specs/XKB/ch20.xml

<chapter id='server_database_of_keyboard_components'>
<title>Server Database of Keyboard Components</title>

<para>
The X server maintains a database of keyboard components, identified by
component type. The database contains all the information necessary to build a
complete keyboard description for a particular device, as well as to assemble
partial descriptions. Table 20.1 identifies the component types and the type of
information they contain.
</para>

<table frame='none'>
<title>Server Database Keyboard Components</title>
<tgroup cols='3'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>Component Type</entry>
  <entry>Component Primary Contents</entry>
  <entry>May also contain</entry>
  </row>
</thead>
<tbody>
  <row rowsep='0'>
    <entry>Keymap</entry>
    <entry>
<para>Complete keyboard description</para>
<para>Normally assembled using a complete component from each of the other types</para>
    </entry>
    <entry></entry>
  </row>
  <row rowsep='0'>
    <entry>Keycodes</entry>
    <entry>
<para>Symbolic name for each key</para>
<para>Minimum and maximum legal keycodes</para>
    </entry>
    <entry>
<para>Aliases for some keys</para>
<para>Symbolic names for indicators</para>
<para>Description of indicators physically present</para>
    </entry>
  </row>
  <row rowsep='0'>
    <entry>Types</entry>
    <entry>Key types</entry>
    <entry>
Real modifier bindings and symbolic names for some virtual modifiers
    </entry>
  </row>
  <row rowsep='0'>
    <entry>Compatibility</entry>
    <entry>Rules used to assign actions to keysyms</entry>
    <entry>
<para>Maps for some indicators</para>
<para>Real modifier bindings and symbolic names for some virtual modifiers</para>
    </entry>
  </row>
  <row rowsep='0'>
    <entry>Symbols</entry>
    <entry>
<para>Symbol mapping for keyboard keys</para>
<para>Modifier mapping</para>
<para>Symbolic names for groups</para>
    </entry>
    <entry>
<para>Explicit actions and behaviors for some keys</para>
<para>Real modifier bindings and symbolic names for some virtual modifiers</para>
    </entry>
  </row>
  <row rowsep='0'>
    <entry>Geometry</entry>
    <entry>Layout of the keyboard</entry>
    <entry>
<para>Aliases for some keys; overrides keycodes component aliases</para>
<para>Symbolic names for some indicators</para>
<para>Description of indicators physically present</para>
    </entry>
  </row>
</tbody>
</tgroup>
</table>

<para>
While a keymap is a database entry for a complete keyboard description, and
therefore logically different from the individual component database entries,
the rules for processing keymap entries are identical to those for the
individual components. In the discussion that follows, the term component is
used to refer to either individual components or a keymap.
</para>

<para>
There may be multiple entries for each of the component types. An entry may be
either <emphasis>
complete</emphasis>
 or <emphasis>
partial</emphasis>
. Partial entries describe only a piece of the corresponding keyboard component
and are designed to be combined with other entries of the same type to form a
complete entry.
</para>

<para>
For example, a partial symbols map might describe the differences between a
common ASCII keyboard and some national layout. Such a partial map is not
useful on its own because it does not include those symbols that are the same
on both the ASCII and national layouts (such as function keys). On the other
hand, this partial map can be used to configure <emphasis>
any</emphasis>
 ASCII keyboard to use a national layout.
</para>

<para>
When a keyboard description is built, the components are processed in the order
in which they appear in Table 20.1; later definitions override earlier ones.
</para>

<sect1 id='component_names'>
<title>Component Names</title>

<para>
Component names have the form "<emphasis>
class(member)</emphasis>
" where <emphasis>
class</emphasis>
 describes a subset of the available components for a particular type and the
optional <emphasis>
member</emphasis>
 identifies a specific component from that subset. For example, the name
"atlantis(acme)" for a symbols component might specify the symbols used for the
atlantis national keyboard layout by the vendor "acme." Each class has an
optional <emphasis>
default</emphasis>
 member — references that specify a class but not a member refer to the
default member of the class, if one exists. Xkb places no constraints on the
interpretation of the class and member names used in component names.
</para>

<para>
The <emphasis>
class</emphasis>
 and <emphasis>
member</emphasis>
 names are both specified using characters from the Latin-1 character set. Xkb
implementations must accept all alphanumeric characters, minus (‘-’) and
underscore (‘_’) in class or member names, and must not accept parentheses,
plus, vertical bar, percent sign, asterisk, question mark, or white space. The
use of other characters is implementation-dependent.
</para>

</sect1>
<sect1 id='listing_the_known_keyboard_components'>
<title>Listing the Known Keyboard Components</title>

<para>
You may ask the server for a list of components for one or more component
types. The request takes the form of a set of patterns, one pattern for each of
the component types, including a pattern for the complete keyboard description.
To obtain this list, use <emphasis>
XkbListComponents</emphasis>
.
</para>

<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
XkbComponentListPtr<emphasis>
 XkbListComponents</emphasis>
(<emphasis>
dpy</emphasis>
, <emphasis>
device_spec</emphasis>
, <emphasis>
ptrns</emphasis>
, <emphasis>
max_inout</emphasis>
)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Display *      <emphasis>
            dpy</emphasis>
;            /* connection to 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'>
XkbComponentNamesPtr                  <emphasis>
ptrns</emphasis>
;            /* namelist for components of interest */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
int *                  <emphasis>
max_inout</emphasis>
;            /* max # returned names, # left over */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>

<para>
<emphasis>
XkbListComponents</emphasis>
 queries the server for a list of component names matching the patterns
specified in <emphasis>
ptrns</emphasis>
. It waits for a reply and returns the matching component names in an <emphasis>
XkbComponentListRec</emphasis>
 structure. When you are done using the structure, you should free it using
<emphasis>
XkbFreeComponentList</emphasis>
. <emphasis>
device_spec</emphasis>
 indicates a particular device in which the caller is interested. A server is
allowed (but not required) to restrict its reply to portions of the database
that are relevant for that particular device.
</para>


<para>
<emphasis>
ptrns</emphasis>
 is a pointer to an <emphasis>
XkbComponentNamesRec</emphasis>
, described below. Each of the fields in <emphasis>
ptrns</emphasis>
 contains a pattern naming the components of interest. Each of the patterns is
composed of characters from the ISO <emphasis>
Latin1</emphasis>
 encoding, but can contain only parentheses, the wildcard characters
‘<emphasis>
?</emphasis>
’ and ‘<emphasis>
*</emphasis>
’, and characters permitted in a component class or member name (see section
20.1). A pattern may be <emphasis>
NULL</emphasis>
, in which case no components for that type is returned. Pattern matches with
component names are case sensitive. The ‘<emphasis>
?</emphasis>
’ wildcard matches any single character, except a left or right parenthesis;
the ‘<emphasis>
*</emphasis>
’ wildcard matches any number of characters, except a left or right
parenthesis. If an implementation allows additional characters in a component
class or member name other than those required by the Xkb extension (see
section 20.1), the result of comparing one of the additional characters to
either of the wildcard characters is implementation-dependent.
</para>


<para>
If a pattern contains illegal characters, the illegal characters are ignored.
The matching process is carried out as if the illegal characters were omitted
from the pattern.
</para>


<para>
<emphasis>
max_inout</emphasis>
 is used to throttle the amount of data passed to and from the server. On
input, it specifies the maximum number of names to be returned (the total
number of names in all component categories). Upon return from <emphasis>
XkbListComponents</emphasis>
, <emphasis>
max_inout</emphasis>
 contains the number of names that matched the request but were not returned
because of the limit.
</para>


