Sybren A. Stüvel
70b1c09d7a
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
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