Re: [NTG-context] ligatures/substituation at word boundaries

28 Jul 2017


      On 7/27/2017 8:09 PM, Ulrike Fischer wrote:
...
Is it possible to refer in fonts.handlers.otf.addfeature to the word
boundary? The luatex manual speaks of a virtual "left_boundary"
char, but I couldn't find a way to use it.
\startluacode
     fonts.handlers.otf.addfeature {
         name = "ltest",
         type = "ligature",
         data = {
             ['1'] = { "a", "b" },
             ['2'] = { "d", "a" },
         }
     }
\stopluacode
%how to replace only the start a????
\startluacode
     fonts.handlers.otf.addfeature {
         name = "wtest",
         type = "ligature",
         data = {
             ['1'] = { "left_boundary", "a" },
         }
     }
\stopluacode
\definefontfeature[wtest][wtest=yes]
\definefontfeature[ltest][ltest=yes]
\starttext
\definedfont[file:dejavu-serif.ttf*default]%
{\addff{ltest} ababa\par}
{\addff{wtest} ababa\par}
\stoptext
It is possible to check against spaces in contextual lookups. There 
isn't something like left boundary. I added some test code to the beta 
but keep in mind that this will only work with self-made features. (I 
have to check performance impact because I don't like making contextual 
lookups measurable slower due to some hardly used feature. First test 
show that it behaves ok.) In the test code below 0xFFFC is the boundary 
(this 0xFFFC check is the new thing). I adapted a few more things in the 
loader so best check that out too.
I'll upload a beta.

Hans

\starttext

\startluacode
     fonts.handlers.otf.addfeature {
         name    = "test-a",
         type    = "chainsubstitution",
         lookups = {
             {
                 type = "substitution",
                 data = {
                     ["a"] = "A",
                     ["b"] = "B",
                     ["c"] = "C",
                     ["d"] = "D",
                 },
             },
             {
                 type = "ligature",
                 data = {
                     ['1'] = { "a", "b" },
                     ['2'] = { "c", "d" },
                 },
             },
         },
         data = {
             rules = {
                 {
                     before  = { { " ", 0xFFFC } },
                     current = { { "a" }, { "b" } },
                     lookups = { 2 },
                 },
                 {
                     current = { { "c" }, { "d" } },
                     after   = { { 0xFFFC, " " } },
                     lookups = { 2 },
                 },
                 {
                     current = { { "a" } },
                     after   = { { "b" } },
                     lookups = { 1 },
                 },
                 {
                     current = { { "c" } },
                     after   = { { "d" } },
                     lookups = { 1 },
                 },
             },
         },
     }

     fonts.handlers.otf.addfeature {
         name    = "test-b",
         type    = "chainsubstitution",
         lookups = {
             {
                 type = "ligature",
                 data = {
                     ['1'] = { "a", "b" },
                     ['2'] = { "c", "d" },
                 },
             },
         },
         data = {
             rules = {
                 {
                     -- the space is redundant as 0xFFFC contains it
                     before  = { { " ", 0xFFFC } },
                     current = { { "a" }, { "b" } },
                     lookups = { 1 },
                 },
                 {
                     current = { { "c" }, { "d" } },
                     -- the space is redundant as 0xFFFC contains it
                     after   = { { 0xFFFC, " " } },
                     lookups = { 1 },
                 },
             },
         },
     }

     fonts.handlers.otf.addfeature {
         name    = "test-c",
         type    = "chainsubstitution",
         lookups = {
             {
                 type = "ligature",
                 data = {
                     ['1'] = { "a", "b" },
                     ['2'] = { "c", "d" },
                 },
             },
         },
         data = {
             rules = {
                 {
                     before  = { { " " } },
                     current = { { "a" }, { "b" } },
                     lookups = { 1 },
                 },
                 {
                     current = { { "c" }, { "d" } },
                     after   = { { " " } },
                     lookups = { 1 },
                 },
             },
         },
     }

\stopluacode

\definefontfeature[test-a][test-a=yes]
\definefontfeature[test-b][test-b=yes]
\definefontfeature[test-c][test-c=yes]

\startbuffer
abababcdcd abababcdcd abababcdcd
\stopbuffer

\typebuffer

\definedfont[file:dejavu-serif.ttf*default,test-a] \getbuffer \blank
\definedfont[file:dejavu-serif.ttf*default,test-b] \getbuffer \blank
\definedfont[file:dejavu-serif.ttf*default,test-c] \getbuffer \blank

\stoptext


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