I installed a fresh Neon (dev unstable), removed the preinstalled files from /etc/fonts, copied your files to /etc/fonts and applied this patch.
Still cannot reproduce your issue.

I still cannot reproduce your issue. Any idea what I could try?

• Current kcm / new kcm's advanced tab

In D12925#302675, @ngraham wrote:

With this latest version, the issue I mentioned earlier persists for me. I did briefly get sub-pixel rendering again to work by switching the hinting style to Full, but then after switching back to something else and then back to Full again, it no longer worked and I was back to no sub-pixel rendering again. Feels kinda buggy.

Either way, we first need to implement tabs with a decent look&feel in Kirigami (resolve bugs 394295 and 394296) .

• fix writing config temporarily (previews) with missing local config entries

So we keep the separator line in the advanced mode and drop the tabs from D12849#263660 ?

We already discussed in D12849 if we should split the current layout into two tabs.
I like the idea of a simple mode and using tabs here seems like a good idea.
But we might want to have three tabs (Simple, Fonts fine-tuning, Rendering fine-tuning).

could you give me all those files?

Works for me....

• fix previews

I am not sure about the case when neither global nor local configs exist for subpixel or hint.
On my system it seems like rgb subpixel rendering with slight hinting is used when no configs exist. But I cannot find any documentation on this.

• Merge branch 'master' of git://anongit.kde.org/plasma-desktop into arcpatch-D12925
• Merge branch 'master' of git://anongit.kde.org/plasma-desktop into arcpatch-D12925
• also drop vendor-default-option for subpixel and hint

• split changes to previewimageprovider.cpp to a separate commit

Big sorry for being away for so long. I had some things to do that took much more time than initally planned.
Many thanks to those who fixed the bugs I introduced or created workarounds...

Rebase on master. Partial rewrite.

Sorry for the delay...
I planned to land this together with D12849 and D12925.

In D12925#264085, @rkflx wrote:

I'll resume testing once this works a bit better. I'd say let's not rush this, and get it right for 5.14.

• i18n

In D12849#263865, @rkflx wrote:

Did not review the code, but I noticed some warnings in addition to those mentioned above:

share/kpackage/kcms/kcm_fonts/contents/ui/main.qml:230:25: QML Image: Invalid image provider: image://preview/0_0.png
…
share/kpackage/kcms/kcm_fonts/contents/ui/main.qml:273:17: QML SpinBox: Binding loop detected for property "value"

The first isn't critical and exists since the previews were introduced. I will try to fix this in a separate commit.
The second on doesn't show up for me...

• title case for 'Choose a Font'

• remove unintentionally committed debug lines

That would be this one:

In D12849#262919, @progwolff wrote:

In D12925#263459, @mart wrote:

if it removes the vendor default option, how can i ask to not touch the global/local defaults in any way?

• Fix 'disabled from'

In D12849#263302, @broulik wrote:

We were always told by VDG that tabs are bad and a 5 km vertically scrolling list is better no matter what. So be consistent, please.

From what I could find there is no TabView in QtQuickControls2 or Kirigami.
This is how it's done in Kirigami Gallery:

In D12849#262903, @ngraham wrote:

@progwolff, what happened to the frame for the tabbed view?

Did it the wrong way. Is fixed now.

• fix tabbar frame

Using tabs there are some problems with Kirigami now:

• fix button widths

• use tabs

• Use radio buttons. Use spacing instead of Separator. Simplify max(...).

In D12849#262782, @rkflx wrote:

In D12849#262781, @progwolff wrote:

In D12849#262777, @rkflx wrote:

BTW, what's the difference between Vendor Default and the regular Defaults button? Either we provide an option to reset to the default for every single option separately, or for none at all.

Here "Vendor Default" means that no value is written to the user's ~/.config/fontconfig/fonts.conf. There might be a system wide config file though that has different settings.

But the same argument holds basically for any system-wide default setting? The only difference here is that normally defaults are provided via KConfigXT, while here it comes from fontconfig. Could we simply read the vendor default value, display it in the UI and finally if the user's choice is different, write it to the user's config?

In D12849#262777, @rkflx wrote:

How about joining the options instead?

You mean like this?

In D12849#261837, @ngraham wrote:

We might want to take the opportunity to also center-align the titles, which it better-looking for these centered formlayout style UIs.

Section titles in form layouts are left-aligned. This would have to be changed in Kirigami. @mart, am I right?

In D12220#247232, @mwolff wrote:

Overall, imo, I really think we should instead fix clang upstream so that we can re-enable this feature as we got it through libclang. See also:

https://phabricator.kde.org/D8857
https://bugs.llvm.org/show_bug.cgi?id=35333

In D12220#247155, @mwolff wrote:

I'm very unsure about this. On one hand, this obviously looks better in your screenshots. On the other hand, what if we encounter comments that are formatted with some other syntax?

Do you have examples for comments in a different syntax? I only know javadoc, which is quite similar.
Maybe there is a way to add the proposed functionality to the clang backend instead. This way we could be sure that the comments we parse are always doxygen comments.

• fix newline escape sequence

• fix @see

In D12220#246563, @croick wrote:

This is great! Could you add \ref, \link and \endlink as well?

• remove newline

In D11768#236348, @broulik wrote:

Still, that folder exists by default

Are you sure? It might be created by some weird startup script or something else. Also, a user can choose to change the location of the Desktop folder. Just wanting to make sure this change (which I'm totally in favor of, don't get me wrong) doesn't break or have unwanted side-effects.

• giant comments

• split buddyComponent and checkableBuddyComponent
• toggle checkbox on shortcut activated

In D11289#229340, @mart wrote:

can you provide screenshots as well t see how does it look?

I tested it with several running applications, including windows with different apect ratios and combined previews for multiple instances of the same application. Looks great in every case.

Could you please rebase on current master?

@hein might be right here.
If it's the single-click/double-click thing or this issue here: People who are happy with the status quo won't reach out to us.
Maybe we need to discuss at a different place if and how we can learn about the opinion of the majority of KDE/Plasma users, before we change things that are possibly only broken for few.

There seems to be a problem with the overflow menu:

Marked some typos. Note that I am not a native speaker, so please re-check them.

@davidedmundson ping?

I tried to unclutter the old kcm / new advanced mode a bit.
What do you think about this?

I remember that the dark tooltips felt strange to me when I started using breeze.
Now that I am used to it, I actually prefer the dark tooltips because of their high contrast to the other GUI elements.

• remove nullptr check, use const QString, style

• remove unnecessary semicolon

• Use QWebEnginePage::selectedText()

In D11118#221546, @ngraham wrote:

• Try to break it every way we can

Couldn't break it so far

I really like that install button. Maybe it could be added to KWidgetsAddons?
I see usecases in Okular for installing backends or in Telepathy for installing plugins.