Implement noLayoutClosure flag, closes #22

Author: papandreou

README.md

@@ -52,6 +52,7 @@ Options:
 - `targetFormat` - the format to output, can be either `'sfnt'`, `'woff'`, or `'woff2'`.
 - `preserveNameIds` - an array of numbers specifying the extra name ids to preserve in the `name` table. By default the harfbuzz subsetter drops most of these. Use case described [here](https://github.com/papandreou/subset-font/issues/7).
 - `variationAxes` - an object specifying a full or partial instancing of variation axes in the font. Only works with variable fonts. See the example above.
+- `noLayoutClosure` - don't perform glyph closure for layout substitution (GSUB). Equivalent to `hb-subset --no-layout-closure` and `pyftsubset --no-layout-closure`.
 
 For backwards compatibility reasons, `'truetype'` is supported as an alias for `'sfnt'`.
 

index.js

@@ -27,6 +27,7 @@ async function subsetFont(
     targetFormat = fontverter.detectFormat(originalFont),
     preserveNameIds,
     variationAxes,
+    noLayoutClosure,
   } = {}
 ) {
   if (typeof text !== 'string') {
@@ -76,6 +77,13 @@ async function subsetFont(
     }
   }
 
+  if (noLayoutClosure) {
+    exports.hb_subset_input_set_flags(
+      input,
+      exports.hb_subset_input_get_flags(input) | 0x00000200 // HB_SUBSET_FLAGS_NO_LAYOUT_CLOSURE
+    );
+  }
+
   // Add unicodes indices
   const inputUnicodes = exports.hb_subset_input_unicode_set(input);
   for (const c of text) {

test/index.js

@@ -253,6 +253,51 @@ describe('subset-font', function () {
     });
   });
 
+  // https://github.com/papandreou/subset-font/issues/22
+  describe('with an icon font', function () {
+    before(async function () {
+      this.materialIconsFont = await readFile(
+        pathModule.resolve(
+          __dirname,
+          '..',
+          'testdata',
+          'MaterialIcons-Regular.ttf'
+        )
+      );
+    });
+
+    describe('without the noLayoutClosure flag', function () {
+      it('should retain more glyphs', async function () {
+        const result = await subsetFont(
+          this.materialIconsFont,
+          `_abcdefghijklmnopqrstuvwxyz0123456789${String.fromCodePoint(
+            0xe5c5,
+            0xe5c8
+          )}`
+        );
+
+        expect(result.length, 'to be greater than', 300000);
+      });
+    });
+
+    describe('with the noLayoutClosure flag', function () {
+      it('should retain more glyphs', async function () {
+        const result = await subsetFont(
+          this.materialIconsFont,
+          `_abcdefghijklmnopqrstuvwxyz0123456789${String.fromCodePoint(
+            0xe5c5,
+            0xe5c8
+          )}`,
+          {
+            noLayoutClosure: true,
+          }
+        );
+
+        expect(result.length, 'to be less than', 3000);
+      });
+    });
+  });
+
   describe('with a truncated font', function () {
     before(async function () {
       this.truncatedTtfFont = (