[kde] [Bug 491015] New: [Wayland] Blurry fonts in Plasma shell and KDE apps when dual monitor and internal monitor is scaled

[Andrea Ippolito]

https://bugs.kde.org/show_bug.cgi?id=491015

            Bug ID: 491015
           Summary: [Wayland] Blurry fonts in Plasma shell and KDE apps
                    when dual monitor and internal monitor is scaled
    Classification: I don't know
           Product: kde
           Version: unspecified
          Platform: Other
                OS: Linux
            Status: REPORTED
          Keywords: regression
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: andrea.ippo at gmail.com
  Target Milestone: ---

Hi, this is an attempt to summarize bug report 488108, which has become too
noisy at this point.

I am experiencing a font blurriness problem ever since I updated 6.0.4 to
6.0.5, as if antialiasing was off somehow.

>From the screenshots I'm going to share this might look like a barely
noticeable issue, but IRL it really has an impact on the UX.
Whichever KDE/plasma app I use on my external display now has blurry fonts, it
looks a bit hazy as if my eyes were tired, which of course causes extra strain
on might induce headaches etc.

The only way to reliably make this issue objective/perceivable by others (short
of having them sit in front of my screen), is to zoom in on some screenshots
and focus on specific details.

Specifically, I advise on concentrating on lower case letter "e" and its
horizontal stroke, since it's the best metric I could find (but of course the
blurriness is not limited to that character). Please follow the "e"s in the
screenshots below. Zoom in as much as needed and you'll eventually see the
difference (again, it looks subtle on screenshots, but trust me the issue
exists and has a real impact on the overall UX even from .5 meters away)

In the "bad" screenshots you will see the horizontal stroke is a blur of TWO
horizontal rows of pixels.
In the "good" screenshots you will see that this stroke is made of a SINGLE
horizontal row of pixels -> this provides for a sharp, well rendered font

Now some bullet point recap:

- Problem only affects the fonts within the "content" areas of KDE apps (and
plasma widgets, e.g. Application launcher). The title bars are strangely NOT
affected
- I can only reproduce this with a dual monitor setup, and when scaling is
applied as follows:
        - Both displays at 100% -> no problem
        - *Internal* (laptop) display scaled (e.g. 120%), external 100% ->
fonts on *external* display blurry
        - External display scaled (e.g. 120%), internal 100% -> no problem
        - Both displays scaled (e.g. 120%) -> no problem
        - bottom line, this is never visible on the internal display, but it is
on the external one, depending on the *internal's* scaling
        - I can easily capture side-by-side screenshots of the issue by:
          - opening a KDE app (e.g. Dolphin) with my starting conditions on the
internal display's scaling factor
          - changing internal display's scaling factor
          - open another instance of the same app and put it side by side with
the previously opened instance
        - for Plasma workspace screenshots (e.g. Application Launcher widget),
since I can't "run" another plasma "window" I just capture a screenshot before,
then do a systemctl --user restart plasma-plasmashell.service, reopen the
widget and capture the second screenshot
- This started happening since upgrading 6.0.4 to 6.0.5
- I'm using Wayland, haven't tried with an X11 session
- Things tried (no success): https://bugs.kde.org/show_bug.cgi?id=488108#c6

I'm posting links to a screenshot selection from 488108 (please remember the
"e" rule):
- Application launcher compared with different scale factors -> blurry:
https://bugsfiles.kde.org/attachment.cgi?id=170944 not blurry:
https://bugsfiles.kde.org/attachment.cgi?id=170945
- Kate compared with different scale factors: blurry in the window at the top,
crisp in the one at the bottom:
https://bugsfiles.kde.org/attachment.cgi?id=170943
- close-up photos with different scale factors + systemctl restart plasma:
crisp: https://bugsfiles.kde.org/attachment.cgi?id=171070 blurry:
https://bugsfiles.kde.org/attachment.cgi?id=171069
- Title bar crisp, content blurry, proving that even when reproducing the
issue, the title bar fonts are NOT affected. Taking Konsole as an example:
https://bugsfiles.kde.org/attachment.cgi?id=171227, but also visible on Kate:
https://bugsfiles.kde.org/attachment.cgi?id=171225 and Dolphin:
https://bugsfiles.kde.org/attachment.cgi?id=171226

Feel free to read the whole history/attachments in report 488108.

I had reported 488108 under kwin but I'm putting this one under general, since
I don't know if the problem comes from some KDE framework module, some external
dependency (QT), or who knows what, so please I ask KDE devs to categorize as
they see fit.

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