read underline_thickness and x-height

llohse · llohse · commit 8009a09028b5 · 2026-02-03T09:35:25.000+01:00
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -732,6 +732,8 @@ class DejaVuSansFonts(DejaVuFonts):
         0:    'DejaVu Sans',
     }
 
+def _to_device_units(font_units, fontsize, units_per_EM, dpi):
+    return font_units / units_per_EM * fontsize / 72 * dpi
 
 class UnicodeMathFonts(TruetypeFonts):
     """
@@ -760,6 +762,32 @@ def _get_font(self, font: str | int) -> FT2Font:
 
         return super()._get_font(font)
 
+    def get_xheight(self, fontname: str, fontsize: float, dpi: float) -> float:
+        font = self._get_font('mathfont')
+
+        os2 = font.get_sfnt_table('OS/2')
+        height_raw = os2.get('sxHeight')
+        if height_raw is not None:
+            # use value of OS/2 table, if present
+            x_height = _to_device_units(height_raw, fontsize, font.units_per_EM, dpi)
+        else:
+            # fall back to measure height of the x glyph
+            num = get_unicode_index('x')
+            font.set_size(fontsize, dpi)
+            glyph_index = font.get_char_index(num)
+            glyph = font.load_glyph(glyph_index, flags=self.load_glyph_flags)
+            x_height = glyph.height / 64
+
+        return x_height
+
+    def get_underline_thickness(self, font: str, fontsize: float, dpi: float) -> float:
+        font = self._get_font('mathfont')
+        thickness_raw = font.underline_thickness
+        # alternative: use font.get_sfnt_tables('OS/2').get('yStrikeoutSize')
+        underline_thickness = _to_device_units(thickness_raw, fontsize, font.units_per_EM, dpi)
+
+        return underline_thickness
+
     def _get_glyph(self, fontname: str, font_class: str,
                    sym: str) -> tuple[FT2Font, CharacterCodeType, bool]:
         # `fontname' is one of rm cal it tt sf bf bfit default bb frak scr regular
