[9fans] combining characters

[rog@vitanuova.com]

erik wrote:
> rob has suggested passing uncomposed characters to libdraw and handling
> the problem there.  but there's one problem with that.  how do you stick
> a nonspacing horn onto an arbitrary letter?  how do you put a grave accent
> on top of that?  (transliterations of cryllic to the roman alphabet use some 
> double- and triple- accented letters which do not exist in precombined form
> within unicode.)

perhaps there are actually two problems here:
1) how to get libdraw to map back from a sequence of combining characters
to a character in the font that represents that sequence.
2) how to draw sequences of combining characters that don't exist in precombined
form within unicode. it's quite possible that one might wish to provide
pre-rendered glyphs for some of these sequences - the current font format
can't deal with that.

another issue is dealing with code (e.g. libframe) that assumes that
characters do not overstrike - i.e. that there's a 1-1 correspondence
between Runes and glyphs.

yet another is how one should deal with character-based indexing, for instance
indexing in sam expressions - does /é/-#0+#1 point to the character after
the unadorned e, or after the whole sequence?

it'd be nice to sort this issue out properly; surely it shouldn't be
too hard?