Re: outside decomposed, inside precomposed

From: Richard Cook (rscook@socrates.berkeley.edu)
Date: Thu Oct 14 2004 - 15:36:39 CST

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    On Oct 13, 2004, at 1:42 PM, Eric Muller wrote:

    > Going back to the original scenario, to make my point clearer:
    >
    > System A, a subset of FileMaker, has {U+0065, U+0303, U+1EBD} as its
    > repertoire. When presented with the input <U+0065, U+0303>, it
    > produces the output <U+1EBD>.
    >
    > System B, my rendering system, has {U+0065, U+0303} as its repertoire.
    > When presented with the input <U+0065, U+0303>, it produces a correct
    > rendering. When presented with the input <U+1EBD> it outputs a smiley.
    >
    > Both systems are conformant (I would hope), yet putting them together
    > does not mean that the result is automatically conformant, even on the
    > intersection of their repertoire. Hence, one cannot attribute the
    > problem that Richard is seeing to either system. The problem belongs
    > to Richard, when he did put the two systems together.

    Well, if it belongs to me, I'll happily give it away for free to anyone
    willing to take it off my hands.

    > If we want some automatic guarantee of conformance for combinations of
    > conformant systems, then we need at least to impose that the
    > repertoire supported by conformant implementations be closed under
    > canonical equivalence. Such a condition is not there today. It has
    > interesting consequences: e.g. U+2FA1C is canonically equivalent to
    > U+9F3B, so the BMP is not closed under canonical equivalence, so no
    > conformant system could make its repertoire exactly the BMP.

    If someone wants to normalize my text into precomposed things, that's
    all well and good, so long as there's a fallback mechanism for
    rendering via a font which may have only the decomposed parts.

    I don't know if this is the same as saying that "we need at least to
    impose that the repertoire supported by conformant implementations be
    closed under canonical equivalence".

    But, I say this after spending *way* too much time yesterday adding
    precomposed things to my font. You might think that I can rationalize
    it, thinking that now the diacritic placement will be somewhat better
    than it was before. But I thought the diacritic placement was adequate
    to begin with. And I can't predict what new precomposed things I might
    need to support in the future.

    -Richard



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