PNG output with PGF backend fails with pdftocairo exit code 99

[narpfel]

Bug report

Bug summary

When the PGF backend is selected, saving figures to a PNG image does not work because invoking pdftocairo fails with exit code 99. Saving to a PDF file and then invoking pdftocairo with the same arguments works.

Code for reproduction

# plot_to_png.py
import matplotlib as mpl
mpl.use("pgf")
from matplotlib import pyplot as plt

plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig("test.png")

Executing this leads to

me@home:/tmp/mpl » python plot_to_png.py 
Traceback (most recent call last):
  File "plot_to_png.py", line 6, in <module>
    plt.savefig("test.png")
  File "/usr/lib/python3.6/site-packages/matplotlib/pyplot.py", line 697, in savefig
    res = fig.savefig(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/figure.py", line 1572, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backend_bases.py", line 2244, in print_figure
    **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 961, in print_png
    self._print_png_to_fh(fh, *args, **kwargs)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 941, in _print_png_to_fh
    converter(fname_pdf, fname_png, dpi=self.figure.dpi)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_pgf.py", line 197, in cairo_convert
    check_output(cmd, shell=True, stderr=subprocess.STDOUT)
  File "/usr/lib/python3.6/subprocess.py", line 336, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.6/subprocess.py", line 418, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['pdftocairo', '-singlefile', '-png', '-r 100', '/tmp/mpl_pgf_klhh_fnt/figure.pdf', '/tmp/mpl_pgf_klhh_fnt/figure']' returned non-zero exit status 99.
me@home:/tmp/mpl » 

Expected outcome

This should produce a PNG file of a linear graph.

Saving to a PDF file and then calling pdftocairo works:

# plot_to_pdf.py
import matplotlib as mpl
mpl.use("pgf")
from matplotlib import pyplot as plt

plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig("test.pdf")

me@home:/tmp/mpl » python plot_to_pdf.py 
me@home:/tmp/mpl » pdftocairo -singlefile -png -r 100 /tmp/mpl/test.pdf /tmp/mpl/test
me@home:/tmp/mpl » echo $?
0
me@home:/tmp/mpl » 

Used program versions

• Arch Linux

• Python 3.6.0 (default, Jan 16 2017, 12:12:55) 
  [GCC 6.3.1 20170109] on linux
  

  from the Arch repo
• Matplotlib version 2.0.0, also installed from Arch repo
• pdftocairo version 0.52.0, also from Arch repo (package is named poppler)

Prior to updating to Matplotlib 2.0.0 (from 1.5.3) and pdftocairo 0.52.0 (from 0.51.0), this worked.

[QuLogic]

Worked in 1.5.3, so marking critical; also because I've got a fix already written...

[dstansby]

This is fixed in 2.0.x