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Fix center of rotation with rotation_mode='anchor' #29199

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Merged
merged 1 commit into from
Jun 10, 2025
+30 −4
Merged

Fix center of rotation with rotation_mode='anchor' #29199

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18 changes: 14 additions & 4 deletions lib/matplotlib/backends/backend_agg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -197,10 +197,20 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
xo, yo = font.get_bitmap_offset()
xo /= 64.0
yo /= 64.0
xd = d * sin(radians(angle))
yd = d * cos(radians(angle))
x = round(x + xo + xd)
y = round(y + yo + yd)

rad = radians(angle)
xd = d * sin(rad)
yd = d * cos(rad)
# Rotating the offset vector ensures text rotates around the anchor point.
# Without this, rotated text offsets incorrectly, causing a horizontal shift.
# Applying the 2D rotation matrix.
rotated_xo = xo * cos(rad) - yo * sin(rad)
rotated_yo = xo * sin(rad) + yo * cos(rad)
# Subtract rotated_yo to account for the inverted y-axis in computer graphics,
# compared to the mathematical convention.
x = round(x + rotated_xo + xd)
y = round(y - rotated_yo + yd)

self._renderer.draw_text_image(font, x, y + 1, angle, gc)

def get_text_width_height_descent(self, s, prop, ismath):
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Binary file added lib/matplotlib/tests/baseline_images/test_text/rotation_anchor.png
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16 changes: 16 additions & 0 deletions lib/matplotlib/tests/test_text.py
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Expand Up @@ -301,6 +301,22 @@ def test_alignment():
ax.set_yticks([])


@image_comparison(baseline_images=['rotation_anchor.png'], style='mpl20',
remove_text=True)
def test_rotation_mode_anchor():
fig, ax = plt.subplots()

ax.plot([0, 1], lw=0)
ax.axvline(.5, linewidth=.5, color='.5')
ax.axhline(.5, linewidth=.5, color='.5')

N = 4
for r in range(N):
ax.text(.5, .5, 'pP', color=f'C{r}', size=100,
rotation=r/N*360, rotation_mode='anchor',
verticalalignment='center_baseline')


@image_comparison(['axes_titles.png'])
def test_axes_titles():
# Related to issue #3327
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