On Wayland, options don't influence compositing as on X11. For example,
kwin cannot easily switch between compositing modes, etc.
One can still force kwin_wayland to reinitialize compositing by using
the dbus api.
With the current vision for how output backends work, the compositor
should take up more responsibilities. There are a few good reasons: some
things just don't make sense to be in backends, to allow sharing code
across backends easier, etc. On the other hand, we have X11, with its
own ways of doing things which are not always compatible with what we
want to do on Wayland.
The goal of this patch is to start splitting the compositor into
platform specific counterparts, with potentially moving X11 compositing
in kwin_x11. The main benefit of this is that we will be able to
push forward with wayland things more freely. Ideally it would be great
if we could make kwin_x11 have its own low level compositing code paths
that are nicely encapsulated in that executable and don't leak into
libkwin abstractions.
The biggest drawback of this approach is that there is going to be some
code duplication between x11 and wayland compositing code paths. But I
expect it to be the case only for a short term until we start landing
more abstractions in kwin_wayland, e.g. render devices, proper output
layer support, etc.
The main motivation behind this change is to encapsulate X11 compositor
implementation to the point that it can be moved from libkwin to
kwin_x11.
There are two options: either get rid of suspend and resume requests, or
add suspend and resume virtual functions in the Compositor. The apps
must definitely not rely on the dbus api, they must use the X11 api.
Compositing suspension api works only on X11 and it's quite obscure,
it's not used by any other KDE component.
So this patch goes for the most simplest option: dropping the requests.
This allows checking if the given override redirect is the composite
overlay window without resorting to platform specific implementation of
Compositor.
Currently, the Workspace is responsible for rerouting
X11Window::blockingCompositingChanged to
X11Compositor::updateClientCompositingBlocking(). It has a few issues:
if the client is initially blocking compositing, it's not going to work
as expected. The second issue is that it creates a coupling between
platform specific compositor implementation and generic Workspace. It's
a blocker for moving X11Compositor to kwin_x11 executable, etc.
