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Slightly better positioning of subscripts and superscripts of fractions #21850

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Slightly better positioning of subscripts and superscripts of fractions #21850

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156b99a
Implement the TeX alignment of subscripts [skip ci]
tfpf Jun 10, 2022
6d2815c
Align both subscript and superscript the way TeX does.
tfpf Jun 11, 2022
584166e
Fix Flake8 errors.
tfpf Jun 11, 2022
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37 changes: 28 additions & 9 deletions lib/matplotlib/_mathtext.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1830,6 +1830,7 @@ def set_names_and_parse_actions():
| p.underset
| p.sqrt
| p.overline
| p.auto_delim
)

p.simple <<= (
Expand Down Expand Up @@ -2206,6 +2207,16 @@ def subsuper(self, s, loc, toks):
result = Hlist([vlist])
return [result]

# Set the minimum shifts for the superscript and subscript (node756).
constants = _get_font_constant_set(state)
if isinstance(nucleus, Char):
shift_up = 0
shift_down = 0
else:
drop_amount = constants.subdrop * xHeight * SHRINK_FACTOR
shift_up = nucleus.height - drop_amount
shift_down = nucleus.depth + drop_amount

# We remove kerning on the last character for consistency (otherwise
# it will compute kerning based on non-shrunk characters and may put
# them too close together when superscripted)
Expand All @@ -2232,7 +2243,6 @@ def subsuper(self, s, loc, toks):
nucleus = Hlist([nucleus])

# Handle regular sub/superscripts
constants = _get_font_constant_set(state)
lc_height = last_char.height
lc_baseline = 0
if self.is_dropsub(last_char):
Expand All @@ -2254,35 +2264,44 @@ def subsuper(self, s, loc, toks):
subkern = 0

if super is None:
# node757
# Align subscript without superscript (node757).
x = Hlist([Kern(subkern), sub])
x.shrink()
if self.is_dropsub(last_char):
shift_down = lc_baseline + constants.subdrop * xHeight
else:
shift_down = constants.sub1 * xHeight
shift_down = max(shift_down, constants.sub1 * xHeight,
x.height - xHeight * 4 / 5)
x.shift_amount = shift_down
else:
# Align superscript (node758).
x = Hlist([Kern(superkern), super])
x.shrink()
if self.is_dropsub(last_char):
shift_up = lc_height - constants.subdrop * xHeight
else:
shift_up = constants.sup1 * xHeight
shift_up = max(shift_up, constants.sup1 * xHeight,
x.depth + xHeight / 4)
if sub is None:
x.shift_amount = -shift_up
else: # Both sub and superscript
else:
# Align subscript with superscript (node759).
y = Hlist([Kern(subkern), sub])
y.shrink()
if self.is_dropsub(last_char):
shift_down = lc_baseline + constants.subdrop * xHeight
else:
shift_down = constants.sub2 * xHeight
# If sub and superscript collide, move super up
clr = (2.0 * rule_thickness -
shift_down = max(shift_down, constants.sub2 * xHeight)
# If the subscript and superscript are too close to each other,
# move the subscript down.
clr = (4 * rule_thickness -
((shift_up - x.depth) - (y.height - shift_down)))
if clr > 0.:
shift_up += clr
shift_down += clr
clr = xHeight * 4 / 5 - shift_up + x.depth
if clr > 0:
shift_up += clr
shift_down -= clr
x = Vlist([
x,
Kern((shift_up - x.depth) - (y.height - shift_down)),
Expand Down