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This removes a lot of unnecessary code that is generated by
the compiler automatically.
In very few cases, a defaulted destructor in a .cc file is
still necessary, because of forward declarations in the header.
I removed some defaulted virtual destructors, because they are not
necessary, when the parent class has a virtual destructor already.
Defaulted constructors are only necessary when there is another
constructor, but the class should still be default constructible.
Differential Revision: https://developer.blender.org/D10911
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Write custom properties (aka ID properties) to Alembic, to the
`.userProperties` compound property.
Manifest Task: https://developer.blender.org/T50725
Scalar properties (so single-value/non-array properties) are written as
single-element array properties to Alembic. This is also what's done by
Houdini and Maya exporters, so it seems to be the standard way of doing
things. It also simplifies the implementation.
Two-dimensional arrays are flattened by concatenating all the numbers
into a single array. This is because ID properties have a limited type
system. This means that a 3x3 "matrix" could just as well be a list of
three 3D vectors.
Alembic has two container properties to store custom data:
- `.userProperties`, which is meant for properties that aren't
necessarily understood by other software packages, and
- `.arbGeomParams`, which can contain the same kind of data as
`.userProperties`, but can also specify that these vary per face of a
mesh. This property is mostly intended for renderers.
Most industry packages write their custom data to `.arbGeomParams`.
However, given their goals I feel that `.userProperties` is the more
appropriate one for Blender's ID Properties.
The code is a bit more involved than I would have liked. An
`ABCAbstractWriter` has a `uniqueptr` to its `CustomPropertiesExporter`,
but the `CustomPropertiesExporter` also has a pointer back to its owning
`ABCAbstractWriter`. It's the latter pointer that I'm not too happy
with, but it has a reason. Getting the aforementioned `.userProperties`
from the Alembic library will automatically create it if it doesn't
exist already. If it's not used to actually add custom properties to, it
will crash the Alembic CLI tools (and maybe others too). This is what
the pointer back to the `ABCAbstractWriter` is used for: to get the
`.userProperties` at the last moment, when it's 100% sure at least one
custom property will be written.
Differential Revision: https://developer.blender.org/D8869
Reviewed by: sergey, dbystedt
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Replace nested `namespace blender { namespace io { namespace alembic {`
with `namespace blender::io::alembic {`.
No functional changes.
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Add support for object data instancing. This is used when the objects
are instances, for example when duplicated by a particle system, or
instanced by the duplication system (collection-duplicating empties,
vertex/face duplis, etc.)
Since Alembic already deduplicates data, this doesn't make the resulting
Alembic files any smaller. They will be faster to write, though, when
there is a lot of instanced geometry, as the deduplication system won't
have to do any comparisons.
This instancing support is still limited, in the sense that only object
data is instanced and all transforms are still written explicitly. A
future improvement could be to support instancing entire collection
hierarchies.
Blender's Alembic importer has no understanding of these Alembic
instances yet, and will thus happily duplicate the data on import.
The USD Alembic plugin seems to have problems understanding the
instancing. There might also be other software with similar issues.
Because of this, instancing can be turned off in the exporter (it's on
by default).
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