We now rely on toplevels receiving and forwarding all the events
the windowing should be able to handle. Event masks are no longer a
way to determine whether an event is deliverable ot a widget.
Events will always be delivered in the three captured/target/bubbled
phases, widgets can now just attach GtkEventControllers and let those
handle the events.
Those are now needless and wrong, as we get guarantees that handled
events will contain widget-relative coordinates. A side effect is
that these events are very possibly not explicitly sent to the
GdkWindow that implementations expect, any extra checks performed
through gtk_gesture_set_window() will be wrong, so the function has
been dropped entirely.
This was only every implemented under X11, and with CSD,
this is clearly in the application realm. We should not
pretend that we can support it on the toolkit level.
https://bugzilla.gnome.org/show_bug.cgi?id=775061
gtk_snapshot_pop() => removed
gtk_snapshot_pop_and_append() => gtk_snapshot_pop()
So now there is no way to get a rendernode out of the snapshotting API
until you gtk_snapshot_finish().
... and use it.
The function is a bit awkward because it requires 2 calls to
gtk_snapshot_pop(), but once you accept that, it's very convenient to
use, as can be seen by the 2 implementations.
Now that every call to GtkCellArea is a snapshot call and no more cairo
calls are left, move the actual differentiation between Cairo and
Snapshot down to the cell renderer.
It is now possible to call push() subfunctions for simple container
nodes with just a single child. So you can for example
gtk_snapshot_push_clip() a clip region that all the nodes that get
appended later will then obey.
gtk_snapshot_pop() will then not return a container node, but a clip
node containing the container node (and similar for the transform
example).
This is implemented internally by providing a "collect function" when
pushing that is called when popping to collects all the accumulated
nodes and combine them into the single node that gets returned.
To simplify things even more, gtk_snapshot_pop_and_append() has been
added, which pops the currently pushed node and appends it to the
parent.
The icon rendering code has been converted to this approach.
We want to split nodes into containers and nodes that do actual drawing.
So pushing nodes that do drawing is exactly the wrong thing.
Also fix up GtkPopover. There's no need for it to push anything.
GtkCellView has a gadget, so peopl can do all their shenanigans with
CSS.
And the original use case (overriding the background so that the
cellview's GdkWindow shares the background color of the combobox) is
outdated since we have transparent backgrounds.
