Testing points and rays against boxes is substantially cheaper - in
fact, almost trivial - compared to triangles. Check if the actor's
paint volume doesn't intersect with the current pick point / ray,
and skip recursing altogether in those cases.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1520>
ClutterPickStack is a new boxed type that stores the vertices
and clip rectangles. It is meant to be a byproduct of picking,
and takes over most of what ClutterStage currently does.
It introduces a 'seal' system, inspired by MetaKmsUpdate. After
the pick operation is done, and the rectangles are collected,
the pick stack is sealed, and is not allowed to be externally
modified anymore. Internally, it still can invalidate pick
records when an actor is destroyed.
For now, it handles both the clip rectangles, and the matrix
stack, separatedly. Future commits will rearrange this.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1509
Just as with painting, add a pick context that carries pick related
temporary state when doing actor picking. It is currently unused, and
will at least at first still carry around a framebuffer to deal track
view transforms etc.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/935
