Linux console fonts

[Andries.Brouwer@cwi.nl]

Tibetan is one of the many languages that do not have
all symbols available precomposed in Unicode.
(Roughly speaking, one writes syllable symbols like KA and
needs superscripted or subscripted symbols to change the vowel
and make KE,KI,KO,KU. Devanagari uses a similar system.
The principle for Arabic and Hebrew when written with
vowels is somewhat similar.)

The present Linux console font code associates a Unicode
symbol to each font element. But precomposed syllables
do not have a Unicode value.

I wonder whether people have already constructed solutions
for this type of situation.

(So, in general one needs a rendering machine that finds
which symbol is the appropriate one in the given context,
like Greek sigma has two forms depending on whether it is
word-final or not. But when this machine has decided upon
the right form to use it has to select this form from some
font, and the index cannot be a Unicode symbol in general.)

Is there a standard solution in the X world?
If this is an unsolved problem, I imagine I'll change
the format of the Unicode table attached to psf console fonts
so that it can have a sequence of Unicode values attached to
a single glyph [not as alternatives, like today, but as base
symbol followed by combining accents].
This would allow one to use the kernel as rendering machine
in all simple situations, namely where a precomposed form is
already available in the font.

It is a pity that Unicode combining accents come after instead
of before the base symbol. This means that the display routine
may have to back up and change the previously displayed symbol.


Andries

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