[XeTeX] Let's discuss \mathchar again

[Will Robertson]

On 12/12/2005, at 20:07 , Bruno Voisin wrote:

> Le 12 déc. 05 à 04:02, Will Robertson a écrit :
>
>> However, you've said in the past that TeX uses special TFM metrics  
>> for maths typesetting that aren't provided for in unicode fonts;  
>> is there more to this story than the extra fontdimens? Because if  
>> so, we are indeed unable to proceed.
>>
>> [...]
>>
>> Or is it all a moot point because you need voodoo in the maths  
>> font (that OpenType can't provide) to tell TeX what to do?
>
> I'm just wondering whether the STIX fonts, when finally released,  
> would answer these questions partly (being Unicode math fonts if I  
> understood correctly). But yes, you'd basically have to rewrite  
> plain TeX (and probably LaTeX as well), whose treatment of maths is  
> very deeply tied to the idiosyncratic encodings of the Computer  
> modern 7-bit math fonts. Or did the Omega people dealt with this in  
> some clever way already?
>
> As for STIX, some (postponed) target dates are finally available at  
> <http://www.stixfonts.org/>: beta March 2006, general release May  
> 2006.

The most recent update to any maths system related to TeX is  
"newmath", which provides a logical encoding for 256-glyph maths  
fonts, separated by functionality and and few other considerations.  
It's been released, and works, but no-one got around to actually  
supporting it with any fonts. (Maths fonts don't tend to be released  
that often, anyway, and older ones like lucida already had they  
packages written that hard-coded all the glyph locations.)

With newmath, it's only a matter of getting the fonts, and specifying  
the new maths family; in the same way that T1 encoding will give  
consistent text glyphs between fonts.

If I had access to unicode glyphs with \mathchar, I would attempt to  
get around to doing the same thing with maths, but at this stage I'm  
not sure at the fundamental level how TeX (and thus XeTeX) puts  
glyphs where they go in maths mode.

As far as I'm aware, only extensible delimiters and things require  
specific metric information that isn't provided by unicode; but I  
*believe* that there is no other restriction.

Then it's only a matter of wiring up the tables, like Ross has done  
with xunicode, and providing methods for easily grabbing the  
mathematical letters from the correct spot. (That is, grabbing the  
*unicode* maths characters "abc" from plain ascii "abc" input.) Both  
font mappings or regular LaTeX methods perform this job adequately. I  
suspect we'll run out of maths families, however, since every shape  
will need its own family unless we resort to writing things like  
\calA, \calB, \calC for calligraphic letters.

And all of this can be tested in the Code2001 font, which has crude  
but serviceable glyphs pretty much everywhere.

THEN, when STIX comes out, all this work will be really useful. I'm  
aware of one other big maths font project that is well on its way,  
and this is definitely where maths font technology is going to go in  
the future.

Will