NAME¶
XkbKeyAction - Returns the key action
SYNOPSIS¶
XkbAction
XkbKeyAction (XkbDescPtr xkb, KeyCode
keycode, int idx);
ARGUMENTS¶
- - xkb
- Xkb description of interest
- - keycode
- keycode of interest
- - idx
- index for group and shift level
DESCRIPTION¶
A key action defines the effect key presses and releases have on the internal
state of the server. For example, the expected key action associated with
pressing the Shift key is to set the Shift modifier. There is zero or one key
action associated with each keysym bound to each key.
Just as the entire list of key symbols for the keyboard mapping is held in the
syms field of the client map, the entire list of key actions for the
keyboard mapping is held in the
acts array of the server map. The total
size of
acts is specified by
size_acts, and the number of
entries is specified by
num_acts.
The
key_acts array, indexed by keycode, describes the actions associated
with a key. The
key_acts array has
min_key_code unused entries
at the start to allow direct indexing using a keycode. If a
key_acts
entry is zero, it means the key does not have any actions associated with it.
If an entry is not zero, the entry represents an index into the
acts
field of the server map, much as the
offset field of a KeySymMapRec
structure is an index into the
syms field of the client map.
The reason the
acts field is a linear list of XkbActions is to reduce the
memory consumption associated with a keymap. Because Xkb allows individual
keys to have multiple shift levels and a different number of groups per key, a
single two-dimensional array of KeySyms would potentially be very large and
sparse. Instead, Xkb provides a small two-dimensional array of XkbActions for
each key. To store all of these individual arrays, Xkb concatenates each array
together in the
acts field of the server map.
The key action structures consist only of fields of type char or unsigned char.
This is done to optimize data transfer when the server sends bytes over the
wire. If the fields are anything but bytes, the server has to sift through all
of the actions and swap any nonbyte fields. Because they consist of nothing
but bytes, it can just copy them out.
XkbKeyAction returns the key action indexed by
idx in the
two-dimensional array of key actions associated with the key corresponding to
keycode.idx may be computed from the group and shift level of interest
as follows:
idx = group_index * key_width + shift_level
STRUCTURES¶
The KeySymMapRec structure is defined as follows:
#define XkbNumKbdGroups 4
#define XkbMaxKbdGroup (XkbNumKbdGroups-1)
typedef struct { /∗ map to keysyms for a single keycode
*/
unsigned char kt_index[XkbNumKbdGroups]; /∗ key type index for
each group */
unsigned char group_info; /∗ # of groups and out of range group
handling */
unsigned char width; /∗ max # of shift levels for key */
unsigned short offset; /∗ index to keysym table in syms array
*/
} XkbSymMapRec, *XkbSymMapPtr;