Provided by: libx11-doc_1.6.9-2ubuntu1_all bug


       XkbKeyAction -  Returns the key action


       XkbAction XkbKeyAction (XkbDescPtr xkb, KeyCode keycode, int idx);


       - xkb  Xkb description of interest

       - keycode
              keycode of interest

       - idx  index for group and shift level


       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


       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;