInsertEventTypeHandler</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>int <parameter>event_type</parameter></paramdef>
   <paramdef>XtPointer <parameter>select_data</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
   <paramdef>XtListPosition <parameter>position</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which this event handler is being registered.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_type</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event type for which to call this event handler.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>select_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies data used to request events of the specified type from the server,
or NULL.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event handler to be called.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the event handler.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>position</emphasis>
    </term>
    <listitem>
      <para>
Specifies when the event handler is to be called relative to other
previously registered handlers.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>
registers a procedure with the
dispatch mechanism that is to be called when an event that matches the
specified <emphasis remap='I'>event_type</emphasis> is dispatched to the specified <emphasis remap='I'>widget</emphasis>.
</para>

<para>
If <emphasis remap='I'>event_type</emphasis> specifies one of the core X protocol events, then
<emphasis remap='I'>select_data</emphasis> must be a pointer to a value of type
<function>EventMask</function>,
indicating
the event mask to be used to select for the desired event.  This event
mask is included in the value returned by
<xref linkend='XtBuildEventMask' xrefstyle='select: title'/>.
If the widget is realized,
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>
calls
<function>XSelectInput</function>
if necessary.  Specifying NULL for <emphasis remap='I'>select_data</emphasis> is equivalent to
specifying a pointer to an event mask containing 0.  This is similar
to the
<xref linkend='XtInsertRawEventHandler' xrefstyle='select: title'/>
function.
</para>

<para>
If <emphasis remap='I'>event_type</emphasis> specifies an extension event type, then the semantics of
the data pointed to by <emphasis remap='I'>select_data</emphasis> are defined by the extension
selector registered for the specified event type.
</para>

<para>
In either case the Intrinsics are not required to copy the data
pointed to by <emphasis remap='I'>select_data</emphasis>, so the caller must ensure that it remains
valid as long as the event handler remains registered with this value
of <emphasis remap='I'>select_data</emphasis>.
</para>

<para>
The <emphasis remap='I'>position</emphasis> 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
<function>XtListTail</function>,
which registers this event handler after any previously
registered handlers for this event type.
</para>

<para>
Each widget has a single registered event handler list, which will
contain any procedure/client_data pair exactly once if it is
registered with
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>,
regardless of the manner
in which it is registered and regardless of the value(s)
of <emphasis remap='I'>select_data</emphasis>.  If the procedure is already registered with the
same <emphasis remap='I'>client_data</emphasis> value, the specified mask augments the existing
mask and the procedure is repositioned in the list.
</para>

<para>
To remove an event handler registered with
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>,
use
<xref linkend='XtRemoveEventTypeHandler' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRemoveEventTypeHandler'>
<funcprototype>
<funcdef>void <function>XtRemoveEventTypeHandler</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>int <parameter>event_type</parameter></paramdef>
   <paramdef>XtPointer <parameter>select_data</parameter></paramdef>
   <paramdef>XtEventHandler <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget for which the event handler was registered.  Must be of class Core or any subclass thereof.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_type</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event type for which the handler was registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>select_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies data used to deselect events of the specified type
from the server, or NULL.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event handler to be removed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the additional client data with which the procedure was registered.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRemoveEventTypeHandler' xrefstyle='select: title'/>
function unregisters an event handler
registered with
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>
for the specified event type.
The request is ignored if <emphasis remap='I'>client_data</emphasis> does not match the value given
when the handler was registered.
</para>

<para>
If <emphasis remap='I'>event_type</emphasis> specifies one of the core X protocol events,
<emphasis remap='I'>select_data</emphasis> must be a pointer to a value of type
<function>EventMask, indicating the event</function>
mask to be used to deselect for the appropriate event.  If the widget
is realized,
<xref linkend='XtRemoveEventTypeHandler' xrefstyle='select: title'/>
calls
<function>XSelectInput</function>
if necessary.
Specifying NULL for <emphasis remap='I'>select_data</emphasis> is equivalent to specifying a pointer
to an event mask containing 0.  This is similar to the
<xref linkend='XtRemoveRawEventHandler' xrefstyle='select: title'/>
function.
</para>

