Improve font spec for SVG font referencing.

The 'font: ...' shorthand is much more concise than setting each
property separately: This replaces e.g.
`"font-family:DejaVu Sans;font-size:12px;font-style:book;font-weight:book;"`
by `"font: 400 12px 'DejaVu Sans'"`.
Note that the previous font weight was plain wrong...

Also this revealed a bug in generate_css (we shouldn't run it through
escape_attrib, as quotes (e.g. around the font family name) get
mangled); and we don't need to load the font at all (we should just
report whatever font the user actually requested).

Author: anntzer

lib/matplotlib/backends/backend_svg.py

@@ -14,15 +14,13 @@
 from PIL import Image
 
 import matplotlib as mpl
-from matplotlib import _api, cbook
+from matplotlib import _api, cbook, font_manager as fm
 from matplotlib.backend_bases import (
      _Backend, _check_savefig_extra_args, FigureCanvasBase, FigureManagerBase,
      RendererBase, _no_output_draw)
 from matplotlib.backends.backend_mixed import MixedModeRenderer
 from matplotlib.colors import rgb2hex
 from matplotlib.dates import UTC
-from matplotlib.font_manager import findfont, get_font
-from matplotlib.ft2font import LOAD_NO_HINTING
 from matplotlib.mathtext import MathTextParser
 from matplotlib.path import Path
 from matplotlib import _path
@@ -94,6 +92,12 @@ def escape_attrib(s):
     return s
 
 
+def _quote_escape_attrib(s):
+    return ('"' + escape_cdata(s) + '"' if '"' not in s else
+            "'" + escape_cdata(s) + "'" if "'" not in s else
+            '"' + escape_attrib(s) + '"')
+
+
 def short_float_fmt(x):
     """
     Create a short string representation of a float, which is %f
@@ -159,8 +163,8 @@ def start(self, tag, attrib={}, **extra):
         for k, v in {**attrib, **extra}.items():
             if v:
                 k = escape_cdata(k)
-                v = escape_attrib(v)
-                self.__write(' %s="%s"' % (k, v))
+                v = _quote_escape_attrib(v)
+                self.__write(' %s=%s' % (k, v))
         self.__open = 1
         return len(self.__tags) - 1
 
@@ -262,15 +266,7 @@ def generate_transform(transform_list=[]):
 
 
 def generate_css(attrib={}):
-    if attrib:
-        output = StringIO()
-        attrib = attrib.items()
-        for k, v in attrib:
-            k = escape_attrib(k)
-            v = escape_attrib(v)
-            output.write("%s:%s;" % (k, v))
-        return output.getvalue()
-    return ''
+    return "; ".join(f"{k}: {v}" for k, v in attrib.items())
 
 
 _capstyle_d = {'projecting': 'square', 'butt': 'butt', 'round': 'round'}
@@ -464,8 +460,8 @@ def _make_flip_transform(self, transform):
                 .translate(0.0, self.height))
 
     def _get_font(self, prop):
-        fname = findfont(prop)
-        font = get_font(fname)
+        fname = fm.findfont(prop)
+        font = fm.get_font(fname)
         font.clear()
         size = prop.get_size_in_points()
         font.set_size(size, 72.0)
@@ -1128,16 +1124,23 @@ def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
             style['opacity'] = short_float_fmt(alpha)
 
         if not ismath:
-            font = self._get_font(prop)
-            font.set_text(s, 0.0, flags=LOAD_NO_HINTING)
-
             attrib = {}
-            style['font-family'] = str(font.family_name)
-            style['font-weight'] = str(prop.get_weight()).lower()
-            style['font-stretch'] = str(prop.get_stretch()).lower()
-            style['font-style'] = prop.get_style().lower()
-            # Must add "px" to workaround a Firefox bug
-            style['font-size'] = short_float_fmt(prop.get_size()) + 'px'
+
+            font_parts = []
+            if prop.get_style() != 'normal':
+                font_parts.append(prop.get_style())
+            if prop.get_variant() != 'normal':
+                font_parts.append(prop.get_variant())
+            weight = fm.weight_dict[prop.get_weight()]
+            if weight != 400:
+                font_parts.append(f'{weight}')
+            font_parts.extend([
+                f'{short_float_fmt(prop.get_size())}px',
+                f'{prop.get_family()[0]!r}',  # ensure quoting
+            ])
+            style['font'] = ' '.join(font_parts)
+            if prop.get_stretch() != 'normal':
+                style['font-stretch'] = prop.get_stretch()
             attrib['style'] = generate_css(style)
 
