feat: add ability to retrieve only the ligature ranges

princjef · May 3, 2018 · f120430 · f120430
1 parent 8b5b89c
commit f120430
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Showing 5 changed files with 62 additions and 17 deletions.
diff --git a/README.md b/README.md
@@ -63,6 +63,11 @@ following keys:
    be rendered together to produce the ligatures in the output sequence. The
    ranges are inclusive on the left and exclusive on the right
 
+#### `findLigatureRanges(text)`
+
+Scans the provided text for font ligatures, returning an array of ranges where
+ligatures are located.
+
 **Params**
 
  * `text` [*string*] - text to search for ligatures

diff --git a/bench/all.js b/bench/all.js
@@ -19,49 +19,49 @@ setup(async () => {
 
 test('Fira Code: code.txt', (context, iteration) => {
     const line = code[iteration % code.length];
-    context.fira.findLigatures(line);
+    context.fira.findLigatureRanges(line);
     return line.length;
 });
 
 test('Fira Code: noLigatures.txt', (context, iteration) => {
     const line = noLigatures[iteration % noLigatures.length];
-    context.fira.findLigatures(line);
+    context.fira.findLigatureRanges(line);
     return line.length;
 });
 
 test('Iosevka: code.txt', (context, iteration) => {
     const line = code[iteration % code.length];
-    context.iosevka.findLigatures(line);
+    context.iosevka.findLigatureRanges(line);
     return line.length;
 });
 
 test('Iosevka: noLigatures.txt', (context, iteration) => {
     const line = noLigatures[iteration % noLigatures.length];
-    context.iosevka.findLigatures(line);
+    context.iosevka.findLigatureRanges(line);
     return line.length;
 });
 
 test('Monoid: code.txt', (context, iteration) => {
     const line = code[iteration % code.length];
-    context.monoid.findLigatures(line);
+    context.monoid.findLigatureRanges(line);
     return line.length;
 });
 
 test('Monoid: noLigatures.txt', (context, iteration) => {
     const line = noLigatures[iteration % noLigatures.length];
-    context.monoid.findLigatures(line);
+    context.monoid.findLigatureRanges(line);
     return line.length;
 });
 
 test('Ubuntu Mono: code.txt', (context, iteration) => {
     const line = code[iteration % code.length];
-    context.ubuntu.findLigatures(line);
+    context.ubuntu.findLigatureRanges(line);
     return line.length;
 });
 
 test('Ubuntu Mono: noLigatures.txt', (context, iteration) => {
     const line = noLigatures[iteration % noLigatures.length];
-    context.ubuntu.findLigatures(line);
+    context.ubuntu.findLigatureRanges(line);
     return line.length;
 });
 

diff --git a/src/index.spec.ts b/src/index.spec.ts
@@ -309,10 +309,16 @@ for (const { font, input, glyphs, ranges } of [
     ...monoidCases,
     ...otherCases
 ]) {
-    test(`${font}: '${input}'`, async t => {
+    test(`findLigatures() > ${font}: '${input}'`, async t => {
         const inst = await load(font);
         const result = inst.findLigatures(input);
         t.deepEqual(result.outputGlyphs, glyphs);
         t.deepEqual(result.contextRanges, ranges);
     });
+
+    test(`findLigatureRanges() > ${font}: '${input}'`, async t => {
+        const inst = await load(font);
+        const result = inst.findLigatureRanges(input);
+        t.deepEqual(result, ranges);
+    });
 }
diff --git a/src/index.ts b/src/index.ts
@@ -44,37 +44,63 @@ class FontImpl implements Font {
             };
         }
 
-        let result: number[] = glyphIds.slice();
+        const result = this._findInternal(glyphIds.slice());
+
+        return {
+            inputGlyphs: glyphIds,
+            outputGlyphs: result.sequence,
+            contextRanges: result.ranges
+        };
+    }
+
+    findLigatureRanges(text: string): [number, number][] {
+        // Short circuit the process if there are no possible ligatures in the
+        // font
+        if (this._lookupGroups.length === 0) {
+            return [];
+        }
+
+        const glyphIds: number[] = [];
+        for (const char of text) {
+            glyphIds.push(this._font.charToGlyphIndex(char));
+        }
+
+        const result = this._findInternal(glyphIds);
+
+        return result.ranges;
+    }
+
+    private _findInternal(sequence: number[]): { sequence: number[]; ranges: [number, number][]; } {
         const individualContextRanges: [number, number][] = [];
 
         for (const lookup of this._lookupGroups) {
             switch (lookup.lookupType) {
                 // https://docs.microsoft.com/en-us/typography/opentype/spec/gsub#lookuptype-6-chaining-contextual-substitution-subtable
                 case 6:
-                    for (let index = 0; index < result.length; index++) {
+                    for (let index = 0; index < sequence.length; index++) {
                         for (const table of lookup.subtables) {
                             let res: SubstitutionResult | null = null;
                             switch (table.substFormat) {
                                 case 1:
                                     res = processGsubType6Format1(
                                         table,
-                                        result,
+                                        sequence,
                                         index,
                                         this._font.tables.gsub.lookups
                                     );
                                     break;
                                 case 2:
                                     res = processGsubType6Format2(
                                         table,
-                                        result,
+                                        sequence,
                                         index,
                                         this._font.tables.gsub.lookups
                                     );
                                     break;
                                 case 3:
                                     res = processGsubType6Format3(
                                         table,
-                                        result,
+                                        sequence,
                                         index,
                                         this._font.tables.gsub.lookups
                                     );
@@ -94,11 +120,11 @@ class FontImpl implements Font {
                     break;
                 // https://docs.microsoft.com/en-us/typography/opentype/spec/gsub#lookuptype-8-reverse-chaining-contextual-single-substitution-subtable
                 case 8:
-                    for (let index = result.length - 1; index >= 0; index--) {
+                    for (let index = sequence.length - 1; index >= 0; index--) {
                         for (const table of lookup.subtables) {
                             const res = processGsubType8Format1(
                                 table,
-                                result,
+                                sequence,
                                 index
                             );
 
@@ -137,7 +163,7 @@ class FontImpl implements Font {
             }
         }
 
-        return { inputGlyphs: glyphIds, outputGlyphs: result, contextRanges };
+        return { sequence, ranges: contextRanges };
     }
 }
 

diff --git a/src/types.ts b/src/types.ts
@@ -33,4 +33,12 @@ export interface Font {
      * @param text String to search for ligatures
      */
     findLigatures(text: string): LigatureData;
+
+    /**
+     * Scans the provided text for font ligatures, returning an array of ranges
+     * where ligatures are located.
+     *
+     * @param text String to search for ligatures
+     */
+    findLigatureRanges(text: string): [number, number][];
 }