This problem exists also in KDE4. Plasmoids looks terrible when are rotated. Reproducible: Always Steps to Reproduce: 1. Add widget to the desktop area 2. Rotate to the angle different than 0/90/180/270 Actual Results: Widget without any form of antyaliasing. Expected Results: Beautifully rendered widget :) Archlinux (current) Linux 4.3.3-2-ck Nvidia 358.16 Xserver 1.18.0 Problem also occur on older version (of KDE/X/Nvidia driver).
Created attachment 96644 [details] example of bug
On KDE4 there was no such trouble, borders didn't have aliasing, everything was smooth but in KDE5 everything is aliased including letters.
Can confirm this bug in: Distribution: KDE neon Developer Edition - Stable Branches Plasma: 5.11.4 Frameworks: 5.41.0 Qt: 5.9.3 Kernel 4.10.0-40-generic Type: 64-bit
This was fixed in Plasma 5.20.