<para>
If <emphasis remap='I'>event_type</emphasis> specifies an extension event type, then the semantics of
the data pointed to by <emphasis remap='I'>select_data</emphasis> are defined by the extension
selector registered for the specified event type.
</para>

<para>
To register a procedure to select extension events for a widget, use
<xref linkend='XtRegisterExtensionSelector' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtRegisterExtensionSelector'>
<funcprototype>
<funcdef>void <function>XtRegisterExtensionSelector</function></funcdef>
   <paramdef>Display *<parameter>display</parameter></paramdef>
   <paramdef>int <parameter>min_event_type</parameter></paramdef>
   <paramdef>int <parameter>max_event_type</parameter></paramdef>
   <paramdef>XtExtensionSelectProc <parameter>proc</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the display for which the extension selector is to be registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>min_event_type</emphasis>
    </term>
    <listitem>
      <para></para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>max_event_type</emphasis>
    </term>
    <listitem>
      <para>
Specifies the range of event types for the extension.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the extension selector procedure.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies additional data to be passed to the extension selector.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtRegisterExtensionSelector' xrefstyle='select: title'/>
function registers a procedure to arrange
for the delivery of extension events to widgets.
</para>

<para>
If <emphasis remap='I'>min_event_type</emphasis> and <emphasis remap='I'>max_event_type</emphasis> match the parameters
to a previous call to
<xref linkend='XtRegisterExtensionSelector' xrefstyle='select: title'/>
for the same <emphasis remap='I'>display</emphasis>, then <emphasis remap='I'>proc</emphasis> and <emphasis remap='I'>client_data</emphasis>
replace the previously
registered values.  If the range specified by <emphasis remap='I'>min_event_type</emphasis>
and <emphasis remap='I'>max_event_type</emphasis> overlaps the range of the parameters to a
previous call for the same display in any other way, an error results.
</para>

<para>
When a widget is realized,
after the <emphasis remap='I'>core.realize</emphasis> method is called,
the Intrinsics check to see if any event
handler specifies an event type within the range of a registered
extension selector.  If so, the Intrinsics call each such selector.
If an event type handler is added or removed, the Intrinsics 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 Intrinsics
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.
</para>

<para>
An extension selector is of type
<xref linkend='XtExtensionSelectProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtExtensionSelectProc'>
<funcprototype>
<funcdef>typedef void <function>(*XtExtensionSelectProc)</function></funcdef>

   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>int *<parameter>event_types</parameter></paramdef>
   <paramdef>XtPointer *<parameter>select_data</parameter></paramdef>
   <paramdef>int <parameter>count</parameter></paramdef>
   <paramdef>XtPointer <parameter>client_data</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget that is being realized or is having
an event handler added or removed.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_types</emphasis>
    </term>
    <listitem>
      <para>
Specifies a list of event types that the widget has
registered event handlers for.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>select_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies a list of the select_data parameters specified in
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>count</emphasis>
    </term>
    <listitem>
      <para>
Specifies the number of entries in the <emphasis remap='I'>event_types</emphasis> and <emphasis remap='I'>select_data</emphasis>
lists.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>client_data</emphasis>
    </term>
    <listitem>
      <para>
Specifies the additional client data with which the procedure was registered.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The <emphasis remap='I'>event_types</emphasis> and <emphasis remap='I'>select_data</emphasis> lists will always have the
same number of elements, specified by <emphasis remap='I'>count</emphasis>.
Each event type/select data pair represents one call to
<xref linkend='XtInsertEventTypeHandler' xrefstyle='select: title'/>.
</para>

