Before this commit, the window switcher skipped all the child windows.
However, as child windows not marked as modal dialogs can lose focus
(ref. `desktop_focus_view()`), it will make sense to include them in the
window switcher so that users can refocus them with keyboard.
This behavior follows KWin.
We declared `cycle_state` struct in `labwc.h` and `cycle_osd_scene`
struct in `output.h`, which was unclean in terms of separation of
concerns.
So this commit firstly moves `cycle_state` to `cycle.h`, then replaces
`cycle_osd_scene` in `output.h` with `cycle_osd_output` in `cycle.h`
which is dynamically allocated in a similar manner to
`session_lock_output`. This ensures that all states about alt-tabbing
are stored in `server->cycle`.
Also, this commit fixes a rare memory leak in `output->cycle_osd.items`
when an output is destroyed while alt-tabbing, by freeing it when the
osd tree is destroyed.
Add a new configuration option to control the window switcher traversal order.
`order="focus"` cycling is convenient for quick toggling, but some users - me as well -
prefer a stable taskbar-like order which can now be achieved with `order="age"`.
I think `<windowSwitcher><osd output="keyboard">` is a bit unclear and
hard to interpret as "show OSD in the output with keyboard focus". Also,
we use "cursor" instead of "pointer" in other configurations like
`<placement policy="cursor">` and `<action name="ShowMenu" atCursor="">`.
So let's replace `output="all|pointer|keyboard"` with
`output="all|cursor|focused"`. In documentation, I reordered them to
`output="all|focused|cursor"` as "focused" feels like a bit more
sophisticated and general policy.
This allows changing the cycled order in the future, e.g. focused order vs
created order.
Functionally, this commit also changes the initially selected window;
before this commit, the previous/next of the topmost window was always
selected, but now the previous/next of the active window is selected first
if it is in the cycled list. This won't change behaviors for most users,
but this ensures that the user can go back to the focused window with
Alt-Tab + Alt-Shift-Tab even when it is not the topmost window.
This commit fixes the TODO in the previous commit by trying to preserve
the selected view when a view is destroyed during window cycling.
This commit clarifies the lifecycle of the window switcher (cycle) by:
- init_cycle(): initializes the window switcher (e.g. OSD).
- update_cycle(): updates the window switcher states including OSD,
preview and outlines.
- destroy_cycle(): clears all the window switcher states.
This commit temporarily regresses by not trying to preserve the selected
view when a view is destroyed. This will be addressed in the next commit.
With this approach, we only need to store cycle->dummy_node instead of
cycle->preview_anchor and cycle->preview_parent and we don't need to care
about annoying cases like when the previewed window has no siblings or
when a window tracked by cycle->preview_anchor is destroyed.
We were using the word "osd" to describe the window switcher, but it can
be used with on-screen display (OSD) disabled by
`<windowSwitcher><osd show="false">`. Let's use "cycle" instead to avoid
confusion.
