Signals for when any window changes in any way

[Amy C <mathematical coffee gmail com>]

Hi all,

I'm currently having fun porting xpenguins to a gnome shell extension
(yes pointless I know, but fun), and I basically need to keep track of
where every window is on the screen at all times. This is so that
toons can walk on the windows as if they were physical objects.

I'm trying to decide between two ways of doing this:

1) for each frame of the animation, loop through all the windows &
build up the region, just as a union of rectangles.

2) listen to the following events and update the region whenever it gets fired:
- window tracker: "minimize", "maximize", "unmaximize", "switch-workspace"
- for each workspace: "window-added", "window-removed"
- whenever the workspace that XPenguins is running in is destroyed:
"notify::n-workspaces"

- whenever a window moves or changes size (including while they are
resizing/dragging): ??what event signal??
- whenever window stacking order changes ??what event signal??

In case it's relevant, "rebuilding the window region" means looping
through all windows on the specified workspace and adding their
`get_outer_rect()` to a list.

Now 1) is simple, but perhaps is inefficient - I'm using a
Clutter.Timeline (for now) to do the animation, and (I think) it does
one new frame per monitor refresh rate (roughly). So rebuilding the
window region could get slow, especially since users aren't usually
moving their windows around all the time.

Number 2) seems a little better in that the window region is only
updated when it needs to be, which is almost certainly going to be
less than once per frame.
However since there are so many events to connect up, I'm a bit
worried about missing some. Have I covered all of them above? All I
need is a list of window rectangles that is *always* up-to-date, so
I'm after any events pertaining to this.
Also, what is the relevant signal for windows changing
size/position/stacking order? (If you resize or move a window over a
toon it'll get squashed.)

If anyone has another idea of how I can do this, I'm all ears.

cheers!
Amy