Incorrect hatching in legend for PDF backend

[jpallister]

When using hatching in a legend, the PDF backend does not draw the hatching if the previous label is empty:

from matplotlib import pyplot as plt

fig = plt.figure()

a = plt.Rectangle([0,0], 0, 0, facecolor="green", hatch="//")
b = plt.Rectangle([0,0], 0, 0, facecolor="blue", hatch="//")

fig.legend([a,b,a,b], ["","","",""])

plt.savefig("test.pdf")
plt.show()

The displayed legend (from plt.show) is:

The legend saved in the PDF is:

If one of the labels is non-empty:

fig.legend([a,b,a,b], ["","","X",""])

the following hatching is displayed correctly

[tacaswell]

weird.

attn @jkseppan

[tacaswell]

I suspect that there is a graphics context which is not getting properly reset.

[jpallister]

The following commit fixes the issue in this case:
232c50d

However, I don't know enough to say whether this is the right thing to do. The problem does seem to be the hatch pattern is not reapplied in the PDF backend though.

[tacaswell]

@jpallister Great! I also do not know enough about the internals of pdf's to tell if that is the right solution (it seems a bit brittle as I think it depends on the order of the commands), but I am convinced that this is the right place.

Can you put in a PR with that commit and maybe add a test, (see #4472 for an example of adding a pdf only test). Even if this is not the final solution, having the commit in a PR greatly helps us with the review process.

[tacaswell]

maybe related: #3023

[tacaswell]

Closed by merging #4474