RE: Printing and Displaying Dependent Vowels

From: jameskass@att.net
Date: Sat Mar 27 2004 - 17:03:50 EST

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    Peter Jacobi wrote,

    > Using the Linux version of Abiword, which uses the Pango renderer,
    > both the Code 2000 and the MS Latha font display the vowel signs without the
    > unwanted dotted circle. NBSP and normal SPACE give identical results.
    > For Code 2000 only, the dotted circle or a similiar ersatz glypg (the
    > screenshot is
    > not that clear) is drawn for the two-part vowel signs U+0BCA, U+0BCB and
    > U+0BCC
    > between the two parts.

    U+0B82 TAMIL SIGN ANUSVARA is substituted and re-positioned in the compound
    glyphs of Code2000 for the normal dotted circle in the default glyphs for
    U+0BCA, U+0BCB, and U+0BCC.

    This is only expected to appear with a rendering system which does not support
    OpenType. This is because the default glyphs for these "surroundrant" vowel signs
    would never be drawn on the screen. Rather, the expected approach from the
    rendering engine is to use the component glyphs for these three vowel signs, such
    as U+0BC7 for the left part of U+0BCA, and U+0BBE for the right-side portion.

    If the presence of these default glyphs in Code2000 is making problems, they can
    be adjusted. (Just because I expect a rendering engine to take a certain approach,
    doesn't mean that a rendering engine will take that approach!)

    On Windows, as others have noted, the rendering engine ("Uniscribe") inserts the
    dotted circle glyph (if the font has a dotted circle glyph) into the display. The
    dotted circle character is not inserted into the text, of course.

    So, if the question is how to make an OpenType font *not* display the dotted
    circle on Windows with Uniscribe, one idea would be to add a spacing glyph to
    U+25CC (DOTTED CIRCLE) in the font. This spacing glyph should be a no-contour
    glyph, perhaps with the same advance width as U+0020. I've not tried this,
    but it might just work.

    Another approach is to simply use a non-OpenType Unicode TrueType font for
    Tamil. The dotted circles don't seem to ever appear unless the font-in-use has
    OpenType tables covering the script-in-use.

    Best regards,

    James Kass

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