[luatex] otf fonts (ligatures, cache, etc.)

[Taco Hoekwater]

Elie Roux wrote:
> Karl Berry a écrit :
>>     for example 1/4 (I'm sure there are more pertinent examples
>> For example, "ffi" and "ffl" are standard ligatures in English.
>>   
> 
> In most latine languages too, but these are special, as the mechanism 
> is: ffi -> f_fi -> f_f_i, and you can't have this mechanism on 1/4, 
> because 1_/ does not exist, where f_f does.

In an opentype font, you can have things like

   f f i -> f_f_i

in a single lookup step and the font would be perfectly legal even
if it didn't have an f_f glyph at all.

TeX's ligature building can't do that, it absolutely has to go
through an "f_f i" stage. This means that if you want a fully
reliable font system, you will have to do node list processing
even for simple ligatures (and definitely for 'frac').

Best wishes,
Taco