Filter's changeRect() and merging problems

[Dmitry Kazakov]

Well, i've understood the problem if needRect/changeRect. It can be
merged with any need/change rect, the only thing we need - a separate
needRect for every layer. And a temporary buffer, where to put
projections to. This can be easily done with a recursion algorithm.
Change rects grow on forward way of recursion, need rects - on a way
backward.

Atm, i'm thinking over how to make getting rects, updating
projections, merging, all three in a uniform way.

I think, it should be somewhat "down-top" approach (in comparison with
our current "top-down" way). And everything should be based on a
recursion. That is just an idea. Don't know whether it's feasable.

--
Dmitry Kazakov