xenocara/lib/libX11/man/xkb/XkbKeyAction.man

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.TH XkbKeyAction __libmansuffix__ __xorgversion__ "XKB FUNCTIONS"
.SH NAME
XkbKeyAction \-  Returns the key action
.SH SYNOPSIS
.HP
.B XkbAction XkbKeyAction
.BI "(\^XkbDescPtr " "xkb" "\^,"
.BI "KeyCode " "keycode" "\^,"
.BI "int " "idx" "\^);"
.if n .ti +5n
.if t .ti +.5i
.SH ARGUMENTS
.TP
.I \- xkb
Xkb description of interest
.TP
.I \- keycode
keycode of interest
.TP
.I \- idx
index for group and shift level
.SH DESCRIPTION
.LP
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
.I syms 
field of the client map, the entire list of key actions for the keyboard mapping 
is held in the 
.I acts 
array of the server map. The total size of 
.I acts 
is specified by 
.I size_acts, 
and the number of entries is specified by 
.I num_acts. 

The 
.I key_acts 
array, indexed by keycode, describes the actions associated with a key. The
.I key_acts 
array has 
.I min_key_code 
unused entries at the start to allow direct indexing using a keycode. If a
.I 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 
.I acts 
field of the server map, much as the 
.I offset 
field of a KeySymMapRec structure is an index into the 
.I syms 
field of the client map. 

The reason the 
.I 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 
.I 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.

.I XkbKeyAction 
returns the key action indexed by 
.I idx 
in the two-dimensional array of key actions associated with the key 
corresponding to 
.I keycode.idx 
may be computed from the group and shift level of interest as follows:
.nf

    idx = group_index * key_width + shift_level
.fi    
.SH STRUCTURES
.LP
The KeySymMapRec structure is defined as follows:
.nf

    #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;

.fi