specs/XKB/ch04.xml

<chapter id='xkb_events'>
<title>Xkb Events</title>

<para>
The primary way the X server communicates with clients is by sending X events
to them. Some events are sent to all clients, while others are sent only to
clients that have requested them. Some of the events that can be requested are
associated with a particular window and are only sent to those clients who have
both requested the event and specified the window in which the event occurred.
</para>


<para>
The Xkb extension uses events to communicate the keyboard status to interested
clients. These events are not associated with a particular window. Instead, all
Xkb keyboard status events are reported to all interested clients, regardless
of which window currently has the keyboard focus and regardless of the grab
state of the keyboard.<footnote><para>The one exception to this rule is the
XkbExtensionDeviceNotify event report that is sent when a client attempts to
use an unsupported feature of an X Input Extension device (see section 21.4).
</para></footnote> <!-- xref -->
</para>


<para>
The X server reports the events defined by the Xkb extension to your client
application only if you have requested them. You may request Xkb events by
calling either <emphasis>
XkbSelectEvents</emphasis>
 or <emphasis>
XkbSelectEventDetails</emphasis>
. <emphasis>
XkbSelectEvents</emphasis>
 requests Xkb events by their event type and causes them to be reported to your
client application under all circumstances. You can specify a finer granularity
for event reporting by using <emphasis>
XkbSelectEventDetails</emphasis>
; in this case events are reported only when the specific detail conditions you
specify have been met.
</para>

<sect1 id='xkb_event_types'>
<title>Xkb Event Types</title>

<para>
The Xkb Extension adds new event types to the X protocol definition. An Xkb
event type is defined by two fields in the X event data structure. One is the
<emphasis>
type</emphasis>
 field, containing the <emphasis>
base event code.</emphasis>
 This base event code is a value the X server assigns to each X extension at
runtime and thatidentifies the extension that generated the event; thus, the
event code in the <emphasis>
type</emphasis>
 field identifies the event as an Xkb extension event, rather than an event
from another extension or a core X protocol event. You can obtain the base
event code via a call to <emphasis>
XkbQueryExtension</emphasis>
 or <emphasis>
XkbOpenDisplay</emphasis>
. The second field is the Xkb event type, which contains a value uniquely
identifying each different Xkb event type. Possible values are defined by
constants declared in the header file &lt;X11/extensions/Xkb.h&gt;.
</para>


<para>
Table 4.1 lists the categories of events defined by Xkb and their associated
event types, as defined in <emphasis>
Xkb.h</emphasis>
. Each event is described in more detail in the section referenced for that
event.
</para>

<table frame='none'>
<title>Xkb Event Types</title>
<tgroup cols='4'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>Event Type</entry>
  <entry>Conditions Generating Event</entry>
  <entry>Section</entry>
  <entry>Page</entry>
</row>
</thead>
<tbody>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbNewKeyboardNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard geometry; keycode range change</para>
  </entry>
  <entry>
    <para>19</para>
  </entry>
  <entry>
    <para>187</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para>
    <emphasis>XkbMapNotify</emphasis>
    </para>
  </entry>
  <entry>
    <para>Keyboard mapping change</para>
  </entry>
  <entry>
    <para>14.4</para>
  </entry>
  <entry>
    <para>122</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbStateNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard state change</para>
  </entry>
  <entry>
    <para>5.4</para>
  </entry>
  <entry>
    <para>25</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbControlsNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard controls state change</para>
  </entry>
  <entry>
    <para>10.11</para>
  </entry>
  <entry>
    <para>79</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbIndicatorStateNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard indicators state change</para>
  </entry>
  <entry>
    <para>8.5</para>
  </entry>
  <entry>
    <para>45</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbIndicatorMapNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard indicators map change</para>
  </entry>
  <entry>
    <para>8.5</para>
  </entry>
  <entry>
    <para>45</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbNamesNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard name change</para>
  </entry>
  <entry>
    <para>18.5</para>
  </entry>
  <entry>
    <para>185</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbCompatMapNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard compatibility map change</para>
  </entry>
  <entry>
    <para>17.5</para>
  </entry>
  <entry>
    <para>178</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbBellNotify</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard bell generated</para>
  </entry>
  <entry>
    <para>9.4</para>
  </entry>
  <entry>
    <para>52</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbActionMessage</emphasis></para>
  </entry>
  <entry>
    <para>Keyboard action message</para>
  </entry>
  <entry>
    <para>16.1.11</para>
  </entry>
  <entry>
    <para>155</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbAccessXNotify</emphasis></para>
  </entry>
  <entry>
    <para>AccessX state change</para>
  </entry>
  <entry>
    <para>10.6.4</para>
  </entry>
  <entry>
    <para>65</para>
  </entry>
</row>
<row rowsep='0'>
  <entry>
    <para><emphasis>XkbExtensionDeviceNotify</emphasis></para>
  </entry>
  <entry>
    <para>Extension device change</para>
  </entry>
  <entry>
    <para>21.6</para>
  </entry>
  <entry>
    <para>207</para>
  </entry>
</row>
</tbody>
</tgroup>
</table>

