Use glyph indices for font tracking in vector formats

With libraqm, string layout produces glyph indices, not character codes,
and font features may even produce different glyphs for the same
character code (e.g., by picking a different Stylistic Set). Thus we
cannot rely on character codes as unique items within a font, and must
move toward glyph indices everywhere.

Author: QuLogic

lib/matplotlib/_mathtext.py

@@ -37,7 +37,7 @@
 
 if T.TYPE_CHECKING:
     from collections.abc import Iterable
-    from .ft2font import CharacterCodeType, Glyph
+    from .ft2font import CharacterCodeType, Glyph, GlyphIndexType
 
 
 ParserElement.enable_packrat()
@@ -86,7 +86,7 @@ class VectorParse(NamedTuple):
     width: float
     height: float
     depth: float
-    glyphs: list[tuple[FT2Font, float, CharacterCodeType, float, float]]
+    glyphs: list[tuple[FT2Font, float, GlyphIndexType, float, float]]
     rects: list[tuple[float, float, float, float]]
 
 VectorParse.__module__ = "matplotlib.mathtext"
@@ -131,7 +131,7 @@ def __init__(self, box: Box):
     def to_vector(self) -> VectorParse:
         w, h, d = map(
             np.ceil, [self.box.width, self.box.height, self.box.depth])
-        gs = [(info.font, info.fontsize, info.num, ox, h - oy + info.offset)
+        gs = [(info.font, info.fontsize, info.glyph_id, ox, h - oy + info.offset)
               for ox, oy, info in self.glyphs]
         rs = [(x1, h - y2, x2 - x1, y2 - y1)
               for x1, y1, x2, y2 in self.rects]
@@ -213,7 +213,7 @@ class FontInfo(NamedTuple):
     fontsize: float
     postscript_name: str
     metrics: FontMetrics
-    num: CharacterCodeType
+    glyph_id: GlyphIndexType
     glyph: Glyph
     offset: float
 
@@ -374,7 +374,8 @@ def _get_info(self, fontname: str, font_class: str, sym: str, fontsize: float,
                   dpi: float) -> FontInfo:
         font, num, slanted = self._get_glyph(fontname, font_class, sym)
         font.set_size(fontsize, dpi)
-        glyph = font.load_char(num, flags=self.load_glyph_flags)
+        glyph_id = font.get_char_index(num)
+        glyph = font.load_glyph(glyph_id, flags=self.load_glyph_flags)
 
         xmin, ymin, xmax, ymax = (val / 64 for val in glyph.bbox)
         offset = self._get_offset(font, glyph, fontsize, dpi)
@@ -396,7 +397,7 @@ def _get_info(self, fontname: str, font_class: str, sym: str, fontsize: float,
             fontsize=fontsize,
             postscript_name=font.postscript_name,
             metrics=metrics,
-            num=num,
+            glyph_id=glyph_id,
             glyph=glyph,
             offset=offset
         )
@@ -426,8 +427,7 @@ def get_kern(self, font1: str, fontclass1: str, sym1: str, fontsize1: float,
             info1 = self._get_info(font1, fontclass1, sym1, fontsize1, dpi)
             info2 = self._get_info(font2, fontclass2, sym2, fontsize2, dpi)
             font = info1.font
-            return font.get_kerning(font.get_char_index(info1.num),
-                                    font.get_char_index(info2.num),
+            return font.get_kerning(info1.glyph_id, info2.glyph_id,
                                     Kerning.DEFAULT) / 64
         return super().get_kern(font1, fontclass1, sym1, fontsize1,
                                 font2, fontclass2, sym2, fontsize2, dpi)

lib/matplotlib/_text_helpers.py

@@ -14,7 +14,7 @@
 class LayoutItem:
     ft_object: FT2Font
     char: str
-    glyph_idx: GlyphIndexType
+    glyph_index: GlyphIndexType
     x: float
     prev_kern: float
 

lib/matplotlib/backends/_backend_pdf_ps.py

@@ -20,27 +20,27 @@ def _cached_get_afm_from_fname(fname):
         return AFM(fh)
 
 
-def get_glyphs_subset(fontfile, characters):
+def get_glyphs_subset(fontfile, glyphs):
     """
-    Subset a TTF font
+    Subset a TTF font.
 
