Don't try to find TeX-only fonts when layouting TeX text.

anntzer · anntzer · commit 89629460ffbb · 2019-01-12T22:39:32.000+01:00
Text.is_math_text is only ever called with self.get_usetex() as second
argument, so just change it to a private method (Text._preprocess_math)
that calls self.get_usetex() internally; deprecate is_math_text which
is clearly a private internal helper.  This also helps clarifying that
usetex mode is only ever called if self.get_usetex() is True (in the
textobj.is_math_text(...) line, textobj is actually the same object(!)
as self so shares the same get_usetex() value).

In Text._get_layout, if self.get_usetex() is True (and only in that
case), self._fontproperties can refer to a TeX-only font (e.g. "Computer
Modern Roman").  If that's the case, don't try to call
renderer.get_text_width_height_descent with ismath=False, as that would
trigger a font resolution that can fail (perhaps there's no "Computer
Modern Roman" font available in the font cache; it may only be available
to TeX) and cause a spurious warning.
diff --git a/doc/api/next_api_changes/2019-01-13-AL.rst b/doc/api/next_api_changes/2019-01-13-AL.rst
@@ -0,0 +1,4 @@
+Deprecations
+````````````
+
+``Text.is_math_text`` is deprecated.
diff --git a/lib/matplotlib/text.py b/lib/matplotlib/text.py
@@ -286,11 +286,12 @@ def _get_layout(self, renderer):
 
         # Full vertical extent of font, including ascenders and descenders:
         _, lp_h, lp_d = renderer.get_text_width_height_descent(
-            "lp", self._fontproperties, ismath=False)
+            "lp", self._fontproperties,
+            ismath="TeX" if self.get_usetex() else False)
         min_dy = (lp_h - lp_d) * self._linespacing
 
         for i, line in enumerate(lines):
-            clean_line, ismath = self.is_math_text(line, self.get_usetex())
+            clean_line, ismath = self._preprocess_math(line)
             if clean_line:
                 w, h, d = renderer.get_text_width_height_descent(
                     clean_line, self._fontproperties, ismath=ismath)
@@ -697,8 +698,7 @@ def draw(self, renderer):
                 y = y + posy
                 if renderer.flipy():
                     y = canvash - y
-                clean_line, ismath = textobj.is_math_text(line,
-                                                          self.get_usetex())
+                clean_line, ismath = textobj._preprocess_math(line)
 
                 if textobj.get_path_effects():
                     from matplotlib.patheffects import PathEffectRenderer
@@ -1152,6 +1152,7 @@ def set_text(self, s):
             self.stale = True
 
     @staticmethod
+    @cbook.deprecated("3.1")
     def is_math_text(s, usetex=None):
         """
         Returns a cleaned string and a boolean flag.
@@ -1174,6 +1175,27 @@ def is_math_text(s, usetex=None):
         else:
             return s.replace(r'\$', '$'), False
 
+    def _preprocess_math(self, s):
+        """
+        Return the string *s* after mathtext preprocessing, and the kind of
+        mathtext support needed.
+
+        - If *self* is configured to use TeX, return *s* unchanged except that
+          a single space gets escaped, and the flag "TeX".
+        - Otherwise, if *s* is mathtext (has an even number of unescaped dollar
+          signs), return *s* and the flag True.
+        - Otherwise, return *s* with dollar signs unescaped, and the flag
+          False.
+        """
+        if self.get_usetex():
+            if s == " ":
+                s = r"\ "
+            return s, "TeX"
+        if cbook.is_math_text(s):
+            return s, True
+        else:
+            return s.replace(r"\$", "$"), False
+
     def set_fontproperties(self, fp):
         """
         Set the font properties that control the text.
