[Gllug] Xmodmap Help

[Nix]

[I don't believe I blew an hour on this. It's been too long since I
 did any X keyboard hacking... or my mind has gone. Probably the latter.]

On 21 Sep 2010, Krishna Birth verbalised:

> Firstly please note that all k / K letters on this posting are altered to ~
> / ~ (spiritual reasons.)

You changed the letter K to a black rectangle? Is this something to do
with the monolith from 2001?
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(Your assumption that most people on this *UK* mailing list will have
Devanagari glyphs in the fonts on their machine is unlikely to be
accurate, so both your chosen characters got replaced with the glyph for
U+FFFD REPLACEMENT CHARACTER. I had to dig around in Unicode tables just
to figure out what on earth you were trying to represent. In any case,
replacing common English characters like that is *fiercely* annoying. As
a tactic to make people not want to help you, messing with English words
by replacing individual letters with letters from other writing systems
is a superb one. You're lucky I didn't put thorns in all ?e appropriate
places in ?is response. At least ?e ?orn has deep historical roots in
English, but even it is fiercely annoying to any modern reader who
doesn't also happen to read Middle English for a hobby.)

Nonetheless I have read through the noise. I can't be nasty like that
without being nice to make up for it. Also, X keyboarding is interesting
if you have no life like me.

First, a caveat: my interest in this area lies mostly in the handling of
keyboards with unusual layouts, so while I've done quite a lot of Xkb
stuff I'm not an expert on the sort of thing you'll need for this by a
long chalk, though I do have a reasonable idea of what is and is not
possible in the X keyboard model (and I'm sorry to say that what you
suggest appears not to be possible, at least not the way you suggest).
If anyone here is more of an expert, I'm sure they'll pipe up.
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> I am sorry to thrust this project to you (mailing list).  I am loo~ing for
> advice or if you have the time to construct a ~eyboard mapping.  There seems
> to be some problem regarding "if you assign Mode_switch and ISO_Level3_Shift
> to different keys, you can assign up to six characters to one key!"
> see http://tr.opensuse.org/SDB:Using_the_Extra_Keys_on_the_Keyboard

You shouldn't be using xmodmap at all. It is obsolete, terribly limited,
and when used on systems that are already configured via Xkb (i.e. all
Linux systems you are ever likely to see) it is also incredibly
confusing because the interactions between the two configuration systems
are irregular at best and demented at worst. In particular, xmodmap
can't cope with Mode_switch very well at all, and has no understanding
of compose sequences. Peter Hutterer in
<http://who-t.blogspot.com/2010/06/keyboard-configuration-its-complicated.html>
calls it a 'keyboard deconfiguration' tool, which I think is quite
accurate: if you use it on modern systems, your keyboard is likely to
work worse after you ran it than it did before.

Unfortunately its replacement, Xkb, is not terribly well documented (in
much the same way as the sun is 'quite bright'). Again Peter Hutterer
comes through with some nice stuff:
<http://who-t.blogspot.com/2008/09/rmlvo-keyboard-configuration.html>.

Doug Palmer's _Unreliable Guide to Xkb Configuration_ at
<http://www.charvolant.org/~doug/xkb/xkb.pdf> is the only halfway decent
approach to a manual I have ever seen, but it too was written by someone
desperately trying to figure out how the thing worked. There doesn't
seem to be anything useful written by the actual implementors (and Xkb
went through at least two major generations in any case, so anything you
find about the first generation will be inaccurate, and any docs written
at the time the second generation was implemented are likely to assume
knowledge of the first!)

The XKb configuration in x.org is normally kept in /usr/share/X11/xkb,
which is itself built from datafiles in the xkeyboard-config project
<http://freedesktop.org/wiki/Software/XKeyboardConfig>. That's probably
the upstream source you should be looking at for Mode_switch et al.

(But not for compose sequences. See below.)

> The diacritics are usually typed with non-diacritic letter.   It would be
> nice to have facility to use both in convenient way e.g. toggling with a
> Fonts / Scripts ~ey by permanently turning the Caps Loc~ to a Fonts /
> Scripts ~ey.
>
> Could this be done - When this Fonts / Scripts  ~ey is pressed with a letter
> ~ey it toggles to diacritic letter 1 or 2 or  3 (depending on how many
> diacritics are there connected with a 'target' letter) - this toggling will

Yes. This sort of thing (toggling the meaning of all keys at once when
Mode_switch is hit) is indeed what Mode_switch is for. You just can't
(as far as I know) teach it how to do this with xmodmap. (And if you can,
you probably shouldn't. xmodmap is rusty and horrible.)

> need to factor in a 'remain at same spot' and toggle these diacritics
> feature.  When the Fonts / Scripts ~ey is released then the cursor would
> move to the next base.

It looks like you need Mode_switch or the Compose key or possibly both.
The Compose key lets you string together long strings of keys to produce
a single keysym: Mode_switch (and ISO_Level3_Swift) let you change the
meaning of everything on the keyboard in one fell swoop. Mode_switch is
meant to flip between e.g. writing systems; ISO_Level3_Shift is meant as
a way to provide an 'extra shift key' to flip between things within a
single writing system. (However, they *can* be used for quite different
purposes.)

