Move listing of Type1 glyph widths to backend_pdf.

DviFont.widths (the widths of each glyph in a font) is only used
by backend_pdf to embed (classic, Type1) TeX fonts; deprecate that
attribute and instead compute it where needed.  This change is in
preparation for supporting {xe,lua}tex, where DviFont can also refer to
OpenType fonts which would be embedded via a different mechanism into
the pdf file, and which can contain so many glyphs that explicitly
listing the width of each one would be wasteful.

Author: anntzer

doc/api/next_api_changes/deprecations/29817-AL.rst

@@ -0,0 +1,3 @@
+``DviFont.widths``
+~~~~~~~~~~~~~~~~~~
+... is deprecated with no replacement.

lib/matplotlib/backends/backend_pdf.py

@@ -991,15 +991,19 @@ def _embedTeXFont(self, fontinfo):
 
         # Widths
         widthsObject = self.reserveObject('font widths')
-        self.writeObject(widthsObject, fontinfo.dvifont.widths)
+        tfm = fontinfo.dvifont._tfm
+        # convert from TeX's 12.20 representation to 1/1000 text space units.
+        widths = [(1000 * tfm.width.get(char, 0)) >> 20
+                  for char in range(max(tfm.width, default=-1) + 1)]
+        self.writeObject(widthsObject, widths)
 
         # Font dictionary
         fontdictObject = self.reserveObject('font dictionary')
         fontdict = {
             'Type':      Name('Font'),
             'Subtype':   Name('Type1'),
             'FirstChar': 0,
-            'LastChar':  len(fontinfo.dvifont.widths) - 1,
+            'LastChar':  len(widths) - 1,
             'Widths':    widthsObject,
             }
 

lib/matplotlib/dviread.py

@@ -577,12 +577,8 @@ class DviFont:
     size : float
        Size of the font in Adobe points, converted from the slightly
        smaller TeX points.
-    widths : list
-       Widths of glyphs in glyph-space units, typically 1/1000ths of
-       the point size.
-
     """
-    __slots__ = ('texname', 'size', 'widths', '_scale', '_vf', '_tfm')
+    __slots__ = ('texname', 'size', '_scale', '_vf', '_tfm')
 
     def __init__(self, scale, tfm, texname, vf):
         _api.check_isinstance(bytes, texname=texname)
@@ -591,12 +587,10 @@ def __init__(self, scale, tfm, texname, vf):
         self.texname = texname
         self._vf = vf
         self.size = scale * (72.0 / (72.27 * 2**16))
-        try:
-            nchars = max(tfm.width) + 1
-        except ValueError:
-            nchars = 0
-        self.widths = [(1000*tfm.width.get(char, 0)) >> 20
-                       for char in range(nchars)]
+
+    widths = _api.deprecated("3.11")(property(lambda self: [
+        (1000 * self._tfm.width.get(char, 0)) >> 20
+        for char in range(max(self._tfm.width, default=-1) + 1)]))
 
     def __eq__(self, other):
         return (type(self) is type(other)

lib/matplotlib/dviread.pyi

@@ -56,12 +56,13 @@ class Dvi:
 class DviFont:
     texname: bytes
     size: float
-    widths: list[int]
     def __init__(
         self, scale: float, tfm: Tfm, texname: bytes, vf: Vf | None
     ) -> None: ...
     def __eq__(self, other: object) -> bool: ...
     def __ne__(self, other: object) -> bool: ...
+    @property
+    def widths(self) -> list[int]: ...
 
 class Vf(Dvi):
     def __init__(self, filename: str | os.PathLike) -> None: ...