Library Overrides¶
Library Overrides is a system designed to allow editing linked data, while keeping it in sync with the original library data. Most types of linked data-blocks can be overridden, and the properties of these overrides can then be edited. When the library data changes, unmodified properties of the overridden one will be updated accordingly.
ملاحظة
The old proxy system has been deprecated in Blender 3.0, and fully removed in Blender 3.2. Automatic conversion from proxies to library overrides happens when loading a blend-file, but results on complex characters are not guaranteed and may need manual fixes.
Library overrides supports:
Multiple independent overrides of a same linked data (e.g. having the same character multiple times in the same scene).
Adding new modifiers and constraints, anywhere in the stack.
Recursively chaining overrides (i.e. link and override overrides from another library file, etc.).
ملاحظة
There are known issues that have to be addressed. See the main task of the project, for more details.
تحذير
While in most cases library overrides data is preserved across a loss of reference linked data (if e.g. the library file becomes unavailable or is relocated), there are some exceptions.
The main one is probably posed (but not animated) armature objects, when their Armature obdata itself is not overridden. The Pose bones of an armature object are fully linked to the bones of its Armature obdata, if the later goes missing, the pose bones are definitively lost.
ملاحظة
Proper Collections Layout Matters
For library overrides to work well, it is much better if all the collections needed by the character are children of the root (linked and instantiated) one, such that there is a clear hierarchy. Otherwise, some data may not be properly automatically overridden, and other operations may be less reliable.
Override Hierarchies¶
Hierarchy is a very important concept to understand when working with library overrides. In Blender, a real-life asset (a character, a prop, a set, etc.) is almost never made of a single data-block, but is rather a group of data-blocks with dependency relationships to each-other. E.g. a character will typically have an armature object, several geometry objects, rig-controllers objects, the object data for all of these objects, materials, textures, etc.
These relationships can be represented as a tree, with a root data-block 'linking-in' all its dependencies, recursively. With library overrides, typically, the root of the hierarchy is also the data-block that is directly linked when importing the asset (usually a collection).
This concept of hierarchy can also be seen as some sort of super meta-data-block. It is critical when there are several overrides of the same linked data, since it allows to clearly identify a given data-block to one override, leaving no ambiguity to processes that affect the whole hierarchy (e.g. resyncing overrides with their linked data). It also allows to share relationships between data-blocks of different hierarchies, like a parenting relationships between two different overrides of a same character.
Animation & Overrides¶
Due to current design of animation data in Blender, what is editable in overrides' animations can change greatly depending on whether animation data was already defined in the linked reference data-block. Animation data is created for a datablock if it gets animated by keyframes, or through drivers.
In general, an overrides can do much more with its animation data if no animation data exists in its linked reference data-block.
Keyframes (a.k.a. F-Curves)
Keyframed animation belongs to another data-block (an Action one). So it is possible to assign a purely local Action data-block replacing the one linked from the library. This will completely replace the keyframed animation from the linked data though, and not override it in any way.
Overridden Action data-blocks only support a very limited amount of editing. For example, an existing F-Curve can be muted, but its keyframes cannot be edited, and no new F-Curve can be added.
Drivers
If the linked reference data has animation data, then its overrides only have limited possibilities to edit the existing drivers. For example, it will be possible to change the exisitng target of a driver, but it won't be possible to add new drivers, or new targets to an existing driver.
If the linked reference data has no animation data, then its overrides will create a new one when they get some drivers defined. Drivers can then be fully edited, added or removed, just as with purely local data-blocks.
NLA
The NLA editor data also belongs to the animation data of a data-block. However, this data does support some greater level of edition in overrides, including moving or resizing existing strips from the linked data, and adding new local strips.
Resyncing Overrides¶
The relationships between linked data-blocks can change, resulting in outdated overrides. When this happens, overrides need to be resynced to match the new structure of their hierarchy. Overrides are automatically resynced if needed on blend-files opening. However, it may be needed to resynced them manually sometimes, see Troubleshoot an Override Hierarchy.
نصيحة
Blender is also able to resync library overrides from external libraries, that are then linked into a working file. However, this is a costly process that needs to be fully redone every time the working file is loaded, since Blender cannot edit/modify the external library directly.
So users linking overrides (or creating recursive overrides) should ensure that their library files are regularly updated, to avoid this overhead on file load (typically, opening and saving those library files should be enough to update them).
نصيحة
Auto resyncing can be disabled in the Experimental Preferences.
Non-Editable Overrides¶
For technical reasons (how relationships between data-blocks are stored), Blender needs to create overrides of a lot of data-blocks, even when only one or two of them actually needs to be edited by the user. To reduce the amount of information and risk of potential unwanted editing, most of these data-blocks are now marked as non-editable by default. This can be changed once the override has been created.
Make an Override¶
Reference
- Editor:
3D Viewport, Outliner, Properties
- Mode:
Object Mode
- Menu:
- Shortcut:
Shift-LMB on the 'linked'/'overridden' button of an ID Widget.
