IDs like embedded ones (master collections, root node trees) cannot be
linked, and thus cannot be real override themselves.
Since they are managed by their owner ID, that one will also have the
overrides for their locally edited properties.
We still need a way to mark them as overridden though, for various UI
and override-internal purposes, this is done using a new ID flag.
Note that since Shae Keys are not linkable, and their pointers are not
editable in RNA, they are also considered as embedded from override
point of view.
This will not give any noticeable improvements in common editing tasks,
since then usually only a very few IDs are changed and checked for
override updates.
However, it makes full override diffing process several times faster
(happens usually when saving a .blend file, but could also help e.g.
when multi-editing several override objects at the same time...).
By using own path construction instead of handy printf-like functions,
we get a 10% improvement on overall diffing process!
This remains way to slow on some complex production characters, but
always good to have still.
Now all overrides are handled that way. Performances of the process look
decent enough, even with production characters...
If performance issues still arise, we'll investigate other solutions.
This should also make T73154 obsolete now.
This commit enables basic copy of overrides on generic ID level, as well
as from (deep) copy operators for objects and collections.
So e.g. if your linked overridden caracter is in a collection, you can
now (from the outliner) Duplicate that override collection to get a new
overriding copy of the character.
We still need operators (new or modifying existing ones) to handle that
from 3DView e.g.
Note that deep copy code for objects/collections (and incidently
animdata) had to be modified to avoid duplicating/making local IDs that
remain linked ones being used by overrides ones.
Local datablocks (including overrides) need to have a unique name, which
can then differ from the reference linked one (especially when there are
several local overrides of a same linked data).
Issue is, ID name is a 'rna name property', and as such used as
reference when dealing with override of collections of IDs, so we cannot
have a changing name.
The solution implemented here should work and is simple, but it may have
some issues in corner cases (time will say), it is not really robust.
Alternative solution would be to store ID pointers as reference in
override operations, instead of there name. But that would potentially
add quiet a lot of overhead to foreach looping in `lib_query.c`.
Note this only changes cases where the variable was declared inside
the for loop. To handle it outside as well is a different challenge.
Differential Revision: https://developer.blender.org/D7320
