- Should I also make it work for when the dst is smaller than the src?
- If not, should the FIXME() in 1/2 be promoted to an error? Otherwise we might have segfaults, writing out of scope.
I think leaving it as a FIXME is fine, in the sense of "we don't know what to do with this, and it's a bridge we can cross when we get to" (and I find it rather unlikely that we will, personally).
- Should I use copy_plane(), introduced in 2/2 also in the implementation of the other formats? Changing what needs to be changed to preserve behavior of course.
I would at least use it for the manual cases, but leaving the memcpy() fast path seems like a good idea.