bionic (3) XkbKeyAction.3.gz

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;