</sect1>
<sect1 id='xkb_event_data_structures'>
<title>Xkb Event Data Structures</title>

<para>
Xkb reports each event it generates in a unique structure holding the data
values needed to describe the conditions the event is reporting. However, all
Xkb events have certain things in common. These common features are contained
in the same fields at the beginning of all Xkb event structures and are
described in the <emphasis>
XkbAnyEvent</emphasis>
 structure:
</para>

<para><programlisting>
typedef struct {
      int                type;        /* Xkb extension base event code */
      unsigned long      serial;      /* X server serial number for event */
      Bool               send_event;  /* <emphasis> True</emphasis> =&gt; synthetically generated */
      Display *          display;     /* server connection where event
generated */
      Time               time;        /* server time when event generated */
      int                xkb_type;    /* Xkb minor event code */
      unsigned int       device;      /* Xkb device ID, will not be
                                         <emphasis>XkbUseCoreKbd</emphasis> */
} <emphasis>XkbAnyEvent</emphasis>
;
</programlisting></para>

<para>
For any Xkb event, the <emphasis>
type</emphasis>
 field is set to the base event code for the Xkb extension, assigned by the
server to all Xkb extension events. The <emphasis>
serial</emphasis>
, <emphasis>
send_event</emphasis>
, and <emphasis>
display</emphasis>
 fields are as described for all X11 events. The <emphasis>
time</emphasis>
 field is set to the time when the event was generated and is expressed in
milliseconds. The <emphasis>
xkb_type</emphasis>
 field contains the minor extension event code, which is the extension event
type, and is one of the values listed in Table 4.1. The <emphasis>
device</emphasis>
 field contains the keyboard device identifier associated with the event. This
is never <emphasis>
XkbUseCoreKbd</emphasis>
, even if the request that generated the event specified a device of <emphasis>
XkbUseCoreKbd</emphasis>
. If the request that generated the event specified <emphasis>
XkbUseCoreKbd</emphasis>
, <emphasis>
device</emphasis>
 contains a value assigned by the server to specify the core keyboard. If the
request that generated the event specified an X input extension device,
<emphasis>
device</emphasis>
 contains that same identifier.
</para>


<para>
Other data fields specific to individual Xkb events are described in subsequent
chapters where the events are described.
</para>


</sect1>
<sect1 id='selecting_xkb_events'>
<title>Selecting Xkb Events</title>

<para>
Xkb events are selected using an event mask, much the same as normal core X
events are selected. However, unlike selecting core X events, where you must
specify the selection status (on or off) for all possible event types whenever
you wish to change the selection criteria for any one event, Xkb allows you to
restrict the specification to only the event types you wish to change. This
means that you do not need to remember the event selection values for all
possible types each time you want to change one of them.
</para>


<para>
Many Xkb event types are generated under several different circumstances. When
selecting to receive an Xkb event, you may specify either that you want it
delivered under all circumstances, or that you want it delivered only for a
subset of the possible circumstances.
</para>

<para>
You can also deselect an event type that was previously selected for, using the
same granularity.
</para>

<para>
Xkb provides two functions to select and deselect delivery of Xkb events.
<emphasis>
XkbSelectEvents</emphasis>
 allows you to select or deselect delivery of more than one Xkb event type at
once. Events selected using <emphasis>
XkbSelectEvents</emphasis>
 are delivered to your program under all circumstances that generate the
events. To restrict delivery of an event to a subset of the conditions under
which it occurs, use <emphasis>
XkbSelectEventDetails</emphasis>
. <emphasis>
XkbSelectEventDetails</emphasis>
 only allows you to change the selection conditions for a single event at a
time, but it provides a means of fine-tuning the conditions under which the
event is delivered.
</para>


<para>
To select and / or deselect for delivery of one or more Xkb events and have
them delivered under all conditions, use <emphasis>
XkbSelectEvents</emphasis>
.
</para>

<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
Bool <emphasis>
XkbSelectEvents</emphasis>
(<emphasis>
display, device_spec, bits_to_change, values_for_bits</emphasis>
)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Display *      <emphasis>
display</emphasis>
;      /* connection to the X server */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int      <emphasis>
device_spec</emphasis>
;      /* device ID, or <emphasis>
XkbUseCoreKbd</emphasis>
 */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned long int      <emphasis>
bits_to_change;      </emphasis>
/* determines events to be selected / deselected */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned long int      <emphasis>
values_for_bits</emphasis>
;      /* 1=&gt;select, 0-&gt;deselect; for events in <emphasis>
bits_to_change</emphasis>
 */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>

