Re: [ft-devel] [OpenType] Question about LookupFlag (fwd)

[Behdad Esfahbod]

On Mon, 4 Apr 2005, George Williams wrote:

> On Mon, 2005-04-04 at 00:50, Behdad Esfahbod wrote:
> > I'm all confused about how one is supposed to handle LookupFlag.
> > The OpenType spec once says [1]: "The LookupFlag specifies lookup
> > qualifiers that assist a text-processing client in substituting
> > or positioning glyphs."  and the LookupFlag bit enumeration
> > defines:
>
> Personally I've never understood what the point of "IgnoreBaseGlyphs"
> and "IgnoreLigatures" might be. I can see contexts in which IgnoreMarks
> might be useful (building ligatures in non-latin scripts perhaps), but
> the other two seem pointless.

I can see some uses for those two, like for example in Nastaleeq
style of Persian/Arabic script, which it may happen that the dots
in two letters form a ligature, or the dot simply move around a
bit, but the current spec is too limited to allow that, since you
don't have any control on how many BaseGlyphs/Ligatures may be
ignored, etc...

> It also isn't clear to me why "right to left" needs to be specified.
> Unless opentype is allowing support for boustrophedon scripts then
> l2r/r2l is determined by the script which has already been specified in
> the script/lang table. I've never seen any mention of boustrophedon in
> the OT spec so I tend to doubt that interpretation...

Seems like "right to left" is extremely helpful in Nastaleeq
again.  In Nastaleeq, glyphs on the right move up, such that the
leftmost glyph in a word is sitting on the baseline.  The "right
to left" bit as I understand it allows for specifying which side
of the combination should sit on the baseline.

> I expect you need to find someone from Adobe/MS who really worked on the
> OT spec to explain it. And since they didn't answer...

sigh..


--behdad
http://behdad.org/