Bug report

Bug summary

I am encountering a few seemingly related issues but can't exactly define what's happening. They broadly relate to unexpected changes in how plots are scaled and appear in the context of using the transform objects attached to the Axes. I assume they are caused by changes in autoscaling in 3.2, but don't know whether they are a bug or if previous code was relying on undefined behavior (the release notes are a little vague about what actually changed).

Code for reproduction

Here is a simple example derived from an issue in seaborn rugplot (mwaskom/seaborn#2015)

import numpy as np
import matplotlib as mpl
import matplotlib.transforms as tx
from matplotlib.collections import LineCollection
import matplotlib.pyplot as plt

a = [1, 2, 4]
height = .2

xy_pairs = np.column_stack([np.repeat(a, 2), np.tile([0, height], len(a))])
line_segs = xy_pairs.reshape([len(a), 2, 2])

f, ax = plt.subplots()
trans = tx.blended_transform_factory(ax.transData, ax.transAxes)
ax.add_collection(LineCollection(line_segs, transform=trans))
ax.autoscale_view(scalex=True, scaley=False)

Actual outcome

With matplotlib 3.2.1:

Expected outcome

With matplotlib 3.1.2:

Matplotlib version

• Operating system: macos
• Matplotlib version: 3.2.1
• Matplotlib backend (print(matplotlib.get_backend())): ipython inline

Other information

Linking another seaborn issue (mwaskom/seaborn#2013) where there has been a similar change in behavior with matplotlib 3.2 but where it's harder to extract a standalone issue.