Created attachment 113232 [details] Dolphin with badly scaled icon sizes I'm running Plasma 5.12.5 on Kubuntu 18.04, and HiDPI seems partly broken. It was working at first on clean install, but broke somewhere when updating to the latest packages. I've installed very little non-stock software so I'm not sure what could have broken it. I have scale set to exactly 2.0. Basic scaling of fonts works, but anything involving icons and graphics doesn't work -- margins are all off, icons are tiny, etc. I've tried setting and re-setting the scale factor a few times but it does nothing. In the past, stuff like this was sometimes fixed by setting PLASMA_USE_QT_SCALING, and I usually set that up by default. But now, PLASMA_USE_QT_SCALING seems to have no effect at all. Is there some change made very recently that disables this environment variable? Is there some other environment variable being set that this depends on? GDK_SCALE and GDK_DPI_SCALE still work pretty well for scaling GTK apps; the problem seems limited to Qt.
This may be a symptom of a more general problem on my machine, as I just noticed other random graphics settings are also off, such as cursor settings. Some applications seem to work fine (Chrome), but whenever the cursor is over the desktop, it suddenly switches back to Breeze-Dark. Likewise with Dolphin. This is not strictly related to HiDPI, but I'm leaving it here in the hopes that it might leave some clues as to the problem - perhaps some kind of system or render settings have gotten corrupted?
Actually, sorry, I managed to fix this. Something had corrupted my system settings, so by deleting all files of the form k* in .config, the problem fixed itself. I'm not sure how they got corrupted or if some routine update did this, but if so the bug has nothing to do with HiDPI support.