NAME

       directvnc-kbmapping - Details of keyboard mapping file syntax for directvnc(1)

Xmodmap Keyboard Layout File Syntax

       General  syntax of the xmodmap keyboard layout file is described in the xmodmap(1x) manual
       page. For the purposes of keyboard switching implementation in  directvnc,  the  following
       subset of its syntax is used:

       Comments  (lines  starting  with  an exclamation mark) are recognized as such, and ignored
       Expressions using keycode are recognized with up to four keysym values, used as  described
       in the mentioned manual page Other xmodmap expressions will be ignored.  So, the following
       is a valid syntax of an xmodmap file that can  be  converted  into  a  directvnc  keyboard
       layout file:

                Key    Base     Shift          Mode               Mode+Shift

       keycode  13     = 4      dollar         4                  quotedbl
       keycode  14     = 5      percent        5                  colon
       keycode  15     = 6      asciicircum    6                  comma
       keycode  16     = 7      ampersand      7                  period
       keycode  24     = q      Q              Cyrillic_shorti    Cyrillic_SHORTI
       keycode  25     = w      W              Cyrillic_tse       Cyrillic_TSE
       keycode  26     = e      E              Cyrillic_u         Cyrillic_U
       keycode  27     = r      R              Cyrillic_ka        Cyrillic_KA

       An example of a xmodmap file for Cyrillic input can be found ????

Directvnc Keyboard Layout File Syntax

       The  xmodmap  file  uses  character  identifiers to identify keysyms that keycodes will be
       translated to. While this works in the original xmodmap program which acts as a client  to
       the  X  server  it  loads  keyboard  layout  into (xmodmap queries the X server to convert
       symbolic keysym identifiers into numeric), directvnc is not supposed to interact with  the
       remote  Xvnc  server  this  way.  Instead,  a  derivative  format  is used, which contains
       hexadecimal codes for keysyms:

       keycode 13 0x034 0x024 0x034 0x022
       keycode 14 0x035 0x025 0x035 0x03a
       keycode 15 0x036 0x05e 0x036 0x02c
       keycode 16 0x037 0x026 0x037 0x02e
       keycode 24 0x071 0x051 0x6ca 0x6ea
       keycode 25 0x077 0x057 0x6c3 0x6e3
       keycode 26 0x065 0x045 0x6d5 0x6f5
       keycode 27 0x072 0x052 0x6cb 0x6eb
       keycode 28 0x074 0x054 0x6c5 0x6e5
       keycode 29 0x079 0x059 0x6ce 0x6ee
       keycode 30 0x075 0x055 0x6c7 0x6e7

       The keycode keyword does not play any role at the moment, but is preserved for the  future
       extensions, when other xmodmap expressions may also be recognized.

Conversion From One to Another

       As  noted  above,  directvnc  does  not  query the remote Xvnc server for keysyms' numeric
       values.  There  is  the  keysymdef.h  include  file  which  contains  all  the   necessary
       information. In particular, considering this (a small portion of the keysymdef.h file):

       #define XK_Q                   0x051
       #define XK_q                   0x071
       #define XK_Cyrillic_shorti     0x6ca
       #define XK_Cyrillic_SHORTI     0x6ea

       it becomes clear how to convert

       keycode 24   = q   Q   Cyrillic_shorti   Cyrillic_SHORTI

       into

       keycode 24 0x071 0x051 0x6ca 0x6ea

       The  directvnc-xmapconv(1)  utility  reads an xmodmap syntax file from standard input, and
       writes the directvnc compatible syntax file to standard output.

       Inside, the script runs its standard  input  through  the  C  preprocessor  including  the
       keysymdef.h  file  and  prepending each keysym identifier with XK_. The directvnc keyboard
       layout file mentioned earlier was produced exactly this way out of the  xmodmap  file  for
       Cyrillic input.

Key Modifiers Logic

       The  directvnc's  keyboard  layout  switching  module  holds  an  internal table where the
       contents of the keyboard layout file is read into.  The  module  intercepts  all  keyboard
       input  obtained  from  DirectFB,  and  uses  keyboard  scan code plus 8 (also known as the
       MIN_KEYCODE constant) as index into that table to determine whether any mapping exists for
       a given keycode.

       The  directvnc's  keyboard  layout  switching module uses the ScrollLock key as mode lock:
       when its LED is on, the third or fourth keysym would  be  transmitted  (depending  on  the
       Shift  and  CapsLock  status); when Scroll lock LED is off, the first or the second keysym
       would be transmitted.

       The Alt or AltGr keys are not used to control keyboard mode.

       For letters, Shift and CapsLock are XORed. For numbers, CapsLock does not apply.

       If Ctrl is pressed, or there was no keyboard layout file specified, or the keyboard layout
       file  does  not  contain  any  mapping for a given keycode, directvnc performs its default
       translation of keyboard code into a keysym  using  its  hardcoded  ISO-8859-1  translation
       table.

SEE ALSO

       directvnc(1), directvnc-xmapconv(1), xmodmap(1)

AUTHOR

       Dimitry Golubovsky, Loris Boillet

                                           Jul 30, 2011                    directvnc-kbmapping(7)