Add face.getTableFeatureTags()

Author: khaledhosny

hb.symbols

@@ -67,6 +67,7 @@ _hb_draw_funcs_set_close_path_func
 _hb_glyph_info_get_glyph_flags
 _hb_language_from_string
 _hb_ot_layout_table_get_script_tags
+_hb_ot_layout_table_get_feature_tags
 _hb_ot_layout_script_get_language_tags
 _hb_ot_layout_language_get_feature_tags
 _hb_ot_var_get_axis_infos

hbjs.js

@@ -159,6 +159,30 @@ function hbjs(Module) {
         }
         return tags;
       },
+      /**
+       * Return all features enumerated in the specified face's
+       * GSUB table or GPOS table.
+       * @param {string} table: The table to query, either "GSUB" or "GPOS".
+       **/
+      getTableFeatureTags: function (table) {
+        var tableTag = hb_tag(table);
+        var startOffset = 0;
+        var featureCount = STATIC_ARRAY_SIZE;
+        var featureCountPtr = Module.stackAlloc(4);
+        var featureTagsPtr = Module.stackAlloc(STATIC_ARRAY_SIZE * 4);
+        var tags = [];
+        while (featureCount == STATIC_ARRAY_SIZE) {
+          Module.HEAPU32[featureCountPtr / 4] = featureCount;
+          exports.hb_ot_layout_table_get_feature_tags(ptr, tableTag, startOffset,
+            featureCountPtr, featureTagsPtr);
+          featureCount = Module.HEAPU32[featureCountPtr / 4];
+          var scriptTags = Module.HEAPU32.subarray(featureTagsPtr / 4,
+            featureTagsPtr / 4 + featureCount);
+          tags.push(...Array.from(scriptTags).map(_hb_untag));
+          startOffset += featureCount;
+        }
+        return tags;
+      },
       /**
        * Return language tags in the given face's GSUB or GPOS table, underneath
        * the specified script index.

test/index.js

@@ -54,6 +54,20 @@ describe('Face', function () {
     expect(face.getTableScriptTags('GPOS')).to.deep.equal(['DFLT', 'cyrl', 'dev2', 'deva', 'grek', 'latn']);
   });
 
+  it('getTableFeatureTags returns tags for a font', function () {
+    blob = hb.createBlob(fs.readFileSync(path.join(__dirname, 'fonts/noto/NotoSans-Regular.ttf')));
+    face = hb.createFace(blob);
+    expect(face.getTableFeatureTags('GSUB')).to.deep.equal([
+      'aalt', 'abvs', 'akhn', 'blwf', 'blwf', 'blws', 'c2sc', 'case', 'ccmp', 'ccmp',
+      'ccmp', 'ccmp', 'cjct', 'cjct', 'dnom', 'frac', 'half', 'half', 'half', 'half',
+      'haln', 'liga', 'lnum', 'locl', 'locl', 'locl', 'locl', 'locl', 'locl', 'locl',
+      'locl', 'locl', 'locl', 'locl', 'locl', 'nukt', 'numr', 'onum', 'ordn', 'pnum',
+      'pres', 'pres', 'psts', 'rkrf', 'rphf', 'rtlm', 'salt', 'sinf', 'smcp', 'ss03',
+      'ss04', 'ss06', 'ss07', 'subs', 'sups', 'tnum', 'vatu', 'zero'
+    ]);
+    expect(face.getTableFeatureTags('GPOS')).to.deep.equal(['abvm', 'blwm', 'dist', 'kern', 'mark', 'mkmk']);
+  });
+
   it('getScriptLanguageTags returns tags for a font', function () {
     blob = hb.createBlob(fs.readFileSync(path.join(__dirname, 'fonts/noto/NotoSans-Regular.ttf')));
     face = hb.createFace(blob);