Implement subsetting for PS backend

aitikgupta · aitikgupta · commit a036962e5abf · 2021-07-14T12:37:10.000+05:30
diff --git a/lib/matplotlib/backends/backend_ps.py b/lib/matplotlib/backends/backend_ps.py
@@ -7,16 +7,18 @@
 from enum import Enum
 import functools
 import glob
-from io import StringIO
+from io import BytesIO, StringIO, TextIOWrapper
 import logging
 import math
 import os
 import pathlib
+import tempfile
 import re
 import shutil
 from tempfile import TemporaryDirectory
 import time
 
+from fontTools import subset
 import numpy as np
 
 import matplotlib as mpl
@@ -27,7 +29,7 @@
     GraphicsContextBase, RendererBase)
 from matplotlib.cbook import is_writable_file_like, file_requires_unicode
 from matplotlib.font_manager import get_font
-from matplotlib.ft2font import LOAD_NO_HINTING, LOAD_NO_SCALE
+from matplotlib.ft2font import LOAD_NO_HINTING, LOAD_NO_SCALE, FT2Font
 from matplotlib._ttconv import convert_ttf_to_ps
 from matplotlib.mathtext import MathTextParser
 from matplotlib._mathtext_data import uni2type1
@@ -954,8 +956,36 @@ def print_figure_impl(fh):
                         fh.write(_font_to_ps_type3(font_path, glyph_ids))
                     else:
                         try:
-                            convert_ttf_to_ps(os.fsencode(font_path),
-                                              fh, fonttype, glyph_ids)
+                            _log.debug(
+                                f"SUBSET {font_path} characters: "
+                                f"{''.join(chr(c) for c in chars)}"
+                            )
+                            fontdata = getSubset(
+                                font_path, "".join(chr(c) for c in chars)
+                            )
+                            _log.debug(
+                                f"SUBSET {font_path} "
+                                f"{os.stat(font_path).st_size} "
+                                f"↦ {len(fontdata)}"
+                            )
+
+                            # give ttconv a subsetted font
+                            # along with updated glyph_ids
+                            with tempfile.NamedTemporaryFile(
+                                suffix=".ttf"
+                            ) as tmp:
+                                tmp.write(fontdata)
+                                tmp.seek(0, 0)
+                                font = FT2Font(tmp.name)
+                                glyph_ids = [
+                                    font.get_char_index(c) for c in chars
+                                ]
+                                convert_ttf_to_ps(
+                                    os.fsencode(tmp.name),
+                                    fh,
+                                    fonttype,
+                                    glyph_ids,
+                                )
                         except RuntimeError:
                             _log.warning(
                                 "The PostScript backend does not currently "