-    Reads the named fontfile and restricts the font to the characters.
+    Reads the named fontfile and restricts the font to the glyphs.
 
     Parameters
     ----------
     fontfile : str
         Path to the font file
-    characters : str
-        Continuous set of characters to include in subset
+    glyphs : set[int]
+        Set of glyph IDs to include in subset.
 
     Returns
     -------
     fontTools.ttLib.ttFont.TTFont
         An open font object representing the subset, which needs to
         be closed by the caller.
     """
-
-    options = subset.Options(glyph_names=True, recommended_glyphs=True)
+    options = subset.Options(glyph_names=True, recommended_glyphs=True,
+                             retain_gids=True)
 
     # Prevent subsetting extra tables.
     options.drop_tables += [
@@ -71,7 +71,7 @@ def get_glyphs_subset(fontfile, characters):
 
     font = subset.load_font(fontfile, options)
     subsetter = subset.Subsetter(options=options)
-    subsetter.populate(text=characters)
+    subsetter.populate(gids=glyphs)
     subsetter.subset(font)
     return font
 
@@ -97,10 +97,10 @@ def font_as_file(font):
 
 class CharacterTracker:
     """
-    Helper for font subsetting by the pdf and ps backends.
+    Helper for font subsetting by the PDF and PS backends.
 
-    Maintains a mapping of font paths to the set of character codepoints that
-    are being used from that font.
+    Maintains a mapping of font paths to the set of glyphs that are being used from that
+    font.
     """
 
     def __init__(self):
@@ -110,10 +110,11 @@ def track(self, font, s):
         """Record that string *s* is being typeset using font *font*."""
         char_to_font = font._get_fontmap(s)
         for _c, _f in char_to_font.items():
-            self.used.setdefault(_f.fname, set()).add(ord(_c))
+            glyph_index = _f.get_char_index(ord(_c))
+            self.used.setdefault(_f.fname, set()).add(glyph_index)
 
     def track_glyph(self, font, glyph):
-        """Record that codepoint *glyph* is being typeset using font *font*."""
+        """Record that glyph index *glyph* is being typeset using font *font*."""
         self.used.setdefault(font.fname, set()).add(glyph)
 
 

lib/matplotlib/backends/backend_cairo.py

@@ -8,6 +8,7 @@
 
 import functools
 import gzip
+import itertools
 import math
 
 import numpy as np
@@ -248,13 +249,12 @@ def _draw_mathtext(self, gc, x, y, s, prop, angle):
         if angle:
             ctx.rotate(np.deg2rad(-angle))
 
-        for font, fontsize, idx, ox, oy in glyphs:
+        for (font, fontsize), font_glyphs in itertools.groupby(
+                glyphs, key=lambda x: (x[0], x[1])):
             ctx.new_path()
-            ctx.move_to(ox, -oy)
-            ctx.select_font_face(
-                *_cairo_font_args_from_font_prop(ttfFontProperty(font)))
+            ctx.select_font_face(*_cairo_font_args_from_font_prop(ttfFontProperty(font)))
             ctx.set_font_size(self.points_to_pixels(fontsize))
-            ctx.show_text(chr(idx))
+            ctx.show_glyphs([(idx, ox, -oy) for _, _, idx, ox, oy in font_glyphs])
 
         for ox, oy, w, h in rects:
             ctx.new_path()

lib/matplotlib/backends/backend_pdf.py

@@ -960,9 +960,9 @@ def writeFonts(self):
             else:
                 # a normal TrueType font
                 _log.debug('Writing TrueType font.')
-                chars = self._character_tracker.used.get(filename)
-                if chars:
-                    fonts[Fx] = self.embedTTF(filename, chars)
+                glyphs = self._character_tracker.used.get(filename)
+                if glyphs:
+                    fonts[Fx] = self.embedTTF(filename, glyphs)
         self.writeObject(self.fontObject, fonts)
 
     def _write_afm_font(self, filename):
@@ -1136,9 +1136,8 @@ def _get_xobject_glyph_name(self, filename, glyph_name):
 end
 end"""
 
