Try to mimic LaTeX's fraction alignment

tfpf · tfpf · commit b1723b6415e0 · 2021-07-24T01:40:02.000+05:30
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -2751,6 +2751,9 @@ def subsuper(self, s, loc, toks):
 
     def _genfrac(self, ldelim, rdelim, rule, style, num, den):
         state = self.get_state()
+        cap_height = state.font_output.get_metrics(
+            state.font, mpl.rcParams['mathtext.default'],
+            'H', state.fontsize, state.dpi).height
         thickness = state.font_output.get_underline_thickness(
             state.font, state.fontsize, state.dpi)
 
@@ -2759,17 +2762,28 @@ def _genfrac(self, ldelim, rdelim, rule, style, num, den):
         if style is not self._MathStyle.DISPLAYSTYLE:
             num.shrink()
             den.shrink()
+            min_clearance = 0.5 * thickness
+        else:
+            min_clearance = 1.5 * thickness
         cnum = HCentered([num])
         cden = HCentered([den])
         width = max(num.width, den.width)
         cnum.hpack(width, 'exactly')
         cden.hpack(width, 'exactly')
-        vlist = Vlist([cnum,                      # numerator
-                       Vbox(0, thickness * 2.0),  # space
-                       Hrule(state, rule),        # rule
-                       Vbox(0, thickness * 2.0),  # space
-                       cden                       # denominator
-                       ])
+
+        vlist_builder = []
+        if cnum.height < cap_height:
+            cnum.height = cap_height
+        vlist_builder.append(cnum)
+        numerator_padding = max(
+            cap_height * 3/5 - cnum.depth, min_clearance) - thickness
+        vlist_builder.append(Vbox(0, numerator_padding))
+        vlist_builder.append(Hrule(state, rule))
+        denominator_padding = max(
+            4/3 * cap_height - cden.height, min_clearance) + thickness
+        vlist_builder.append(Vbox(0, denominator_padding))
+        vlist_builder.append(cden)
+        vlist = Vlist(vlist_builder)
 
         # Shift so the fraction line sits in the middle of the
         # minus sign
@@ -2780,9 +2794,8 @@ def _genfrac(self, ldelim, rdelim, rule, style, num, den):
         metrics = state.font_output.get_metrics(
             state.font, mpl.rcParams['mathtext.default'],
             minus_sign, state.fontsize, state.dpi)
-        shift = (cden.height -
-                 ((metrics.ymax + metrics.ymin) / 2 -
-                  thickness * 1.5))
+        shift = (denominator_padding + cden.height -
+                 (metrics.ymax + metrics.ymin) / 2 - thickness / 2)
         vlist.shift_amount = shift
 
         result = [Hlist([vlist, Hbox(thickness * 2.)])]
