Prevent adding identity transforms to the document

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Add subset for PDF/UA
 - Fix for line breaks in list items (#1486)
 - Fix for soft hyphen not being replaced by visible hyphen if necessary (#457)
+- Optimize output files by ignoring identity transforms
 
 ### [v0.14.0] - 2023-11-09
 

lib/mixins/vector.js

@@ -289,6 +289,10 @@ export default {
 
   transform(m11, m12, m21, m22, dx, dy) {
     // keep track of the current transformation matrix
+    if (m11 === 1 && m12 === 0 && m21 === 0 && m22 === 1 && dx === 0 && dy === 0) {
+      // Ignore identity transforms
+      return this;
+    }
     const m = this._ctm;
     const [m0, m1, m2, m3, m4, m5] = m;
     m[0] = m0 * m11 + m2 * m12;

tests/unit/vector.spec.js

@@ -164,4 +164,26 @@ describe('Vector Graphics', () => {
       });
     });
   });
+
+  describe('translate', () => {
+    test('identity transform is ignored', () => {
+      const docData = logData(document);
+      const vectorStream = Buffer.from(`1 0 0 -1 0 792 cm\n1 0 0 1 0 0 cm\n`, 'binary');
+
+      document
+        .translate(0, 0);
+      document.end();
+
+      expect(docData).not.toContainChunk([
+        `5 0 obj`,
+        `<<
+/Length 33
+>>`,
+        `stream`,
+        vectorStream,
+        `\nendstream`,
+        `endobj`
+      ]);
+    });
+  });
 });