* It looks like data output from host to device is not quite
pixel-perfect. I tried to select 444 RGB only and disable YCbCr 444/422,
but I'm not certain that worked since my laptop AMD GPU does not provide
adequate debugging facilities.
pattern sync depends on the x/y position of the pattern.
* Also, the windowing logic seems to be kind of bugged. It paints the
window only in the vsync interval *above* the window.
