Run SwingSet2 on Linux using JDK 9 or 11, specify -Dsun.java2d.uiScale=2
It all looks good.
Now specify -Dsun.java2d.xrender=false, and lots of things are clipped.

So the non-default X11 pipeline isn't ready for hidpi.
Since it is not the default, and is almost never needed any more, and there is also the workaround
of disabling (or not enabling) hidpi, it may be that we just should say the X11 pipeline does not support
hidpi.