[XeTeX] Kerning

[Jonathan Kew]

On 19 Jun 2007, at 6:23 am, John Was wrote:

> Hello

Hello John,

> I wonder if there exists, or there are plans for, a facility to  
> modify the kerns of a Unicode and/or outline font within XeTeX  
> without specifically editing the font

It's a request that has come up a few times, in varying forms.  
There's no current work in this area (unless someone is working on a  
patch that I don't know about!), but it's something I would like to  
get to eventually. The actual design of such a feature is still open  
to suggestions...

> something like:
>
> \myfont = "Minion Pro"[:myfont.krn] at 11pt
>
> The file myfont.krn would be a list of user-defined kerns to be  
> applied to \myfont only within the document

Yes, this sort of thing would be possible, in principle - though note  
that kerns will have to be expressed in terms of glyphs, not  
characters. (Consider a font with many swash variants of "T" - you  
don't necessarily want the same kerns between each of these and  
adjacent glyphs.)

> If this works in principle, it could be extended to include  
> automatic invocation of ligatures,

This is somewhat less likely to happen, because of the added  
complexity of making it interact properly with the existing layout  
features in the font (e.g, GPOS kern features). Additional kern pairs  
could be applied after the standard layout is complete, as a final  
step. Glyph changes here, on the other hand, ought to interact with  
the rest of the OpenType layout process - in ways that would require  
some careful consideration.

> perhaps even from a different font

And this is *much* less likely to be implemented. At this point, it's  
starting to sound like building a whole new version of the "virtual  
font" infrastructure. I don't think that's a good way forward in the  
modern world. Better to focus on creating (or stimulating the  
creation of) fonts that do actually contain the character & glyph  
repertoire and behavior you need.

JK

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