In the purely paint node based rendering future, ClutterEffects
simply add more paint nodes to the tree when painting the actor.
This is the leap to achieve that future.
Add paint nodes to pre_paint, paint, and post_paint, and move the
ClutterEffectNode creation to _clutter_effect_paint().
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1355>
When painting, actors rely on semi global state tracked by the state to
get various things needed for painting, such as the current draw
framebuffer. Having state hidden in such ways can be very deceiving as
it's hard to follow changes spread out, and adding more and more state
that should be tracked during a paint gets annoying as they will not
change in isolation but one by one in their own places. To do this
better, introduce a paint context that is passed along in paint calls
that contains the necessary state needed during painting.
The paint context implements a framebuffer stack just as Cogl works,
which is currently needed for offscreen rendering used by clutter.
The same context is passed around for paint nodes, contents and effects
as well.
In this commit, the context is only introduced, but not used. It aims to
replace the Cogl framebuffer stack, and will allow actors to know what
view it is currently painted on.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/935
All those effects have the same basic pattern of setting a
color of a pipeline, then drawing a rect with cogl_rectangle().
Thus, replacing those was as easy as retrieving the draw
framebuffer and calling cogl_framebuffer_draw_rectangle() on it.
In cogl use cogl-config.h and in clutter use clutter-build-config.h. We
can't use clutter-config.h in clutter because its already used and
installed.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
