That's really cool.
I ended up directly patching the font, but the patch itself would
probably be easier to produce with some scripting. I'll definitely
play around with your code.
Thanks Hans!
2016-01-07 13:43 GMT+01:00 Hans Hagen :
> 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?
>
>
> As we have a way to define additional features in context i played a bit
> with contextual lookups. As a result we now have an additional type
> chainsubstitution. In due time I will document this better (once it's
> settled). I still need to think of a way to kick this into place at a
> specific location in the sequence.
>
> Btw, contrary to fea extensions (not supported in the new font loader
> anyway) these are runtime extensions i.e. not cached.
>
> I'll upload a beta.
>
> --
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "stest",
> type = "substitution",
> data = {
> a = "X",
> b = "P",
> }
> }
> \stopluacode
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "atest",
> type = "alternate",
> data = {
> a = { "X", "Y" },
> b = { "P", "Q" },
> }
> }
> \stopluacode
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "mtest",
> type = "multiple",
> data = {
> a = { "X", "Y" },
> b = { "P", "Q" },
> }
> }
> \stopluacode
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "ltest",
> type = "ligature",
> data = {
> ['1'] = { "a", "b" },
> ['2'] = { "d", "a" },
> }
> }
> \stopluacode
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "ktest",
> type = "kern",
> data = {
> a = { b = -500 },
> }
> }
> \stopluacode
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name= "ytest",
> type= "chainsubstitution",
> -- flags = { false, false, false, false },
> lookups = {
> {
> type = "substitution",
> data = {
> ["b"] = "B",
> ["c"] = "C",
> },
> },
> },
> -- steps= {
> -- {
> -- rules = {
> -- {
> -- before = { { "a" } },
> -- current = { { "b", "c" } },
> -- lookups = { 1 },
> -- },
> -- },
> -- },
> -- },
> data = {
> rules = {
> {
> before = { { "a" } },
> current = { { "b", "c" } },
> lookups = { 1 },
>
