FWIW, I just went ahead and played with the 'clear screen' idea a bit, and it's of course doable by playing around with the framebuffer...
It's not pretty, but it works

.
(Cf. current_ss_preview() in the
ScreenSavers KUAL ext).
(Yes, that means that a crazy person should be able to build a crappy image viewer around KUAL

).