This patch makes that work using 1 of 2 options:
1. Add all missing enums to the switch statement
or
2. Cast the switch argument to a uint to avoid having to do that (mostly
for GdkEventType).
I even found a bug while doing that: clearing a GtkImage with a surface
did not notify thae surface property.
The reason for enabling this flag even though it is tedious at times is
that it is very useful when adding values to an enum, because it makes
GTK immediately warn about all the switch statements where this enum is
relevant.
And I expect changes to enums to be frequent during the GTK4 development
cycle.
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.
When there is no externally allocated baseline, we should
do the same thing that GtkBox does, and determine one from
the children that want baseline alignment.
This commit adds a GtkCenterBox::baseline-position property
with setters and getters.
The center widget in GtkBox was only introduced to use it in
GtkActionBar. However, the implementation there is much more complex
than it needs to be, so move the center widget into GtkActionBar instead
and later remove it from GtkBox.
