Bind hb_ot_layout_feature_get_lookups()

Author: khaledhosny

harfbuzz.symbols

@@ -78,6 +78,7 @@ _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_layout_feature_get_lookups
 _hb_ot_layout_get_glyph_class
 _hb_ot_layout_feature_get_name_ids
 _hb_ot_name_list_names

src/face.ts

@@ -244,6 +244,43 @@ export class Face {
     return tags;
   }
 
+  /**
+   * Fetches a list of all lookups enumerated for the specified feature, in
+   * the specified face's GSUB table or GPOS table.
+   * @param table The table to query, either "GSUB" or "GPOS".
+   * @param featureIndex The index of the requested feature.
+   * @returns An array of lookup indexes.
+   */
+  getFeatureLookups(table: string, featureIndex: number): number[] {
+    const sp = Module.stackSave();
+    const tableTag = hb_tag(table);
+    let startOffset = 0;
+    let lookupCount = STATIC_ARRAY_SIZE;
+    const lookupCountPtr = Module.stackAlloc(4);
+    const lookupIndexesPtr = Module.stackAlloc(STATIC_ARRAY_SIZE * 4);
+    const lookups: number[] = [];
+    while (lookupCount == STATIC_ARRAY_SIZE) {
+      Module.HEAPU32[lookupCountPtr / 4] = lookupCount;
+      exports.hb_ot_layout_feature_get_lookups(
+        this.ptr,
+        tableTag,
+        featureIndex,
+        startOffset,
+        lookupCountPtr,
+        lookupIndexesPtr,
+      );
+      lookupCount = Module.HEAPU32[lookupCountPtr / 4];
+      const lookupIndexes = Module.HEAPU32.subarray(
+        lookupIndexesPtr / 4,
+        lookupIndexesPtr / 4 + lookupCount,
+      );
+      lookups.push(...Array.from(lookupIndexes as Uint32Array));
+      startOffset += lookupCount;
+    }
+    Module.stackRestore(sp);
+    return lookups;
+  }
+
   /**
    * Get the GDEF class of the requested glyph.
    * @param glyph The glyph to get the class of.

test/index.test.js

@@ -246,6 +246,18 @@ describe("Face", function () {
     });
   });
 
+  it("getFeatureLookups returns the lookups for a feature", function () {
+    let blob = new hb.Blob(
+      fs.readFileSync(path.join(__dirname, "fonts/noto/NotoSans-Regular.ttf")),
+    );
+    let face = new hb.Face(blob);
+    const ligaIndex = face.getTableFeatureTags("GSUB").indexOf("liga");
+    expect(face.getFeatureLookups("GSUB", ligaIndex)).to.deep.equal([39]);
+    const kernIndex = face.getTableFeatureTags("GPOS").indexOf("kern");
+    expect(face.getFeatureLookups("GPOS", kernIndex)).to.deep.equal([0, 2]);
+    expect(face.getFeatureLookups("GSUB", 9999)).to.deep.equal([]);
+  });
+
   it("getGlyphClass returns the class of a glyph", function () {
     let blob = new hb.Blob(
       fs.readFileSync(path.join(__dirname, "fonts/noto/NotoSans-Regular.ttf")),