<para>
To register a procedure to dispatch events of a specific type within
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>,
use
<xref linkend='XtSetEventDispatcher' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtSetEventDispatcher'>
<funcprototype>
<funcdef>XtEventDispatchProc <function>XtSetEventDispatcher</function></funcdef>
   <paramdef>Display *<parameter>display</parameter></paramdef>
   <paramdef>int <parameter>event_type</parameter></paramdef>
   <paramdef>XtEventDispatchProc <parameter>proc</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>display</emphasis>
    </term>
    <listitem>
      <para>
Specifies the display for which the event dispatcher is to be registered.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event_type</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event type for which the dispatcher should be invoked.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>proc</emphasis>
    </term>
    <listitem>
      <para>
Specifies the event dispatcher procedure.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtSetEventDispatcher' xrefstyle='select: title'/>
function registers the event dispatcher procedure specified by <emphasis remap='I'>proc</emphasis>
for events with the type <emphasis remap='I'>event_type</emphasis>.  The previously registered
dispatcher (or the default dispatcher if there was no previously registered
dispatcher) is returned.  If <emphasis remap='I'>proc</emphasis> is NULL, the default procedure is
restored for the specified type.
</para>

<para>
In the future, when
<xref linkend='XtDispatchEvent' xrefstyle='select: title'/>
is called with an event type of <emphasis remap='I'>event_type</emphasis>, the specified <emphasis remap='I'>proc</emphasis>
(or the default dispatcher) is invoked to determine a widget
to which to dispatch the event.
</para>

<para>
The default dispatcher handles the Intrinsics modal cascade and keyboard
focus mechanisms, handles the semantics of <emphasis remap='I'>compress_enterleave</emphasis>
and <emphasis remap='I'>compress_motion</emphasis>, and discards all extension events.
</para>

<para>
An event dispatcher procedure pointer is of type
<xref linkend='XtEventDispatchProc' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtEventDispatchProc'>
<funcprototype>
<funcdef>typedef Boolean <function>(*XtEventDispatchProc)</function></funcdef>
   <paramdef>XEvent *<parameter>event</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>event</emphasis>
    </term>
    <listitem>
      <para>
Passes the event to be dispatched.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The event dispatcher procedure should determine whether this event is of
a type that should be dispatched to a widget.
</para>

<para>
If the event should be dispatched to a widget, the event dispatcher
procedure should determine the appropriate widget to receive the
event, call
<function>XFilterEvent</function>
with the window of this widget, or
<function>None</function>
if the event is to be discarded, and if
<function>XFilterEvent</function>
returns
<function>False</function>,
dispatch the event to the widget using
<xref linkend='XtDispatchEventToWidget' xrefstyle='select: title'/>.
The procedure should return
<function>True</function>
if either
<function>XFilterEvent</function>
or
<xref linkend='XtDispatchEventToWidget' xrefstyle='select: title'/>
returned
<function>True</function>
and
<function>False</function>
otherwise.
</para>

<para>
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
<function>True</function>
if it successfully dispatched the event and
<function>False</function>
otherwise.
</para>

<para>
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
<xref linkend='XtGetKeyboardFocusWidget' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtGetKeyboardFocusWidget'>
<funcprototype>
<funcdef>Widget <function>XtGetKeyboardFocusWidget</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to get forwarding information for.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtGetKeyboardFocusWidget' xrefstyle='select: title'/>
function returns the widget that would be the end result of keyboard
event forwarding for a keyboard event for the specified widget.
</para>

<para>
To dispatch an event to a specified widget, use
<xref linkend='XtDispatchEventToWidget' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtDispatchEventToWidget'>
<funcprototype>
<funcdef>Boolean <function>XtDispatchEventToWidget</function></funcdef>
   <paramdef>Widget <parameter>widget</parameter></paramdef>
   <paramdef>XEvent *<parameter>event</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>widget</emphasis>
    </term>
    <listitem>
      <para>
Specifies the widget to which to dispatch the event.
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis remap='I'>event</emphasis>
    </term>
    <listitem>
      <para>
Specifies a pointer to the event to be dispatched.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
The
<xref linkend='XtDispatchEventToWidget' xrefstyle='select: title'/>
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 <emphasis remap='I'>continue_to_dispatch</emphasis>
value returned by each handler.
The Intrinsics behave as if event handlers were registered at the head
of the list for
<function>Expose</function>,
<function>NoExpose</function>,
<function>GraphicsExpose</function>,
and
<function>VisibilityNotify</function>
events to invoke the widget's expose procedure according to the exposure
compression rules and to update the widget's <emphasis remap='I'>visible</emphasis> field
if <emphasis remap='I'>visible_interest</emphasis> is
<function>True</function>.
These internal event handlers never set <emphasis remap='I'>continue_to_dispatch</emphasis> to
<function>False</function>.
</para>

