Just as with painting, add a pick context that carries pick related
temporary state when doing actor picking. It is currently unused, and
will at least at first still carry around a framebuffer to deal track
view transforms etc.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/935
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
If an effect is active and it overrides the paint volume, we should
always recompute the paint volume when requested and not use the
cache, since the paint volume override can change from call to
call depending on what phase of painting we are in. For instance,
if we are part way through painting effects and request the
paint volume, the paint volume should only go up to the current
effect, but in a later call to compute repaint regions, the
paint volume needs to expand to accomadate the effect.
This still involves a lot of recomputation in the case of effects -
in a later clutter version it would be worth adding an API to
allow effects to explicitly recompute and return a new the paint
volume up to the current effect as opposed to recomputing
the cached one.
