The depsgraph CoW mechanism is a bit of a misnomer. It creates an
evaluated copy for data-blocks regardless of whether the copy will
actually be written to. The point is to have physical separation between
original and evaluated data. This is in contrast to the commonly used
performance improvement of keeping a user count and copying data
implicitly when it needs to be changed. In Blender code we call this
"implicit sharing" instead. Importantly, the dependency graph has no
idea about the _actual_ CoW behavior in Blender.
Renaming this functionality in the despgraph removes some of the
confusion that comes up when talking about this, and will hopefully
make the depsgraph less confusing to understand initially too. Wording
like "the evaluated copy" (as opposed to the original data-block) has
also become common anyway.
Pull Request: https://projects.blender.org/blender/blender/pulls/118338
`UUID` generally stands for "universally unique identifier". The session identifier that
we use is neither universally unique, nor does it follow the standard. Therefor, the term
"session uuid" is confusing and should be replaced.
In #116888 we briefly talked about a better name and ended up with "session uid".
The reason for "uid" instead of "id" is that the latter is a very overloaded term in Blender
already.
This patch changes all uses of "uuid" to "uid" where it's used in the context of a
"session uid". It's not always trivial to see whether a specific mention of "uuid" refers
to an actual uuid or something else. Therefore, I might have missed some renames.
I can't think of an automated way to differentiate the case.
BMesh also uses the term "uuid" sometimes in a the wrong context (e.g. `UUIDFaceStepItem`)
but there it also does not mean "session uid", so it's *not* changed by this patch.
Pull Request: https://projects.blender.org/blender/blender/pulls/117350
