Re: Combining marks with two letters

From: John Hudson (john@tiro.ca)
Date: Mon Feb 11 2008 - 13:01:32 CST

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    Philippe Verdy wrote:

    > Michael Everson wrote:
    >> t + double-inverted-breve + dot above + s, I should think.

    > Seems illogical. The dot above is not double. This looks like defective for
    > me, the dot above is attached to no letter, so we would get either:
    > * t+double-inverted-breve, then the dot would be badly positioned, and the s
    > would not be below the souble-inverted-breve; or
    > * t+dot-above next to a simple s, and a double inverted breve above all.
    > I see no reason why the dot would move in the center between the two base
    > letters. This is an unexpected deviation from the expected behavior of the
    > dot above.

    If the dot is ordered after the double-inverted-breve, it can be positioned relative to
    the double-inverted-breve using mark-to-mark positioning. The double-inverted-breve will
    likely have dumb positioning, i.e. it will be centered on the division between the
    sidebearings of the two letter glyphs (more refined positioning of double-width marks over
    specific pairs of letters is very complex and requires multiple contextual positioning
    lookups). But the positioning of secondary marks relative to the double-inverted-breve is
    easily controllable via mark-to-mark positioning *if that is what is desired*.

    A difficulty arises if user expectations vary: i.e. if some users want the dot to be
    positioned above the t and others want it centered on the double-inverted-breve. The
    default positioning must be one or the other.

    It is possible to provide for user-controlled variation in the positioning, but with the
    current sent of OpenType Layout features this would require first a stylistic variant
    glyph substitution of the secondary mark, which would assume a distinct position.

    John Hudson 

    -- 
Tiro Typeworks        www.tiro.com
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