Documentserver: Blurry fonts in Firefox with custom zoom

[forteller]

Hi. Not sure if it's this NextCloud app or the server or what, but when using OnlyOffice trough NextCloud all the content in the documents are really blurry. Both the text and the numbers/letters and lines in spreadsheets. I'm using NC 17 on Owncube, with the OnlyOffice app v 4.1.4. It's the same for ODF and OOXML files.

My browser is Firefox 72.0.1, Ubuntu 19.10. Let me know if I can help with any more info. Hope you can move this if this is the wrong place for this bug report. This is my first one with you. Thank you so much for all the great work you're doing!

[Rita-Bubnova]

Hello, @forteller.
Blur seems to be related to your browser scale.
What scale is set in your browser?

[forteller]

Ah, yes, looks like it is. In the screenshots it's at 120%. But I checked now, and it's blurry at any scale larger than 100%, except for 200%. I't hard to check for scales smaller than 100%.

I don't have this issue with any other websites or web apps.

[Rita-Bubnova]

@forteller, we are aware of this problem and plan to fix it in the future.

[magikmw]

Any timeline on this one? We're currently testing this setup and the blur will surely turn away users, as it's distracting and frankly looks unprofessional.

Any way we can help?

[Rita-Bubnova]

@magikmw, we hope to fix this in next major release.

[nukeador]

I can confirm this issue on Firefox, document content fonts are always burry, no matter the hinting mode selected. I also reported this over here:

https://webcompat.com/issues/59717

Zoom settings don't solve the issue.

Personally this makes really painful to use on Firefox and I don't plan to replace my browser with other comercial user-tracking alternatives.

[nukeador]

OK, so I managed to improve the blurriness by reduzing Firefox zoom to 80% and then using the document zoom to make the text readable (140%). Note the screen resolution is 3840x2400 and OS scaling is set to 250%.

[emilio]

See https://github.com/webcompat/web-bugs/issues/59717#issuecomment-726019954. How is the canvas size determined?

[emilio]

Given that if I spoof the user-agent as Chrome it works correctly, it seems like some UA-sniffing issue.

These bits look related:

https://github.com/ONLYOFFICE/sdkjs/blob/4c25a716cd5832e854518ff70780ee27138d56a1/common/browser.js#L187