This was only living in gtkcontainer.c for historic
reasons. Move it closer to where it belongs, and
rename it from 'idle' to 'layout', since it is
really about the layout phase of the frame clock,
nowadays.
The border is now drawn on the frame node, not using an internal border
node, so we are no longer able to align the label to vertically overlap
the border. The property no longer performs its original purpose, & nor
is it a useful candidate for giving a new role, so no point keeping it.
https://bugzilla.gnome.org/show_bug.cgi?id=778886
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.
Turns out that the destination is the last parameter, not the first one.
This fixes the flickering in the first page of the widget-factory when
using the expander on page 2.
The fact that it doesn’t reuse the existing GtkLabel if present is not
immediately obvious to users (or is it just me?), so clarify that the
pre-existing :label-widget, if any, is always removed and replaced.
It does weird clipping that
(a) nobody likes
(b) is hard to support in the new rendering world.
So we take the easy way out.
The actual frame is now drawn by the frame node around the label.
Add a new ::measure vfunc similar to GtkCssGadget's that widget
implementations have to override instead of the old get_preferred_width,
get_preferred_height, get_preferred_width_for_height,
get_preferred_height_for_width and
get_preferred_height_and_baseline_for_width.
We were adding the border gadget size and the label widget size in any
case, but when calculating the width, we want the maximum of those two,
not the sum.
https://bugzilla.gnome.org/show_bug.cgi?id=760482
Setting label-yalign should affect the border gadget, but we need to
compensate for its position by moving the child down or up, depending on
the border gadget's position, so the child never moves.
https://bugzilla.gnome.org/show_bug.cgi?id=762123
