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[Bug]: compressed layout setting can be forgotten on second save #24954

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rcomer opened this issue Jan 12, 2023 · 7 comments · Fixed by #24971
Closed

[Bug]: compressed layout setting can be forgotten on second save #24954

rcomer opened this issue Jan 12, 2023 · 7 comments · Fixed by #24971
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topic: geometry manager LayoutEngine, Constrained layout, Tight layout
Milestone
v3.7.0

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@rcomer
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rcomer commented Jan 12, 2023 •
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Bug summary

I'm not sure whether this is really a bug or I'm just using an inconsistent combination of options. Under some specific circumstances (see below) compressed layout is not applied the second time a figure is saved.

Code for reproduction

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

arr = np.arange(100).reshape((10, 10))

matplotlib.rcParams['figure.constrained_layout.use'] = True

fig, ax_dict = plt.subplot_mosaic('AB;AC', figsize=(6, 9), width_ratios=[3, 2],
                                  layout='compressed')

for key in ["B", "C"]:
    ax_dict[key].imshow(arr)
    
fig.savefig("test1.png", bbox_inches="tight")
fig.savefig("test2.png", bbox_inches="tight")

Actual outcome

test1.png
test1

test2.png
test2

Expected outcome

Both images should look like the first.

Additional information

If I do not set the rcParams, all is well. If I do not set bbox_inches="tight" in my calls to savefig, the images are identical (but I have too much white space top and bottom). Maybe there is a better option than bbox_inches="tight" when using compressed layout?

For context, my real example is a script that makes several figures. For most of them I want constrained layout, so I set that once in the rcParams for convenience. Only one figure needs "compressed", and I am saving twice because I want both a png and a pdf. Fixed it in my current example by just reverting the rcParams setting for the one figure.

Operating system

RHEL7

Matplotlib Version

3.6.2 and main

Matplotlib Backend

QtAgg

Python version

3.9 and 3.11

Jupyter version

No response

Installation

conda
@rcomer rcomer added the topic: geometry manager LayoutEngine, Constrained layout, Tight layout label Jan 12, 2023
@jklymak
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jklymak commented Jan 12, 2023

Yeah we do some dancing around when we save with bbox inches - so this seems to get caught in that. I tried to track it down, but the figure-saving stack is full of context managers, and I can't see where the layout manager gets reset. Hopefully someone more cognizant of that part of the codebase can explain.

@rcomer
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rcomer commented Jan 12, 2023

Thanks for looking @jklymak 🙂

@QuLogic
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QuLogic commented Jan 13, 2023

I think it is set (temporarily) here;

matplotlib/lib/matplotlib/backend_bases.py

Lines 2356 to 2357 in 018c5ef

# we have already done layout above, so turn it off:
stack.enter_context(self.figure._cm_set(layout_engine='none'))

@jklymak
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jklymak commented Jan 13, 2023

It is, but I don't understand what _cm_set does to reset the layout engine after this. Somehow it is dropping the old layout engine and making a new one, and the new one doesn't know that the old one was a 'compressed' engine.

@QuLogic
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QuLogic commented Jan 13, 2023

It calls get_{kwarg} and after running calls set({kwarg}={old value}). So here it calls oldvalue = figure.get_layout_engine() and figure.set(layout_engine=oldvalue). Is figure.set_layout_engine(figure.get_layout_engine()) working correctly?

@rcomer
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rcomer commented Jan 13, 2023 •
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I am way out of my depth here but

import matplotlib.pyplot as plt

plt.rcParams['figure.constrained_layout.use'] = True
fig = plt.figure(layout="compressed")

print(fig.get_layout_engine()._compress)
fig.set_layout_engine(fig.get_layout_engine())
print(fig.get_layout_engine()._compress)

fig.savefig('foo.png', bbox_inches='tight')
print(fig.get_layout_engine()._compress)
True
True
False

Without the rcParams line, fig.get_layout_engine() returns None after the savefig.

@rcomer
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rcomer commented Jan 13, 2023

I think the problem is the call to adjust_bbox

matplotlib/lib/matplotlib/backend_bases.py

Lines 2349 to 2350 in 018c5ef

restore_bbox = _tight_bbox.adjust_bbox(
self.figure, bbox_inches, self.figure.canvas.fixed_dpi)

which explicity calls

matplotlib/lib/matplotlib/_tight_bbox.py

Line 21 in a3011df

fig.set_layout_engine(None)

which will use the default constrained layout engine if the rcParams is set

matplotlib/lib/matplotlib/figure.py

Lines 2599 to 2610 in a3011df

if layout is None:
if mpl.rcParams['figure.autolayout']:
layout = 'tight'
elif mpl.rcParams['figure.constrained_layout.use']:
layout = 'constrained'
else:
self._layout_engine = None
return
if layout == 'tight':
new_layout_engine = TightLayoutEngine(**kwargs)
elif layout == 'constrained':
new_layout_engine = ConstrainedLayoutEngine(**kwargs)

@rcomer rcomer mentioned this issue Jan 13, 2023
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@tacaswell tacaswell added this to the v3.7.0 milestone Jan 13, 2023
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topic: geometry manager LayoutEngine, Constrained layout, Tight layout
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FIX: adjust_bbox should not modify layout engine rcomer/matplotlib
4 participants
@tacaswell @QuLogic @jklymak @rcomer