Aurélien Aptel wrote:

> Are you sure this won't break the rest of the code? (which relies
> heavily on clipping) It sure looks cleaner but the rest of the code
> uses ns_focus/unfocus.

Fairly sure.  What's needed here is a temporary change to the graphics
state in the middle of a redisplay; we change the clipping rectangle, draw
the underwave, then restore the previous clipping rectangle, if any.
ns_focus/ns_unfocus can't be used to do that; they're intended to be used
at the beginning and end of redisplay.