Center of rotation for text with rotation_mode='anchor' · Issue #13044 · matplotlib/matplotlib · GitHub

Bug report

After fixing an obvious vertical offset bug in #13029 the rotation

import matplotlib.pyplot as plt
plt.plot([0, 1], lw=0)
plt.axvline(.5, linewidth=.5, color='.5')
plt.axhline(.5, linewidth=.5, color='.5')

N = 4
for r in range(N):
    plt.text(.5, .5, 'pP', color=plt.get_cmap('jet')(r/N), size=100, rotation=r/N*360, va='center_baseline', rotation_mode='anchor')

looks like this:

I'm not sure if this is now 100% as desired:

The vertical position of the rotation point is not exactly at y=0.5 (slightly shifted down).
The horizontal position of the rotation point is not at x=0.5 but at the left edge of the first letter.

Is this intended or are there still other bugs in the position calculation?

Labelled as

"Good first issue": You just have to follow the rotation code.
"Difficulty medium": Understand the mathematics for the rotation center and adjust it.

We should also check that this is consistent between the backends (ie, png / svg / pdf all have the same problem).

@timhoffm Looks like the problem is not with the rotation center, but with the bounding box and the text:

import matplotlib.pyplot as plt

fig, axes = plt.subplots(2, 2)
for idx, ax in enumerate(axes.flatten()):
      ax.axvline(.5, linewidth=.5, color='.5')
      ax.axhline(.5, linewidth=.5, color='.5')
      ax.text(
          .5, .5, 'pP', size=50,
          bbox=dict(facecolor='None', edgecolor='red', pad=0),
          rotation=idx*90,
          va='center_baseline',
          rotation_mode='anchor'
      )

and this will produce

Hi everyone, I am Zareef, and I am very new to contributing to open source projects. I was wondering if me and my friend could contribute to this issue for a class at my university.

@safdarzareef You are very welcome to contribute if you think you're basically able to resolve the issue. While we're available for targeted questions, we don't have the capacity for close mentoring (We had some bad experiences in the past from university class contributors that essentially needed as step-by-step guidance how to approach and resolve the issue).

Also there's already a proposed patch #19114. So first step would be to check that and determine if this is a good approach and only needs some additions.

This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!

Is this issue still open? If yes, does this make sense or look little better? @timhoffm

import matplotlib.pyplot as plt

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

N = 4
for r in range(N):
    text = plt.text(.5, .5, 'pP', color=plt.get_cmap('jet')(r/N), size=100, rotation=r/N*360, va='center_baseline', rotation_mode='anchor')
    text.set_rotation(r/N*360) 
    text.set_position((.5, .5)) 

plt.show()

seems like it handles this issue -> The vertical position of the rotation point is not exactly at y=0.5 (slightly shifted down).

Update: This still seems to be a problem and the issue appears to be related to the bounding box of the rotated text not being correct.

@tacaswell tried making this change!

import matplotlib.pyplot as plt
import numpy as np

def add_rotated_text(ax, text, x, y, angle, size=50, color='black', bbox_pad=0):
    rotation_rad = np.deg2rad(angle)
    x_adjusted = x + 0.03 * np.cos(rotation_rad)
    y_adjusted = y + 0.03 * np.sin(rotation_rad)
    
    text_obj = ax.text(
        x_adjusted, y_adjusted, text, size=size,
        rotation=angle,
        va='center',
        rotation_mode='anchor',
        color=color
    )
    
    # Set a fixed padding value for the bounding box
    text_obj.set_bbox(dict(facecolor='None', edgecolor='red', pad=bbox_pad))

# Create a 2x2 grid of subplots
fig, axes = plt.subplots(2, 2)

# Loop through subplots and add rotated text
for idx, ax in enumerate(axes.flatten()):
    ax.axvline(.5, linewidth=.5, color='.5')
    ax.axhline(.5, linewidth=.5, color='.5')
    add_rotated_text(ax, 'pP', .5, .5, idx*90, bbox_pad=0)  # Specify bbox_pad here

# Add labels and title
fig.suptitle('Rotated Text Example')
axes[1, 0].set_xlabel('X-axis')
axes[1, 1].set_xlabel('X-axis')
axes[0, 0].set_ylabel('Y-axis')
axes[1, 0].set_ylabel('Y-axis')

plt.show()

@timhoffm Hello! I'm Evelyn, and I'm interested in helping resolve this issue. Can me and my friends work on this issue?

@evelyn-lo sure. This is a classic debug topic. You need to find out why the behavior is like it is. It's likely somewhere in the numerics of the calculation.

Hi, I’m a new contributor interested in working on this issue. If it’s still available, I’d like to investigate it and try implementing a fix.

#29199 will fix this; there is no need to work on this now.

The text-overhaul branch is now merged to main.

Center of rotation for text with rotation_mode='anchor' · Issue #13044 · matplotlib/matplotlib · GitHub

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Center of rotation for text with rotation_mode='anchor' #13044

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Center of rotation for text with rotation_mode='anchor' · Issue #13044 · matplotlib/matplotlib · GitHub

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Center of rotation for text with rotation_mode='anchor' #13044

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timhoffm commented on Jul 7, 2020

tacaswell commented on Jul 12, 2020

dzh527 commented on Jul 15, 2020

safdarzareef commented on Apr 6, 2021

timhoffm commented on Apr 7, 2021

github-actions commented on May 26, 2023

coder-brunette commented on Sep 22, 2023

tacaswell commented on Sep 22, 2023

coder-brunette commented on Sep 23, 2023

evelyn-lo commented on Apr 20, 2025

timhoffm commented on Apr 21, 2025

sahil-11116 commented on Mar 5, 2026

QuLogic commented on Mar 19, 2026

QuLogic commented on Apr 10, 2026

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