Re: (bug?) wrong hyphenation with external fonts

[Hans Hagen <pragma@wxs.nl>]

On 2/5/2016 8:47 AM, Pablo Rodriguez wrote:
> On 02/04/2016 10:13 PM, Hans Hagen wrote:
>> On 2/4/2016 9:27 PM, Pablo Rodriguez wrote:
>>> [...]
>>> The ff-ligature prevents hyphenation with TeX Gyre Pagella, but not with
>>> MinionPro. (This is the opposite of what I reported before.)
>>
>> it depends on the complexity of the ligature .. ff is not so much an
>> issue but you can have ff + i = ffi etc and we need to deal with kerning
>> too (it depends a bit on how the opentype features are applied and we
>> can handle quite some weird ligature implementations)
>>
>> the latest mechanism in context can deal with quite some situations but
>> at some point has to make decisions (in order not to loose for instance
>> kerns; double chained ligatures would result in way more overhead and is
>> not worth the trouble)
>>
>> one might wonder if we never had these  f[fil] ligatures of if ancient
>> technology had provides hundreds of them combining upto 4 characters etc
>> etc.
>
> Many thanks for the explanation, Hans.
>
> I see the decisions ConTeXt has to make may be compromises in some cases.

the f + f can become a ff glyph but also a special first or second f or 
even two special f's and the same can happen with this result and the 
following i which can become a special i, or just the i partly overlayed 
or a ligature or break the ff into f and fi or there can be no 
replacements but just kerning

tex does have a concept of chained discretionary nodes (max 2) but that 
is pretty complex; such a chained discretionary node set + complex 
ligatures is no fun to deal with and because we also want to do other 
things in context (font handling is only one of the many things we do at 
that level)

we don't want to build a solution tree of thousands of possibilities to 
feed into the par builder (the current mechanism is already quite 
complex but still quite fast too) just for the sake of an occasional 
three character ligature in latin which is not even always permitted due 
to language constraints

Hans

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                                           Hans Hagen | PRAGMA ADE
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