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mathtext: Fetch quad width & axis height from font metrics #31110

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Merged
QuLogic merged 2 commits into from
Mar 1, 2026
Merged

mathtext: Fetch quad width & axis height from font metrics #31110

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692df3f
mathtext: Fetch axis height from font metrics
QuLogic Feb 7, 2026
383028b
mathtext: Fetch quad width from font metrics
QuLogic Feb 7, 2026
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75 changes: 58 additions & 17 deletions lib/matplotlib/_mathtext.py
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Original file line number Diff line number Diff line change
Expand Up @@ -312,6 +312,12 @@ def get_axis_height(self, font: str, fontsize: float, dpi: float) -> float:
"""
raise NotImplementedError()

def get_quad(self, font: str, fontsize: float, dpi: float) -> float:
"""
Get the size of a quad for the given *font* and *fontsize*.
"""
raise NotImplementedError()

def get_xheight(self, font: str, fontsize: float, dpi: float) -> float:
"""
Get the xheight for the given *font* and *fontsize*.
Expand Down Expand Up @@ -414,11 +420,25 @@ def _get_info(self, fontname: str, font_class: str, sym: str, fontsize: float,
)

def get_axis_height(self, fontname: str, fontsize: float, dpi: float) -> float:
# The fraction line (if present) must be aligned with the minus sign. Therefore,
# the height of the latter from the baseline is the axis height.
metrics = self.get_metrics(
fontname, mpl.rcParams['mathtext.default'], '\u2212', fontsize, dpi)
return (metrics.ymax + metrics.ymin) / 2
consts = _get_font_constants(self, fontname)
if consts.axis_height is not None:
return consts.axis_height * fontsize * dpi / 72
else:
# The fraction line (if present) must be aligned with the minus sign.
# Therefore, the height of the latter from the baseline is the axis height.
metrics = self.get_metrics(
fontname, mpl.rcParams['mathtext.default'], '\u2212', fontsize, dpi)
return (metrics.ymax + metrics.ymin) / 2

def get_quad(self, fontname: str, fontsize: float, dpi: float) -> float:
consts = _get_font_constants(self, fontname)
if consts.quad is not None:
return consts.quad * fontsize * dpi / 72
else:
# With no other option, we measure the size of an 'm'.
metrics = self.get_metrics(
fontname, mpl.rcParams['mathtext.default'], 'm', fontsize, dpi)
return metrics.advance

def get_xheight(self, fontname: str, fontsize: float, dpi: float) -> float:
# Some fonts report the wrong x-height, while some don't store it, so
Expand Down Expand Up @@ -950,6 +970,13 @@ class FontConstantsBase:
# and scriptscript styles.
denom2: T.ClassVar[float] = 1.1

# The height of a horizontal reference line used for positioning elements in a
# formula, similar to a baseline, as a multiple of design size.
axis_height: T.ClassVar[float | None] = None

# The size of a quad space in LaTeX, as a multiple of design size.
quad: T.ClassVar[float | None] = None


class ComputerModernFontConstants(FontConstantsBase):
# Previously, the x-height of Computer Modern was obtained from the font
Expand All @@ -974,14 +1001,18 @@ class ComputerModernFontConstants(FontConstantsBase):
num3 = 465286 / _x_height
denom1 = 719272 / _x_height
denom2 = 361592 / _x_height
# These come from the cmsy10.tfm metrics, scaled so they are in multiples of design
# size.
axis_height = 262144 / 2**20
quad = 1048579 / 2**20


class STIXFontConstants(FontConstantsBase):
script_space = 0.1
delta = 0.05
delta_slanted = 0.3
delta_integral = 0.3
# These values are extracted from the TeX table of STIXGeneral.ttf using FreeType,
# These values are extracted from the TeX table of STIXGeneral.ttf using FontForge,
# and then divided by design xheight, since we multiply these values by the scaled
# xheight later.
_x_height = 450
Expand All @@ -995,6 +1026,10 @@ class STIXFontConstants(FontConstantsBase):
num3 = 474 / _x_height
denom1 = 756 / _x_height
denom2 = 375 / _x_height
# These come from the same TeX table, scaled by Em size so they are in multiples of
# design size.
axis_height = 250 / 1000
quad = 1000 / 1000


class STIXSansFontConstants(STIXFontConstants):
Expand All @@ -1004,7 +1039,7 @@ class STIXSansFontConstants(STIXFontConstants):