-    def embedTTF(self, filename, characters):
+    def embedTTF(self, filename, glyphs):
         """Embed the TTF font from the named file into the document."""
-
         font = get_font(filename)
         fonttype = mpl.rcParams['pdf.fonttype']
 
@@ -1153,7 +1152,7 @@ def cvt(length, upe=font.units_per_EM, nearest=True):
             else:
                 return math.ceil(value)
 
-        def embedTTFType3(font, characters, descriptor):
+        def embedTTFType3(font, glyphs, descriptor):
             """The Type 3-specific part of embedding a Truetype font"""
             widthsObject = self.reserveObject('font widths')
             fontdescObject = self.reserveObject('font descriptor')
@@ -1200,15 +1199,13 @@ def get_char_width(charcode):
             # Make the "Differences" array, sort the ccodes < 255 from
             # the multi-byte ccodes, and build the whole set of glyph ids
             # that we need from this font.
-            glyph_ids = []
             differences = []
             multi_byte_chars = set()
-            for c in characters:
-                ccode = c
-                gind = font.get_char_index(ccode)
-                glyph_ids.append(gind)
+            charmap = {gind: ccode for ccode, gind in font.get_charmap().items()}
+            for gind in glyphs:
                 glyph_name = font.get_glyph_name(gind)
-                if ccode <= 255:
+                ccode = charmap.get(gind)
+                if ccode is not None and ccode <= 255:
                     differences.append((ccode, glyph_name))
                 else:
                     multi_byte_chars.add(glyph_name)
@@ -1222,7 +1219,7 @@ def get_char_width(charcode):
                 last_c = c
 
             # Make the charprocs array.
-            rawcharprocs = _get_pdf_charprocs(filename, glyph_ids)
+            rawcharprocs = _get_pdf_charprocs(filename, glyphs)
             charprocs = {}
             for charname in sorted(rawcharprocs):
                 stream = rawcharprocs[charname]
@@ -1259,7 +1256,7 @@ def get_char_width(charcode):
 
             return fontdictObject
 
-        def embedTTFType42(font, characters, descriptor):
+        def embedTTFType42(font, glyphs, descriptor):
             """The Type 42-specific part of embedding a Truetype font"""
             fontdescObject = self.reserveObject('font descriptor')
             cidFontDictObject = self.reserveObject('CID font dictionary')
@@ -1269,9 +1266,8 @@ def embedTTFType42(font, characters, descriptor):
             wObject = self.reserveObject('Type 0 widths')
             toUnicodeMapObject = self.reserveObject('ToUnicode map')
 
-            subset_str = "".join(chr(c) for c in characters)
-            _log.debug("SUBSET %s characters: %s", filename, subset_str)
-            with _backend_pdf_ps.get_glyphs_subset(filename, subset_str) as subset:
+            _log.debug("SUBSET %s characters: %s", filename, glyphs)
+            with _backend_pdf_ps.get_glyphs_subset(filename, glyphs) as subset:
                 fontdata = _backend_pdf_ps.font_as_file(subset)
             _log.debug(
                 "SUBSET %s %d -> %d", filename,
@@ -1319,11 +1315,11 @@ def embedTTFType42(font, characters, descriptor):
             cid_to_gid_map = ['\0'] * 65536
             widths = []
             max_ccode = 0
-            for c in characters:
-                ccode = c
-                gind = font.get_char_index(ccode)
-                glyph = font.load_char(ccode,
-                                       flags=LoadFlags.NO_SCALE | LoadFlags.NO_HINTING)
+            charmap = {gind: ccode for ccode, gind in font.get_charmap().items()}
+            for gind in glyphs:
+                glyph = font.load_glyph(gind,
+                                        flags=LoadFlags.NO_SCALE | LoadFlags.NO_HINTING)
+                ccode = charmap[gind]
                 widths.append((ccode, cvt(glyph.horiAdvance)))
                 if ccode < 65536:
                     cid_to_gid_map[ccode] = chr(gind)
@@ -1361,11 +1357,10 @@ def embedTTFType42(font, characters, descriptor):
                             (len(unicode_groups), b"\n".join(unicode_bfrange)))
 