<para>
The component name patterns used to describe the request are passed to
<emphasis>
XkbListComponents</emphasis>
 using an <emphasis>
XkbComponentNamesRec</emphasis>
 structure. This structure has no special allocation constraints or
interrelationships with other structures; allocate and free this structure
using standard <emphasis>
malloc</emphasis>
 and <emphasis>
free</emphasis>
 calls or their equivalent:
</para>

<para><programlisting>
typedef struct _XkbComponentNames {
      char *       keymap;    /* keymap names */
      char *       keycodes;  /* keycode names */
      char *       types;     /* type names */
      char *       compat;    /* compatibility map names */
      char *       symbols;   /* symbol names */
      char *       geometry;  /* geometry names */
} <emphasis>XkbComponentNamesRec</emphasis>, *XkbComponentNamesPtr;
</programlisting></para>

<para>
<emphasis>
XkbListComponents</emphasis>
 returns a pointer to an <emphasis>
XkbComponentListRec</emphasis>
:
</para>

<para><programlisting>
typedef struct _XkbComponentList {
      int                  num_keymaps;     /* number of entries in keymap */
      int                  num_keycodes;    /* number of entries in keycodes */
      int                  num_types;       /* number of entries in types */
      int                  num_compat;      /* number of entries in compat */
      int                  num_symbols;     /* number of entries in symbols */
      int                  num_geometry;    /* number of entries in geometry;
      XkbComponentNamePtr  keymap;          /* keymap names */
      XkbComponentNamePtr  keycodes;        /* keycode names */
      XkbComponentNamePtr  types;           /* type names */
      XkbComponentNamePtr  compat;          /* compatibility map names */
      XkbComponentNamePtr  symbols;         /* symbol names */
      XkbComponentNamePtr  geometry;        /* geometry names */
} <emphasis>XkbComponentListRec</emphasis>, *XkbComponentListPtr;
</programlisting></para>

<para><programlisting>
typedef struct _XkbComponentName {
      unsigned short         flags;     /* hints regarding component name */
      char *                 name;      /* name of component */
} <emphasis>XkbComponentNameRec</emphasis>, *XkbComponentNamePtr;
</programlisting></para>

<para>
Note that the structure used to specify patterns on input is an <emphasis>
XkbComponentNamesRec</emphasis>
, and that used to hold the individual component names upon return is an
<emphasis>
XkbComponentNameRec</emphasis>
 (no trailing ‘s’ in Name).
</para>


<para>
When you are done using the structure returned by <emphasis>
XkbListComponents</emphasis>
, free it using <emphasis>
XkbFreeComponentList</emphasis>
.
</para>


<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
void <emphasis>
XkbFreeComponentList</emphasis>
(list)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
XkbComponentListPtr                   list;      /* pointer to <emphasis>
XkbComponentListRec</emphasis>
 to free */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>


</sect1>
<sect1 id='component_hints'>
<title>Component Hints</title>

<para>
A set of flags is associated with each component; these flags provide
additional hints about the component’s use. These hints are designated by bit
masks in the flags field of the <emphasis>
XkbComponentNameRec</emphasis>
 structures contained in the <emphasis>
XkbComponentListRec</emphasis>
 returned from <emphasis>
XkbListComponents</emphasis>
. The least significant byte of the flags field has the same meaning for all
types of keyboard components; the interpretation of the most significant byte
is dependent on the type of component. The flags bits are defined in Table
20.2. The symbols hints in Table 20.2 apply only to partial symbols components
(those with <emphasis>
XkbLC_Partial</emphasis>
 also set); full symbols components are assumed to specify all of the pieces.
</para>


<para>
The alphanumeric, modifier, keypad or function keys symbols hints should
describe the primary intent of the component designer and should not be simply
an exhaustive list of the kinds of keys that are affected. For example,
national keyboard layouts affect primarily alphanumeric keys, but many affect a
few modifier keys as well; such mappings should set only the <emphasis>
XkbLC_AlphanumericKeys</emphasis>
 hint. In general, symbols components should set only one of the four flags
(<emphasis>
XkbLC_AlternateGroup</emphasis>
 may be combined with any of the other flags).
</para>

