Re: ct, fj and blackletter ligatures

From: John Hudson (
Date: Sat Nov 02 2002 - 13:19:41 EST

  • Next message: John Hudson: "Re: ct, fj and blackletter ligatures"

    At 07:24 11/2/2002, Thomas Lotze wrote:

    >On Sat, 2 Nov 2002 07:18:43 -0000
    >"William Overington" <> wrote:
    > > In relation to regular Unicode the policy is that no more ligatures
    > > are to be encoded. My own view is that this should change. However,
    > > that is unlikely to do so.
    >I agree with you. Ligatures may have semantics that can be composed from
    >characters already Unicode encoded, but they are separate glyphs whose
    >shape cannot be inferred from that of others but has to be designed
    >separately and stored somewhere in a font.

    Thomas, please go and read the FAQ and the relevant parts of the Unicode
    Standard before you start agreeing with William. Yes, ligatures are
    separate glyphs, but not every glyph in a font needs to be encoded. A ct
    ligature is a variant glyph representation of the characters c and t; it
    does not need to be encoded, because it is possible to display the
    character sequence ct with a ligature using font layout features. Unicode
    is a *character* encoding standard, not a glyph encoding scheme. As
    previously noted, the handful of Latin ligatures included in the Alphabet
    Presentation Forms block are included only for backwards compatibility with
    non-Unicode standards that did not have a good character/glyph distinction.

    Please also note, and this is very important, that using Private Use Area
    codepoints for elements that are meant to represent sequences of characters
    in normal text, such as ligatures is a REALLY BAD IDEA. This has been
    explained to William dozens of times, but he appears to be too wrapped up
    in his own erroneous brilliance to listen to reason. If you use PUA
    codepoints for glyph variants in text, you immediately lose all the
    benefits of a clean character/glyph distinction: you cannot sort text, you
    cannot spellcheck text, you cannot search text, and you have absolutely no
    guarantee that another user is going to be able to correctly display your text.

    Let me put it another way. Think about the paradigm you are working within
    if you encode every glyph variant in a font. I see you standing in front of
    a tray of metal type, hunting and picking for the little bit of lead that
    *looks* correct. You pick up a bit of metal that has a ct ligature on the
    end of it, and you put it in your composing stick. The semantic
    relationship of that piece of metal to the letters c and t exists only in
    your mind. The piece of metal is dumb: it carries no meaning. That is the
    paradigm you are working in if you are typesetting text on a computer using
    PUA codepoints for glyph variants. A PUA codepoint in a stream of text is
    as meaningless as the piece of metal with a ligature on the end. You are
    applying an analogue, metal type paradigm to digital text processing, and
    in the process you are losing most of the benefits of using a computer.
    Does that make any sense?

    If you are interested in learning more about font layout features for glyph
    variants, and how a smart font format like OpenType works with the Unicode
    Standard, you might find this article at the Microsoft Typography website

    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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