Re: active strings in luatex?

[Hans Hagen <pragma@wxs.nl>]

Arthur Reutenauer wrote:
>> if i know the precise specs i can build it into the utf collapser
> 
>   I can work that out for you, but we need to think about how to treat
> all this consistently, in particular with respect to the questions Mojca
> raised:
> 
>   · Equivalent sequences need to be treated the same way (c + combining
>     caron == ccaron).
>   · If we need to compose a glyph out of other glyphs, it may be
>     accounted for by some OpenType feature (in particular GPOS 'mark'
>     and 'mkmk').
>   · If nothing else is available, the good ol' TeX way using \accent is
>     still valid, but we need to preserve the original Unicode data in
>     the PDF (for searching, etc.).

(1) mkiv already has (actually it was one of the first thing 
simplemented) an utf composition handler; this one is initialized using 
the big char table which has information about the formal composition 
sequences

an option is to add more to this (like the lcaron); fo rthose who want 
to play with it i added a command (beta upload)

\definecomposedutf 318 108 126 % lcaron

keep in mind that this acts on the input, so it may mess up definitions 
that contain l~ sequences; any input processing cq. token processing 
(later stage) is kind of dangerous

(2) it is possible (but no handy interface yet, i may make it a 
'context' font feature) to complete a font with all it's composed char 
susing virtual fotn trickery (see mk.pdf) which resolves the missing 
glyph issue

(3) letter this year (after mplib) we will pick up a 'glyph not present 
in font' callback that's on our agenda

(4) another option is to deal with it in the node list handlers, but if 
possible i want to avoid this (the more passes, the slower)

[there is already quite some framework present in mikv, but not always 
interfaced; much of this is also used in performance testing and such 
and some is reported in mk.pdf]


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