Working round a Qt bug always needs a Qt bug report referenced in a code comment.

The original workaround from QQC2-desktop-style (which I copied here) doesn't have that, sadly. I'm looking for it...

The closest I could find was https://bugreports.qt.io/browse/QTBUG-42606, which Kai filed for this exact issue, but only for 2x scale factors. It was closed as Cannot Reproduce. I have filed a new one: https://bugreports.qt.io/browse/QTBUG-67007

Did you actually properly test this, ie. without scaling? I can't see how this would be working:
1.) You're missing import QtQuick.Window 2.2
2.) There's no such property Window.devicePixelRatio, it's Screen.devicePixelRatio (which is also in the Window import, but that seems also wrong in the qqc2-desktop-style you got this from)

Thanks for finding bug report.

+1 from me.

You prompted me to look https://codereview.qt-project.org/222827 turns out it was a ridiculously easy fix.

Has the advantage that it'll fix the QQC1 desktop theme labels; but I'm ok with an interim fix.

In D11244#223654, @broulik wrote:

Did you actually properly test this, ie. without scaling? I can't see how this would be working:
1.) You're missing import QtQuick.Window 2.2
2.) There's no such property Window.devicePixelRatio, it's Screen.devicePixelRatio (which is also in the Window import, but that seems also wrong in the qqc2-desktop-style you got this from)

Yes, I did fully test with:

• No scale factor
• 1.2x scale factor
• 2x scale factor
• PLASMA_USE_QT_SCALING=1 both on and off for each one

Everything seemed to work fine. Window.devicePixelRatio is what QQC2-desktop-style used, so I just copied it. If there's something else more appropriate, I'm happy to use that instead, or fix the imports, or whatever. Again, this patch does work--though maybe by accident?

In D11244#223663, @davidedmundson wrote:

Thanks for finding the bug report.

+1 from me.

You prompted me to look https://codereview.qt-project.org/222827; turns out it was a ridiculously easy fix.

Has the advantage that it'll fix the QQC1 desktop theme labels; but I'm ok with an interim fix.

Wow, fantastic! I look forward to the day when we can remove all of this code, then. :)

Here's the bug tracking the QQC2 issue: https://bugs.kde.org/show_bug.cgi?id=391780

FWIW, by coincidence someone in the VDG room today actually independently noticed the difference between the two rendering styles (In Discover, which uses Kirigami, which uses the QQC2 label). You can see it in the following image:

Qt on the top, Native on the bottom. So yeah, we do want to make sure we're always using NativeRendering unless using QtRendering is required to avoid an even worse visual issue.

If and when David's Qt patch is merged, we can #ifdef this here and in QQC2-desktop-style so eventually even people who use non-integer scale factors can have the nicest possible text rendering.

You've added a load of bug reports about the kcms.
This patch won't change them at all.

if they're somewhat related but not risolutive for some of those bugs, use CCBUG: instead

So this is weird. I thought this patch fixes those KCMs, because I can get them into a fixed state, but it doesn't persist after a reboot. Steps to reproduce:

• Start with no scale factor
• Open System Settings → Display & Monitor → Display → Scale and turn on 1.3x scaling
• Restart system settings (and optionally KWin, to get bigger titlebars
• Navigate to L&f KCM. It looks amazing!
  
• Reboot the machine
• Navigate to L&f KCM again.Text is once again ugly and pixellated, boo!

Either way, that's probably a separate issue that I'll have to dig into later and address in a separate patch. I think this one is ready for final review now.

Friendly ping!