Re: [Freefont-bugs] ligatures

[Denis Jacquerye]

On 15/02/2008, Steve White <address@hidden> wrote:
> Karl,
>
>
>  On Fri, Feb 15, 2008 at 1:09 AM, Karl Berry <address@hidden> wrote:
>  >     1) What applications use the ligatures?
>  >
>  >  It is certainly possible to end up using them in TeX, one way or another.
>  >  I imagine in OpenOffice or whatever, they could also be used, if you
>  >  insert the character code where the st ligature is :).
>  >
>
> I mean, what applications make use of the automatic replacement of
>  strings by ligatures?
>  OpenOffice seems not to.
>

Applications should use mandatory ligatures ('liga' tag). One of  the
reason they don't is because they didn't use to and people would
rather not have old documents look different between older versions
and newer versions. Things like Word, OO won't use them but publishing
or graphics apps most probably will.

>  >     2) In the TrueType fonts
>  >
>  >  This is another topic, but is TrueType the main target format at this
>  >  point?  (I hope not.)
>  >
>
> Well, it's an important question.
>
>  Up to now, FreeFont has always packaged only TrueType binaries.
>  I see that Vista has largely switched to OpenType, and it is supposed
>  to work on Mac's and modern X.
>  Should we switch to OpenType, then?

FreeFont is already TrueType with OpenType tables, so it is OpenType.

>
>  >     3) What is the intent of the distinction between discretionary vs
>  >     mandatory ligatures?
>  >
>  >  Probably just what you said.
>  >
>  >
>  >     Is it that some scripts are unreadable without ligatures?
>  >
>  >  Yes.  Arabic and related languages, among others, have a complex concept
>  >  of ligatures, which is necessary for even minimally acceptable
>  >  typesetting.
>  >
>  >
>  >     Myself, I think the 'ffi' etc ligatures are important to good
>  >     typesetting,
>  >
>  >  Certainly.  (Well, depending on the font design, a few fonts are
>  >  intentionally designed so that the ffi et al. look ok without
>  >  ligatures.  Anyway ...
>  >
>  >
>  >     almost never sees the conjoined 'st' ligature.  Can that distinction
>  >     be made in the font as well?
>  >
>  >  I don't know, perhaps in OpenType?  I don't know if there are standard
>  >  features relating to this.
>  >
>  >  In any case, I'm most familiar with TeX's tfm metric files.  These can
>  >  specify the ligatures used "by default"; ordinarily ffi and the like
>  >  would be, while st would not be.  The user would type \st{} in the
>  >  document or some such to explicitly specify they wanted it.
>  >
>
> This seems quite sensible to me.
>
>  It's just that the simple distinction "obligatory" vs "discretionary"
>  seems inadequate to cover the various uses of ligatures.
>  You might say "ffi" is obilgatory and "st" isn't,
>  but the meaning of "obligatory" here is quite different from Arabic,
>  where the text may be illegible without it.
>
>  I'm trying to sort out the proper use of these distinctions.
>
>  How about this:
>    Make "st" not a replacement at all (e.g.-to do by hand)
>    Make "ffi" etc discretionary except in monospace, where it is no 
> replacement
>    Leave Arabic ligatures as they are, using obligatory to indicate
>  sine qua non.
>

Shapers might apply the 'liga' features by default in Arabic script
and not in Latin script, but it should be applied either way since it
is mandatory. The 'dlig'  is discretionary and should be enabled
through the user interface.
Ligatures should be 'dlig' in Mono fonts, standard ones like 'fi'
could be 'liga' in regular fonts but it's not obligatory (these
character sequences could have special kerning instead for example).
Anyway, having standard ligature vs discretionary ones is a design
issue in Latin script.

Cheers,
-- 
Denis Moyogo Jacquerye