<para>
<xref linkend='XtDispatchEventToWidget' xrefstyle='select: title'/>
returns
<function>True</function>
if any event handler was called and
<function>False</function>
otherwise.
</para>
</sect2>
</sect1>

<sect1 id="Using_the_Intrinsics_in_a_Multi_Threaded_Environment">
<title>Using the Intrinsics in a Multi-Threaded Environment</title>
<para>
The Intrinsics may be used in environments that offer multiple threads
of execution within the context of a single process.  A multi-threaded
application using the Intrinsics must explicitly initialize the toolkit
for mutually exclusive access by calling
<xref linkend='XtToolkitThreadInitialize' xrefstyle='select: title'/>.
</para>
<sect2 id="Initializing_a_Multi_Threaded_Intrinsics_Application">
<title>Initializing a Multi-Threaded Intrinsics Application</title>
<para>
To test and initialize Intrinsics support for mutually exclusive thread
access, call
<xref linkend='XtToolkitThreadInitialize' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtToolkitThreadInitialize'>
<funcprototype>
<funcdef>Boolean <function>XtToolkitThreadInitialize</function></funcdef>
   <paramdef><parameter>void</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<xref linkend='XtToolkitThreadInitialize' xrefstyle='select: title'/>
returns <function>True</function> if the Intrinsics support mutually exclusive thread
access, otherwise it returns <function>False</function>. <xref linkend='XtToolkitThreadInitialize' xrefstyle='select: title'/>
must be called before
<xref linkend='XtCreateApplicationContext' xrefstyle='select: title'/>,
<xref linkend='XtAppInitialize' xrefstyle='select: title'/>,
<xref linkend='XtOpenApplication' xrefstyle='select: title'/>,
or
<function>XtSetLanguageProc</function>
is called. <xref linkend='XtToolkitThreadInitialize' xrefstyle='select: title'/> may be called more than once;
however, the application writer must ensure that it is not called
simultaneously by two or more threads.
</para>
</sect2>

<sect2 id="Locking_tk_Data_Structures">
<title>Locking X Toolkit Data Structures</title>
<para>
The Intrinsics 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 Intrinsics process
global data.
</para>

<para>
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.
</para>

<para>
Most application writers will have little need to use locking as the
Intrinsics 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:
</para>
<programlisting>
        ...
        XtAppLock(app_context);
        XtCvtStringToPixel(dpy, args, num_args, fromVal, toVal, closure_ret);
        XtAppUnlock(app_context);
        ...
</programlisting>
<para>
When the application relies upon
<xref linkend='XtConvertAndStore' xrefstyle='select: title'/>
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.
</para>

<para>
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:
</para>
<programlisting>
#include &lt;X11/CoreP.h&gt;
Boolean BeingDestroyed (Widget widget)
{
        Boolean ret;
        XtAppLock(XtWidgetToApplicationContext(widget));
        ret = widget-&gt;core.being_destroyed;
        XtAppUnlock(XtWidgetToApplicationContext(widget));
        return ret;
}
</programlisting>
<para>
A client that wishes to atomically call two or more Intrinsics functions
must lock the application context.  For example:
</para>
<programlisting>
        ...
        XtAppLock(XtWidgetToApplicationContext(widget));
        XtUnmanageChild (widget1);
        XtManageChild (widget2);
        XtAppUnlock(XtWidgetToApplicationContext(widget));
        ...
</programlisting>
<sect3 id="Locking_the_Application_Context">
<title>Locking the Application Context</title>
<para>
To ensure mutual exclusion of application context, display, or
widget internal state, use
<function>XtAppLock.</function>
</para>

