Re: ct, fj and blackletter ligatures

From: John Hudson (
Date: Sat Nov 02 2002 - 16:40:39 EST

  • Next message: Thomas Lotze: "Re: ct, fj and blackletter ligatures"

    At 14:59 11/2/2002, Doug Ewell wrote:

    > > It should be noted that using ZWJ is a valid way to encode the
    > > desirability of a ligature in plain text, but it is far from being a
    > > guarantee of displaying such a ligature. There are a lot of fonts out
    > > there with glyph substitution lookups that will correctly display
    > > something like a ct ligature using layout features (discretionary,
    > > controlled by the user) in OT savvy apps like Adobe InDesign, but
    > > will do so only for the sequence c+t. Ironically, the sequence
    > > c+ZWJ+t is more likely *not* to display as a ligature, since the ZWJ
    > > interferes with the sequence recognised by the font lookups.

    >Using ZWJ to control ligation is admittedly a new concept, and it may
    >not have been taken up yet by many vendors, but that seems like a really
    >poor reason to discourage the Unicode approach.
    >Proprietary layout features in OT-savvy apps like InDesign might get the
    >job done, but wouldn't it be better if app vendors and font vendors
    >would follow the Unicode Standard recommendation? You never know, it
    >might even reduce the number of requests to encode ligatures.

    But using ZWJ still requires proprietary layout features in OT-savvy apps.
    Whenever you're mapping from a character sequence to an unencoded glyph
    variant, you need a higher level protocol than is provided in a character
    encoding standard. c+ZWJ+t needs to be resolved to a ct ligature, and that
    requires a font level lookup and a line layout engine that understands and
    implements such lookups.

    The useful thing that the ZWJ does is to provide authors with a means to
    explicitly request ligation in a plain text document, but this is a *very*
    unusual requirement outside of a couple of obscure scripts (e.g. Old
    Hungarian). When someone sits down to type a typical English language
    document (or German, or French, etc.), he generally does not think about
    ligatures at all: he types his language in the commonly accepted manner,
    inputting character codes. Ligatures are a *typographical* feature of the
    Latin, not an orthographic one. Authors, by which I mean any user creating
    a document, do not think about ligatures unless they happen to be
    specialists, e.g. palaeographers, working with documents in which features
    such as ligatures are germane to the content. In probably 98% of all Latin
    script documents, standard ligature substitution should be automatic and
    global, which is what current smart font and professional layout
    applications provide (of course, users can turn ligatures off, globally or
    on an individual basis).

    There are hundreds of thousands of books and periodicals published every
    year, almost all of them using standard ligatures in accordance with 500
    years of typographical convention. I suggest that, at most, a handful of
    authors gave any thought to ligation while they were writing their texts,
    either because they are specialists working in document studies, or because
    they feel the need to meddle in the typographer's job.

    So, from this it should be obvious that we need automatic ligature
    substitution in higher level protocols using smart font features, because
    most documents that should have ligatures when published will not have them
    encoded in the text source. This is the reality of publishing, and it is
    the market on which the vast majority of font developers are focused. In
    this market, ZWJ ligation is rightly viewed as unnecessary except for a
    very small minority of specialist uses that will probably require
    specialist fonts from specialist foundries.

    Far from discouraging my colleagues from supporting ZWJ in font lookups,
    I've made proposals on the OpenType list suggesting how this might be done
    in a way that is easy, does not conflict with current ligature
    implementations, and respects authorial intent (by using the Required
    Ligatures <rlig> feature instead of the optional Standard Ligatures <liga>
    feature). I don't expect many people to do this, since ZWJ ligation
    provides a solution to something that almost no one sees as a problem.

    Finally, I don't think it is right to characterise ZWJ ligation as 'the
    Unicode approach' if the implication is that the approach taken in smart
    font technologies like OpenType, AAT and Graphite are somehow anti-Unicode.
    All these technologies are based on Unicode text processing, and the
    Unicode character/glyph model is the basis of the higher level protocols
    that they provide.

    John Hudson

    Tiro Typeworks
    Vancouver, BC

    It is necessary that by all means and cunning,
    the cursed owners of books should be persuaded
    to make them available to us, either by argument
    or by force. - Michael Apostolis, 1467

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