XkbApplyCompatMapToKey essentially performs the operation
described in Core Keyboard Mapping to Xkb Keyboard Mapping Transformation to
a specific key. This updates the behavior, actions, repeat status, and
virtual modifier bindings of the key.
Core Keyboard Mapping to Xkb Keyboard Mapping
Transformation
When a core protocol keyboard mapping request is received by the
server, the server's core keyboard map is updated, and then the Xkb map
maintained by the server is updated. Because a client may have explicitly
configured some of the Xkb keyboard mapping in the server, this automatic
regeneration of the Xkb keyboard mapping from the core protocol keyboard
mapping should not modify any components of the Xkb keyboard mapping that
were explicitly set by a client. The client must set explicit override
controls to prevent this from happening (see Explicit Components-Avoiding
Automatic Remapping by the Server). The core-to-Xkb mapping is done as
follows:
Explicit Components-Avoiding Automatic Remapping by the
Server
Whenever a client remaps the keyboard using core protocol
requests, Xkb examines the map to determine likely default values for the
components that cannot be specified using the core protocol.
This automatic remapping might replace definitions explicitly
requested by an application, so the Xkb keyboard description defines an
explicit components mask for each key. Any aspects of the automatic
remapping listed in the explicit components mask for a key are not changed
by the automatic keyboard mapping.
The explicit components masks are held in the explicit
field of the server map, which is an array indexed by keycode. Each entry in
this array is a mask that is a bitwise inclusive OR of the values shown in
Table 1.
Table 1 Explicit Component
Masks |
Bit in Explicit Mask |
Value |
Protects Against |
ExplicitKeyType1 |
(1<<0) |
Automatic determination of the key type associated with Group1. |
ExplicitKeyType2 |
(1<<1) |
Automatic determination of the key type associated with Group2. |
ExplicitKeyType3 |
(1<<2) |
Automatic determination of the key type associated with Group3. |
ExplicitKeyType4 |
(1<<3) |
Automatic determination of the key type associated with Group4. |
ExplicitInterpret |
(1<<4) |
Application of any of the fields of a symbol interpretation to the key
in question. |
ExplicitAutoRepeat |
(1<<5) |
Automatic determination of auto-repeat status for the key, as specified
in a symbol interpretation. |
ExplicitBehavior |
(1<<6) |
Automatic assignment of the XkbKB_Lock behavior to the key, if the
XkbSI_LockingKey flag is set in a symbol interpretation. |
ExplicitVModMap |
(1<<7) |
Automatic determination of the virtual modifier map for the key based on
the actions assigned to the key and the symbol interpretations that match
the key. |
- 1.
- Map the symbols from the keys in the core keyboard map to groups and
symbols on keys in the Xkb keyboard map. The core keyboard mapping is of
fixed width, so each key in the core mapping has the same number of
symbols associated with it. The Xkb mapping allows a different number of
symbols to be associated with each key; those symbols may be divided into
a different number of groups (1-4) for each key. For each key, this
process therefore involves partitioning the fixed number of symbols from
the core mapping into a set of variable-length groups with a variable
number of symbols in each group. For example, if the core protocol map is
of width five, the partition for one key might result in one group with
two symbols and another with three symbols. A different key might result
in two groups with two symbols plus a third group with one symbol. The
core protocol map requires at least two symbols in each of the first two
groups.
- 1a.
- For each changed key, determine the number of groups represented in the
new core keyboard map. This results in a tentative group count for each
key in the Xkb map.
- 1b.
- For each changed key, determine the number of symbols in each of the
groups found in step 1a. There is one explicit override control associated
with each of the four possible groups for each Xkb key, ExplicitKeyType1
through ExplicitKeyType4. If no explicit override control is set for a
group, the number of symbols used for that group from the core map is two.
If the explicit override control is set for a group on the key, the number
of symbols used for that Xkb group from the core map is the width of the
Xkb group with one exception: because of the core protocol requirement for
at least two symbols in each of groups one and two, the number of symbols
used for groups one and two is the maximum of 2 or the width of the Xkb
group.
- 1c.
- For each changed key, assign the symbols in the core map to the
appropriate group on the key. If the total number of symbols required by
the Xkb map for a particular key needs more symbols than the core protocol
map contains, the additional symbols are taken to be NoSymbol keysyms
appended to the end of the core set. If the core map contains more symbols
than are needed by the Xkb map, trailing symbols in the core map are
discarded. In the absence of an explicit override for group one or two,
symbols are assigned in order by group; the first symbols in the core map
are assigned to group one, in order, followed by group two, and so on. For
example, if the core map contained eight symbols per key, and a particular
Xkb map contained 2 symbols for G1 and G2 and three for G3, the symbols
would be assigned as (G is group, L is shift level):
G1L1 G1L2 G2L1 G2L2 G3L1 G3L2 G3L3
If an explicit override control is set for group one or two, the symbols are
taken from the core set in a somewhat different order. The first four
symbols from the core set are assigned to G1L1, G1L2, G2L1, G2L2,
respectively. If group one requires more symbols, they are taken next, and
then any additional symbols needed by group two. Group three and four
symbols are taken in complete sequence after group two. For example, a key
with four groups and three symbols in each group would take symbols from
the core set in the following order:
G1L1 G1L2 G2L1 G2L2 G1L3 G2L3 G3L1 G3L2 G3L3 G4L1 G4L2 G4L3
As previously noted, the core protocol map requires at lease two symbols in
groups one and two. Because of this, if an explicit override control for
an Xkb key is set and group one and / or group two is of width one, it is
not possible to generate the symbols taken from the core protocol set and
assigned to position G1L2 and / or G2L2.
