This commit takes the 'Slotted Actions' out of the experimental phase.
As a result:
- All newly created Actions will be slotted Actions.
- Legacy Actions loaded from disk will be versioned to slotted Actions.
- The new Python API for slots, layers, strips, and channel bags is
available.
- The legacy Python API for accessing F-Curves and Action Groups is
still available, and will operate on the F-Curves/Groups for the first
slot only.
- Creating an Action by keying (via the UI, operators, or the
`rna_struct.keyframe_insert` function) will try and share Actions
between related data-blocks. See !126655 for more info about this.
- Assigning an Action to a data-block will auto-assign a suitable Action
Slot. The logic for this is described below. However, There are cases
where this does _not_ automatically assign a slot, and thus the Action
will effectively _not_ animate the data-block. Effort has been spent
to make Action selection work both reliably for Blender users as well
as keep the behaviour the same for Python scripts. Where these two
goals did not converge, reliability and understandability for users
was prioritised.
Auto-selection of the Action Slot upon assigning the Action works as
follows. The first rule to find a slot wins.
1. The data-block remembers the slot name that was last assigned. If the
newly assigned Action has a slot with that name, it is chosen.
2. If the Action has a slot with the same name as the data-block, it is
chosen.
3. If the Action has only one slot, and it has never been assigned to
anything, it is chosen.
4. If the Action is assigned to an NLA strip or an Action constraint,
and the Action has a single slot, and that slot has a suitable ID
type, it is chosen.
This last step is what I was referring to with "Where these two goals
did not converge, reliability and understandability for users was
prioritised." For regular Action assignments (like via the Action
selectors in the Properties editor) this rule doesn't apply, even though
with legacy Actions the final state ("it is animated by this Action")
differs from the final state with slotted Actions ("it has no slot so is
not animated"). This is done to support the following workflow:
- Create an Action by animating Cube.
- In order to animate Suzanne with that same Action, assign the Action
to Suzanne.
- Start keying Suzanne. This auto-creates and auto-assigns a new slot
for Suzanne.
If rule 4. above would apply in this case, the 2nd step would
automatically select the Cube slot for Suzanne as well, which would
immediately overwrite Suzanne's properties with the Cube animation.
Technically, this commit:
- removes the `WITH_ANIM_BAKLAVA` build flag,
- removes the `use_animation_baklava` experimental flag in preferences,
- updates the code to properly deal with the fact that empty Actions are
now always considered slotted/layered Actions (instead of that relying
on the user preference).
Note that 'slotted Actions' and 'layered Actions' are the exact same
thing, just focusing on different aspects (slot & layers) of the new
data model.
The "Baklava phase 1" assumptions are still asserted. This means that:
- an Action can have zero or one layer,
- that layer can have zero or one strip,
- that strip must be of type 'keyframe' and be infinite with zero
offset.
The code to handle legacy Actions is NOT removed in this commit. It will
be removed later. For now it's likely better to keep it around as
reference to the old behaviour in order to aid in some inevitable
bugfixing.
Ref: #120406
43d7558e5b