Currently object bounds (`object.runtime.bb`) are lazily initialized
when accessed. This access happens from arbitrary threads, and
is unprotected by a mutex. This can cause access to stale data at
best, and crashes at worst. Eager calculation is meant to keep this
working, but it's fragile.
Since e8f4010611, geometry bounds are cached in the geometry
itself, which makes this object-level cache redundant. So, it's clearer
to build the `BoundBox` from those cached bounds and return it by
value, without interacting with the object's cached bounding box.
The code change is is mostly a move from `const BoundBox *` to
`std::optional<BoundBox>`. This is only one step of a larger change
described in #96968. Followup steps would include switching to
a simpler and smaller `Bounds` type, removing redundant object-
level access, and eventually removing `object.runtime.bb`.
Access of bounds from the object for mesh, curves, and point cloud
objects should now be thread-safe. Other object types still lazily
initialize the object `BoundBox` cache since they don't have
a data-level cache.
Pull Request: https://projects.blender.org/blender/blender/pulls/113465
1cbd0f5a85