If I run x14c like
examples/c/x14c -dev whatever
on a KDE desktop that is set up with the high or extreme setting to prevent focus stealing (via System Settings ==> Window Behavior ==> Window Behavior ==> Focus Stealing Prevention Level), it works fine for -dev xcairo, -dev qtwidget, and even -dev tk (once I click on the window generated by x14c to give that window focus), but hangs (with top giving 100 per cent of the cpu to x14c indefinitely) for -dev xwin regardless of clicking on the window. If I use -debug, I get one expose event before attempting to click on the window, but then it hangs with two black screens (one with a vertical red line through it) until I hit ctrl-C.
Demo of multiple output streams via the xwin driver.
Running with the second stream as slave to the first.
ExposeEH: x = 92, y = 0, width = 408, height = 410, count = 0, pending
If I set focus stealing prevention to none, low, or medium, all is well with -dev xwin.
In sum it appears with x14c (but no other example) that -dev xwin (but no other device including -dev tk) requires focus stealing (perhaps for the second window?) from the start or otherwise it hangs.