Re: Why people still want to encode precomposed letters

From: Asmus Freytag (
Date: Sun Nov 23 2008 - 13:17:37 CST

  • Next message: Asmus Freytag: "Re: Why people still want to encode precomposed letters"

    On 11/23/2008 4:37 AM, Hans Aberg wrote:
    > On 23 Nov 2008, at 13:08, philip chastney wrote:
    >>> I experimented a bit, one and a half decade ago, with creating the
    >>> Swedish letter (U00C5) in TeX, which then was necessary to do by
    >>> combining an A writing a small circle above it. It turns out to be
    >>> quite complicated, because characters may have a slant, to center
    >>> the circle on. So one needs to have a more advanced font model,
    >>> which for each character contains information where to position
    >>> combining characters. I am not sure about the state of this matter -
    >>> one can have Chinese fonts that combine the radicals - so it ought
    >>> to be possible to do for the combining characters as well.
    >>> as you say, combining marks are not always "centred"
    >> how about changing the terminology, and saying combining marks are
    >> placed on the "main vertical axis"?
    >> with roman-style letters, the main axis would normally be truly
    >> vertical, with italic-style letters the main axis might be anything
    >> from 12 to 18 off the vertical
    >> note that, with italic-style letters, unless it's a perfect circle
    >> showing no contrast, the circle itself may also need to be slanted
    > It is in fact even more complicated, because even it is called
    > one can have, as a matter of rendering style, the ring dipping into
    > the main character, even being partly obscured. So one may not get
    > around recognizing certain combination and provide special designs for
    > those.
    Actually. I suspect that the reason this overlapping exists and is
    considered acceptable has to do with generic factors, in this case, the
    problem of placing a rather "fat" diacritic on top of a tall character.
    To render a disconnected ring, you would need four separate areas of
    alternating black and white, from the top of the line to the top of the
    character (A, in this case). At small sizes, or low resolution, it's
    hard to find that much space. Hence the use of overlapping forms, which
    reduce the space requirement by half (or rather, allow the ring to be
    twice the size it would otherwise have to be).

    With a bit of research, you could find other cases of such adjustment
    and formulate layout principles for diacritics that could help you do a
    better job in the absence of explicit designs. These principles would
    result in a set of rules that's not as simplistic as much that's been
    attempted, but I would predict that when fully developed their
    complexity is not different from other types of text-layout tasks.

    > Hans

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