Hi-DPI support on macOS

Need a Hi-DPI screen to test, but now that resizing works well on Mac shouldn't be too difficult (at least to force a smaller scale and benefit from sharp pixels).

Start by reproducing the issue on a Hi-DPI macOS screen and reviewing the existing Mac resizing behavior described in the issue. Confirm that the interface can use a smaller scale while retaining sharp pixels; done means Hi-DPI rendering works correctly on macOS.

Written by the indexing model from the issue text.