savefig PGF - RuntimeError: Cannot get window extent w/o renderer

[gozzilli]

I'm trying to save a figure in pyplot with tight margins.

The following code works perfectly with a PDF output:

from matplotlib import pyplot as plt
plt.plot(1)
plt.savefig('test.pdf', bbox_inches='tight')

But not with PGF output

plt.savefig('test.pgf', bbox_inches='tight')

as it returns RuntimeError: Cannot get window extent w/o renderer.

I have been suggested that this may be a bug -- see question on Stackoverflow.

matplotlib 1.3.0 on Ubuntu 13.04

python -c "from matplotlib import pyplot as plt; plt.plot(1); plt.savefig('test.pgf', bbox_inches='tight');"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 561, in savefig
    return fig.savefig(*args, **kwargs)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/figure.py", line 1410, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt4agg.py", line 161, in print_figure
    FigureCanvasAgg.print_figure(self, *args, **kwargs)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/backend_bases.py", line 2169, in print_figure
    bbox_inches = self.figure.get_tightbbox(renderer)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/figure.py", line 1551, in get_tightbbox
    bb.append(ax.get_tightbbox(renderer))
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/axes.py", line 9153, in get_tightbbox
    bb_xaxis = self.xaxis.get_tightbbox(renderer)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/axis.py", line 1055, in get_tightbbox
    renderer)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/axis.py", line 1038, in _get_tick_bboxes
    extent = tick.label1.get_window_extent(renderer)
  File "PYTHONPATH/matplotlib-1.3.0rc2-py2.7-linux-x86_64.egg/matplotlib/text.py", line 751, in get_window_extent
    raise RuntimeError('Cannot get window extent w/o renderer')
RuntimeError: Cannot get window extent w/o renderer

[mdboom]

@pwuertz: As the PGF guy, I thought I'd bring this to your attention.

[pwuertz]

There is indeed a problem I couldn't solve. The way the tight bbox mechanism currently works is to draw a figure to a dummy stream as some kind of initialization. Then it grabs the active Renderer in order to determine the text element sizes and thus the figure size. So the backend must support writing to a stream,.

I implemented stream support in backend_pgf for the ".pdf" and ".png" output, so tight bbox works here. Pgf output on the other hand may consist of multiple files if a figure includes raster images. There is no meaningful way of writing this to a stream, so I denied streams as a target if the output type is ".pgf". This is why tight bbox fails here.

To fix this one could eliminate that dummy save-figure procedure in the tight bbox routine and use the get_renderer method that is also used by tight_layout. At least if I understood the tight bbox mechanism correctly? If so, I could give it a try.