You may be able to get closer to what you want with

Option "XkbLayout" "in"
Option "XkbVariant" "bolnagri"

in your InputDevice section in xorg.conf.

This keyboard layout is described here, with geometry:
<http://www.indlinux.org/wiki/index.php/BolNagri>. It may at least be a
useful starting point. (Or you may already have considered and
discounted it. I don't know.)

> Referring to the above 32 diacritics, in theory a diacritic letter  could
> have up to 7 diacritics 'sign' variations per letter:

This feels very much like a job for a (large) compose table. I don't
think Mode_switch could do it alone. (Obviously you also need a
keybinding for the compose key!)

You can easily add a compose table for your preferred language if X11
supports it by adding it to the Compose file in the appropriate
directory under /usr/share/X11/locale/ (their format is hopefully
obvious from inspection); if such a directory doesn't exist yet, you can
often start by copying the contents of one of the directories under
/usr/share/X11/locale to one named after your preferred locale, adding
that to compose.dir, and hacking at it.

If you want anyone else to be able to use these compose sequences, you
probably want to contribute them upstream, to Xlib. The Xlib upstream
lives on the xorg at lists.freedesktop.org mailing list and is generally
receptive to suggestions for keysym additions, especially if they are
real characters in living human languages, like these seem to be: adding
Klingon or Ogham characters may be a different matter. However, given
that recent X compose sequence additions included sequences for U+24B6
CIRCLED LATIN CAPITAL LETTER A (the international symbol for anarchism)
and U+1F64C PERSON RAISING BOTH HANDS IN CELEBRATION (the international
symbol for Unicode standards geeks with too much time on their hands), I
suspect that additions for your characters would be a shoo-in, although
there may be arguing about which actual compose sequences are
appropriate to generate them.

> Thus if you can turn the Caps Loc~ into a Fonts / Scripts ~ey that can allow
> up to 7 diacritics variations using this toggle approach:

The specific toggle approach you suggest is not implementable under X,
as far as I know. Mode_switch and ISO_Level3_Shift let you get as high
as four (and, with difficulty, six) symbols, but there is no way to tie
those into the keyboard in such a way as to make 'repeatedly tap' work
right. A custom input method could do it, I think, but that is even more
black magic than hacking the compose tables. Again, ask on the xorg list
(but note that the skilled X keyboard and input method hackers are
really, really busy people, and there are only about three of them, so
if you mess with all your letter k's in your mail to the xorg list, they
are almost certain to decide that it is too much trouble to read
anything you write. That's the nature of high-traffic lists, I'm
afraid.)

To me a compose sequence seems easier to remember and (much, much)
easier to implement than a custom input method. What's wrong with typing
COMPOSE L C in your preferred locale to get access to U+004C LATIN
CAPITAL LETTER L U+0310 COMBINING CANDRABINDU?

There is unfortunately no way to have compose sequences for both COMPOSE L
*and* COMPOSE L C, or it might have done what you want: but the way X
compose sequences work is that the instant an appropriate sequence is
completed, it is emitted to the app without delay, paying no attention
to the state of the compose key, so you can't have one compose sequence
be a superset of another like that. I think. But of course a lot of this
is totally undocumented, so there may well be some mysterious way to use
the X composition system to do what you want. Again, the place to ask is
the xorg list.

(Normally I'd suggest avoiding the combining diacritical marks: to this
day a lot of applications have awful support for combining characters.
However, you appear to have no choice in this case: some of the
characters you want appear only to be available in the combining form.)

> "if you assign Mode_switch and ISO_Level3_Shift to different keys, you can
> assign up to six characters to one key!"
> see http://tr.opensuse.org/SDB:Using_the_Extra_Keys_on_the_Keyboard
> Does this mean it is possible?  Could 7 characters to one ~ey be possible?

Yes, but you have to hit different keys *first* (compose, or
mode_switch, or both). It's not a matter of 'hit repeatedly'. I think
only a custom IM could do that. But, in any case, I think a compose
sequence is likely to be nicer to use anyway.

> 1. Toggle other ~eyboard mapped layouts for example, languages and
> diacritics.

Language toggling is what Mode_switch is for. It lets you flip the
definitions of potentially *every* key on the keyboard simultaneously
(actaully, it always does that, but in most keyboard maps many keys are
bound to the same thing in both modes, especially the non-alphanumeric
ones.)

> 2. Access other fonts through toggling (Fonts / Scripts ~ey + another ~ey)
> without needing going every time to the particular application's micro
> layer.

That's certainly impossible without per-application assistance. In any
case, there is no X 'change font' keysym that applications could
responds to. You could add one, but then you'd have to change all the
affected applications as well. It's a lot of work.

> It would be nice to have some person/s on board and get these things done.

The X list is without a doubt the place to go. (Or, at least, one place
to go. A list dedicated to improving X support for input in Indian
languages under X/Linux/Unix/... would probably also be useful, but I
have no idea whether any such lists exist. Probably they do, but I can't
google for them as I don't speak a single one of the likely-required
languages, being a typical English pathetic monoglot.)
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