<para>
This request changes the Xkb event selection mask for the keyboard specified by
<emphasis>
device_spec</emphasis>
.
</para>


<para>
Each Xkb event that can be selected is represented by a bit in the <emphasis>
bits_to_change</emphasis>
 and <emphasis>
values_for_bits</emphasis>
 masks. Only the event selection bits specified by the <emphasis>
bits_to_change</emphasis>
 parameter are affected; any unspecified bits are left unchanged. To turn on
event selection for an event, set the bit for the event in the <emphasis>
bits_to_change</emphasis>
 parameter and set the corresponding bit in the <emphasis>
values_for_bits</emphasis>
 parameter. To turn off event selection for an event, set the bit for the event
in the <emphasis>
bits_to_change</emphasis>
 parameter and do not set the corresponding bit in the <emphasis>
values_for_bits</emphasis>
 parameter. The valid values for both of these parameters are an inclusive
bitwise OR of the masks shown in Table 4.2. There is no interface to return
your client’s current event selection mask. Clients cannot set other
clients’ event selection masks.
</para>


<para>
If a bit is not set in the <emphasis>
bits_to_change</emphasis>
 parameter, but the corresponding bit is set in the <emphasis>
values_for_bits</emphasis>
 parameter, a <emphasis>
BadMatch</emphasis>
 protocol error results. If an undefined bit is set in either the <emphasis>
bits_to_change</emphasis>
 or the <emphasis>
values_for_bits</emphasis>
 parameter, a <emphasis>
BadValue</emphasis>
 protocol error results.
</para>


<para>
All event selection bits are initially zero for clients using the Xkb
extension. Once you set some bits, they remain set for your client until you
clear them via another call to <emphasis>
XkbSelectEvents</emphasis>
.
</para>


<para>
<emphasis>
XkbSelectEvents</emphasis>
 returns <emphasis>
False</emphasis>
 if the Xkb extension has not been initilialized and <emphasis>
True</emphasis>
 otherwise.
</para>


<para>
To select or deselect for a specific Xkb event and optionally place conditions
on when events of that type are reported to your client, use <emphasis>
XkbSelectEventDetails</emphasis>
. This allows you to exercise a finer granularity of control over delivery of
Xkb events with <emphasis>
XkbSelectEvents</emphasis>
.
</para>


<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
Bool <emphasis>
XkbSelectEventDetails</emphasis>
(<emphasis>
display, device_spec, event_type, bits_to_change</emphasis>
, <emphasis>
values_for_bits</emphasis>
)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Display *      <emphasis>
display</emphasis>
;      /* connection to the X server */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int      <emphasis>
device_spec</emphasis>
;      /* device ID, or <emphasis>
XkbUseCoreKbd</emphasis>
 */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int      <emphasis>
event_type</emphasis>
;      /* Xkb event type of interest */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned long int      <emphasis>
bits_to_change</emphasis>
;      /* event selection details */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned long int      <emphasis>
values_for_bits</emphasis>
;      /* values for bits selected by <emphasis>
bits_to_change</emphasis>
 */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>

<para>
While <emphasis>
XkbSelectEvents</emphasis>
 allows multiple events to be selected, <emphasis>
XkbSelectEventDetails</emphasis>
 changes the selection criteria for a single type of Xkb event. The
interpretation of the <emphasis>
bits_to_change</emphasis>
 and <emphasis>
values_for_bits</emphasis>
 masks depends on the event type in question.
</para>


<para>
<emphasis>
XkbSelectEventDetails</emphasis>
 changes the Xkb event selection mask for the keyboard specified by <emphasis>
device_spec</emphasis>
 and the Xkb event specified by <emphasis>
event_type</emphasis>
. To turn on event selection for an event detail, set the bit for the detail in
the <emphasis>
bits_to_change</emphasis>
 parameter and set the corresponding bit in the <emphasis>
values_for_bits</emphasis>
 parameter. To turn off event detail selection for a detail, set the bit for
the detail in the <emphasis>
bits_to_change</emphasis>
 parameter and do not set the corresponding bit in the <emphasis>
values_for_bits</emphasis>
 parameter.
</para>


<para>
If an invalid event type is specified, a <emphasis>
BadValue</emphasis>
 protocol error results. If a bit is not set in the <emphasis>
bits_to_change</emphasis>
 parameter, but the corresponding bit is set in the <emphasis>
values_for_bits</emphasis>
 parameter, a <emphasis>
BadMatch</emphasis>
 protocol error results. If an undefined bit is set in either the <emphasis>
bits_to_change</emphasis>
 or the <emphasis>
values_for_bits</emphasis>
 parameter, a <emphasis>
BadValue</emphasis>
 protocol error results.
</para>


