Widgets can now set their favorite cursor using public API.
This is very necessary because all cursor-setting APIs are still
setting it on their GdkWindow, which by now is the toplevel - oops.
When a widget unparents its child widget manually in finalize, this can
lead to the parent-set signal being emitted for those child widgets. The
parent already has a ref_count of 0 though, so it can't be used in a
meaningful way. Specifically, emitting the signal will already try to
ref the parent which prints a critical.
Since GtkWidget already has a "parent" property, one can use its notify
signal instead to get notified when the parent widget changes.
Since gtk+ draws more than the widget and allocates more size to it than
it knows about, this flag doesn't work anymore. Removing it (or setting
it to TRUE for widgets that used to set it to FALSE) fixes drawing
invalidation when these widgets get allocated a new size.
Since setting a clip is mandatory for almost all widgets, we can as well
change the size-allocate signature to include a out_clip parameter, just
like GtkCssGadget did. And since we now always propagate baselines, we
might as well pass that one on to size-allocate.
This way we can also make sure to transform the clip returned from
size-allocate to parent-coordinates, i.e. the same coordinate space
priv->allocation is in.
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.
We now try to emulate cairo_t:
We keep a stack of nodes via push/pop and a transform matrix.
So whenever a new node is added to the snapshot, we transform it
by the current transform matrix and append it to the current node.
Before, we would immediately invalidate the GdkWindow of the widget, now
we call the parent's GtkWidgetClass.queue_draw_child() function.
This allows the parent to track redraw queueing of children.
By default GtkWidgetClass.queue_draw_child() will again chain up to its
parent while respecting the GdkWindow hierarchy for clipping.
GtkWindow is then the only widget actually invalidating the GdkWindow.
This essentially moves redraw queueing from GDK to GTK.