<table frame='none'>
<title>XkbComponentNameRec Flags Bits</title>
<tgroup cols='4'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>Component Type</entry>
  <entry>Component Hints (flags)</entry>
  <entry>Meaning</entry>
  <entry>Value</entry>
</row>
</thead>
<tbody>
<row rowsep='0'>
    <entry>All Components</entry>
    <entry><para><emphasis>XkbLC_Hidden</emphasis></para></entry>
    <entry>Do not present to user</entry>
    <entry>(1L&lt;&lt;0)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_Default</emphasis></entry>
    <entry>Default member of class</entry>
    <entry>(1L&lt;&lt;1)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_Partial</emphasis></entry>
    <entry>Partial component</entry>
    <entry>(1L&lt;&lt;2)</entry>
</row>
<row rowsep='0'>
    <entry>Keymap</entry>
    <entry>none</entry>
    <entry></entry>
    <entry></entry>
</row>
<row rowsep='0'>
    <entry>Keycodes</entry>
    <entry>none</entry>
    <entry></entry>
    <entry></entry>
</row>
<row rowsep='0'>
    <entry>Types</entry>
    <entry>none</entry>
    <entry></entry>
    <entry></entry>
</row>
<row rowsep='0'>
    <entry>Compatibility</entry>
    <entry>none</entry>
    <entry></entry>
    <entry></entry>
</row>
<row rowsep='0'>
    <entry>Symbols</entry>
    <entry><emphasis>XkbLC_AlphanumericKeys</emphasis></entry>
    <entry>Bindings primarily for alphanumeric keyboard section</entry>
    <entry>(1L&lt;&lt;8)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_ModifierKeys</emphasis></entry>
    <entry>Bindings primarily for modifier keys</entry>
    <entry>(1L&lt;&lt;9)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_KeypadKeys</emphasis></entry>
    <entry>Bindings primarily for numeric keypad keys</entry>
    <entry>(1L&lt;&lt;10)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_FunctionKeys</emphasis></entry>
    <entry>Bindings primarily for function keys</entry>
    <entry>(1L&lt;&lt;11)</entry>
</row>
<row rowsep='0'>
    <entry></entry>
    <entry><emphasis>XkbLC_AlternateGroup</emphasis></entry>
    <entry>Bindings for an alternate group</entry>
    <entry>(1L&lt;&lt;12)</entry>
</row>
<row rowsep='0'>
    <entry>Geometry</entry>
    <entry>none</entry>
    <entry></entry>
    <entry></entry>
  </row>
</tbody>
</tgroup>
</table>

</sect1>
<sect1 id='building_a_keyboard_description_using_the_server_database'>
<title>Building a Keyboard Description Using the Server Database</title>

<para>
A client may request that the server fetch one or more components from its
database and use those components to build a new server keyboard description.
The new keyboard description may be built from scratch, or it may be built
starting with the current keyboard description for a particular device. Once
the keyboard description is built, all or part of it may be returned to the
client. The parts returned to the client need not include all of the parts used
to build the description. At the time it requests the server to build a new
keyboard description, a client may also request that the server use the new
description internally to replace the current keyboard description for a
specific device, in which case the behavior of the device changes accordingly.
</para>


<para>
To build a new keyboard description from a set of named components, and to
optionally have the server use the resulting description to replace an active
one, use <emphasis>
XkbGetKeyboardByName</emphasis>
.
</para>