             # Add XObjects for unsupported chars
-            glyph_ids = []
-            for ccode in characters:
-                if not _font_supports_glyph(fonttype, ccode):
-                    gind = full_font.get_char_index(ccode)
-                    glyph_ids.append(gind)
+            glyph_ids = [
+                gind for gind in glyphs
+                if not _font_supports_glyph(fonttype, charmap[gind])
+            ]
 
             bbox = [cvt(x, nearest=False) for x in full_font.bbox]
             rawcharprocs = _get_pdf_charprocs(filename, glyph_ids)
@@ -1450,9 +1445,9 @@ def embedTTFType42(font, characters, descriptor):
             }
 
         if fonttype == 3:
-            return embedTTFType3(font, characters, descriptor)
+            return embedTTFType3(font, glyphs, descriptor)
         elif fonttype == 42:
-            return embedTTFType42(font, characters, descriptor)
+            return embedTTFType42(font, glyphs, descriptor)
 
     def alphaState(self, alpha):
         """Return name of an ExtGState that sets alpha to the given value."""
@@ -2215,28 +2210,32 @@ def draw_mathtext(self, gc, x, y, s, prop, angle):
         oldx, oldy = 0, 0
         unsupported_chars = []
 
+        font_charmaps = {}
         self.file.output(Op.begin_text)
-        for font, fontsize, num, ox, oy in glyphs:
-            self.file._character_tracker.track_glyph(font, num)
+        for font, fontsize, glyph_index, ox, oy in glyphs:
+            self.file._character_tracker.track_glyph(font, glyph_index)
             fontname = font.fname
-            if not _font_supports_glyph(fonttype, num):
+            if font not in font_charmaps:
+                font_charmaps[font] = {gind: ccode
+                                       for ccode, gind in font.get_charmap().items()}
+            ccode = font_charmaps[font].get(glyph_index)
+            if ccode is None or not _font_supports_glyph(fonttype, ccode):
                 # Unsupported chars (i.e. multibyte in Type 3 or beyond BMP in
                 # Type 42) must be emitted separately (below).
-                unsupported_chars.append((font, fontsize, ox, oy, num))
+                unsupported_chars.append((font, fontsize, ox, oy, glyph_index))
             else:
                 self._setup_textpos(ox, oy, 0, oldx, oldy)
                 oldx, oldy = ox, oy
                 if (fontname, fontsize) != prev_font:
                     self.file.output(self.file.fontName(fontname), fontsize,
                                      Op.selectfont)
                     prev_font = fontname, fontsize
-                self.file.output(self.encode_string(chr(num), fonttype),
+                self.file.output(self.encode_string(chr(ccode), fonttype),
                                  Op.show)
         self.file.output(Op.end_text)
 
-        for font, fontsize, ox, oy, num in unsupported_chars:
-            self._draw_xobject_glyph(
-                font, fontsize, font.get_char_index(num), ox, oy)
+        for font, fontsize, ox, oy, glyph_index in unsupported_chars:
+            self._draw_xobject_glyph(font, fontsize, glyph_index, ox, oy)
 
         # Draw any horizontal lines in the math layout
         for ox, oy, width, height in rects:
@@ -2399,7 +2398,7 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
                     singlebyte_chunks[-1][2].append(item.char)
                     prev_was_multibyte = False
                 else:
-                    multibyte_glyphs.append((item.ft_object, item.x, item.glyph_idx))
+                    multibyte_glyphs.append((item.ft_object, item.x, item.glyph_index))
                     prev_was_multibyte = True
             # Do the rotation and global translation as a single matrix
             # concatenation up front
@@ -2409,7 +2408,6 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
                              -math.sin(a), math.cos(a),
                              x, y, Op.concat_matrix)
             # Emit all the 1-byte characters in a BT/ET group.
-
             self.file.output(Op.begin_text)
             prev_start_x = 0
             for ft_object, start_x, kerns_or_chars in singlebyte_chunks: