mc/lib

Solving keyboard related problems
with XTERM
and GNU Midnight Commander
(and other programs as well).

Xterm brings a handful of problems with input keys and their translations.
Some of these problems include xterm's failure to make a difference between
shifted and not shifted function keys (many keyboards do not have more than
10 or 12 function keys, so it is useful to generate higher function keys (11
- 20) by pressing Shift and function key - 10 (e.g. Shift+F3 is F13). Xterm
also doesn't send Alt+character and Meta+character as something other than
plain character. Also, home key does not work on most systems. And keypad
operator characters (+, -, /, *) send different sequences than normal +, -,
/, * (or sometimes do not send anything).

Please note that if you want to use the Alt key on an XTerm, you have to
make sure you use:

XTerm*eightBitInput: false

Otherwise, you will just get accented keys.

Fortunately this can be solved, since xterm is written on top of the
X Toolkit Intrinsics, which has a built-in feature of event translation
tables that can be specified using X resources. This doesn't apply to rxvt,
where the only solution to this problem would be patching rxvt's sources and
recompiling. So from now on, we are speaking only about xterm (and its
modifications, like color_xterm and ansi_xterm).

Xterm brings two new Xt widgets (if you don't know what they are it doesn't
matter), vt100 and tek4014 (these are used for the terminal display in vt100
and tektronics mode). The translation table is specified in
*vt100.translations and *tek4014.translations resources.
You can see a sample in xterm.ad file in this directory.

If you want to install these translations, bear in mind that you have to
keep your terminfo and termcap in sync with these. So if you install
xterm.ad, you have to install xterm.ti and xterm.tcap (or do necessary
changes yourself).

xterm.ad has to be loaded into the Xrm (X resource manager), either by xterm
itself or by xrdb utility. There are many places you may want to install it
to; the decision is yours. Preferably it should go to your personal
$HOME/.Xdefaults file (if you have any). This file is automatically loaded
using xrdb whenever you start the X server (it is done by startx and openwin
scripts). Another possibility is to put this into
$X11ROOT/lib/X11/app-defaults/XTerm or wherever your app-defaults file of
xterm is and whatever is its name (sometimes it will have to be XTerm-ansi,
XTerm-color etc.) Or you can put this anywhere and call
xrdb xterm.ad
from any script you run on X11 startup.

xterm.ti (terminfo database source) is installed by running `tic xterm.ti'.
tic will compile it and place it into your TERMINFO directory.

xterm.tcap is the xterm (and xterm-color) termcap entry. It is based on the
newest termcap database from http://www.ccil.org/~esr/ncurses.html, but
contains a bunch of changes to make all the above mentioned keys work. Even
if mc is compiled so that it uses terminfo, you need to install the termcap
entry so that other programs which use termcap will behave correctly. You
have to edit your /etc/termcap and replace xterm and xterm-color entries
with those from xterm.tcap.

The xterm.ad translation table contains many items (some of them may be
unnecessary) but are included only to make it work on all different xterms
(xterm terminfo and termcap databases have different sequences for the same
keys in every different database, so xterm.ad works as a stardard to make
xterm.ti and termcap happy). If you find that xterm works well even if you
delete some lines from the translations, feel free to do it.

By default, Alt+character keys received by mc are generated in xterm.ad by
Alt modifier plus the key. On some systems, you may want to change this to
the Meta modifier (e.g. if the Alt modifier is missing). You do it by
replacing a letter s at the beginning of table lines with letter m.

And what you might want to know, if you are going to change anything, is:
Each line looks like
modifierskeyname: string("something") \n\
where modifiers can be:
a for alt
m for meta
c for control
button1 (2, 3) for mouse buttons.

The string is generated whenever the named key is pressed while the
modifiers are in a state matching the specification. Naming a modifier
specifies that the modifier must be pressed. A ~ in front of a modifier
name specifies that the modifier must NOT be pressed. If the set of
modifiers is preceded by !, unmentioned modifiers must not be
pressed; otherwise their state is ignored.

After you specify a name of the key (if you don't know a canonical
name of any key, see $X11ROOT/include/X11/keysymdef.h (keynames are the
names there without leading XK_). Then there can be any sequence of string
statements which send the string to the tty line, as if the user typed that
sequence of characters. If it has the form string(0xXX), where X's are
hexadecimal digits, then the ascii character of that value is sent rather
than 0xXX.

This is a subset of all the translation table features. If you want a
complete reference, see xterm(1) and X Toolkit Intrinsics manual Appendix B.

Please, if you find any problems or errors in this stuff, let me know by
e-mail to
mc-devel@gnome.org.