Am 2013-05-01 11:30, schrieb Jonathan Kew:
On 30/4/13 21:49, Behdad Esfahbod wrote:
On 13-04-28 05:27 PM, Georg Duffner wrote:
Hi,
I posted this on the XeTeX list. Khaled meant it could have something
to do
with
http://cgit.freedesktop.org/harfbuzz/commit/?id=607feb7cff0e50f8738d2e49ca463fc9d7d494de
Recently I’ve changed the behaviour of liga. The f-ligatures are now
formed by
component glyphs which get substituted by means of contextual chaining
lookups. Thus, instead of
sub f f by f_f; the lookup is now sub f' f by f._f;
What you should be doing is:
sub f' f' by f._f f;
Not sure if the format supports that. However, I understand that this
would
cause a problem in that every other f won't be substituted.
We really do want to ignore ZWNJ in backtrack/lookahead. The problem
is that
you are abusing those contexts to do a ligation using single
substitutions.
Jonathan, do you have any suggestions?
Presumably, the way to handle this as a font developer is to explicitly
handle the ZWNJ, by adding something like
sub f' zwnj f by f;
>
ahead of the existing rule. That should in effect block the "ligature"
when ZWNJ is present, if I'm understanding correctly.
It wouldn’t change anything, as zwnj is ignored in contextual chaining
lookups.
The relevant lookups are
feature liga:
sub [ f f.DEU ]' [ f f.DEU ] by f._f;
feature calt:
sub @DEFAULT_F' uni200C @SHORT_F by @SHORT_F;
They appear in this order in the font. IMO, ZWNJ should prevent lookup
liga. I also thought of reverting the order, having first calt and then
liga, but this wouldn’t change anything, as ZWNJ is ignored in
contextual chaining.
I’d like you to consider, that ZWNJ is very uncommon in latin script,
so, if it appears, you can be sure it has been inserted on purpose for
breaking up a context. Therefore I don’t think it should be ignored. At
the moment I only know of one keyboard layout for latin that has ZWNJ,
which is the new german layout, standardized last year.
Best regards,
Georg
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