[Matplotlib-users] possible regression in plt.draw (mpl 1.4.3 -> 1.5.0) when using fig.text using transformations

[Oliver Willekens]

Dear matplotlib users and developers,

I’m using plt.draw() to force the rendering of all artists and then, based
on their newly calculated positions, place a text label on the figure
window in figure coordinates.

The goal is to add a text label near the conventional y-axis, at the top,
right-aligned. Example code that demonstrates the problem:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl
print(mpl.__version__)

x = np.linspace(0, 50)
y = 4*np.sin(x) + 5

fig = plt.figure(figsize=(18,9.8))
ax = fig.add_axes((0.1, 0.1, 0.8, 0.8),
    frameon=True,
    aspect='equal',
    adjustable='box',
    xlim=(x.min(), x.max()),
    ylim=(0, 10),
    xticks=[x.min(), x.max()],
    yticks=[0, 10],
    xlabel='dimension (unit)')
ax.plot(x, y)
plt.draw()  # force redraw

ylabel_pos = fig.transFigure.inverted().transform_point(ax.transAxes.transform_point((0,1)))
label1 = fig.text(ylabel_pos[0], ylabel_pos[1], "label1", ha="right",
va="bottom")
plt.savefig('/tmp/test_pre_mpl_v_{}.png'.format(mpl.__version__))
ylabel_pos = fig.transFigure.inverted().transform_point(ax.transAxes.transform_point((0,1)))
label2 = fig.text(ylabel_pos[0], ylabel_pos[1], "label2", ha="right",
va="bottom")
plt.savefig('/tmp/test_post_mpl_v_{}.png'.format(mpl.__version__))

The code shows that in mpl 1.4.3 both label1 and label2 end up at the same
(desired) position. However, mpl 1.5.0 and 1.5.1 (just installed to check)
show that label1 is at a height of 0.9 in the figure coordinates. After the
first call to savefig, the figure is rendered with the axes getting a new
height and width (due to the call to aspect='equal', adjustable='box') and
so the subsequent call to savefig renders label2 in the correct position.

Using ax.text(x=0, y=1, s='label', transform=ax.transAxes, ha="right",
va="bottom") gets the job done alright (both in 1.4.3, as well as 1.5.0),
but the call to fig.text using the subsequent transforms should have
worked, I believe, and so this seems to indicate something has changed in
the rendering of a rescaled axes using plt.draw.

Kind regards,
Oliver

P.S. I posted this to the older sourceforge mailing list as well, by
accident. Hadn’t changed the send-to address yet, even though Thomas
Caswell had pointed it out to me already in August 2015. My apologies.
​
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