XkbKeyNumActions(3) - Man pages

XkbKeyNumActions(3) XKB FUNCTIONS XkbKeyNumActions(3)

NAME
XkbKeyNumActions - Computes the number of actions associated with the
key corresponding to keycode

SYNOPSIS

int XkbKeyNumActions (XkbDescPtr xkb, KeyCode keycode);

ARGUMENTS
xkb Xkb description of interest

keycode
keycode of interest

DESCRIPTION
A key action defines the effect key presses and releases have on the in-
ternal state of the server. For example, the expected key action associ-
ated 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 in-
dividual keys to have multiple shift levels and a different number of
groups per key, a single two-dimensional array of KeySyms would poten-
tially be very large and sparse. Instead, Xkb provides a small two-di-
mensional array of XkbActions for each key. To store all of these indi-
vidual 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 un-
signed 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.

XkbKeyNumActions computes the number of actions associated with the key
corresponding to keycode. This should be the same value as the result
of XkbKeyNumSyms.

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;