[NTG-context] GSUB LookupType 6 in fea file not working

Hans Hagen pragma at wxs.nl
Wed Jan 6 17:43:52 CET 2016


On 1/6/2016 5:28 PM, Paolo Brasolin wrote:
> Hello.
>
> I am trying to add some custom ligatures to a font using a feature file.
> Everything works just fine, until I try what is called a chained
> contextual substitution, i.e. a GSUB lookup of type 6.
> I am studying the specs from
> http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html#5.f
>
> A simple example.fea that does not work for me is:
>
>
> languagesystem dflt dflt;
>
> lookup FOOBAR {
>    sub B by Q ;
> } FOOBAR;
>
> feature foba {
>    sub [A] B' lookup FOOBAR;
> } foba ;
>
>
> I'd expect it to replace B with Q only when preceeded by A.
> The same rule expressed with a lookup of type 8 works just fine:
>
>
> languagesystem dflt dflt;
>
> feature foba {
>    sub [A] B' by Q;
> } foba ;
>
>
> Ultimately I would need to use multiple inline lookups, something like
>    sub [A]' B' lookup FOO C' lookup BAR;
>
> Are inline lookups unsupported by the engine?
> That would seem strange to me.
> I'm probably missing some point, but I'm unable to find more documentation.
> Am I using the wrong syntax?

the new font loaders doesn't support fea files (i have a basic parser 
but it's not included as i'm still not sure if it should be .. fea files 
assume stable fonts and so)

\usemodule[oldotf]

might work ok for you

Hans

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