Using listener here, although I suspect we should be using message
subscriber only. That said, this mimics the behaviour of the buttons
main region.
As for the original bug report what was happening was that when
switching between viewlayers (or when creating one) we may not get the
same active object. So the context breadcrumbs are different.
And the bug itself was that we were missing a redraw on view layer
change.
Aka all the thousand of reports duplicated here.
I should have seen this coming, since I had to add a hack in the first
place because things were "not working".
I should have figured out earlier that COW handles base in a really
special way, with its own special object_runtime_backup hack.
LaplacianDeform binding handling is a catastrophee in CoW context,
because half of the binding (the laplacian solver cache thingy) is not
saved, and can be re-generated on the fly from stored vcos.
This means that binding is not only done when hitting 'bind' button, but
also at file load, and when some things change.
And this utterly breaks with CoW design, not sure how to fix, will add a
task about that.
But this also means that NULL laplacian solver cache pointer is not a
good check to know whether it is binded or not, only stored vcos are
relevant for that (and the binding flag, of course).
This fixes/clarifies Surface Deform evaluation code that does the
binding, since that part should only be called outside of depsgraph
evaluation, with orig data-blocks and not CoW ones.
Now we have a decent amount of asserts and checks to ensure eveything
works as expected.
Also had to add a special case to get target's mesh in binding case,
since often target's evaluated mesh is not available, in that case (and
in that case only), we can actually compute that mesh (because we are
out of depsgraph evaluation).
Binding and unbinding *has* to happen outside of 'normal' depsgraph
evaluation of modifiers now that we have CoW, otherwise persistent data
stored in modifier data are always lost!
Note that this is only first step of the fix, modifiers code needs also
some work. Surfacedeform one is in next commit, Laplacian case is much,
much more complicated to handle, given how it uses its cached data. :(
