[Fontinst] LIG plus kerning

Lars Hellström Lars.Hellstrom at math.umu.se
Tue Oct 19 23:43:59 CEST 2004

At 19.46 +0200 04-10-19, Ulrich Dirr wrote:
>I've tried to substitute three consecutive dots by 'ellipsis'. I tell
>fontinst if there's a dot to look further if there's a second dot. If it's
>the case I replace this with a dummy char. If another dot follows the dummy
>char then it is replaced by the 'ellipsis' char.
>Is this a correct approach?

No, but it's the best you can do with TeX, and it is no worse than the --
and --- ligatures for en- and emdash.

The main reason it is not really a correct approach is that it uses the
font (way out on the output side of TeX) to decode the input. A better
approach (which is only available in Omega) would be to use an OTP for this
(but I'm not entirely sure Omega allows you to apply these at a sensible
position in the input->output chain either).

These reservations are mainly based on theoretical considerations, so a lot
of the time you won't get in any trouble if you go ahead anyway, but
occationally it will come out wrong.

>But it looks like that the kerning information for, e.g., 'zero'+'ellipsis'
>is discarded. It will only be kerned when the 'ellipsis' char is entered
>directly but not with the ligature mechanism. Is there a way to get this

Not really, since this is a fundamental limitation of the TeX ligaturing
mechanism: kerns and ligatures are formed in a single pass over the text,
so the right hand side of a kerning or ligature pair will always be a raw
character. (Maybe you can get it right if you do something really clever
with the more exotic ligaturing instructions and additional dummy
characters, but that it most likely not worth the trouble.)

>Can I combine this 'two-step'-ligatures with individual kerning pairs?

Kerns to its right will work as usual. Kerns on its left have no effect
since the ligature has not yet been formed when that kern position is

Similar problems occur in the T1 encoding for the >> and << ligatures.

>BTW What is the difference between 'latin' and 'newlatin' (v1.926), which
>one is to be preferred, or where can I read about it?

You can start by LaTeXing newlatin.mtx.

>(it looks like small
>caps fonts are spaced out a bit more with newlatin)

Not impossible. newlatin.mtx should be more consistent about which sets of
glyphs it uses, and this may make such a difference.

Lars Hellström

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