The arrow length is different with or without bbox parameter when using ax.annotate

Community
1

There is a github issue related this discuss: https://github.com/matplotlib/matplotlib/issues/26441

When using ax.annotate to draw text with arrow, the text is not aligned with the arrow. You can see some texts are overlapping with the arrow, but some texts are far away from arrow:

import matplotlib.pyplot as plt

anchor_rate = [1000, 1660.89, 3220.62, 5927.36]
anchor_psnr = [31.799098, 34.155477, 36.053423, 36.5]

fig, ax = plt.subplots(figsize=(8, 6))
ax1, = ax.plot(anchor_rate, anchor_psnr, marker="o", linestyle="", color='#1f77b4', label="Anchor")

ax.annotate(f"(5927.36kbps, 36.5dB)",
            (5927.36, 36.5),
            textcoords="offset points",
            arrowprops=dict(arrowstyle="]->", connectionstyle="arc3", color='#1f77b4'),
            xycoords='data',
            xytext=(-1.6921283813438717, 14.904251123120897),
            color='#1f77b4',
            ha='center',
            va='bottom',
            transform_rotates_text=True, rotation=6.47724215379907, rotation_mode='anchor'
            )

plt.show()

image
image800×600 11.1 KB

But when adding bbox parameter to ax.annotate, the text seems aligned:

import matplotlib.pyplot as plt

anchor_rate = [1000, 1660.89, 3220.62, 5927.36]
anchor_psnr = [31.799098, 34.155477, 36.053423, 36.5]

fig, ax = plt.subplots(figsize=(8, 6))
ax1, = ax.plot(anchor_rate, anchor_psnr, marker="o", linestyle="", color='#1f77b4', label="Anchor")

ax.annotate(f"(5927.36kbps, 36.5dB)",
            (5927.36, 36.5),
            textcoords="offset points",
            arrowprops=dict(arrowstyle="]->", connectionstyle="arc3", color='#1f77b4'),
            xycoords='data',
            xytext=(-1.6921283813438717, 14.904251123120897),
            color='#1f77b4',
            ha='center',
            va='bottom',
            bbox=dict(boxstyle="rarrow,pad=0.3",
                      fc="lightblue", ec="steelblue", lw=2),
            transform_rotates_text=True, rotation=6.47724215379907, rotation_mode='anchor'
            )

plt.show()

image
image800×600 13.4 KB

Is this the expected behavior?

2

The text looks to be in exactly the same spot to me (maybe set alpha < 1 to show the axes lines behind the arrow). Is it the arrow pointing to the data that is the problem? The square bracket tail seems to be too far down the arrow?

3

Seems that my description is not accurate. Actually, I want to express that the arrow is different with or without bbox parameters:

  1. with bbox, the arrow header is near to the text
  2. without bbox, the arrow header is away from the text, there is a big gap between the text and text.

I expect that, no matter there is bbox parameter or not, the arrow header should be near to text, which means there should not be a big gap like the above image.