directvnc-kbmapping(7)					 Miscellaneous Information Manual				    directvnc-kbmapping(7)

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 transmit-
       ted.

       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)