<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
XkbDescPtr <emphasis>
XkbGetKeyboardByName</emphasis>
(<emphasis>
dpy</emphasis>
, <emphasis>
device_spec</emphasis>
, <emphasis>
names</emphasis>
, <emphasis>
want</emphasis>
, <emphasis>
need</emphasis>
, <emphasis>
load</emphasis>
)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Display *      <emphasis>
            dpy</emphasis>
;            /* connection to 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'>
XkbComponentNamesPtr                  <emphasis>
names</emphasis>
;            /* names of components to fetch */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int                  <emphasis>
want</emphasis>
;            /* desired structures in returned record */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int                  <emphasis>
need</emphasis>
;            /* mandatory structures in returned record */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Bool                  <emphasis>
load</emphasis>
;            /* <emphasis>
True</emphasis>
 =&gt; load into <emphasis>
device_spec</emphasis>
 */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>

<para>
<emphasis>
names</emphasis>
 contains a set of expressions describing the keyboard components the server
should use to build the new keyboard description. <emphasis>
want</emphasis>
 and <emphasis>
need</emphasis>
 are bit fields describing the parts of the resulting keyboard description that
should be present in the returned <emphasis>
XkbDescRec</emphasis>
.
</para>


<para>
The individual fields in <emphasis>
names</emphasis>
 are <emphasis>
component expressions</emphasis>
 composed of keyboard component names (no wildcarding as may be used in
<emphasis>
XkbListComponents</emphasis>
), the special component name symbol ‘%’, and the special operator
characters ‘<emphasis>
+</emphasis>
’ and ‘<emphasis>
|</emphasis>
’. A component expression is parsed left to right, as follows:
</para>

<itemizedlist>
<listitem>
  <para>
The special component name "<emphasis>
computed</emphasis>
" may be used in <emphasis>
keycodes</emphasis>
 component expressions and refers to a component consisting of a set of
keycodes computed automatically by the server as needed.
  </para>
</listitem>
<listitem>
  <para>
The special component name "<emphasis>
canonical</emphasis>
" may be used in <emphasis>
types</emphasis>
 component expressions and refers to a partial component defining the four
standard key types: <emphasis>
ALPHABETIC</emphasis>
, <emphasis>
ONE_LEVEL</emphasis>
, <emphasis>
TWO_LEVEL</emphasis>
, and <emphasis>
KEYPAD</emphasis>
.
  </para>
</listitem>
<listitem>
  <para>
The special component name ‘<emphasis>
%</emphasis>
’ refers to the keyboard description for the device specified in <emphasis>
device_spec</emphasis>
 or the keymap names component. If a keymap names component is specified that
does not begin with ‘+’ or ‘|’ and does not contain ‘<emphasis>
%</emphasis>
’, then ‘<emphasis>
%</emphasis>
’ refers to the description generated by the keymap names component.
Otherwise, it refers to the keyboard description for <emphasis>
device_spec</emphasis>
.
  </para>
</listitem>
<listitem>
  <para>
The ‘<emphasis>
+</emphasis>
’ operator specifies that the following component should <emphasis>
override</emphasis>
 the currently assembled description; any definitions that are present in both
components are taken from the second.
  </para>
</listitem>
<listitem>
  <para>
The ‘<emphasis>
|</emphasis>
’ operator specifies that the next specified component should <emphasis>
augment</emphasis>
 the currently assembled description; any definitions that are present in both
components are taken from the first.
  </para>
</listitem>
<listitem>
  <para>
If the component expression begins with an operator, a leading ‘<emphasis>
%</emphasis>
’ is implied.
  </para>
</listitem>
<listitem>
  <para>
If any unknown or illegal characters appear anywhere in the expression, the
entire expression is invalid and is ignored.
  </para>
</listitem>
</itemizedlist>

<para>
For example, if <emphasis>
names-&gt;symbols</emphasis>
 contained the expression "+de", it specifies that the default member of the
"de" class of symbols should be applied to the current keyboard mapping,
overriding any existing definitions (it could also be written "+de(default)").
</para>


