Re: [xep-support] Rendering Unicode combined diacritic characters

From: Nikolai Grigoriev (grig@renderx.com)
Date: Thu May 20 2004 - 03:22:38 PDT

  • Next message: Jim Skelton: "Re: [xep-support] Rendering Unicode combined diacritic characters"

    Jim,

    > I'm finding that when displaying a PDF file generated
    > from XEP, that Unicode combining diacritics don't
    > render correctly.

    You are right. XEP does not do any special processing
    for combining diacritics: it just displays diacritic signs
    as a standalone characters. (They show above their
    preceding characters only by virtue of their glyph metrics).

    I admit this is a drawback in XEP; but it is not an easy
    one to overcome. Proper diacritic placement requires
    parsing of complex font structures; we don't have immediate
    plans in that direction.

    > You'll notice that the barred i does have
    > the acute accent over it (though a little too far
    > left), but the dot on the i is retained (it shouldn't
    > be retained when combined with an acute accent).
    > This character is represented by x0268 x0301.

    I don't see how we could achieve this, unless there
    is a special glyph for barred dotless i. XEP certainly
    cannot decompose glyph descriptions from fonts.

    > Microsoft's Unicode rendering engine (Uniscribe),
    > only recently was able to render these character
    > combinations correctly. There are other unicode
    > rendering schemes, such as SIL's graphite...

    We don't use any third-party Unicode processors:
    our past experience made us very suspicious to
    external components, as it seriously undermines
    portability.

    Best regards,
    Nikolai Grigoriev
    RenderX

    ----- Original Message -----
    From: "Jim Skelton" <jimskelton@yahoo.com>
    To: <xep-support@renderx.com>
    Sent: Tuesday, May 18, 2004 3:36 AM
    Subject: [xep-support] Rendering Unicode combined diacritic characters

    I'm finding that when displaying a PDF file generated
    from XEP, that Unicode combining diacritics don't
    render correctly. An example of this is at
    http://www3.telus.net/osis/CNT.2john.pdf -- in the
    title, 3rd word from the left, you'll notice that the
    acute accent over the e dieresis is too low. This
    character is represented by the two glyphs x00EB
    x0301. The latter glyph is a combining diacritic,
    meaning that it overstrikes the preceding character.
    In theory, the rendering engine should place the
    combining diacritic at the correct height, depending
    on the metrics of the base character.

    Another example of this is in the acute accent over
    barred i, found in the first line of regular text, 2nd
    word over. You'll notice that the barred i does have
    the acute accent over it (though a little too far
    left), but the dot on the i is retained (it shouldn't
    be retained when combined with an acute accent). This
    character is represented by x0268 x0301.

    The embedded font used in this PDF file is a Unicode
    font which contains a lot of the latin character
    subsets.

    Is there something that can be done to render Unicode
    combining diacritics correctly? I noticed that
    Microsoft's Unicode rendering engine (Uniscribe), only
    recently was able to render these character
    combinations correctly. There are other unicode
    rendering schemes, such as SIL's graphite...

    --Jim

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