Re: Unicode TTF question

From: Eric Muller (
Date: Wed Aug 24 2005 - 15:29:39 CDT

  • Next message: Richard Wordingham: "Re: Windows Glyph Handling"

    Michael Everson wrote:

    > At 18:06 +0100 2005-08-24, Bob Hallissy wrote:
    >> It is technically impossible, at least as far as TrueType and
    >> OpenType are
    >> concerned, as these formats can contain a maximum of 65535 glyphs, and
    >> there are more characters than that in Unicode.
    > Why can't that be changed? Just curious.

    The format is essentially binary, and there are *many* places that
    specify a sixteen bit slot for a glyph id; extending the format would be
    a major undertaking in itself. Furthermore, to ensure that existing
    fonts are still valid, this would essentially lead to a duplication of
    most of the tables, etc. Then, all implementations (layout engine,
    tools, etc) would have to be extended, and some cannot be easily
    touched. Then, there are all the formats derived from TT/OT which may
    have inherited the 16 bit limit. Then, there are all the implementations
    of those formats.

    This is considerable work that has to be justified by the result: the
    ability to create a single font that covers all of Unicode. Even if the
    sixteen bit barrier was removed, the likelyhood of such a font to ever
    exist is essentially nil; it is already the case that we do not have a
    complete coverage of Unicode in any number of fonts. Furthermore, the
    mere complexity of such a font would be close to intractable; certainly,
    it would have many bugs for a long time, making it not too useful anyway.

    Finally, there are other problems which cannot be addressed by a single
    font, and more or less require some kind of font aggregation mechanism.
    When you have such a mechanism, the need for a single font decreases

    So, yes, the limit can be removed, but the benefit is not worth the cost.


    This archive was generated by hypermail 2.1.5 : Wed Aug 24 2005 - 15:30:43 CDT