1676215 - Font kerning incorrect subpixel anti-aliasing is getting intermittently disabled. Caused by KDE?

Status: UNCONFIRMED

(Core :: Graphics: Text, defect, P3)

Description

[swoogan]

Attachment: font.png

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:82.0) Gecko/20100101 Firefox/82.0

Steps to reproduce:

View Roboto font on various sites on Ubuntu Linux 20.04.

Things I have tried:

• Uninstall and reinstall Roboto
• apt purge firefox
• Run in safe mode
• Use a new profile
• Using a different computer

Actual results:

Font kerning is inccorrect. Some letters are squished together, others are spaced out. Fonts will dance when hovering over them. This happens on multiple sites, but does not happen consistently between computers.

Expected results:

Fonts should display normally.

Comment 1

[swoogan]

Attachment: fonts-2020-11-09_12.53.01.mp4

Demonstrates the "dancing" of the font's kerning.

Comment 2

[Lee Salzman [:lsalzman]]

Can you please attach your "about:support" information?

Comment 3

[swoogan]

Attachment: data.json

Comment 4

[Lee Salzman [:lsalzman]]

Okay, looks like you're using basic layers and not WR here. That's good at least.

It looks like subpixel anti-aliasing is getting intermittently disabled by some sort of hover effect in the page. Jonathan?

Comment 5

[Jonathan Kew [:jfkthame]]

swoogan, can you give the address of the site shown in the video in Comment 1, please? It seems likely there's something in the page's CSS that is affecting how the text is rendered, so it would be helpful if we could take a look to try and understand what's happening here.

Comment 6

[swoogan]

The website is https://www.medvedtrader.com/www/frontend

However, the main issue is with the kerning of Roboto on all sites: GMail, Twitter, MedVed Trader, etc... I have two computers, a desktop and a laptop, and it is bad on both. I recently upgraded from Kubuntu 18.04 to 20.04, and I've only noticed the issue afterwards. In fact, it's so bad that I uninstalled the Roboto font to fall back to Arial on GMail. Even Arial isn't ideal, I still notice strange gaps around 'e' and 'i'.

The issue depicted in the video only happens on my laptop and not my desktop.

Perhaps this issue is related to KDE Plasma or something like Wayland. I'm not sure what all changed between 18.04 and 20.04.

Comment 7

[swoogan]

It turns out that GMail is still using Roboto even though I uninstalled it and that is why it is still bad.

I experimented with changing the CSS in the developer tools and when I removed Roboto the rendering improved. I erroneously believed that if I uninstalled the font from my system, it would then use Arial on the page, hence the confusion.

Just now, I changed the font from using a 0.2 space to 0 and the rendering improved. Other values like 0.4 and 0.8 increased the spacing, but did not change the fact that 'i' and 'e' have inconsistent spacing around them.

Comment 8

[swoogan]

Attachment: kerning 100%.png

Here is with the page scaling at 100%. Notice the large gap in front of the 'i' in kerning and the 'e' in incorrect.

Note that this image has been scaled by 2x from its original size.

Comment 9

[swoogan]

Attachment: kerning 110%.png

Here is with the page scaling at 110%. Notice the large gap after the 'i' in kerning and the 'i' in incorrect? There is also a somewhat large gap before the 'e' in kerning and incorrect.

Note that this image has been scaled by 2x from its original size.

Comment 10

[swoogan]

I have a few new pieces of info:

1. The "dancing" of the fonts came back with a vengeance. It happens on Google Hangouts, LinkedIn, and Twitter among other sites. They all seem to have Roboto as the font and I can induce the dancing by rolling over some text on the site.
2. I can eliminate it by setting "Sub-pixel rendering" to None in the KDE System Settings. So, it appears that Lee's intuition is correct regarding the sub-pixel anti-aliasing being intermittently disabled.
3. I can eliminate the font issues (what I called incorrect kerning) by enabling the "Force Font DPI" setting. I've tested with 166 and 120. These settings make the rendering nice, but the fonts too big to be practical.

Incidentally, I found that a new application I installed was rendering the font in the same way, which indicates a system problem and not a Firefox problem. I believe the application is built with Electron, which is curious since Chromium doesn't seem to have any problems.

I am leaving this ticket open because the sub-pixel rendering induced "dancing" could still be a Firefox issue, but feel free to close this if it seems as though it's a KDE issue.

Lastly, as I mentioned before, I have two computers with the same versions of everything. The one that has issues has a display with 165.63 PPI and the other where it doesn't happen is 81 PPI.

Comment 11

[Wayne Mery (:wsmwk)]

(In reply to swoogan from comment #10)

...
Incidentally, I found that a new application I installed was rendering the font in the same way, which indicates a system problem and not a Firefox problem. I believe the application is built with Electron, which is curious since Chromium doesn't seem to have any problems.

I am leaving this ticket open because the sub-pixel rendering induced "dancing" could still be a Firefox issue, but feel free to close this if it seems as though it's a KDE issue.

Are we still undecided if this is KDE?