Fix loading of Type1 "native" charmap.

anntzer · anntzer · commit d31d6746839b · 2025-04-14T12:13:10.000+02:00
Type1 fonts have a "native" charmap (mapping of indices to glyphs (\*)), which is simply the order in which glyphs are physically listed in the file (see section 2.2 of Type1 reference linked below); this charmap needed when decoding dvi files for usetex mode (as dvi represent glyphs with these indices). Usually, this charmap is tagged as "ADOBE_STANDARD" or "ADOBE_CUSTOM", which is the heuristic we previously used to load it, but it is unclear to me whether this is guaranteed (reference section 10.3), and FreeType may supply its own reencodings (it already does so to try to provide a unicode charmap). Instead, directly read and return the encoding vector via FreeType's Type1-specific API. (The choice to return an mapping of Type1 indices to FreeType-internal indices, rather than Type1 indices to glyph names, is motivated by upcoming changes for {xe,lua}tex support, which also use FreeType-internal indices.) Type1 reference: https://adobe-type-tools.github.io/font-tech-notes/pdfs/T1_SPEC.pdf (\*) Not all glyphs correspond to a unicode codepoint (e.g. a font can contain arbitrary ligatures that are not representable in unicode), which is (one of the reasons) why fonts provide their own indexing methods.
diff --git a/lib/matplotlib/dviread.py b/lib/matplotlib/dviread.py
@@ -1132,7 +1132,6 @@ def _fontfile(cls, suffix, texname):
     import fontTools.agl
 
     from matplotlib.ft2font import FT2Font
-    from matplotlib.textpath import TextToPath
 
     parser = ArgumentParser()
     parser.add_argument("filename")
@@ -1155,14 +1154,13 @@ def _print_fields(*args):
                 print(f"font: {font.texname.decode('latin-1')} "
                       f"(scale: {font._scale / 2 ** 20}) at {fontpath}")
                 face = FT2Font(fontpath)
-                TextToPath._select_native_charmap(face)
                 _print_fields("x", "y", "glyph", "chr", "w")
                 for text in group:
                     if psfont.encoding:
                         glyph_name = _parse_enc(psfont.encoding)[text.glyph]
                     else:
-                        glyph_name = face.get_glyph_name(
-                            face.get_char_index(text.glyph))
+                        encoding_vector = face._get_type1_encoding_vector()
+                        glyph_name = face.get_glyph_name(encoding_vector[text.glyph])
                     glyph_str = fontTools.agl.toUnicode(glyph_name)
                     _print_fields(text.x, text.y, text.glyph, glyph_str, text.width)
             if page.boxes:
diff --git a/lib/matplotlib/textpath.py b/lib/matplotlib/textpath.py
@@ -232,6 +232,7 @@ def get_glyphs_tex(self, prop, s, glyph_map=None,
 
         # Gather font information and do some setup for combining
         # characters into strings.
+        t1_encodings = {}
         for text in page.text:
             font = get_font(text.font_path)
             char_id = self._get_char_id(font, text.glyph)
@@ -241,14 +242,14 @@ def get_glyphs_tex(self, prop, s, glyph_map=None,
                 glyph_name_or_index = text.glyph_name_or_index
                 if isinstance(glyph_name_or_index, str):
                     index = font.get_name_index(glyph_name_or_index)
-                    font.load_glyph(index, flags=LoadFlags.TARGET_LIGHT)
                 elif isinstance(glyph_name_or_index, int):
-                    self._select_native_charmap(font)
-                    font.load_char(
-                        glyph_name_or_index, flags=LoadFlags.TARGET_LIGHT)
+                    if font not in t1_encodings:
+                        t1_encodings[font] = font._get_type1_encoding_vector()
+                    index = t1_encodings[font][glyph_name_or_index]
                 else:  # Should not occur.
                     raise TypeError(f"Glyph spec of unexpected type: "
                                     f"{glyph_name_or_index!r}")
+                font.load_glyph(index, flags=LoadFlags.TARGET_LIGHT)
                 glyph_map_new[char_id] = font.get_path()
 
             glyph_ids.append(char_id)
@@ -269,23 +270,6 @@ def get_glyphs_tex(self, prop, s, glyph_map=None,
         return (list(zip(glyph_ids, xpositions, ypositions, sizes)),
                 glyph_map_new, myrects)
 