class DejaVuSerifFontConstants(FontConstantsBase):
# These values are extracted from the TeX table of DejaVuSerif.ttf using FreeType,
# These values are extracted from the TeX table of DejaVuSerif.ttf using FontForge,
# and then divided by design xheight, since we multiply these values by the scaled
# xheight later.
_x_height = 1063
Expand All @@ -1018,10 +1053,13 @@ class DejaVuSerifFontConstants(FontConstantsBase):
num3 = 970.752 / _x_height
denom1 = 1548.29 / _x_height
denom2 = 768 / _x_height
# These come from the same TeX table, scaled by Em size so they are in multiples of
# design size.
axis_height = 512 / 2048


class DejaVuSansFontConstants(FontConstantsBase):
# These values are extracted from the TeX table of DejaVuSans.ttf using FreeType,
# These values are extracted from the TeX table of DejaVuSans.ttf using FontForge,
# and then divided by design xheight, since we multiply these values by the scaled
# xheight later.
_x_height = 1120
Expand All @@ -1035,6 +1073,9 @@ class DejaVuSansFontConstants(FontConstantsBase):
num3 = 970.752 / _x_height
denom1 = 1548.29 / _x_height
denom2 = 768 / _x_height
# These come from the same TeX table, scaled by Em size so they are in multiples of
# design size.
axis_height = 512 / 2048


# Maps font family names to the FontConstantBase subclass to use
Expand Down Expand Up @@ -1062,17 +1103,20 @@ class DejaVuSansFontConstants(FontConstantsBase):
}


def _get_font_constant_set(state: ParserState) -> type[FontConstantsBase]:
constants = _font_constant_mapping.get(
state.fontset._get_font(state.font).family_name, FontConstantsBase)
def _get_font_constants(fontset: Fonts, font: str) -> type[FontConstantsBase]:
constants = _font_constant_mapping.get(fontset._get_font(font).family_name,
FontConstantsBase)
# STIX sans isn't really its own fonts, just different code points
# in the STIX fonts, so we have to detect this one separately.
if (constants is STIXFontConstants and
isinstance(state.fontset, StixSansFonts)):
if constants is STIXFontConstants and isinstance(fontset, StixSansFonts):
return STIXSansFontConstants
return constants


def _get_font_constant_set(state: ParserState) -> type[FontConstantsBase]:
return _get_font_constants(state.fontset, state.font)


class Node:
"""A node in the TeX box model."""

Expand Down Expand Up @@ -2306,10 +2350,7 @@ def _make_space(self, percentage: float) -> Kern:
key = (state.font, state.fontsize, state.dpi)
width = self._em_width_cache.get(key)
if width is None:
metrics = state.fontset.get_metrics(
'it', mpl.rcParams['mathtext.default'], 'm',
state.fontsize, state.dpi)
width = metrics.advance
width = state.fontset.get_quad('it', state.fontsize, state.dpi)
self._em_width_cache[key] = width
return Kern(width * percentage)

Expand Down
8 changes: 4 additions & 4 deletions lib/matplotlib/tests/test_mathtext.py
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Original file line number Diff line number Diff line change
Expand Up @@ -577,12 +577,12 @@ def test_box_repr():
_mathtext.DejaVuSansFonts(fm.FontProperties(), LoadFlags.NO_HINTING),
fontsize=12, dpi=100))
assert s == textwrap.dedent("""\
Hlist<w=9.51 h=15.30 d=5.00 s=0.00>[
Hlist<w=9.51 h=14.24 d=6.06 s=0.00>[
Hlist<w=0.00 h=0.00 d=0.00 s=0.00>[],
Hlist<w=9.51 h=15.30 d=5.00 s=0.00>[
Hlist<w=9.51 h=15.30 d=5.00 s=0.00>[
Hlist<w=9.51 h=14.24 d=6.06 s=0.00>[
Hlist<w=9.51 h=14.24 d=6.06 s=0.00>[
Hbox,
Vlist<w=7.43 h=20.30 d=0.00 s=5.00>[
Vlist<w=7.43 h=20.30 d=0.00 s=6.06>[
HCentered<w=7.43 h=8.51 d=0.00 s=0.00>[
Glue,
Hlist<w=7.43 h=8.51 d=0.00 s=0.00>[
Expand Down
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