| Summary: | Text rendering in Plasma UI components using Text.Rendering does not respect system's hinting and sub-pixel anti-aliasing settings resulting in blurry fonts | ||
|---|---|---|---|
| Product: | [Frameworks and Libraries] libplasma | Reporter: | Rain <slonkazoid> |
| Component: | components | Assignee: | Plasma Bugs List <plasma-bugs-null> |
| Status: | CONFIRMED --- | ||
| Severity: | normal | CC: | kde, kdedev, kokoko3k, kzn.hartwig1, nate, notmart, nvcosj, skygalaxy19, slonkazoid, stereomato |
| Priority: | NOR | Keywords: | accessibility |
| Version First Reported In: | 6.1 | ||
| Target Milestone: | --- | ||
| Platform: | Fedora RPMs | ||
| OS: | Linux | ||
| Latest Commit: | Version Fixed In: | ||
| Sentry Crash Report: | |||
| Attachments: | zoomed in text on the desktop being rendered with RGB subpixel antialiasing | ||
*** Bug 502664 has been marked as a duplicate of this bug. *** *** Bug 502664 has been marked as a duplicate of this bug. *** *** Bug 503381 has been marked as a duplicate of this bug. *** I found out that the forced RGB subpixel anti-aliasing comes from Qt Quick's renderType "Text.QtRendering". Switching to the renderType "Text.NativeRendering" fixes this issue, because Text.NativeRendering does acknowledge the native font rendering settings. However it seems that the renderType of a Qt Quick application is only changeable at compile-time. I was not able to change the renderType globally via Linux environment variables, so Idk how to fix it for my KDE Plasma desktop and third party Qt Quick apps. I was only able to fix in my own Qt Quick app by adding "renderType: Text.NativeRendering". This is a problem, because I don't have a RGB monitor, but BGR monitor, and the forced RGB subpixel anti-aliasing causes colour-fringing/chromatic aberration for texts in Qt Quick/QML. https://doc.qt.io/qt-6/qml-qtquick-text.html#renderType-prop Oh, that makes perfect sense. Thanks for tracking it down. I recall that we've bounced back and forth a few times between QtRendering and NativeRendering. Unfortunately each one is affected by different bugs' NativeRendering isn't as good with fractional scale factors IIRC. *** Bug 504643 has been marked as a duplicate of this bug. *** *** Bug 506244 has been marked as a duplicate of this bug. *** I dug into this a bit and found that we use QtTextRendering to work around a Qt bug that makes text look really weird at random fractional scale factors: https://bugreports.qt.io/browse/QTBUG-126577 In qqc2-desktop-style (which controls apps, not Plasma) there's some code to use use NativeTextRendering if your scale factor is 1, but Plasma doesn't have that. As a result, everything in Plasma always uses QtTextRendering, which exposes everyone to the different bug of QtRendering failing to respect your hinting and sub-pixel anti-aliasing settings. It would appear this is blocked on https://bugreports.qt.io/browse/QTBUG-126577 being resolved; once it is, we can consider going back to NativeTextRendering. Lowering priority because unfortunately this isn't actionable right now. |
Created attachment 179555 [details] zoomed in text on the desktop being rendered with RGB subpixel antialiasing SUMMARY Sometimes, the text all over plasmashell is rendered using RGB subpixel antialiasing while my system default is set to None. It only seems to happen in plasmashell components- other apps like Firefox, Kate, even System Settings work as expected. STEPS TO REPRODUCE TODO: Have not yet been able to deduce. OBSERVED RESULT As explained prior, see attachment. EXPECTED RESULT Text should be rendered according to the same antialiasing rules the rest of the system abide by *all* the time, not most. SOFTWARE/OS VERSIONS Linux/KDE Plasma: KDE Plasma Version: 6.3.2 KDE Frameworks Version: 6.11.0 Qt Version: 6.8.2 ADDITIONAL INFORMATION Worked around by restarting plasmashell, such as by running `plasmashell --replace`