             if mtext and (angle == 0 or mtext.get_rotation_mode() == "anchor"):
@@ -1197,11 +1200,22 @@ def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
             # Sort the characters by font, and output one tspan for each.
             spans = OrderedDict()
             for font, fontsize, thetext, new_x, new_y in glyphs:
-                style = generate_css({
-                    'font-size': short_float_fmt(fontsize) + 'px',
-                    'font-family': font.family_name,
-                    'font-style': font.style_name.lower(),
-                    'font-weight': font.style_name.lower()})
+                entry = fm.ttfFontProperty(font)
+                font_parts = []
+                if entry.style != 'normal':
+                    font_parts.append(entry.style)
+                if entry.variant != 'normal':
+                    font_parts.append(entry.variant)
+                if entry.weight != 400:
+                    font_parts.append(f'{entry.weight}')
+                font_parts.extend([
+                    f'{short_float_fmt(fontsize)}px',
+                    f'{entry.name!r}',  # ensure quoting
+                ])
+                style = {'font': ' '.join(font_parts)}
+                if entry.stretch != 'normal':
+                    style['font-stretch'] = entry.stretch
+                style = generate_css(style)
                 if thetext == 32:
                     thetext = 0xa0  # non-breaking space
                 spans.setdefault(style, []).append((new_x, -new_y, thetext))

lib/matplotlib/tests/test_backend_svg.py

@@ -216,7 +216,7 @@ def test_unicode_won():
 
 
 def test_svgnone_with_data_coordinates():
-    plt.rcParams['svg.fonttype'] = 'none'
+    plt.rcParams.update({'svg.fonttype': 'none', 'font.stretch': 'condensed'})
     expected = 'Unlikely to appear by chance'
 
     fig, ax = plt.subplots()
@@ -229,9 +229,7 @@ def test_svgnone_with_data_coordinates():
         fd.seek(0)
         buf = fd.read().decode()
 
-    assert expected in buf
-    for prop in ["family", "weight", "stretch", "style", "size"]:
-        assert f"font-{prop}:" in buf
+    assert expected in buf and "condensed" in buf
 
 
 def test_gid():

lib/matplotlib/tests/test_mathtext.py

@@ -1,6 +1,8 @@
 import io
-import os
+from pathlib import Path
 import re
+import shlex
+from xml.etree import ElementTree as ET
 
 import numpy as np
 import pytest
@@ -349,7 +351,7 @@ def test_mathtext_fallback_to_cm_invalid():
      ("stix", ['DejaVu Sans', 'mpltest', 'STIXGeneral'])])
 def test_mathtext_fallback(fallback, fontlist):
     mpl.font_manager.fontManager.addfont(
-        os.path.join((os.path.dirname(os.path.realpath(__file__))), 'mpltest.ttf'))
+        str(Path(__file__).resolve().parent / 'mpltest.ttf'))
     mpl.rcParams["svg.fonttype"] = 'none'
     mpl.rcParams['mathtext.fontset'] = 'custom'
     mpl.rcParams['mathtext.rm'] = 'mpltest'
@@ -363,12 +365,13 @@ def test_mathtext_fallback(fallback, fontlist):
     fig, ax = plt.subplots()
     fig.text(.5, .5, test_str, fontsize=40, ha='center')
     fig.savefig(buff, format="svg")
-    char_fonts = [
-        line.split("font-family:")[-1].split(";")[0]
-        for line in str(buff.getvalue()).split(r"\n") if "tspan" in line
-    ]
+    tspans = (ET.fromstring(buff.getvalue())
+              .findall(".//{http://www.w3.org/2000/svg}tspan[@style]"))
+    # Getting the last element of the style attrib is a close enough
+    # approximation for parsing the font property.
+    char_fonts = [shlex.split(tspan.attrib["style"])[-1] for tspan in tspans]
     assert char_fonts == fontlist
-    mpl.font_manager.fontManager.ttflist = mpl.font_manager.fontManager.ttflist[:-1]
+    mpl.font_manager.fontManager.ttflist.pop()
 
 
 def test_math_to_image(tmpdir):