Distracting and confusing cursor offset

[jebrosen]

Platform: Linux, Firefox version 72.0b4. Chromium appears to be fine.

Screenshot: https://paste.rs/pxS.png (the cursor is positioned on line 12 after the space, but is visually inside it).

Since some time in the last few weeks, I noticed that the cursor sometimes gets offset from the text insert position. When it's bad enough, Backspace deletes the character visually in front of the cursor instead of behind it making editing very frustrating and error-prone.

It seems to be somehow related to the vertical dotted-line indentation hints, as lines with more of these have a worse offset.

I will try bisecting Firefox builds but that might be a while; hopefully others can help reproduce or narrow down the necessary conditions.

[shepmaster]

We haven't made any changes that would affect this in the last few weeks / months. I'd recommend looking through the Ace editor issues to see if anyone else has reported issues.

[shepmaster]

You may also want to see if you can reproduce your issue on the Ace demo page.

[jebrosen]

I can reproduce it on that demo page, but only if I manually set a few elements to have font-family: "Source Code Pro" like is used in the playground. Thanks for that pointer; I'll keep playing with it a bit and see what I can find.

[shepmaster]

only if I manually set a few elements to have font-family: "Source Code Pro"

Hmm. See also #112 and #509. We might be using Ace incorrectly or in a non-supported manner, or that specific font may have issues. You may also want to see if your local version of the font has become corrupted in some fashion (detailed in #112).

[jebrosen]

I have found a workaround. On Arch adobe-source-code-pro-fonts is a transitive dependency of gtk3 so it's pretty much guaranteed to be installed. However, Arch only packages the OTF version of the fonts. After installing the whole font package (https://github.com/adobe-fonts/source-code-pro/releases/tag/2.030R-ro%2F1.050R-it) to ~/.local/share/fonts/ and restarting Firefox, everything works nicely again.

I have no idea why that fixes it, though. Maybe Firefox prefers the TTF version and it happens to be better in some way. Whatever wrong thing happens with the OTF fonts, I think this is a duplicate of the many issues related to the way the Ace Editor calculates its cursor position and not something rust-playground can really fix.

[shepmaster]

Interesting! Thank you for the investigation and feedback!