Merge branch 'undo-experiments' into undo-experiments-remap-history

Merge branch 'master' into undo-experiments

Undo: Initial wip useless to handle ID pointers issues through more mappings.

Don't think this is a working solution in fact, for at least two
reasons:
* Chaining Undo and Redo steps in random paterns with some ID being
reused and others being new all the time would require a very complex
system to keep track of all those changes and keep being able to remap
properly pointers from unread datablocks the the right new memory of
read datablocks.
* As small as it is, there is a risk of pointer collision here, and I
cannot see how to 100% handle it safely and sanely.

Undo: Re-use existing IDs from old bmain: do not search by name.

This is actually a fairly bad idea, since IDs can be renamed...

Only search by pointer value now, this *should* work in all expected
cases once undo/redo fully reuses unchanged data-blocks.

Undo: save/restore DEG closer to the actual undostep.

Revert "Fully WIP code."

This reverts commit d726305d98db6ccfb1f3b4cd9b7b75540e606faa.

Need better cleaner changes here.

Merge branch 'master' into undo-experiments

Merge branch 'master' into undo-experiments

Fully WIP code.

Don't have proper solution yet for issue described in comment in
readfile.h, still investigating...

Merge branch 'master' into undo-experiments

Undo spped-up: remove collections from ignored IDs.

Looks like this is not crashing anymore (though still very bugy), the
others (UI dtat-blocks) we do not really care anyway...

Merge branch 'master' into undo-experiments

undo experiments: actually write at leat one memchunck per ID.

Checked that before, but missed the fact that the flush was done after a
whole ID type process in the main saving loop, now we actually do it
after every ID when using mem undo file saving.

Besides fixing the stupid issue with lots of unchanged IDs being
detected as changed when reading back the undo step, this should also
help reduce undo memory usage in some cases (although I could not detect
that with some quick test...).

Merge branch 'master' into undo-experiments

Undo experiments: remove assert that can only be true in some specific cases.

Undo experiments: proof-of-concept of reusable depsgraph across undo steps.

This is still very sketchy, but seems to work in basic cases. useless
currently, though, as objects are always changed still currently in undo
steps...

Not Yet Working (r)

Merge branch 'master' into undo-experiments

Merge branch 'master' into undo-experiments

Merge branch 'master' into undo-experiments

Merge branch 'master' into undo-experiments