Add overset and underset, symbol group

aitikgupta · aitikgupta · commit c711c4500c9a · 2020-12-22T13:53:00.000+05:30
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -2035,6 +2035,7 @@ def __init__(self):
         p.non_math         = Forward()
         p.operatorname     = Forward()
         p.overline         = Forward()
+        p.overset          = Forward()
         p.placeable        = Forward()
         p.rbrace           = Forward()
         p.rbracket         = Forward()
@@ -2051,8 +2052,10 @@ def __init__(self):
         p.subsuper         = Forward()
         p.subsuperop       = Forward()
         p.symbol           = Forward()
+        p.symbol_group     = Forward()
         p.symbol_name      = Forward()
         p.token            = Forward()
+        p.underset         = Forward()
         p.unknown_symbol   = Forward()
 
         # Set names on everything -- very useful for debugging
@@ -2109,6 +2112,7 @@ def __init__(self):
         p.end_group      <<= p.rbrace.copy()
         p.simple_group   <<= Group(p.lbrace + ZeroOrMore(p.token) + p.rbrace)
         p.required_group <<= Group(p.lbrace + OneOrMore(p.token) + p.rbrace)
+        p.symbol_group   <<= Group(p.lbrace + p.symbol + p.rbrace)
         p.group          <<= Group(
             p.start_group + ZeroOrMore(p.token) + p.end_group
         )
@@ -2168,6 +2172,18 @@ def __init__(self):
             - (p.required_group | Error("Expected \\overline{value}"))
         )
 
+        p.overset <<= Group(
+            Suppress(Literal(r"\overset"))
+            - ((p.required_group + p.symbol_group)
+               | Error("Expected \\overset{value}{symbol}"))
+        )
+
+        p.underset <<= Group(
+            Suppress(Literal(r"\underset"))
+            - ((p.required_group + p.symbol_group)
+               | Error("Expected \\underset{value}{symbol}"))
+        )
+
         p.unknown_symbol <<= Combine(p.bslash + Regex("[A-Za-z]*"))
 
         p.operatorname <<= Group(
@@ -2189,6 +2205,8 @@ def __init__(self):
             | p.dfrac
             | p.binom
             | p.genfrac
+            | p.overset
+            | p.underset
             | p.sqrt
             | p.overline
             | p.operatorname
@@ -2858,6 +2876,40 @@ def binom(self, s, loc, toks):
         return self._genfrac('(', ')', 0.0, self._MathStyle.TEXTSTYLE,
                              num, den)
 
+    def _genset(self, state, value, symbol, shift):
+        thickness = state.font_output.get_underline_thickness(
+            state.font, state.fontsize, state.dpi)
+
+        value.shrink()
+
+        cvalue = HCentered([value])
+        csymbol = HCentered([symbol])
+        width = max(cvalue.width, csymbol.width)
+        cvalue.hpack(width, 'exactly')
+        csymbol.hpack(width, 'exactly')
+
+        metrics = state.font_output.get_metrics(
+            state.font, mpl.rcParams['mathtext.default'],
+            r'\leftrightarrow', state.fontsize, state.dpi)
+
+        # Shift so the symbol sits in the same vertical position
+        shift_amount = csymbol.height/2 - (metrics.ymax + metrics.ymin)/2
+        if shift:
+            vlist = Vlist([csymbol,                    # value
+                           cvalue                      # symbol
+                           ])
+            vlist.shift_amount = shift_amount + cvalue.height
+        else:
+            vlist = Vlist([cvalue,                      # value
+                           Vbox(0, thickness * 1.5),    # space
+                           csymbol                      # symbol
+                           ])
+            vlist.shift_amount = shift_amount
+
+        hlist = [Hlist([vlist, Hbox(thickness * 2.)])]
+
+        return hlist
+
     def sqrt(self, s, loc, toks):
         root, body = toks[0]
         state = self.get_state()
@@ -2921,6 +2973,30 @@ def overline(self, s, loc, toks):
         hlist = Hlist([rightside])
         return [hlist]
 
+    def overset(self, s, loc, toks):
+        assert len(toks) == 1
+        assert len(toks[0]) == 2
+        # Only one symbol
+        assert len(toks[0][1]) == 1
+        state = self.get_state()
+
+        value, symbol = toks[0]
+        symbol = symbol[0]
+
+        return self._genset(state, value, symbol, shift=False)
+
+    def underset(self, s, loc, toks):
+        assert len(toks) == 1
+        assert len(toks[0]) == 2
+        # Only one symbol
+        assert len(toks[0][1]) == 1
+        state = self.get_state()
+
+        value, symbol = toks[0]
+        symbol = symbol[0]
+
+        return self._genset(state, value, symbol, shift=True)
+
     def _auto_sized_delimiter(self, front, middle, back):
         state = self.get_state()
         if len(middle):
