Bug report

When saving a png of a polar plot with the r-origin set "by hand," saving the result as a png plot doesn't work as expected. Saving it as PDF works as expected. Working interactively and saving it with the UI as a png works as expected.

importmatplotlib.pyplotaspltimportnumpyasnpfrommatplotlib.gridspecimportGridSpecnbins=50data=np.random.randint(0,42,nbins)fig=plt.figure()ax_g=fig.add_subplot(polar=True,facecolor="none")theta=np.array(    [np.pi/2-i*2*np.pi/len(data)foriinrange(len(data))])lines=ax_g.plot(theta,data)ax_g.set_rorigin(-78)# Replacing this with ax_g.set_rmin works as expected, so the problem comes from this line.fig.savefig("bug.png")fig.savefig("bug.pdf")

Actual outcome

Expected outcome

bug.pdf

Matplotlib version

• Operating system: Ubuntu
• Matplotlib version: 3.2.1
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg (tried with Agg, and other backends)
• Python version: 3.8.2
• Jupyter version (if applicable): NA
• Other libraries:  NA