I have laptop connected to external monitor via HDMI. In kdm Xsetup script I disable the internal screen (LVDS1 with res 1366x768) and enables the external screen (HDMI1 with res 1920x1200) using the xrandr. After the resolution changes kdm does not resize the used theme but just replicates (tiles) the bacground image. Reproducible: Always Expected Results: Theme should be resized/relayouted when the resolution changes.
Created attachment 82384 [details] make kdm (kgapp) listen to QDekctopWidget resize events I use to issue xrand -o (left|normal) commands in the XSetup script for kdm and the kdm always ignored the new size/orientation. The attached patch makes kdm (kgapp) listen to resize events of the underlying QDesktopWidget and resize its own Widget accordingly. It works well for me.
KDM is unmaintained and not used in KDE Plasma 5. SDDM is the login manager used in KDE Plasma 5. If you still have this same issue with SDDM, please file an issue on the SDDM bugtracker (after doing a search for existing issues first!): https://github.com/sddm/sddm/issues/