Add Fallback '.notdef' Glyph for Improved Cross-Platform TrueType Font Support (py-pdf#1352)

* Add fallback '.notdef' glyph

* add logging for missing .notdef glyph in TrueType fonts & add missing imports

* add test for handling missing .notdef glyph in TrueType fonts. add font missing this glyph.

* update CHANGELOG.md

* Cannot include commercial font

* Generate a more consistent .notdef outline instead of using arbitrary values

* Modify test to use a test font instead of a commercial font

* upload a reference notdef font file

* assign to variable to avoid being a 'pointless-statement'

* Add a comment explaining lazy loading in fontTools.

* Regenerate test font

* Remove test font generation script within test

* Remove unused TTFont import

Author: spacegaori

CHANGELOG.md

@@ -25,6 +25,7 @@ This can also be enabled programmatically with `warnings.simplefilter('default',
 * support for [`v_align` at the row level in tables](https://py-pdf.github.io/fpdf2/Tables.html#setting-vertical-alignment-of-text-in-cells)
 * documentation on [verifying provenance of `fpdf2` releases](https://py-pdf.github.io/fpdf2/#verifying-provenance)
 * documentation on [`fpdf2` internals](https://py-pdf.github.io/fpdf2/Internals.html)
+* support for adding TrueType fonts that are missing the .notdef glyph - [issue #1161](https://github.com/py-pdf/fpdf2/issues/1161)
 ### Fixed
 * [`FPDF.write_html()`](https://py-pdf.github.io/fpdf2/fpdf/fpdf.html#fpdf.fpdf.FPDF.write_html): Fixed rendering of content following `<a>` tags; now correctly resets emphasis style post `</a>` tag: hyperlink styling contained within the tag authority. - [Issue #1311](https://github.com/py-pdf/fpdf2/issues/1311)
 

fpdf/fonts.py

@@ -8,6 +8,7 @@
 """
 
 import re, warnings
+import logging
 
 from bisect import bisect_left
 from collections import defaultdict
@@ -16,6 +17,7 @@
 from typing import List, Optional, Tuple, Union
 
 from fontTools import ttLib
+from fontTools.pens.ttGlyphPen import TTGlyphPen
 
 try:
     import uharfbuzz as hb
@@ -37,6 +39,8 @@ def __deepcopy__(self, _memo):
 from .syntax import Name, PDFObject
 from .util import escape_parens
 
+LOGGER = logging.getLogger(__name__)
+
 
 @dataclass
 class FontFace:
@@ -267,6 +271,40 @@ def __init__(self, fpdf, font_file_path, fontkey, style):
         )
 
         self.scale = 1000 / self.ttfont["head"].unitsPerEm
+
+        # check if the font is a TrueType and missing a .notdef glyph
+        # if it is missing, provide a fallback glyph
+        if "glyf" in self.ttfont and ".notdef" not in self.ttfont["glyf"]:
+            LOGGER.warning(
+                (
+                    "TrueType Font '%s' is missing the '.notdef' glyph. "
+                    "Fallback glyph will be provided."
+                ),
+                self.fontkey,
+            )
+            # draw a diagonal cross .notdef glyph
+            (xMin, xMax, yMin, yMax) = (
+                self.ttfont["head"].xMin,
+                self.ttfont["head"].xMax,
+                self.ttfont["head"].yMin,
+                self.ttfont["head"].yMax,
+            )
+            pen = TTGlyphPen(self.ttfont["glyf"])
+            pen.moveTo((xMin, yMin))
+            pen.lineTo((xMax, yMin))
+            pen.lineTo((xMax, yMax))
+            pen.lineTo((xMin, yMax))
+            pen.closePath()
+            pen.moveTo((xMin, yMin))
+            pen.lineTo((xMax, yMax))
+            pen.closePath()
+            pen.moveTo((xMax, yMin))
+            pen.lineTo((xMin, yMax))
+            pen.closePath()
+
+            self.ttfont["glyf"][".notdef"] = pen.glyph()
+            self.ttfont["hmtx"][".notdef"] = (xMax - xMin, yMax - yMin)
+
         default_width = round(self.scale * self.ttfont["hmtx"].metrics[".notdef"][0])
 
         os2_table = self.ttfont["OS/2"]

test/fonts/Roboto-Regular-without-notdef.ttf

@@ -144,6 +144,16 @@ def test_add_font_uppercase():
     assert pdf.fonts is not None and len(pdf.fonts) != 0  # fonts add successful
 
 
+def test_add_font_missing_notdef_glyph(caplog):
+    pdf = FPDF()
+    pdf.add_font(family="Roboto", fname=HERE / "Roboto-Regular-without-notdef.ttf")
+    assert pdf.fonts is not None and len(pdf.fonts) != 0  # fonts add successful
+    assert (
+        "TrueType Font 'roboto' is missing the '.notdef' glyph. "
+        "Fallback glyph will be provided."
+    ) in caplog.text
+
+
 def test_font_missing_glyphs(caplog):
     pdf = FPDF()
     pdf.add_page()