Code review comment for lp:~smspillaz/compiz-core/compiz-core.work_923683

One small caveat is that I haven't merged lp:compiz-core into this one today, which includes the region fixes.

> Does DecorWindow::moveNotify really need to computeShadowRegion on EVERY window whenever a single window moves?

Yes it does. There are some optimizations we can do there to make it only compute regions on certain windows. I've done them before, so its not too hard. Not for this branch.

> From what I can tell, the problem is that moveNotify is called much more often with this branch. However moveNotify is far too expensive to call so often, mostly due to DecorWindow::moveNotify.

So I think there are three optimizations which can be applied here, all of which are quite involved, so I'll need to put them in separate branches.

Firstly, we need to throttle motion events, so they aren't dispatched spuriously. That's easy enough to do.

The second which is a bit more complicated is to also throttle dispatch of serverGeometry updates / moveNotify / XConfigureWindow as well. There are some plugins which need immediate move notify updates but probably not immediate move notify updates 1000 times a second.

Another optimization is to only call XConfigureWindow when we actually need to update the server side position and not necessarily all the time. This does mean that serverGeometry will be "ahead" of whats being sent to the server, but that's OK since we can just flush the changes on demand (and besides, its meant to be ahead, which is why its there).

Incidentally, I'm not able to get such high readings in callgrind for window movement, but I guess this is a case-by-case thing.