It was only done so the background would connect visually to the popover
tail, but then it brings aliasing issues when the border is drawn over the
background. Instead, overdraw the tail, so it also fills the gap left by
the border.
If pointing_to starts falling outside of the parent scrollable allocation,
the popover will be automatically hidden, and shown back again when
pointing_to scrolls back to visibility.
If the rect a handle points to starts falling outside of the parent
scrollable allocation, the handle will be automatically hidden, and
shown again when the rectangle is visible too.
When all popovers are removed on destroy(), if a popover is nested into
(eg. with relative_to within) another popover, the removal of one can
lead to the other being removed while the hashtable is being iterated,
which would lead to undefined behavior in further iterations.
Then, use a GList to store popovers, iterating can be made more resilient
on these situations, and unless on pathological cases there's not going
to be as many of those popovers as to cause performance decreases at the
times those are iterated.
The popovers may return keyboard grabs to previous widgets, so if
called after unsetting the focus, the window may be left with a
dangling GtkWidget that would cause crash at later dispose() calls.
With only get_preferred_width and get_preferred_height implemented,
we end up calling the GtkBin height_for_width implmementation, which
knows nothing about the margins and paddings that GtkPopover needs.
As a result, a listbox added to a popover was getting cut off
at the bottom.
This property is TRUE by default, when a popover is modal, it
will automatically set a GTK+ grab on the popover, and grab
the keyboard focus into the popover.
The GtkBuilder window containing the complex popover UI was left
dangling, and with a dangling pointer to its former child, causing
crashes on gtk_grab_notify() after the popover was destroyed.
Popovers are strange in the sense that they aren't attached to a
parent directly, they rely on the relative_to widget so the toplevel
is shared, and when they have a parent, it is the toplevel itself,
not relative_to. This also means that there are conditions where the
popover loses it's parent, so they must survive unparenting.
The previous code would be floating the last reference as soon as the
parent is gone, but it was non-obvious who'd own that reference. So
fix this situation by granting the ownership of popovers to their
relative_to widget, an extra reference may be held by the toplevel
when the popover has a parent, but the popover object will be
guaranteed to be alive as long as the parent lives.
This way, memory management of popovers is as hidden from the user
as regular widgets within containers are, users are free to call
gtk_widget_destroy() on a popover, but it'd eventually become
destructed when relative_to is.
When a popover is focused, the focus is forwarded so the first
child what would get the focus actually gets it. Also, implement
correct focus chain, so the keyboard focus stays within the popover
when navigating with keyboard.
This makes it possible to move/resize client-side decorated windows that are
otherwise obscured by a GTK+ grab somewhere else, either a popover within the
window itself or a modal dialog above the window.
This offers the same behavior, but GDK_WINDOW_TEMP windows aren't used
anymore, involving less translations from/to root coordinates, plus no
glitches in having handles snap to content as windows move.
