From: Kenneth Whistler (kenw@sybase.com)
Date: Tue Feb 11 2003 - 01:14:59 EST
John Cowan noted:
> > So formal canonical decompositions are almost entirely
> > confined to separable, accent-like diacritics (acute,
> > grave, diaeresis, and so on). The only significant exceptions are
> > the cedilla and ogonek, which attach smoothly to letter
> > bottoms without otherwise distorting them, and which
> > often have graphic alternates that are, indeed, separated
> > diacritics (comma-like and reverse-comma-like forms).
>
> And the Vietnamese horn.
Yep, and the Vienamese horn. That one was on the
hairy cusp of the decision, and in my opinion was
probably decided wrongly -- the horn is not really a
productive diacritic, and is more akin to the Cyrillic
descender in terms of base letterform distortion. But
that is water under the bridge at this point.
Doug Ewell asked:
> but I still don't see why stroke overlays are lumped in
> with that group. They don't distort the base form any more than
> cedillas and ogoneks do -- and isn't this a glyph issue anyway?
Well, sure, it *is* a glyph issue. But, again, you have to
draw the line somewhere. Where, in the following continuum,
would you draw the line:
z (007A), z-acute (017A), z-bar (01B6), z-curl (0291), ezh (0292),
ezh-curl (0293), ezh-tail (01BA), ...
One of the reasons why the "framers" decided, for Latin, to
draw the line before the bars is that unlike the free-floating
accents, which can be dynamically placed reasonably well by
referring to the overall bounding box and "ink" of the base
character, the bars are rather more sensitive in placement
to the actual shape of the glyph they have to cross. In some
cases, this leads to structurally distinct solutions, as in
the glyph families for b-bar and d-bar (cross the ascender?
cross the bowl?), and so on. It was just far enough over
into the *glyph design in a font* side of the issue to
make decomposition uncomfortable, whereas the placement of
floating accents is just far enough over into the *generative
placement* side of the issue to make sense.
But it was clearly a judgement call, and as Doug noted, the
decision was made long ago, and second-guessing it now
won't make any difference to the actual decompositions
in implementations.
--Ken
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