<funcsynopsis id='XtAppLock'>
<funcprototype>
<funcdef>void <function>XtAppLock</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context to lock.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtAppLock' xrefstyle='select: title'/> 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.
</para>

<para>
To unlock a locked application context, use
<function>XtAppUnlock.</function>
</para>

<funcsynopsis id='XtAppUnlock'>
<funcprototype>
<funcdef>void <function>XtAppUnlock</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context that was previously locked.
    </para>
  </listitem>
  </varlistentry>
</variablelist>


</sect3>
<sect3 id="Locking_the_Process">
<title>Locking the Process</title>
<para>
To ensure mutual exclusion of X Toolkit process global data, a
widget writer must use
<function>XtProcessLock.</function>
</para>

<funcsynopsis id='XtProcessLock'>
<funcprototype>
<funcdef>void <function>XtProcessLock</function></funcdef>
   <paramdef><parameter>void</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<xref linkend='XtProcessLock' xrefstyle='select: title'/> blocks until it is able to acquire the lock.
Widget writers may use XtProcessLock to guarantee mutually exclusive
access to widget static data.
</para>

<para>
To unlock a locked process, use
<xref linkend='XtProcessUnlock' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtProcessUnlock'>
<funcprototype>
<funcdef>void <function>XtProcessUnlock</function></funcdef>
   <paramdef><parameter>void</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
To lock both an application context and the process at the same
time, call
<xref linkend='XtAppLock' xrefstyle='select: title'/>
first and then
<xref linkend='XtProcessLock' xrefstyle='select: title'/>.
To release both locks, call
<xref linkend='XtProcessUnlock' xrefstyle='select: title'/>
first and then
<xref linkend='XtAppUnlock' xrefstyle='select: title'/>.
The order is important to avoid deadlock.
</para>
</sect3>
</sect2>

<sect2 id="Event_Management_in_a_Multi_Threaded_Environment">
<title>Event Management in a Multi-Threaded Environment</title>
<para>
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.
</para>

<para>
To indicate that the event loop should terminate after the current
event dispatch has completed, use
<xref linkend='XtAppSetExitFlag' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppSetExitFlag'>
<funcprototype>
<funcdef>void <function>XtAppSetExitFlag</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtAppMainLoop' xrefstyle='select: title'/>
tests the value of the flag and will return if the flag is <function>True</function>.
</para>

<para>
Application writers who implement their own main loop may test the
value of the exit flag with
<xref linkend='XtAppGetExitFlag' xrefstyle='select: title'/>.
</para>

<funcsynopsis id='XtAppGetExitFlag'>
<funcprototype>
<funcdef>Boolean <function>XtAppGetExitFlag</function></funcdef>
   <paramdef>XtAppContext <parameter>app_context</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<variablelist>
  <varlistentry>
    <term>
      <emphasis remap='I'>app_context</emphasis>
    </term>
    <listitem>
      <para>
Specifies the application context.
    </para>
  </listitem>
  </varlistentry>
</variablelist>

<para>
<xref linkend='XtAppGetExitFlag' xrefstyle='select: title'/>
will normally return <function>False</function>, indicating that event processing
may continue.  When
<xref linkend='XtAppGetExitFlag' xrefstyle='select: title'/>
returns <function>True</function>, the loop must terminate and return to the caller,
which might then destroy the application context.
</para>

<para>
Application writers should be aware that, if a thread is blocked in
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>,
or
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>
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 &ldquo;noticed&rdquo; by the blocked thread.  Any new sources are
&ldquo;noticed&rdquo; the next time one of these functions is called.
</para>

<para>
The Intrinsics manage access to events on a last-in, first-out basis.  If
multiple threads in the same application context block in
<xref linkend='XtAppNextEvent' xrefstyle='select: title'/>,
<xref linkend='XtAppPeekEvent' xrefstyle='select: title'/>,
or
<xref linkend='XtAppProcessEvent' xrefstyle='select: title'/>,
the last thread to call one of these functions is the first
thread to return.
</para>
</sect2>
</sect1>
</chapter>