This is a lot of work for a small payoff - the mouse cursor is now
correctly rendered over the background.
Containers can now specify a custom arrange function which will be
called during arrange_windows instead of the usual path for that
container type. For backgrounds, the function sends it to the back and
sets its geometry to the size of the screen.
This requires some changes I'm not too happy with in arrange_windows
with respect to how containers figure out the arrangemnet of their
children (special cases are undesirable).
Also, if anyone runs a debug build as their actual WM, you should know
that I've made it so swaybg is invoked as `./bin/swaybg` in debug builds
now.
This PR also includes a bunch of unrelated refactoring. This is a pretty
significant change and I can only test it under the x backend, so I'd
appreciate it if you kind folks would review+test it yourselves and
leave some 👍 if you like it.
When querying for an adjacent output we now need an absolute position in
order to know which adjacent output that matches. (The position is
either the current mouse position or the center of the currently focused
container, depending on context.)
If two outputs have one edge each that at least partially align with
each other they now count as adjacent.
Seamless mouse is affected by this and now properly moves and positions
itself between outputs with "uneven" placement (as long as they have at
least some part of the edge adjacent to each other).
When focusing or moving a container in a specified direction the center
of the current focused container decides where to look for an adjacent
output. So if e.g. an output has two adjacent outputs to the right and a
"focus right" command is issued then it's the placement of the currently
focused container that decides which output actually gets focused.
Also, if an output has at least one output adjacent in some direction
but the entire edge is not covered (ie. it has "holes" with no outputs),
then the algorithm will choose the output that is closest to the
currently focused container (this does not apply to seamless mouse, the
pointer will just stop at the edge in that case).
