Merge pull request matplotlib#23638 from tacaswell/svg_generic_fonts

FIX: correctly handle generic font families in svg text-as-text mode

Author: tacaswell

lib/matplotlib/backends/backend_svg.py

@@ -1153,10 +1153,48 @@ def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
             weight = fm.weight_dict[prop.get_weight()]
             if weight != 400:
                 font_parts.append(f'{weight}')
+
+            def _format_font_name(fn):
+                normalize_names = {
+                    'sans': 'sans-serif',
+                    'sans serif': 'sans-serif'
+                }
+                # A generic font family.  We need to do two things:
+                #  1. list all of the configured fonts with quoted names
+                #  2. append the generic name unquoted
+                if fn in fm.font_family_aliases:
+                    # fix spelling of sans-serif
+                    # we accept 3 ways CSS only supports 1
+                    fn = normalize_names.get(fn, fn)
+                    # get all of the font names and fix spelling of sans-serif
+                    # if it comes back
+                    aliases = [
+                        normalize_names.get(_, _) for _ in
+                        fm.FontManager._expand_aliases(fn)
+                    ]
+                    # make sure the generic name appears at least once
+                    # duplicate is OK, next layer will deduplicate
+                    aliases.append(fn)
+
+                    for a in aliases:
+                        # generic font families must not be quoted
+                        if a in fm.font_family_aliases:
+                            yield a
+                        # specific font families must be quoted
+                        else:
+                            yield repr(a)
+                # specific font families must be quoted
+                else:
+                    yield repr(fn)
+
+            def _get_all_names(prop):
+                for f in prop.get_family():
+                    yield from _format_font_name(f)
+
             font_parts.extend([
                 f'{_short_float_fmt(prop.get_size())}px',
-                # ensure quoting
-                f'{", ".join(repr(f) for f in prop.get_family())}',
+                # ensure quoting and expansion of font names
+                ", ".join(dict.fromkeys(_get_all_names(prop)))
             ])
             style['font'] = ' '.join(font_parts)
             if prop.get_stretch() != 'normal':

lib/matplotlib/font_manager.py

@@ -1345,9 +1345,12 @@ def findfont(self, prop, fontext='ttf', directory=None,
         rc_params = tuple(tuple(mpl.rcParams[key]) for key in [
             "font.serif", "font.sans-serif", "font.cursive", "font.fantasy",
             "font.monospace"])
-        return self._findfont_cached(
+        ret = self._findfont_cached(
             prop, fontext, directory, fallback_to_default, rebuild_if_missing,
             rc_params)
+        if isinstance(ret, Exception):
+            raise ret
+        return ret
 
     def get_font_names(self):
         """Return the list of available fonts."""
@@ -1496,8 +1499,11 @@ def _findfont_cached(self, prop, fontext, directory, fallback_to_default,
                 return self.findfont(default_prop, fontext, directory,
                                      fallback_to_default=False)
             else:
-                raise ValueError(f"Failed to find font {prop}, and fallback "
-                                 f"to the default font was disabled")
+                # This return instead of raise is intentional, as we wish to
+                # cache the resulting exception, which will not occur if it was
+                # actually raised.
+                return ValueError(f"Failed to find font {prop}, and fallback "
+                                  f"to the default font was disabled")
         else:
             _log.debug('findfont: Matching %s to %s (%r) with score of %f.',
                        prop, best_font.name, best_font.fname, best_score)
@@ -1516,7 +1522,10 @@ def _findfont_cached(self, prop, fontext, directory, fallback_to_default,
                 return self.findfont(
                     prop, fontext, directory, rebuild_if_missing=False)
             else:
-                raise ValueError("No valid font could be found")
+                # This return instead of raise is intentional, as we wish to
+                # cache the resulting exception, which will not occur if it was
+                # actually raised.
+                return ValueError("No valid font could be found")
 
         return _cached_realpath(result)
 

lib/matplotlib/tests/test_backend_svg.py

@@ -527,3 +527,64 @@ def test_svg_escape():
         fig.savefig(fd, format='svg')
         buf = fd.getvalue().decode()
         assert '<'"&>"' in buf
+
+
+@pytest.mark.parametrize("font_str", [
+    "'DejaVu Sans', 'WenQuanYi Zen Hei', 'Arial', sans-serif",
+    "'DejaVu Serif', 'WenQuanYi Zen Hei', 'Times New Roman', serif",
+    "'Arial', 'WenQuanYi Zen Hei', cursive",
+    "'Impact', 'WenQuanYi Zen Hei', fantasy",
+    "'DejaVu Sans Mono', 'WenQuanYi Zen Hei', 'Courier New', monospace",
+    # These do not work because the logic to get the font metrics will not find
+    # WenQuanYi as the fallback logic stops with the first fallback font:
+    # "'DejaVu Sans Mono', 'Courier New', 'WenQuanYi Zen Hei', monospace",
+    # "'DejaVu Sans', 'Arial', 'WenQuanYi Zen Hei', sans-serif",
+    # "'DejaVu Serif', 'Times New Roman', 'WenQuanYi Zen Hei',  serif",
+])
+@pytest.mark.parametrize("include_generic", [True, False])
+def test_svg_font_string(font_str, include_generic):
+    fp = fm.FontProperties(family=["WenQuanYi Zen Hei"])
+    if Path(fm.findfont(fp)).name != "wqy-zenhei.ttc":
+        pytest.skip("Font may be missing")
+
+    explicit, *rest, generic = map(
+        lambda x: x.strip("'"), font_str.split(", ")
+    )
+    size = len(generic)
+    if include_generic:
+        rest = rest + [generic]
+    plt.rcParams[f"font.{generic}"] = rest
+    plt.rcParams["font.size"] = size
+    plt.rcParams["svg.fonttype"] = "none"
+
+    fig, ax = plt.subplots()
+    if generic == "sans-serif":
+        generic_options = ["sans", "sans-serif", "sans serif"]
+    else:
+        generic_options = [generic]
+
+    for generic_name in generic_options:
+        # test that fallback works
+        ax.text(0.5, 0.5, "There are 几个汉字 in between!",
+                family=[explicit, generic_name], ha="center")
+        # test deduplication works
+        ax.text(0.5, 0.1, "There are 几个汉字 in between!",
+                family=[explicit, *rest, generic_name], ha="center")
+    ax.axis("off")
+
+    with BytesIO() as fd:
+        fig.savefig(fd, format="svg")
+        buf = fd.getvalue()
+
+    tree = xml.etree.ElementTree.fromstring(buf)
+    ns = "http://www.w3.org/2000/svg"
+    text_count = 0
+    for text_element in tree.findall(f".//{{{ns}}}text"):
+        text_count += 1
+        font_info = dict(
+            map(lambda x: x.strip(), _.strip().split(":"))
+            for _ in dict(text_element.items())["style"].split(";")
+        )["font"]
+
+        assert font_info == f"{size}px {font_str}"
+    assert text_count == len(ax.texts)