The order and way include macros were structured was chaotic, with no
real common thread between files. Try to tidy up the mess with some
common scheme, to make things look less messy.
Instead of hardcoded knowledge of certain classes in MetaWindowGroup,
create a generic interface that all actors can implement to get parts of
their regions culled out during redraw, without needing any special
knowledge of how to handle a specific actor.
The names now are a bit suspect. MetaBackgroundGroup is a simple
MetaCullable that knows how to cull children, and MetaWindowGroup is the
"toplevel" cullable that computes the initial two regions. A future
cleanup here could be to merge MetaWindowGroup / MetaBackgroundGroup so
that we only have a generic MetaSimpleCullable, and move the "toplevel"
cullability to be a MetaCullableToplevel.
https://bugzilla.gnome.org/show_bug.cgi?id=714706
Background handling in GNOME is very roundabout at the moment.
gnome-settings-daemon uses gnome-desktop to read the background from
disk into a screen-sized pixmap. It then sets the XID of that pixmap
on the _XROOTPMAP_ID root window property.
mutter puts that pixmap into a texture/actor which gnome-shell then
uses.
Having the gnome-settings-daemon detour from disk to screen means we
can't easily let the compositor handle transition effects when
switching backgrounds. Also, having the background actor be
per-screen instead of per-monitor means we may have oversized
textures in certain multihead setups.
This commit changes mutter to read backgrounds from disk itself, and
it changes backgrounds to be per-monitor.
This way background handling/compositing is left to the compositor.
https://bugzilla.gnome.org/show_bug.cgi?id=682427
