sl0ptty: fix the split guide describing the layout from before the split

Which border the pointer is over was remembered from the last motion event, so
after a click split the guide stayed attached to the old pane and the old edge
until the mouse moved and corrected it.

It is derived during the paint now: draw_split_guide asks the hit list where
the pointer is, using the entries that same pass just registered for that pane.
Drawing and hit-testing already could not disagree; now drawing and the layout
cannot either. The pointer position is the only thing kept.

Same lesson as the hit list, one level up: do not remember what you can derive
from the frame you are drawing.

Regression test splits by clicking a border and then deliberately does not move
the mouse, asserting exactly one pane shows a guide, that it is the pane the
pointer is actually inside, and that it is on the edge the pointer is on.

391 checks green.

0 files changed, 0 insertions, 0 deletions