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
Add a new depsgraph builder class that includes invisible objects and
use that in the Alembic exporter.
Alembic supports three options for visibility, "visible", "inherited",
and "hidden". This means that parents can be hidden and still have
visible children (contrary to USD, where invisibility is used to prune
an entire scene graph subtree). Because of this, the visibility is
stored on the transform node, as that represents the Object in Blender
and thus keeps the Alembic file as close to Blender's own structure as
possible.
Reviewed By: Sergey
Differential Revision: https://developer.blender.org/D8595
The Alembic exporter has been restructured by leverages the
`AbstractHierarchyIterator` introduced by the USD exporter. The produced
Alembic files have not changed much (details below), as the Alembic
writing code has simply been moved from the old exporter to the new. How
the export hierarchy is handled changed a lot, though, and also the way
in which transforms are computed. As a result, T71395 is fixed.
Differences between the old and new exporter, in terms of the produced
Alembic file:
- Duplicated objects now have a unique numerical suffix.
- Matrices are computed differently, namely by simply computing the
evaluated transform of the object relative to the evaluated transform
of its export-parent. This fixes {T71395}, but otherwise should
produce the same result as before (but with simpler code).
Compared to the old Alembic exporter, Subdivision modifiers are now
disabled in a cleaner, more efficient way (they are disabled when
exporting with the "Apply Subdivisions" option is unchecked). Previously
the exporter would move to a new frame, disable the modifier, evaluate
the object, and enable the modifier again. This is now done before
exporting starts, and modifiers are only restored when exporting ends.
Some issues with the old Alembic exporter that have NOT been fixed in
this patch:
- Exporting NURBS patches and curves (see T49114 for example).
- Exporting flattened hierarchy in combination with dupli-objects. This
seems to be broken in the old Alembic exporter as well, but nobody
reported this yet.
Differential Revision: https://developer.blender.org/D7664
Reviewed By: Sergey
