[OpenType] Re: [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
> Eric Muller
> Sent: Wednesday, May 02, 2012 6:49 PM
> To: multiple recipients of OpenType
> Subject: Re: [OpenType] Re: [mpeg-OTspec] Vertical ligatures
> 
> Message from OpenType list:
> 
> 
> > So, if you pass<RLO, f, i, PDF>  to HarfBuzz, we detect that Latin is
> > naturally left-to-right, so we reverse the glyph stream, shape, and
> > reverse back...
> 
> That still leaves the neutrals in limbo.
> 
> 
> > Just wondering, which rtl flag are you referring to? The one in
> > LookupFlag?
> 
> Yes.
> 
> > How about allocating two bits of three reserved bits in LookupFlag to
> > mean "vertical only", and "horizontal only"?
> 
> That's essentially what Peter suggested.
> 
> This seems like a sensible path to me, but I would like to be a bit
> forward-looking, and have a broad enough scope for this additional
> selection mechanism, and consequently also understand the situations it
> won't accommodate (and agree they are not worth handling).
> 
> Also, for the multi-glyph problem,  I would not characterize the
> selection as horizontal/vertical, but rather as the relative
> arrangement of the glyphs, which is what matters to the font designer.
> Essentially, it should be which of the four sides of the first (in
> glyph order) glyph is touching which side of the second glyph. That's
> 16 combinations, of which three are necessary:
> 
> - right side/left side
> - left side/right side
> - bottom side/top side
> 
> The other combinations are not that common and can probably be shaping
> barriers (i.e. shaping happens independently on each side, much like
> bidi level run boundaries today).
> 
> Eric.
> 
> 
> 
> 
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