Arch Linux

Many versions of QT have gone by since this bug was created. Can the opener of this bug please reply back if this is still an issue? Is the problem only in QT5 and not in QT4? What fonts are installed? I am not convinced this is specifically a QT bug regardless, freetype has problems with certain fonts. Waiting for your response.

Yes, this is still an issue with Qt 5.6. The problem is particularly noticeable in "More Settings" of Plasma (5)'s panel settings (attached), and some Window decorations when a window is first opened (triggering a redraw by maximizing then restoring the window makes the text render correctly).

The font in use is Clear Sans, but the problem occurs with all fonts I've tried.

A similar issue occurred in Qt 4 when the native (rather than raster) graphics system was in use, but Qt 5 no longer uses these backends.

In fact, following further investigation, the issue only manifests in KWin in decorations that are defined using SVG files, so I think the bug is in Qt's SVG rendering.

Okay, and this is only an issue in Qt packages and not GTK or other toolkit ones? If you want a fix you can try https://wiki.archlinux.org/index.php/Infinality which uses a patched version of the freetype libraries. It is an unofficial repository but I use it on my laptop and it solved all kerning problems I have ever had in pretty much every program. If you want you can try installing freetype2-infinality-ultimate and report back on if that fixes the problem, if so then it is likely a freetype+QT5 problem. Even if infinality works properly, this bug report is still valid though, as I believe infinality's freetype patchset changes some things to force proper rendering so obviously somewhere there is a problem going on.

Yes, this is only a problem in Qt applications, and I am already using Infinality.

In particular, see my comment about this appearing to be limited to occasions where Qt draws items using SVGs.

Sorry I started typing that message before I received the previous one. Okay I have located where this issue is occurring (Click the menu button on the plasmashell panel and then click more settings) and am seeing it as well, though it is not as pronounced as your link so I did not notice it until I looked very close at the monitor. I will look into this now that I can now replicate and test this myself. Thank you, your response is very much appreciated.

In KWin, you should also be able to see it if you set the Window Decoration to an Aurorae one, then open the save file dialog in Chromium.

FYI, this is Qt  bug 49646  (https://bugreports.qt.io/browse/QTBUG-49646), and KDE bug 355935 (https://bugs.kde.org/show_bug.cgi?id=355935).