-    @staticmethod
-    def _select_native_charmap(font):
-        # Select the native charmap. (we can't directly identify it but it's
-        # typically an Adobe charmap).
-        for charmap_code in [
-                1094992451,  # ADOBE_CUSTOM.
-                1094995778,  # ADOBE_STANDARD.
-        ]:
-            try:
-                font.select_charmap(charmap_code)
-            except (ValueError, RuntimeError):
-                pass
-            else:
-                break
-        else:
-            _log.warning("No supported encoding in font (%s).", font.fname)
-
 
 text_to_path = TextToPath()
 
diff --git a/src/ft2font_wrapper.cpp b/src/ft2font_wrapper.cpp
@@ -498,6 +498,16 @@ PyFT2Font_init(py::object filename, long hinting_factor = 8,
     return self;
 }
 
+static py::str
+PyFT2Font_fname(PyFT2Font *self)
+{
+    if (self->stream.close) {  // Called passed a filename to the constructor.
+        return self->py_file.attr("name");
+    } else {
+        return py::cast<py::str>(self->py_file);
+    }
+}
+
 const char *PyFT2Font_clear__doc__ =
     "Clear all the glyphs, reset for a new call to `.set_text`.";
 
@@ -1431,6 +1441,32 @@ PyFT2Font_get_image(PyFT2Font *self)
     return py::array_t<unsigned char>(dims, im.get_buffer());
 }
 
+const char *PyFT2Font__get_type1_encoding_vector__doc__ = R"""(
+    Return a list mapping CharString indices of a Type 1 font to FreeType glyph indices.
+
+    Returns
+    -------
+    list[int]
+)""";
+
+static std::array<FT_UInt, 256>
+PyFT2Font__get_type1_encoding_vector(PyFT2Font *self)
+{
+    auto face = self->x->get_face();
+    auto indices = std::array<FT_UInt, 256>{};
+    for (auto i = 0u; i < indices.size(); ++i) {
+        auto len = FT_Get_PS_Font_Value(face, PS_DICT_ENCODING_ENTRY, i, nullptr, 0);
+        if (len == -1) {
+            // Explicitly ignore missing entries (mapped to glyph 0 = .notdef).
+            continue;
+        }
+        auto buf = std::make_unique<char[]>(len);
+        FT_Get_PS_Font_Value(face, PS_DICT_ENCODING_ENTRY, i, buf.get(), len);
+        indices[i] = FT_Get_Name_Index(face, buf.get());
+    }
+    return indices;
+}
+
 static const char *
 PyFT2Font_postscript_name(PyFT2Font *self)
 {
@@ -1569,16 +1605,6 @@ PyFT2Font_underline_thickness(PyFT2Font *self)
     return self->x->get_face()->underline_thickness;
 }
 
-static py::str
-PyFT2Font_fname(PyFT2Font *self)
-{
-    if (self->stream.close) {  // Called passed a filename to the constructor.
-        return self->py_file.attr("name");
-    } else {
-        return py::cast<py::str>(self->py_file);
-    }
-}
-
 static py::object
 ft2font__getattr__(std::string name) {
     auto api = py::module_::import("matplotlib._api");
@@ -1761,6 +1787,8 @@ PYBIND11_MODULE(ft2font, m, py::mod_gil_not_used())
              PyFT2Font_get_sfnt_table__doc__)
         .def("get_path", &PyFT2Font_get_path, PyFT2Font_get_path__doc__)
         .def("get_image", &PyFT2Font_get_image, PyFT2Font_get_image__doc__)
+        .def("_get_type1_encoding_vector", &PyFT2Font__get_type1_encoding_vector,
+             PyFT2Font__get_type1_encoding_vector__doc__)
 
         .def_property_readonly("postscript_name", &PyFT2Font_postscript_name,
                                "PostScript name of the font.")
