|
Each duplicated (a.k.a. instanced) object has a Persistent ID, which
identifies a dupli within the context of its duplicator. This ID
consists of several numbers when there are nested duplis (for example a
mesh instancing empties on its vertices, where each empty instances a
collection). When exporting to Alembic/USD, these are used to uniquely
name the duplicated objects in the export.
This commit reverses the order of the persistent ID numbers, so that the
first number identifies the first level of recursion. This produces
trees like this:
ABC
`--Triangle
|--Triangle
|--Empty-1
| `--Pole-1-0
| |--Pole
| `--Block-1-1
| `--Block
|--Empty
| `--Pole-0
| |--Pole
| `--Block-1
| `--Block
|--Empty-2
| `--Pole-2-0
| |--Pole
| `--Block-2-1
| `--Block
`--Empty-0
`--Pole-0-0
|--Pole
`--Block-0-1
`--Block
It is now clearer that `Pole-2-0` and `Block-2-1` are instanced by
`Empty-2`. Before this commit, they would have been named `Pole-0-2` and
`Block-1-2`.
|
|
Exporting a scene to USD or Alembic would fail when there are multiple
duplicates of parent & child objects, duplicated by the same object. For
example, this happens when such a hierarchy of objects is contained in a
collection, and that collection is instanced multiple times by mesh
vertices. The problem here is that the 'parent' pointer of each
duplicated object points to the real parent; Blender would not figure
out properly which duplicated parent should be used.
This is now resolved by keeping track of the persistent ID of each
duplicated instance, which makes it possible to reconstruct the
parent-child relations of duplicated objects. This does use up some
memory for each dupli, so it could be heavy to export a Spring scene
(with all the pebbles and leaves), but it's only a small addition on top
of the USD/Alembic writer objects that have to be created anyway. At
least with this patch, they're created correctly.
Code-wise, the following changes are made:
- The export graph (that maps export parent to its export children) used
to have as its key (Object, Duplicator). This is insufficient to
correctly distinguish between multiple duplis of the same object by
the same duplicator, so this is now extended to (Object, Duplicator,
Persistent ID). To make this possible, new classes `ObjectIdentifier`
and `PersistentID` are introduced.
- Finding the parent of a duplicated object is done via its persistent
ID. In Python notation, the code first tries to find the parent
instance where `child_persistent_id[1:] == parent_persistent_id[1:]`.
If that fails, the dupli with persistent ID `child_persistent_id[1:]`
is used as parent.
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D8233
|