<para>
Here is a slightly more involved example: the expression
"acme(ascii)+de(basic)|iso9995-3" constructs a German (de) mapping for the
ASCII keyboard supplied by the "acme" vendor. The new definition begins with
the symbols for the ASCII keyboard for Acme (<emphasis>
acme(ascii)</emphasis>
), overrides them with definitions for the basic German keyboard (<emphasis>
de(basic)</emphasis>
), and then applies the definitions from the default iso9995-3 keyboard
(<emphasis>
iso9995-3</emphasis>
) to any undefined keys or groups of keys (part three of the iso9995 standard
defines a common set of bindings for the secondary group, but allows national
layouts to override those definitions where necessary).
</para>

<note><para>The interpretation of the above expression components (acme, ascii,
de, basic, iso9995-3) is not defined by Xkb; only the operations and their
ordering are.</para></note>

<para>
Note that the presence of a keymap <emphasis>
names</emphasis>
 component that does not contain ‘<emphasis>
%</emphasis>
’ (either explicit or implied by virtue of an expression starting with an
operator) indicates a description that is independent of the keyboard
description for the device specified in <emphasis>
device_spec</emphasis>
. The same is true of requests in which the keymap names component is empty and
all five other names components contain expressions void of references to
‘<emphasis>
%</emphasis>
’. Requests of this form allow you to deal with keyboard definitions
independent of any actual device.
</para>


<para>
The server parses all non-<emphasis>
NULL</emphasis>
 fields in <emphasis>
names</emphasis>
 and uses them to build a keyboard description. However, before parsing the
expressions in <emphasis>
names</emphasis>
, the server ORs the bits in <emphasis>
want</emphasis>
 and <emphasis>
need</emphasis>
 together and examines the result in relationship to the expressions in
<emphasis>
names</emphasis>
. Table 20.3 identifies the components that are required for each of the
possible bits in <emphasis>
want</emphasis>
 or <emphasis>
need</emphasis>
. If a required component has not been specified in the <emphasis>
names</emphasis>
 structure (the corresponding field is <emphasis>
NULL</emphasis>
), the server substitutes the expression "<emphasis>
%</emphasis>
", resulting in the component values being taken from <emphasis>
device_spec</emphasis>
. In addition, if <emphasis>
load</emphasis>
 is <emphasis>
True</emphasis>
, the server modifies <emphasis>
names</emphasis>
 if necessary (again using a "<emphasis>
%</emphasis>
" entry) to ensure all of the following fields are non-<emphasis>
NULL</emphasis>
: <emphasis>
types</emphasis>
, <emphasis>
keycodes</emphasis>
, <emphasis>
symbols</emphasis>
, and <emphasis>
compat</emphasis>
.<emphasis>
</emphasis>
</para>

<table frame='none'>
<title>Want and Need Mask Bits and Required Names Components</title>
<tgroup cols='3'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>want or need mask bit</entry>
  <entry>Required names Components</entry>
  <entry>value</entry>
  </row>
</thead>
<tbody>
  <row rowsep='0'>
    <entry>XkbGBN_TypesMask</entry>
    <entry>Types</entry>
    <entry>(1L&lt;&lt;0)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_CompatMapMask</entry>
    <entry>Compat</entry>
    <entry>(1L&lt;&lt;1)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_ClientSymbolsMask</entry>
    <entry>Types + Symbols + Keycodes</entry>
    <entry>(1L&lt;&lt;2)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_ServerSymbolsMask</entry>
    <entry>Types + Symbols + Keycodes</entry>
    <entry>(1L&lt;&lt;3)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_SymbolsMask</entry>
    <entry>Symbols</entry>
    <entry>(1L&lt;&lt;1)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_IndicatorMapMask</entry>
    <entry>Compat</entry>
    <entry>(1L&lt;&lt;4)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_KeyNamesMask</entry>
    <entry>Keycodes</entry>
    <entry>(1L&lt;&lt;5)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_GeometryMask</entry>
    <entry>Geometry</entry>
    <entry>(1L&lt;&lt;6)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_OtherNamesMask</entry>
    <entry>Types + Symbols + Keycodes + Compat + Geometry</entry>
    <entry>(1L&lt;&lt;7)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_AllComponentsMask</entry>
    <entry></entry>
    <entry>(0xff)</entry>
  </row>
</tbody>
</tgroup>
</table>