<para>
For each type of Xkb event, the legal event details that you can specify in the
<emphasis>
XkbSelectEventDetails</emphasis>
 request are listed in the chapters that describe each event in detail.
</para>


<sect2 id='event_masks'>
<title>Event Masks</title>

<para>
The X server reports the events defined by Xkb to your client application only
if you have requested them via a call to <emphasis>
XkbSelectEvents</emphasis>
 or <emphasis>
XkbSelectEventDetails</emphasis>
. Specify the event types in which you are interested in a mask, as described
in section 4.3.
</para>


<para>
Table 4.2 lists the event mask constants that can be specified with the  <!-- xref -->
<emphasis>
XkbSelectEvents</emphasis>
 request and the circumstances in which the mask should be specified.
</para>

<table frame='none'>
<title>XkbSelectEvents Mask Constants</title>
<tgroup cols='3'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>Event Mask</entry>
  <entry>Value</entry>
  <entry>Notification Wanted</entry>
</row>
</thead>
<tbody>
  <row rowsep='0'>
    <entry>
<emphasis>XkbNewKeyboardNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;0)</entry>
    <entry>Keyboard geometry change</entry>
  </row>
  <row rowsep='0'>
    <entry>
      <emphasis>XkbMapNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;1)</entry>
    <entry>Keyboard mapping change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<para><emphasis>XkbStateNotifyMask</emphasis></para>
    </entry>
    <entry>(1L&lt;&lt;2)</entry>
    <entry><para>Keyboard state change</para></entry>
  </row>
  <row rowsep='0'>
    <entry>
<para><emphasis>XkbControlsNotifyMask</emphasis></para>
    </entry>
    <entry>(1L&lt;&lt;3)</entry>
    <entry>Keyboard control change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbIndicatorStateNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;4)</entry>
    <entry>Keyboard indicator state change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbIndicatorMapNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;5)</entry>
    <entry>Keyboard indicator map change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbNamesNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;6)</entry>
    <entry>Keyboard name change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbCompatMapNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;7)</entry>
    <entry>Keyboard compat map change</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbBellNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;8)</entry>
    <entry>Bell</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbActionMessageMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;9)</entry>
    <entry>Action message</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbAccessXNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;10)</entry>
    <entry>AccessX features</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbExtensionDeviceNotifyMask</emphasis>
    </entry>
    <entry>(1L&lt;&lt;11)</entry>
    <entry>Extension device</entry>
  </row>
  <row rowsep='0'>
    <entry>
<emphasis>XkbAllEventsMask</emphasis>
    </entry>
    <entry>(0xFFF)</entry>
    <entry>All Xkb events</entry>
  </row>
</tbody>
</tgroup>
</table>

</sect2>
</sect1>
<sect1 id='unified_xkb_event_type'>
<title>Unified Xkb Event Type</title>

<para>
The <emphasis>
XkbEvent</emphasis>
 structure is a union of the individual structures declared for each Xkb event
type and for the core protocol <emphasis>
XEvent</emphasis>
 type. Given an <emphasis>
XkbEvent</emphasis>
 structure, you may use the <emphasis>
type</emphasis>
 field to determine if the event is an Xkb event (<emphasis>
type</emphasis>
 equals the Xkb base event code; see section 2.4). If the event is an Xkb
event, you may then use the <emphasis>
any.xkb_type</emphasis>
 field to determine the type of Xkb event and thereafter access the
event-dependent components using the union member corresponding to the
particular Xkb event type.
</para>

<para><programlisting>
typedef union _XkbEvent {
      int                            type;
      XkbAnyEvent                    any;
      XkbStateNotifyEvent            state;
      XkbMapNotifyEvent              map;
      XkbControlsNotifyEvent         ctrls;
      XkbIndicatorNotifyEvent        indicators;
      XkbBellNotifyEvent             bell;
      XkbAccessXNotifyEvent          accessx;
      XkbNamesNotifyEvent            names;
      XkbCompatMapNotifyEvent        compat;
      XkbActionMessageEvent          message;
      XkbExtensionDeviceNotifyEvent  device;
      XkbNewKeyboardNotifyEvent      new_kbd;
      XEvent                         core;
} <emphasis>XkbEvent</emphasis>;
</programlisting></para>

<para>
This unified Xkb event type includes a normal <emphasis>
XEvent</emphasis>
 as used by the core protocol, so it is straightforward for applications that
use Xkb events to call the X library event functions without having to cast
every reference. For example, to get the next event, you can simply declare a
variable of type <emphasis>
XkbEvent</emphasis>
 and call:
</para>

<para>XNextEvent(dpy,&amp;xkbev.core);</para>
</sect1>
</chapter>