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;