<para>
<emphasis>
need</emphasis>
 specifies a set of keyboard components that the server must be able to resolve
in order for <emphasis>
XkbGetKeyboardByName</emphasis>
 to succeed; if any of the components specified in <emphasis>
need</emphasis>
 cannot be successfully resolved, <emphasis>
XkbGetKeyboardByName</emphasis>
 fails.
</para>


<para>
<emphasis>
want</emphasis>
 specifies a set of keyboard components that the server should attempt to
resolve, but that are not mandatory. If the server is unable to resolve any of
these components, <emphasis>
XkbGetKeyboardByName</emphasis>
 still succeeds. Bits specified in <emphasis>
want</emphasis>
 that are also specified in <emphasis>
need</emphasis>
 have no effect in the context of <emphasis>
want</emphasis>
.
</para>


<para>
If <emphasis>
load</emphasis>
 is <emphasis>
True</emphasis>
, the server updates its keyboard description for <emphasis>
device_spec</emphasis>
 to match the result of the keyboard description just built. If load is
<emphasis>
False</emphasis>
, the server’s description for device <emphasis>
device_spec</emphasis>
 is not updated. In all cases, the parts specified by <emphasis>
want</emphasis>
 and <emphasis>
need</emphasis>
 from the just-built keyboard description are returned.
</para>


<para>
The <emphasis>
names</emphasis>
 structure in an <emphasis>
XkbDescRec</emphasis>
 keyboard description record (see Chapter 18) contains one field for each of
the five component types used to build a keyboard description. When a keyboard
description is built from a set of database components, the corresponding
fields in this <emphasis>
names</emphasis>
 structure are set to match the expressions used to build the component.
</para>


<para>
The entire process of building a new keyboard description from the server
database of components and returning all or part of it is diagrammed in Figure
20.1:
</para>

<mediaobject>
 <imageobject> <imagedata format="SVG" fileref="XKBlib-21.svg"/>
 </imageobject>
 <caption>Building a New Keyboard Description from the Server Database</caption>
</mediaobject>

<para>
The information returned to the client in the <emphasis>
XkbDescRec</emphasis>
 is essentially the result of a series of calls to extract information from a
fictitious device whose description matches the one just built. The calls
corresponding to each of the mask bits are summarized in Table 20.4, together
with the <emphasis>
XkbDescRec</emphasis>
 components that are filled in.
</para>

