RStudio Server Preview: Font rendering in ACE editor broken (again)

Just upgraded a Ubuntu 16.04 VM with RStudio Server Preview v1.3.911 and the rendering of fixed-width font (anti-aliasing?) inside the ACE editor is broken. I attached a screenshot from Chrome on my Ubuntu 19.10 client.

Til now I had only noticed that problem in RStudio Desktop, but the latest Server Preview release is now also affected.


I don't use Ubuntu so I'm not entirely sure if your issue is due to the same root cause as mine, however I did report an issue with macOS Catalina subpixel antialiasing on non-Retina displays here:

Selectively enable subpixel antialiasing on macOS Catalina

A toggle to enable/disable subpixel antialiasing at the application level (e.g., as is available in iTerm2) would appear to be an useful solution to both of our issues.

Indeed, I realize this is a tricky one, probably upstream bug in ACE editor and nothing to do with RStudio's implementation.

Monospace fonts (incl. "Ubuntu Mono") render nicely in Ubuntu / Chrome otherwise (pic below).

How can I locate older RStudio Preview releases to downgrade?

In addition, I can confirm that the offending CSS is related to inline ace_editor.css rules. Removing these rules fix the font rendering for me. I'm just not able to identify which exact rule or combination is the problem.


Showing normal (Ubuntu Mono) font rendering below:


Would you mind filing this as a bug report at

Done! Thank you.

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