"Transform()" returns bad coordinates with ipympl

Bắt đầu bằng cách chạy ví dụ về phép biến đổi Matplotlib được cung cấp ở các chế độ inline và ipympl/widget, sau đó so sánh các kết quả được hiển thị và lưu. Issue hoàn tất khi chế độ widget tạo ra cùng tọa độ và vị trí chú thích như chế độ inline.

Describe the issue

I believe the "transform()" functions of Matplotlib do not behave well in ipympl or widget mode.

Code for reproduction

I simply use the matplotlib example published here:
https://matplotlib.org/3.1.1/tutorials/advanced/transforms_tutorial.html

I copy/paste the code for basic help :

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches

x = np.arange(0, 10, 0.005)
y = np.exp(-x/2.) * np.sin(2*np.pi*x)

fig, ax = plt.subplots()
ax.plot(x, y)
ax.set_xlim(0, 10)
ax.set_ylim(-1, 1)

xdata, ydata = 5, 0
xdisplay, ydisplay = ax.transData.transform_point((xdata, ydata))

bbox = dict(boxstyle="round", fc="0.8")
arrowprops = dict(
    arrowstyle="->",
    connectionstyle="angle,angleA=0,angleB=90,rad=10")

offset = 72
ax.annotate('data = (%.1f, %.1f)' % (xdata, ydata),
            (xdata, ydata), xytext=(-2*offset, offset), textcoords='offset points',
            bbox=bbox, arrowprops=arrowprops)

disp = ax.annotate('display = (%.1f, %.1f)' % (xdisplay, ydisplay),
                   (xdisplay, ydisplay), xytext=(0.5*offset, -offset),
                   xycoords='figure pixels',
                   textcoords='offset points',
                   bbox=bbox, arrowprops=arrowprops)

plt.show()

Actual outcome
I get different results depending on the matplotlib mode :

• on one side, %matplotlib inline gives the result expected and displayed in the example, as below :
  
• on the other side, %matplotlib ipympl or %matplotlib widget give erroneous results, as below :

The result is the same if I download with the "floppy-disk" icon of the widget.

Expected outcome

The result with widget or ipympl mode should be the one of inline mode.

Versions

 3.7.7 (default, Mar 26 2020, 10:32:53) 
[Clang 4.0.1 (tags/RELEASE_401/final)]
ipympl version: 0.5.2
jupyter core     : 4.6.3
jupyter-notebook : 6.0.3
qtconsole        : 4.7.5
ipython          : 7.16.1
ipykernel        : 5.3.3
jupyter client   : 6.1.6
jupyter lab      : 1.2.6
nbconvert        : 5.6.1
ipywidgets       : 7.5.1
nbformat         : 5.0.7
traitlets        : 4.3.3
Known nbextensions:
  config dir: /Users/mmyara/.jupyter/nbconfig
    notebook section
      jupyter-js-widgets/extension  enabled 
      - Validating: OK
  config dir: /opt/miniconda3/etc/jupyter/nbconfig
    notebook section
      jupyter-matplotlib/extension  enabled 
      - Validating: OK
      plotlywidget/extension  enabled 
      - Validating: OK
      jupyter-js-widgets/extension  enabled 
      - Validating: OK
    tree section
      ipyparallel/main  enabled 
      - Validating: OK
JupyterLab v1.2.6
Known labextensions:
   app dir: /opt/miniconda3/share/jupyter/lab
        @jupyter-widgets/jupyterlab-manager v1.1.0  enabled  OK
        @jupyterlab/toc v2.0.0  enabled  OK
        @lckr/jupyterlab_variableinspector v0.4.0  enabled  OK
        jupyter-matplotlib v0.7.1  enabled  OK
        jupyterlab-plotly v4.9.0  enabled  OK
        plotlywidget v4.9.0  enabled  OK```