Create overrides from the selected data-blocks.
Blender automatically create overrides for all required data-blocks to ensure that valid override hierarchies are created.
Only overrides created from selected items will be user-editable.
تحذير
The support for the creation of library overrides from the ID Widget (mainly from within the Properties editor) is limited. While the most common usages should be supported, especially with Objects, meshes, etc., much remains to be implemented.
Selected Items¶
Depending on where from the override is created, there are several ways to 'select' items to be overridden and user-editable.
ملاحظة
This also applies to the other common operations (Reset and Clear).
The Troubleshoot advanced operations only available from the Outliner always apply to a whole override hierarchy.
3DView¶
The selected objects will be considered as selected.
When a selected object is a local Empty instantiating a linked collection, the following will happen: * The Empty object will be removed. * Its linked collection will be overridden, and that override will be instanced in the same collection in the current View Layer. * If the collection contains Armature objects, they will be user-editable. Otherwise, no created override will be defined as user-editable.
Outliner¶
The operation can be applied on either the selected items only, their content only, or both.
نصيحة
Using Selected & Content is an easy way to get all newly created overrides immediately user-editable.
ID Widget¶
Only the linked data-block in the ID Widget is considered as selected, and set as editable once overridden.
Make Editable¶
That same operation can also be used to make existing overrides user-editable, after they have been created, or cleared
Reset an Override¶
Reference
- Editor:
3D Viewport, Outliner, Properties
- Mode:
Object Mode
- Menu:
Reset the selected overrides to their original values (from the linked reference data). Unlike with the Clear operation, the overrides remain fully editable, and are never deleted.
Clear an Override¶
Reference
- Editor:
3D Viewport, Outliner, Properties
- Mode:
Object Mode
- Menu:
- Shortcut:
Shift-LMB on the 'overridden' button of an ID Widget.
Reset the selected overrides to their original values, and if possible without breaking the existing hierarchy, delete them and replace them by their linked reference data. Otherwise, keep the overrides but mark them as non-editable.
Edit an Override¶
Essentially, an override is edited the same way as a regular local data-block. You can use operators on them, edit their properties from various editors, etc. There are some limitations however, most notably Edit Mode is not allowed for overrides. In most cases, as soon as you edit a property, you can see that it's overridden by its teal blue outline/background.
You can also animate overrides, animated properties just replace/supersede overrides then. Note that you cannot override/edit an existing animation, you'll have to create a new action. You can manually define or remove an override from the context menu of the relevant property. If an override is not editable, you have to make it editable first.
Define Overrides¶
Reference
- Editor:
Any
- Mode:
Object Mode
- Property:
Mark a property to be overridden in the local blend file. For array properties all elements will be overridden.
Define Single Override¶
Reference
- Editor:
Any
- Mode:
Object Mode
- Property:
Mark a property to be overridden in the local blend file. For array properties only the selected element will be overridden.
Remove Overrides¶
Reference
- Editor:
Any
- Mode:
Object Mode
- Property:
Remove the property from the overrides. The value of the linked in data-block will be used. For array properties all elements will be removed from the override.
Remove Single Override¶
Reference
- Editor:
Any
- Mode:
Object Mode
- Property:
Remove the property from the overrides. The value of the linked in data-block will be used. For array properties only the selected elements will be removed from the override.
Troubleshoot an Override Hierarchy¶
Reference
- Editor:
Outliner
- Mode:
Object Mode
- Outliner:
These operations are only available from the Outliner contextual menu. They can help fixing a broken override hierarchy.
Resync¶
Reference
- Editor:
Outliner
- Mode:
Object Mode
- Outliner:
The hierarchy of the linked data (the relationships between linked data-blocks) can change. Overrides need to be resynced to match the new hierarchy. This operator will resync the override to match the new hierarchy in the library.
تحذير
While resyncing a library override it is possible that edited overrides get deleted if they are changed in the original library. If this is the case, a warning message will be displayed stating how many overrides were deleted, if the deletion is undesirable the resync can be undone before saving the blend-file.
ملاحظة
This Process is Automatic
Usually, this operation happens automatically when blender detects it is needed, on file load, unless it is disabled in the Experimental Preferences.
Resync Enforce¶
Reference
- Editor:
Outliner
- Mode:
Object Mode
- Outliner:
In some cases, especially with older blend-files that were saved with 'broken' (non-hierarchy-matching) overrides, a regular resync itself cannot rebuild properly the override as expected (e.g. some objects might go missing). To solve this issue, this operator rebuilds the local override from its linked reference, as well as its hierarchy of dependencies, enforcing that hierarchy to match the linked data (i.e. ignoring existing overrides on data-blocks properties). This is similar to a regular resync, but is more forceful, aggressive, at the cost of a potential loss of some overrides on ID pointers properties.
Delete¶
Reference
- Editor:
Outliner
- Mode:
Object Mode
- Outliner:
Remove the whole library override hierarchy, and replace all of these override data-blocks by their original linked data-blocks. This fully reverts the Make operation.