This complicated handling of undo steps in a generic way
especially switching between undo systems that stored data to ones
that accumulated changes.
Now each undo system must treat it's steps as check-point,
internally it can apply/rewind changes.
This commit also fixes projection paint where the object mode wasn't
following the undo steps.
BF-admins agree to remove header information that isn't useful,
to reduce noise.
- BEGIN/END license blocks
Developers should add non license comments as separate comment blocks.
No need for separator text.
- Contributors
This is often invalid, outdated or misleading
especially when splitting files.
It's more useful to git-blame to find out who has developed the code.
See P901 for script to perform these edits.
- Undo that changes modes currently asserts,
since undo is now screen data.
Most likely we will change how object mode and workspaces work
since it's not practical/maintainable at the moment.
- Removed view_layer from particle settings
(wasn't needed and complicated undo).
- Use a single undo history for all operations.
- UndoType's are registered and poll the context to check if they
should be used when performing an undo push.
- Mode switching is used to ensure the state is correct before
undo data is restored.
- Some undo types accumulate changes (image & text editing)
others store the state multiple times (with de-duplication).
This is supported by checking UndoStack.mode `ACCUMULATE` / `STORE`.
- Each undo step stores ID datablocks they use with utilities to help
manage restoring correct ID's.
Needed since global undo is now mixed with other modes undo.
- Currently performs each undo step when going up/down history
Previously this wasn't done, making history fail in some cases.
This can be optimized to skip some combinations of undo steps.
grease-pencil is an exception which has not been updated
since it integrates undo into the draw-session.
See D3113
