Compute correctly the unitsPerEm value from the fontMatrix when converting a font (bug 1539074)

src/core/fonts.js

@@ -798,7 +798,9 @@ function createOS2Table(properties, charstrings, override) {
   const bbox = properties.bbox || [0, 0, 0, 0];
   const unitsPerEm =
     override.unitsPerEm ||
-    1 / (properties.fontMatrix || FONT_IDENTITY_MATRIX)[0];
+    (properties.fontMatrix
+      ? 1 / Math.max(...properties.fontMatrix.slice(0, 4))
+      : 1000);
 
   // if the font units differ to the PDF glyph space units
   // then scale up the values
@@ -3196,7 +3198,9 @@ class Font {
       properties.seacMap = seacMap;
     }
 
-    const unitsPerEm = 1 / (properties.fontMatrix || FONT_IDENTITY_MATRIX)[0];
+    const unitsPerEm = properties.fontMatrix
+      ? 1 / Math.max(...properties.fontMatrix.slice(0, 4))
+      : 1000;
 
     const builder = new OpenTypeFileBuilder("\x4F\x54\x54\x4F");
     // PostScript Font Program

test/pdfs/.gitignore

@@ -649,3 +649,4 @@
 !tracemonkey_freetext.pdf
 !issue17998.pdf
 !pdfjs_wikipedia.pdf
+!bug1539074.pdf

test/test_manifest.json

@@ -10081,5 +10081,12 @@
     "rounds": 1,
     "link": true,
     "type": "eq"
+  },
+  {
+    "id": "bug1539074",
+    "file": "pdfs/bug1539074.pdf",
+    "md5": "73922be020083d54747af18a4d5e0768",
+    "rounds": 1,
+    "type": "eq"
   }
 ]