Make focus part of transactions

Rather than maintain copies of the entire focus stack, this PR
transactionises the focus by introducing two new properties to the
container state and using those when rendering.

* `bool focused` means this container has actual focus. Only one
container should have this equalling true in its current state.
* `struct sway_container *focus_inactive_child` points to the immediate
child that was most recently focused (eg. for tabbed and stacked
containers).

1 files changed, 3 insertions, 0 deletions

diff --git a/include/sway/tree/container.h b/include/sway/tree/container.h
index 11780916..04e50fc6 100644
--- a/include/sway/tree/container.h
+++ b/include/sway/tree/container.h
@@ -68,6 +68,9 @@ struct sway_container_state {
         struct sway_container *parent;
         list_t *children;
 
+        struct sway_container *focused_inactive_child;
+        bool focused;
+
         // View properties
         double view_x, view_y;
         double view_width, view_height;