- 1d.
- For each group on each changed key, assign a key type appropriate for the
symbols in the group.
- 1e.
- For each changed key, remove any empty or redundant groups.
At this point, the groups and their associated symbols have
been assigned to the corresponding key definitions in the Xkb map.
- 2.
- Apply symbol interpretations to modify key operation. This phase is
completely skipped if the ExplicitInterpret override control bit is set in
the explicit controls mask for the Xkb key (see Explicit
Components-Avoiding Automatic Remapping by the Server).
- 2a.
- For each symbol on each changed key, attempt to match the symbol and
modifiers from the Xkb map to a symbol interpretation describing how to
generate the symbol.
- 2b.
- When a match is found in step 2a, apply the symbol interpretation to
change the semantics associated with the symbol in the Xkb key map. If no
match is found, apply a default interpretation.
The symbol interpretations used in step 2 are configurable and may
be specified using XkbSymInterpretRec structures referenced by the
sym_interpret field of an XkbCompatMapRec.
Symbol Interpretations - the XkbSymInterpretRec
Structure
Symbol interpretations are used to guide the X server when it
modifies the Xkb keymap in step 2. An initial set of symbol interpretations
is loaded by the server when it starts. A client may add new ones using
XkbSetCompatMap.
Symbol interpretations result in key semantics being set. When a
symbol interpretation is applied, the following components of server key
event processing may be modified for the particular key involved:
Virtual modifier map
Auto repeat
Key behavior (may be set to XkbKB_Lock)
Key action
The XkbSymInterpretRec structure specifies a symbol interpretation:
typedef struct {
KeySym sym; /* keysym of interest or NULL */
unsigned char flags; /* XkbSI_AutoRepeat, XkbSI_LockingKey */
unsigned char match; /* specifies how mods is interpreted */
unsigned char mods; /* modifier bits, correspond to eight real modifiers */
unsigned char virtual_mod; /* 1 modifier to add to key virtual mod map */
XkbAnyAction act; /* action to bind to symbol position on key */
} XkbSymInterpretRec,*XkbSymInterpretPtr;
If sym is not NULL, it limits the symbol interpretation to keys on which that
particular keysym is selected by the modifiers matching the criteria specified
by mods and match. If sym is NULL, the interpretation may
be applied to any symbol selected on a key when the modifiers match the
criteria specified by mods and match.
match must be one of the values shown in Table 2 and
specifies how the real modifiers specified in mods are to be
interpreted.
Table 2 Symbol Interpretation
Match Criteria |
Match Criteria |
Value |
Effect |
XkbSI_NoneOf |
(0) |
None of the bits that are on in mods can be set, but other bits can
be. |
XkbSI_AnyOfOrNone |
(1) |
Zero or more of the bits that are on in mods can be set, as well as
others. |
XkbSI_AnyOf |
(2) |
One or more of the bits that are on in mods can be set, as well as any
others. |
XkbSI_AllOf |
(3) |
All of the bits that are on in mods must be set, but others may be set
as well. |
XkbSI_Exactly |
(4) |
All of the bits that are on in mods must be set, and no other bits may
be set. |
In addition to the above bits, match may contain the
XkbSI_LevelOneOnly bit, in which case the modifier match criteria specified
by mods and match applies only if sym is in level one
of its group; otherwise, mods and match are ignored and the
symbol matches a condition where no modifiers are set.
#define XkbSI_LevelOneOnly (0x80) /* use mods + match only if sym is level 1 */
If no matching symbol interpretation is found, the server uses a default
interpretation where:
sym = 0
flags = XkbSI_AutoRepeat
match = XkbSI_AnyOfOrNone
mods = 0
virtual_mod = XkbNoModifier
act = SA_NoAction
When a matching symbol interpretation is found in step 2a, the interpretation is
applied to modify the Xkb map as follows.
The act field specifies a single action to be bound to the
symbol position; any key event that selects the symbol causes the action to
be taken. Valid actions are defined in Key Actions.
If the Xkb keyboard map for the key does not have its
ExplicitVModMap control set, the XkbSI_LevelOneOnly bit and symbol position
are examined. If the XkbSI_LevelOneOnly bit is not set in match or
the symbol is in position G1L1, the virtual_mod field is examined. If
virtual_mod is not XkbNoModifier, virtual_mod specifies a
single virtual modifier to be added to the virtual modifier map for the key.
virtual_mod is specified as an index in the range [0..15].
If the matching symbol is in position G1L1 of the key, two bits in
the flags field potentially specify additional behavior modifications:
#define XkbSI_AutoRepeat (1<<0) /* key repeats if sym is in position G1L1 */
#define XkbSI_LockingKey (1<<1) /* set KB_Lock behavior if sym is in psn G1L1 */
If the Xkb keyboard map for the key does not have its ExplicitAutoRepeat control
set, its auto repeat behavior is set based on the value of the
XkbSI_AutoRepeat bit. If the XkbSI_AutoRepeat bit is set, the auto-repeat
behavior of the key is turned on; otherwise, it is turned off.
If the Xkb keyboard map for the key does not have its
ExplicitBehavior control set, its locking behavior is set based on the value
of the XkbSI_LockingKey bit. If XkbSI_LockingKey is set, the key behavior is
set to KB_Lock; otherwise, it is turned off.