HiDPI XQuartz

Introduction

XQuartz doesn't support HiDPI in any reasonable way, but you can sort of make it work on a temporary basis.

Instructions

Assuming you want to run a remote X application, and you want that application to use HiDPI

1. install XQuartz

   for example brew cask install xquartz.

2. enable full screen mode in XQuartz
3. ssh -Snone -X z800.local

   -Snone is important because session multiplexing doesn't work very well with X forwarding.

4. run xterm

   we need an X (non-native) terminal for later.

5. in a native terminal run xrandr --output default --mode 5120x2880 --dpi 218

   unfortunately we can't make this permanent, after this, you will be in high resolution full screen X, with a very tiny xterm.

6. run whatever application from that xterm

   you might need to force HiDPI mode for that application, but it should have all pixels available.

7. to get out of X, press CMD+Opt+A

   unfortunately this turns off the X resolution.

8. to get back into X at the correct resolution, run xrandr --output default --mode 5120x2880 --dpi 218 again in the native terminal.

It's awful, but it works.