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Fix confusion between text height and ascent in metrics calculations. #31107

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Merged
QuLogic merged 1 commit into from
Feb 18, 2026
+43 −42
Merged

Fix confusion between text height and ascent in metrics calculations. #31107

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13 changes: 7 additions & 6 deletions lib/matplotlib/offsetbox.py
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Original file line number Diff line number Diff line change
Expand Up @@ -799,23 +799,24 @@ def get_bbox(self, renderer):
ismath="TeX" if self._text.get_usetex() else False,
dpi=self.get_figure(root=True).dpi)

bbox, info, yd = self._text._get_layout(renderer)
bbox, info = self._text._get_layout(renderer)
_last_line, (_last_width, _last_ascent, last_descent), _last_xy = info[-1]
w, h = bbox.size

self._baseline_transform.clear()

if len(info) > 1 and self._multilinebaseline:
yd_new = 0.5 * h - 0.5 * (h_ - d_)
self._baseline_transform.translate(0, yd - yd_new)
yd = yd_new
self._baseline_transform.translate(0, last_descent - yd_new)
last_descent = yd_new
else: # single line
h_d = max(h_ - d_, h - yd)
h = h_d + yd
h_d = max(h_ - d_, h - last_descent)
h = h_d + last_descent

ha = self._text.get_horizontalalignment()
x0 = {"left": 0, "center": -w / 2, "right": -w}[ha]

return Bbox.from_bounds(x0, -yd, w, h)
return Bbox.from_bounds(x0, -last_descent, w, h)

def draw(self, renderer):
# docstring inherited
Expand Down
72 changes: 36 additions & 36 deletions lib/matplotlib/text.py
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Original file line number Diff line number Diff line change
Expand Up @@ -37,23 +37,22 @@ def _get_textbox(text, renderer):
# called within the _get_textbox. So, it would be better to move this
# function as a method with some refactoring of _get_layout method.

projected_xs = []
projected_ys = []
projected_xys = []

theta = np.deg2rad(text.get_rotation())
tr = Affine2D().rotate(-theta)

_, parts, d = text._get_layout(renderer)
_, parts = text._get_layout(renderer)

for t, wh, x, y in parts:
w, h = wh

xt1, yt1 = tr.transform((x, y))
yt1 -= d
xt2, yt2 = xt1 + w, yt1 + h

projected_xs.extend([xt1, xt2])
projected_ys.extend([yt1, yt2])
for t, (w, a, d), xy in parts:
xt, yt = tr.transform(xy)
projected_xys.extend([
(xt, yt + a),
(xt, yt - d),
(xt + w, yt + a),
(xt + w, yt - d),
])
projected_xs, projected_ys = zip(*projected_xys)

xt_box, yt_box = min(projected_xs), min(projected_ys)
w_box, h_box = max(projected_xs) - xt_box, max(projected_ys) - yt_box
Expand Down Expand Up @@ -434,15 +433,18 @@ def update_from(self, other):

def _get_layout(self, renderer):
"""
Return the extent (bbox) of the text together with
multiple-alignment information. Note that it returns an extent
of a rotated text when necessary.
Return

- the (rotated) text bbox, and
- a list of ``(line, (width, ascent, descent), xy)`` tuples for each line.
"""
thisx, thisy = 0.0, 0.0
lines = self._get_wrapped_text().split("\n") # Ensures lines is not empty.

ws = []
hs = []
# Reminder: The ascent (a) goes from the baseline to the top and the
# descent (d) from the baseline to the bottom; both are (typically)
# nonnegative. The height h is the sum, h = a + d.
wads = [] # (width, ascents, descents)
xs = []
ys = []

Expand All @@ -451,7 +453,8 @@ def _get_layout(self, renderer):
renderer, "lp", self._fontproperties,
ismath="TeX" if self.get_usetex() else False,
dpi=self.get_figure(root=True).dpi)
min_dy = (lp_h - lp_d) * self._linespacing
lp_a = lp_h - lp_d
min_dy = lp_a * self._linespacing

for i, line in enumerate(lines):
clean_line, ismath = self._preprocess_math(line)
Expand All @@ -462,25 +465,21 @@ def _get_layout(self, renderer):
else:
w = h = d = 0

# For multiline text, increase the line spacing when the text
# net-height (excluding baseline) is larger than that of a "l"
# (e.g., use of superscripts), which seems what TeX does.
h = max(h, lp_h)
a = h - d
# To ensure good linespacing, pretend that the ascent (resp.
# descent) of all lines is at least as large as "l" (resp. "p").
a = max(a, lp_a)
d = max(d, lp_d)

ws.append(w)
hs.append(h)

# Metrics of the last line that are needed later:
baseline = (h - d) - thisy
baseline = a - thisy

if i == 0:
# position at baseline
thisy = -(h - d)
else:
# put baseline a good distance from bottom of previous line
thisy -= max(min_dy, (h - d) * self._linespacing)
if i == 0: # position at baseline
thisy = -a
else: # put baseline a good distance from bottom of previous line
thisy -= max(min_dy, a * self._linespacing)

wads.append((w, a, d))
xs.append(thisx) # == 0.
ys.append(thisy)

Expand All @@ -490,6 +489,7 @@ def _get_layout(self, renderer):
descent = d

# Bounding box definition:
ws = [w for w, a, d in wads]
width = max(ws)
xmin = 0
xmax = width
Expand Down Expand Up @@ -587,7 +587,7 @@ def _get_layout(self, renderer):
# now rotate the positions around the first (x, y) position
xys = M.transform(offset_layout) - (offsetx, offsety)

return bbox, list(zip(lines, zip(ws, hs), *xys.T)), descent
return bbox, list(zip(lines, wads, xys))

def set_bbox(self, rectprops):
"""
Expand Down Expand Up @@ -840,7 +840,7 @@ def draw(self, renderer):
renderer.open_group('text', self.get_gid())

with self._cm_set(text=self._get_wrapped_text()):
bbox, info, descent = self._get_layout(renderer)
bbox, info = self._get_layout(renderer)
trans = self.get_transform()

# don't use self.get_position here, which refers to text
Expand Down Expand Up @@ -876,7 +876,7 @@ def draw(self, renderer):

angle = self.get_rotation()

for line, wh, x, y in info:
for line, wad, (x, y) in info:

mtext = self if len(info) == 1 else None
x = x + posx
Expand Down Expand Up @@ -1064,7 +1064,7 @@ def get_window_extent(self, renderer=None, dpi=None):
"want to call 'figure.draw_without_rendering()' first.")

with cbook._setattr_cm(fig, dpi=dpi):
bbox, info, descent = self._get_layout(self._renderer)
bbox, _ = self._get_layout(self._renderer)
x, y = self.get_unitless_position()
x, y = self.get_transform().transform((x, y))
bbox = bbox.translated(x, y)
Expand Down
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