pgf: Support any font in a collection

Note, this only has an effect if set as the global font. Otherwise, just
the font name is recorded, and the TeX engine's normal lookup is
performed.

Author: QuLogic

lib/matplotlib/backends/backend_pgf.py

@@ -38,9 +38,17 @@
 
 def _get_preamble():
     """Prepare a LaTeX preamble based on the rcParams configuration."""
-    font_size_pt = FontProperties(
-        size=mpl.rcParams["font.size"]
-    ).get_size_in_points()
+    def _to_fontspec():
+        for command, family in [("setmainfont", "serif"),
+                                ("setsansfont", "sans\\-serif"),
+                                ("setmonofont", "monospace")]:
+            font_path = fm.findfont(family)
+            path = pathlib.Path(font_path)
+            yield r"  \%s{%s}[Path=\detokenize{%s/}%s]" % (
+                command, path.name, path.parent.as_posix(),
+                f',FontIndex={font_path.face_index:d}' if path.suffix == '.ttc' else '')
+
+    font_size_pt = FontProperties(size=mpl.rcParams["font.size"]).get_size_in_points()
     return "\n".join([
         # Remove Matplotlib's custom command \mathdefault.  (Not using
         # \mathnormal instead since this looks odd with Computer Modern.)
@@ -63,15 +71,8 @@ def _get_preamble():
         *([
             r"\ifdefined\pdftexversion\else  % non-pdftex case.",
             r"  \usepackage{fontspec}",
-        ] + [
-            r"  \%s{%s}[Path=\detokenize{%s/}]"
-            % (command, path.name, path.parent.as_posix())
-            for command, path in zip(
-                ["setmainfont", "setsansfont", "setmonofont"],
-                [pathlib.Path(fm.findfont(family))
-                 for family in ["serif", "sans\\-serif", "monospace"]]
-            )
-        ] + [r"\fi"] if mpl.rcParams["pgf.rcfonts"] else []),
+            *_to_fontspec(),
+            r"\fi"] if mpl.rcParams["pgf.rcfonts"] else []),
         # Documented as "must come last".
         mpl.texmanager._usepackage_if_not_loaded("underscore", option="strings"),
     ])

lib/matplotlib/tests/baseline_images/test_backend_pgf/ttc_pgf.pdf

@@ -1,14 +1,17 @@
 import datetime
 from io import BytesIO
 import os
+from pathlib import Path
 import shutil
+import string
 
 import numpy as np
 from packaging.version import parse as parse_version
 import pytest
 
 import matplotlib as mpl
 import matplotlib.pyplot as plt
+from matplotlib.font_manager import FontProperties, findfont
 from matplotlib.testing import _has_tex_package, _check_for_pgf
 from matplotlib.testing.exceptions import ImageComparisonFailure
 from matplotlib.testing.compare import compare_images
@@ -330,6 +333,23 @@ def test_png_transparency():  # Actually, also just testing that png works.
     assert (t[..., 3] == 0).all()  # fully transparent.
 
 
+@needs_pgf_xelatex
+@pytest.mark.backend('pgf')
+@image_comparison(['ttc_pgf.pdf'], style='mpl20')
+def test_ttc_output():
+    fp = FontProperties(family=['WenQuanYi Zen Hei'])
+    if Path(findfont(fp)).name != 'wqy-zenhei.ttc':
+        pytest.skip('Font wqy-zenhei.ttc may be missing')
+
+    fonts = {'sans-serif': 'WenQuanYi Zen Hei', 'monospace': 'WenQuanYi Zen Hei Mono'}
+    plt.rc('font', size=16, **fonts)
+
+    figs = plt.figure(figsize=(7, len(fonts) / 2)).subfigures(len(fonts))
+    for font, fig in zip(fonts.values(), figs):
+        fig.text(0.5, 0.5, f'{font}: {string.ascii_uppercase}', font=font,
+                 horizontalalignment='center', verticalalignment='center')
+
+
 @needs_pgf_xelatex
 def test_unknown_font(caplog):
     with caplog.at_level("WARNING"):