Axes are drawn at wrong positions

Bug report

Bug summary

The window extent of the axes does not coincide with their position in the figure. This issue occurs in Agg and Cairo backends.

Code for reproduction

The following code produces two axes. A green rectangle is drawn at the bounding box of the axes. A red rectangle is drawn in the space between the axes.

import matplotlib.pyplot as plt

fig, axs = plt.subplots(2, figsize=(4,2), dpi=100)
for ax in axs.flatten():
    ax.set(xticklabels = [], yticklabels=[])
    ax.tick_params(labelbottom=False, bottom=False)

fig.canvas.draw()

bb1 = axs[0].get_window_extent()
bb2 = axs[1].get_window_extent()

rect = plt.Rectangle((bb2.x0, bb2.y1), width=20, height=bb1.y0 - bb2.y1,
                     linewidth=72./fig.dpi, edgecolor="red", facecolor="none", 
                     transform=None)
rect2 = plt.Rectangle((bb2.x0, bb2.y0), width=bb2.width, height=bb2.height,
                     linewidth=72./fig.dpi, edgecolor="limegreen", facecolor="none", 
                     transform=None)
fig.add_artist(rect2)
fig.add_artist(rect)

fig.savefig("borders.png")
plt.show()

Actual outcome

Code run with 100 dpi

Code run with 200 dpi

The green rectangle does not overlay with the axes. The red rectangle does not sit tight on both axes.

Expected outcome

The green rectangle should appear exactly on top of the axes spines. The red rectangle should sit tight on both axes.

Matplotlib version

Operating system: Win8
Matplotlib version: master
Matplotlib backend: Qt5Agg, TkCairo
Python version: 3.6.6

_base.py extends the bbox by self.xaxis.get_tick_padding() and self.yaxis.get_tick_padding(), for, you know, whatever reason. Particularly annoying, as these boxes do not at all cover the ticks; they seem to be in the wrong units...

I'll self-assign and try to fix this....

OK, so the issue was dpi was not being taken into account. And that the algorithm assumed ticks around all the spines.

Currently

ax.get_window_extent currently gives the extent of the axes plus a pad aroudn the outside that is supposed to be the size of the ticks. It applies this regardless of whether the ticks are shown on that axis or not, though it does account for ticks that point in or out.
ax.get_tightbbox currently also accounts for the axis objetcs and all artists in the axes.

Proposal

ax.get_window_extent properly account for tick visibility on each spine.

Don't know if this is the place to bring this up, but I have noticed that this also happens when calling gridspec tight_layout and attempting to set zero as padding. So if you want to introduce a pad in one dimension (eg. h_pad=0, w_pad = 0.5), you need to gs.update the wspace or hspace to achieve the expected.

fig =plt.figure(figsize=(8,10), constrained_layout = False)
gs = mpl.gridspec.GridSpec(2, 1, 
                           figure =fig,
                           width_ratios=[1], height_ratios = [1, 1], wspace = 0, hspace=0)


tax1 = fig.add_subplot(gs[0])
tax2 = fig.add_subplot(gs[1])


for a in [tax1, tax2]:
    a.tick_params(axis = 'both', top=False, bottom=False, right=False, left = False)
    a.set_xticklabels([])
    a.set_yticklabels([])
gs.tight_layout(fig, h_pad = 0, w_pad= 0, pad = 0)

Thats the same bug. #12716 gives the correct layout.

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Axes are drawn at wrong positions #12697

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Axes are drawn at wrong positions #12697

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Bug report

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jklymak commented on Nov 1, 2018

jklymak commented on Nov 2, 2018

jklymak commented on Nov 2, 2018

Currently

Proposal

djakubosky commented on Nov 2, 2018

jklymak commented on Nov 2, 2018

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