[kde] [Bug 492918] New: Font Hinting is Broken on Plasma 6 / Qt / Wayland

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https://bugs.kde.org/show_bug.cgi?id=492918

            Bug ID: 492918
           Summary: Font Hinting is Broken on Plasma 6 / Qt / Wayland
    Classification: I don't know
           Product: kde
           Version: unspecified
          Platform: Fedora RPMs
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: infinality at infinality.net
  Target Milestone: ---

Created attachment 173505
  --> https://bugs.kde.org/attachment.cgi?id=173505&action=edit
Screenshots illustrating the differences - Scaled up 5x for visibility

SUMMARY
I'm experiencing an issue with Plasma 6 on Wayland in scaled modes (anything
other than 100%), and it only seems to impact plasma/Qt applications.  To me,
it looks like it's forcibly turning font hinting off ("hintnone" in fontconfig
terms) rather than using the specified hinting (hintfull).

When scaling is set to 100% (in Display Configuration), fonts are correctly
rendered using the hinter configuration specified in fontconfig.  When scaling
is set to 150% or 200%, it appears to forcibly set "hintnone" or otherwise
prevent hinting.

Note that this is *not* blur due to scaling artifacts.  This appears to be a
problem with how freetype is being asked to hint the fonts when scaling isn't
100%. (i.e. freetype is being asked to not hint the fonts.)

STEPS TO REPRODUCE
1. Set fontconfig configuration to leverage truetype hinting and hintfull
(autohint=false, hintstyle=hintfull).
2. Set KDE fonts to something that leverages truetype full hinting such as
"Segoe UI 9" or "Arial 9", or some font that looks different when hinted at
all.
3. Set scaling to 100% in "Display Configuration", and log out and back in,
examine the rendered fonts.
4. Set scaling to 150% in "Display Configuration", and log out and back in,
examine the rendered fonts.
5. Compare.

OBSERVED RESULT
Fonts appear to not be hinted at anything other than 100%.

EXPECTED RESULT
Fonts should respect the fontconfig hinting configuration at all scales.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma:  Fedora 40
KDE Plasma Version:  6.1.4-1.fc40
KDE Frameworks Version:  6.5.0-1.fc40
Qt Version: 6.7.2-6.fc40

ADDITIONAL INFORMATION
See attachments for examples.  Included are:
- plasma 6 examples taken from the kwrite menubar (but same rendering is
present everywhere in plasma)
- forcibly unhinted examples (for confirmation that plasma isn't hinting fonts
at all)
- correct, properly hinted examples (what plasma *should* look like)

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