[OpenType] [mpeg-OTspec] Vertical ligatures

[Levantovsky, Vladimir]

FYI - forwarding all missing emails to MPEG list

> -----Original Message-----
> From: listmaster at indx.co.uk [mailto:listmaster at indx.co.uk] On Behalf Of
> Ken Lunde
> Sent: Friday, April 27, 2012 8:25 AM
> To: multiple recipients of OpenType
> Subject: Re: [OpenType] [mpeg-OTspec] Vertical ligatures
> 
> Message from OpenType list:
> 
> 
> John,
> 
> You wrote:
> 
> > But to make it so
> > that the vertical ligatures don't end up in horizontal text runs, the
> > font supplies a set of "dummy" vertical alternate glyphs for
> > characters included in vertical ligatures.  The vertical ligature is
> > then defined in terms of these dummy vertical alternate glyphs, such
> > that when the 'vert' feature is applied a vertical ligature results
> > but not in the horizontal case where 'vert' is not used.
> 
> The vertical glyphs that result from applying the 'vert' GSUB feature
> are anything but "dummy" glyphs. The glyphs may look the same as their
> horizontal counterparts (because the glyphs themselves are the same),
> but they have very distinct metrics, in terms of both X- and Y-axis
> shifting, and advances. In other words, they're not dummy glyphs.
> 
> (One reason for distinct horizontal and vertical glyphs is due to the
> fact that the 'vmtx' table supports only Y-axis shifts. Almost all of
> the glyphs in Kazuraki require both X- and Y-axis shifts. I once
> checked into this, and only 1 or 2 percent of the glyphs did not
> require an X-axis shift for the vertical form. If the 'vmtx' table
> could support both types of shifts, the number of vertical-specific
> glyphs would have been significantly reduced, and the only ones that
> would have remained are the "usual suspects": small kana, punctuation,
> brackets, and a few other symbols.)
> 
> The fundamental reason why the 'vert' GSUB feature must be applied
> before the 'liga' GSUB feature is because the vertical ligatures have
> no corresponding horizontal form, and the only pathway to accessing
> them is via the vertical forms of the component characters.
> 
> > This is a somewhat brittle strategy.  For example, fonts like those
> in
> > the Hiragino family, have discretionary ligatures for sequences such
> > as "株式会社" and "アパート", substitutions that yield the same glyph
> as for
> > U+337F and U+3300 respectively.  With the Kazuraki method of ordering
> > 'vert' first, you'd need to create vertical alternates for each of
> the
> > base characters involved in the ligature to get the correct
> > orientation in vertical runs.  For examples, see the proposal for
> > adding text orientation properties to Unicode for use with vertical
> > text. [2]
> >
> > [2] http://unicode.org/reports/tr50/
> 
> Yes, we fully understand that. We would never advocate the Kazuraki-
> style of vert/liga use for general-purpose or mainstream OpenType
> fonts. Our other Japanese fonts will not change to the Kazuraki-style,
> because doing so would be the incorrect thing to do.
> 
> Kazuraki is considered a special-purpose OpenType fonts, and it should
> be treated as such. This is one reason why my earlier comments about
> Kazuraki were stated as being orthogonal, because they should not apply
> to mainstream orgeneral-purpose fonts.
> 
> Also, while Kazuraki includes a complete set of Latin glyphs, we would
> have preferred not to. The way that input methods work, in that they
> depend on Latin glyphs in Japanese fonts, forced us to include such
> glyphs.
> 
> Regards...
> 
> -- Ken
> 
> 
> 
> 
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