Because we have had several reports about significant performance
regressions since we enabled offscreen redirection by default for
handling correct opacity we are now turning this feature off by default.
We feel that clutter should prioritize performance over correctness in
this case. Correct opacity is still possible if required but the
overhead of the numerous offscreen allocations as well as the cost of
many render target switches per-frame seems too high relative the
improvement in quality for many cases.
On reviewing the offscreen_redirect property so we have a way to
disable redirection by default we realized that it makes more sense for
it to take a set of flags instead of an enum so we can potentially
extend the number of things that might result in offscreen redirection.
We removed the ability to say REDIRECT_ALWAYS_FOR_OPACITY, since it
seems that implies you don't trust the implementation of an actor's
has_overlaps() vfunc which doesn't seem right.
The default value if actor::redirect_offscreen is now 0 which
effectively means don't ever redirect the actor offscreen.
