I'm running KDE on Wayland. I've noticed that some Qt applications that render using OpenGL show significant color banding, as if they're running with less-than-24-bit color. What could be causing this, and how can I fix it?
Note, this is not a display output issue, as a) it can be captured in screenshots (see below), and b) it seems to only affect Qt applications that render using OpenGL (although seemingly not kwin, since only some applications are affected despite using HW-accelerated compositing). glxgears does not seem to be affected. Gwenview in particular is affected iff "Animations" are set to "OpenGL".
Here's an example. Kolourpaint (left) is showing the image correctly, but significant banding is present in the plasma (desktop wallpaper, right).
I suspect Qt is, for some reason, "defaulting" to a 16-big (RGB565) GL format, but how do I tell Qt to not do that?
