[mpeg-OTspec] Vertical ligatures

[Ken Lunde]

John,

This is somewhat orthogonal to the discussion. To clarify the Kazuraki usage of vertical ligatures, I should point out that the order of the GSUB features, 'vert' first, then 'liga', is important for correct results. The ordering of the lookups in the 'GSUB' table reflects this, and as long as clients respect the ordering of the lookups, the font works. This is because there are no horizontal versions of the vertical hiragana ligaturesin this particular font.

Also, and perhaps orthogonal to the discussion, the main motivation for using the 'liga' GSUB feature for the vertical hiragana ligatures in Kazuraki was to achieve "on by default" behavior in most of today's applications.

Regards...

-- Ken

On Apr 24, 2012, at 9:27 AM, John Hudson wrote:

> Over on the CSS3 discussion list, John Daggett wrote something that I 
> think should be discussed re. use of vertical ligatures in OpenType fonts:
> 
> The OpenType spec defines a basic set of defaults
> for some scripts in the horizontal case. But for
> the vertical case, there really isn't a clear model
> defined in the spec or in any public documentation
> that I've seen. For example, is the "common
> ligatures" feature ('liga') enabled for upright
> text? The Kazuraki font from Adobe depends on
> 'liga' and 'vert' being enabled for vertical runs
> to get proper vertical ligatures. However, I'm not
> really sure this is the right model for the general
> case, since enabling common ligatures enables lots
> ligatures intended for horizontal runs. For example,
> in stacked Latin you don't want fi-ligatures to be
> used. I think for vertical runs there really should
> be a separate and distinct feature ('vlig'?) for
> vertical ligatures rather than overloading the common
> ligatures ('liga') feature.
> 
> The notion of separate features for vertical layout suggests, at least, 
> not only 'vlig' but also 'dvlg' (discretionary vertical ligatures), so 
> that ligatures may be classed according to default behaviour, as with 
> horizontal ligatures. [Some other horizontal ligature features seem to 
> me redundant, so I don't think we need 'cvlg' for contextual ligatures 
> or 'hvlg' for 'historical' ligatures, but perhaps others may disagree.]
> 
> JH
> 
> -- 
> 
> Tiro Typeworks www.tiro.com
> Gulf Islands, BC tiro at tiro.com
> 
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