Bug report

Depending on DPI, a figure saved as PNG is missing some short lines.

Code for reproduction

importmatplotlibfrommatplotlibimportpyplotaspltimportnumpyasnpmatplotlib.use('agg')# Generate a set of 50 random points.np.random.seed(0)all_x,all_y= (np.random.rand(50)for_inrange(2))# Scatter dots in blue.plt.scatter(all_x,all_y,c='blue',s=2)# Plot very short lines (length 0.001) in red with a small offset on Y.forx,yinzip(all_x,all_y):plt.plot((x,x+0.001), (y+0.01,y+0.01),c='red',linewidth=2)# Save with different resolutionsplt.savefig('bug_96.png',dpi=96)plt.savefig('bug_300.png',dpi=300)

Actual outcome

Depending on export DPI, some short segments (in red, added byplot()) are missing, while all dots (in blue, added byscatter() are always present).

At 96 DPI:

At 300 DPI:

Expected outcome

The segments should be always present, regardless of the resolution.

Matplotlib version

• Operating system: Ubuntu 20.04.2 LTS
• Matplotlib version (import matplotlib; print(matplotlib.__version__)): 3.4.2
• Matplotlib backend (print(matplotlib.get_backend())):agg
• Python version: 3.8.5

Python is installed via apt-get, Matplotlib installed system-wide using PIP.