<table frame='none'>
<title>XkbDescRec Components Returned for Values of Want &amp; Needs</title>
<tgroup cols='3'>
<colspec colsep='0'/>
<colspec colsep='0'/>
<colspec colsep='0'/>
<thead>
<row rowsep='0'>
  <entry>Request (want+need)</entry>
  <entry>Fills in Xkb components</entry>
  <entry>Equivalent Function Call</entry>
  </row>
</thead>
<tbody>
  <row rowsep='0'>
    <entry>XkbGBN_TypesMask</entry>
    <entry>map.types</entry>
    <entry>XkbGetUpdatedMap(dpy, XkbTypesMask, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_ServerSymbolsMask</entry>
    <entry>server</entry>
    <entry>XkbGetUpdatedMap(dpy, XkbAllClientInfoMask, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_ClientSymbolsMask</entry>
    <entry>map, including map.types</entry>
    <entry>XkbGetUpdatedMap(dpy, XkbAllServerInfoMask, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_IndicatorMaps</entry>
    <entry>indicators</entry>
    <entry>XkbGetIndicatorMap(dpy, XkbAllIndicators, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_CompatMapMask</entry>
    <entry>compat</entry>
    <entry>XkbGetCompatMap(dpy, XkbAllCompatMask, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_GeometryMask</entry>
    <entry>geom</entry>
    <entry>XkbGetGeometry(dpy, Xkb)</entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_KeyNamesMask</entry>
    <entry>
<para>names.keys</para>
<para>names.key_aliases</para>
    </entry>
    <entry>
XkbGetNames(dpy, XkbKeyNamesMask | XkbKeyAliasesMask, Xkb)
    </entry>
  </row>
  <row rowsep='0'>
    <entry>XkbGBN_OtherNamesMask</entry>
    <entry>
<para>names.keycodes</para>
<para>names.geometry</para>
<para>names.symbols</para>
<para>names.types</para>
<para>map.types[*].lvl_names[*]</para>
<para>names.compat</para>
<para>names.vmods</para>
<para>names.indicators</para>
<para>names.groups</para>
<para>names.radio_groups</para>
<para>names.phys_symbols</para>
    </entry>
    <entry>
<para>XkbGetNames(dpy, XkbAllNamesMask &amp;</para>
<para>~(XkbKeyNamesMask | XkbKeyAliasesMask),</para>
<para>Xkb)</para>
    </entry>
  </row>
</tbody>
</tgroup>
</table>

<para>
There is no way to determine which components specified in <emphasis>
want</emphasis>
 (but not in <emphasis>
need</emphasis>
) were actually fetched, other than breaking the call into successive calls to
<emphasis>
XkbGetKeyboardByName</emphasis>
 and specifying individual components.
</para>


<para>
<emphasis>
XkbGetKeyboardByName</emphasis>
 always sets <emphasis>
min_key_code</emphasis>
 and <emphasis>
max_key_code</emphasis>
 in the returned <emphasis>
XkbDescRec</emphasis>
 structure.
</para>


<para>
<emphasis>XkbGetKeyboardByName</emphasis>
is synchronous; it sends the request to the server to build a new keyboard
description and waits for the reply. If successful, the return value is
non-<emphasis>NULL</emphasis>.
<emphasis>XkbGetKeyboardByName</emphasis>
generates a <emphasis>BadMatch</emphasis>
protocol error if errors are encountered when building the keyboard
description.
</para>


<para>
If you simply want to obtain information about the current keyboard device,
rather than generating a new keyboard description from elements in the server
database, use <emphasis>
XkbGetKeyboard</emphasis>
 (see section 6.2).
</para>

<informaltable frame='none'>
<tgroup cols='1'>
<colspec colsep='0'/>
<tbody>
  <row rowsep='0'>
    <entry role='functiondecl'>
XkbDescPtr <emphasis>
XkbGetKeyboard</emphasis>
(<emphasis>
dpy</emphasis>
, <emphasis>
which</emphasis>
, <emphasis>
device_spec</emphasis>
)
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
Display *      <emphasis>
      dpy</emphasis>
;            /* connection to X server */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int<emphasis>
            which</emphasis>
;            /* mask of components of <emphasis>
XkbDescRec</emphasis>
 of interest */
    </entry>
  </row>
  <row rowsep='0'>
    <entry role='functionargdecl'>
unsigned int      <emphasis>
      device_spec</emphasis>
;            /* device ID */
    </entry>
</row>
</tbody>
</tgroup>
</informaltable>

<para>
<emphasis>
XkbGetKeyboard</emphasis>
 is used to read the current description for one or more components of a
keyboard device. It calls <emphasis>
XkbGetKeyboardByName</emphasis>
 as follows:
</para>


<para>
<emphasis>
XkbGetKeyboardByName</emphasis>
(<emphasis>
dpy</emphasis>
, <emphasis>
device_spec</emphasis>
, <emphasis>
NULL</emphasis>
, <emphasis>
which</emphasis>
, <emphasis>
which</emphasis>
, <emphasis>
False</emphasis>
).
</para>

</sect1>
</chapter>