Remove used_characters tracking in mathtext.

anntzer · anntzer · commit e3236e975acb · 2022-01-12T00:06:24.000+01:00
Backends that need to track what characters have been used (pdf/ps, for
subsetting purposes) already have their own logic to do so, so don't do
it in mathtext as well.

Changes in Fonts are only touching private API.

Changes in the call signature of MathtextBackendAgg/MathtextBackendPath
look like they are touching public API, but it is in fact impossible for
an external user to construct a valid `box` parameter (this requires
classes defined in `_mathtext`), so `get_results` is effectively private
API from a caller PoV.  It is also impossible to register new
MathtextBackends without touching private API.

Thus, the only difference is in the tuple returned by
MathtextBackendAgg, which now has one fewer element.  Because the return
value is a tuple which is unpacked at the call site, it is not possible
to emit a proper deprecation warning (one would need to know whether the
result is being unpacked to 6 or 7 values).  Callers can work around
this by e.g. unpacking the last item into `*_`.  Note that because this
is only for MathtextBackendAgg (i.e., a raster backend), it is unlikely
that callers actually care about the used_characters info at all.
diff --git a/doc/api/next_api_changes/behavior/22204-AL.rst b/doc/api/next_api_changes/behavior/22204-AL.rst
@@ -0,0 +1,7 @@
+``MathtextBackendAgg.get_results`` no longer returns ``used_characters``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The last item (``used_characters``) in the tuple returned by
+``MathtextBackendAgg.get_results`` has been removed.  In order to unpack this
+tuple in a backward and forward-compatible way, use e.g.
+``ox, oy, width, height, descent, image, *_ = parse(...)``,
+which will ignore ``used_characters`` if it was present.
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -89,7 +89,6 @@ def __init__(self, default_font_prop, mathtext_backend):
         """
         self.default_font_prop = default_font_prop
         self.mathtext_backend = mathtext_backend
-        self.used_characters = {}
 
     def get_kern(self, font1, fontclass1, sym1, fontsize1,
                  font2, fontclass2, sym2, fontsize2, dpi):
@@ -147,7 +146,6 @@ def render_glyph(self, ox, oy, font, font_class, sym, fontsize, dpi):
         parameters (see `get_metrics` for their detailed description).
         """
         info = self._get_info(font, font_class, sym, fontsize, dpi)
-        self.used_characters.setdefault(info.font.fname, set()).add(info.num)
         self.mathtext_backend.render_glyph(ox, oy, info)
 
     def render_rect_filled(self, x1, y1, x2, y2):
@@ -169,14 +167,6 @@ def get_underline_thickness(self, font, fontsize, dpi):
         """
         raise NotImplementedError()
 
-    def get_used_characters(self):
-        """
-        Get the set of characters that were used in the math
-        expression.  Used by backends that need to subset fonts so
-        they know which glyphs to include.
-        """
-        return self.used_characters
-
     def get_sized_alternatives_for_symbol(self, fontname, sym):
         """
         Override if your font provides multiple sizes of the same
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -211,7 +211,7 @@ def draw_path(self, gc, path, transform, rgbFace=None):
 
     def draw_mathtext(self, gc, x, y, s, prop, angle):
         """Draw mathtext using :mod:`matplotlib.mathtext`."""
-        ox, oy, width, height, descent, font_image, used_characters = \
+        ox, oy, width, height, descent, font_image = \
             self.mathtext_parser.parse(s, self.dpi, prop)
 
         xd = descent * sin(radians(angle))
@@ -260,7 +260,7 @@ def get_text_width_height_descent(self, s, prop, ismath):
             return w, h, d
 
         if ismath:
-            ox, oy, width, height, descent, fonts, used_characters = \
+            ox, oy, width, height, descent, font_image = \
                 self.mathtext_parser.parse(s, self.dpi, prop)
             return width, height, descent
 
diff --git a/lib/matplotlib/mathtext.py b/lib/matplotlib/mathtext.py
@@ -134,7 +134,7 @@ def render_rect_filled(self, x1, y1, x2, y2):
                 y = int(y1)
             self.image.draw_rect_filled(int(x1), y, np.ceil(x2), y + height)
 
-    def get_results(self, box, used_characters):
+    def get_results(self, box):
         self.mode = 'bbox'
         orig_height = box.height
         orig_depth  = box.depth
@@ -152,8 +152,7 @@ def get_results(self, box, used_characters):
                   self.width,
                   self.height + self.depth,
                   self.depth,
-                  self.image,
-                  used_characters)
+                  self.image)
         self.image = None
         return result
 
@@ -182,7 +181,7 @@ def render_glyph(self, ox, oy, info):
     def render_rect_filled(self, x1, y1, x2, y2):
         self.rects.append((x1, self.height - y2, x2 - x1, y2 - y1))
 
-    def get_results(self, box, used_characters):
+    def get_results(self, box):
         _mathtext.ship(0, 0, box)
         return self._Result(self.width,
                             self.height + self.depth,
