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x49 opened this issue Apr 24, 2018 · 2 comments
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Saving plot with text annotation and time axis to pgf file errors with multiple backends #11116

x49 opened this issue Apr 24, 2018 · 2 comments
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backend: pgf topic: date handling

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@x49
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x49 commented Apr 24, 2018

Bug report

Writing a simple plot to a pgf file produces a ValueError exception, when saving through png works fine. This occurs explicitly only in the combination of

  1. Having a time axis in the plot
  2. Adding a text annotation into the plot

With no time axis or no annotation, the error does not appear. Tested with Qt5Agg, GTK3Agg, GTK3Cairo.

Code for reproduction

import matplotlib as mpl

mpl.use('Qt5Agg')  ## Error present
# mpl.use('GTK3Agg') ## Error present
# mpl.use('GTK3Cairo') ## Error present
print(mpl.get_backend())

import matplotlib.pyplot as plt
fig, ax = plt.subplots(1,1)


# t = [10, 20]                                        ## This works with text + pgf
t = [mpl.dates.num2date(5), mpl.dates.num2date(5.2)]  ## This is buggy with text + pgf

y = [10, 20]
ax.plot(t,y)

## This works in all cases
fig.savefig('out-1.png')
fig.savefig('out-1.pgf')

## Everything works fine without the text
ax.text(t[0],15,'Test')

fig.savefig('out-2.png') ## This works in all cases
fig.savefig('out-2.pgf') ## This does not work with time x-axis + text

Actual outcome

Qt5Agg
qt5ct: using qt5ct plugin
Traceback (most recent call last):
  File "test.py", line 23, in <module>
    fig.savefig('out-2.pgf') ## This does not work with time x-axis
  File "/usr/lib/python3.6/site-packages/matplotlib/figure.py", line 2035, in savefig
    self.canvas.print_figure(fname, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_qt5agg.py", line 94, in print_figure
    super(FigureCanvasQTAgg, self).print_figure(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backend_bases.py", line 2263, in print_figure
    **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 863, in print_pgf
    self._print_pgf_to_fh(fh, *args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 844, in _print_pgf_to_fh
    self.figure.draw(renderer)
  File "/usr/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/figure.py", line 1475, in draw
    renderer, self, artists, self.suppressComposite)
  File "/usr/lib/python3.6/site-packages/matplotlib/image.py", line 141, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/axes/_base.py", line 2607, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)
  File "/usr/lib/python3.6/site-packages/matplotlib/image.py", line 141, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/text.py", line 755, in draw
    ismath=ismath, mtext=mtext)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 716, in draw_text
    x, y = mtext.get_transform().transform_point(mtext.get_position())
  File "/usr/lib/python3.6/site-packages/matplotlib/transforms.py", line 1533, in transform_point
    return self.transform(np.asarray([point]))[0]
  File "/usr/lib/python3.6/site-packages/matplotlib/transforms.py", line 1446, in transform
    res = self.transform_affine(self.transform_non_affine(values))
  File "/usr/lib/python3.6/site-packages/matplotlib/transforms.py", line 2482, in transform_affine
    return self.get_affine().transform(points)
  File "/usr/lib/python3.6/site-packages/matplotlib/transforms.py", line 1796, in transform
    return self.transform_affine(values)
  File "/usr/lib/python3.6/site-packages/matplotlib/transforms.py", line 1880, in transform_affine
    return affine_transform(points, mtx)
ValueError: object too deep for desired array

Expected outcome
png output is fine in both cases:
out-1.png:
out-1

out-2.png:
out-2

I would expect the pgf file to also be written in the second case.

Matplotlib version

  • Operating system: Arch Linux / 4.15.15-1-ARCH
  • Matplotlib version: 2.2.2
  • Matplotlib backend: Qt5Agg / GTK3Agg / GTK3Cairo
  • Python version: 3.6.5

All packages installed through distribution packages.
@tacaswell
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attn @pwuertz

It looks like "object too deep for desired array" is coming out of numpy and mis-matched dimensions.

@pwuertz
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pwuertz commented Apr 24, 2018

In the example posted here, adding/removing the seemingly unrelated text element to the figure makes the tick labels' Text.get_position() method flip its behavior. Instead of returning float positions it suddenly returns date objects, on which the subsequent get_position().transform_point() call chokes on.

Apparently, there is get_unitless_position() for getting the desired coordinates in such situations. I'll prepare a PR for that.

@pwuertz pwuertz mentioned this issue Apr 24, 2018
Merged
@jklymak jklymak closed this as completed in 1359636 May 2, 2018
jklymak added a commit that referenced this issue May 2, 2018
@jklymak
Merge pull request #11119 from pwuertz/fix_11116
c195412 
PGF: Get unitless positions from Text elements (fix #11116)
@marquistj13 marquistj13 mentioned this issue Aug 5, 2018
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@tacaswell @anntzer @pwuertz @x49