Alembic

AbcMaterial is a module designed to provide schemas and object types for representing materials and material bindings. It sits above the core Abc module and is independent of AbcGeom.

Major Classes

• (I|O)MaterialSchema: Provides an interface for writing data and metadata to a compound property that represents a material definition.
• (I|O)Material: Interfaces a MaterialSchema onto an IObject using an "is a" pattern. Use this to create objects that function as material definitions themselves.
• MaterialFlatten: A utility class used for flattening material inheritance. This is the primary interface for applications that only care about the final resulting material of an object, regardless of whether that material was defined via assignment, local definition, or inheritance.

Alembic supports instancing where one hierarchy can point to another to save space. When reading instanced data, use these methods to identify the relationship:

• isInstanceRoot(): Returns true if this object is the source/root of an instance.
• isInstanceDescendant(): Returns true if this object is an instance of another hierarchy.
• instanceSourcePath(): If the object is an instance root, returns the path to the source hierarchy. Otherwise, returns an empty string.
• getInstancePtr(): Returns the original AbcA::ObjectReaderPtr if the object is an instance.

In Alembic, ScalarSample is a helper class used primarily by Scalar Readers and Writers. It is not intended to be the primary object of exchange for scalar data in your application, as it carries an extra DataType overhead (approximately 2 bytes) that can be wasteful when passing data frequently.

Its main roles are:

1. Comparison: Allowing readers and writers to compare new samples against previously written/read samples.
2. Copying: Facilitating the copying of sample values.
3. Encapsulation: Providing a unified interface for handling different scalar types at the abstract level.

When stitching files that may have non-contiguous time samples, you can control how the output archive handles gaps using the -hold flag.

• Without -hold (Default): Missing samples are filled with an empty sample (oSchema.set(emptySample)).
• With -hold: Missing samples are filled using the value from the previous sample (oSchema.setFromPrevious()).

The AbcExport plugin provides a single command to write Alembic files from Maya. Unlike standard file translators, AbcExport can write multiple files with different settings in a single pass through the frame range.

To use the command, pass a JSON-formatted string to the -j flag containing the specific Alembic export options.

// Write out the entire scene from frame 1 to 100
AbcExport -j "-fr 1 100 -file scene.abc";

// Write out only selected shapes and their ancestor nodes
AbcExport -j "-sl -file scene.abc";

The Alembic Maya plugin provides integration for importing Alembic files into Autodesk Maya. It registers three primary components: a command, a node, and a file translator.

Upon initialization, the plugin displays its version and the version of the underlying Alembic::AbcCoreAbstract library in the Maya information console.

To include AbcMaterial in your Alembic build:

1. Place the AbcMaterial directory within the lib/Alembic directory of your Alembic checkout.
2. Add ADD_SUBDIRECTORY( AbcMaterial ) to the CMakeLists.txt file located within the lib/Alembic directory.
3. Compile the project using CMake.

# Add this to lib/Alembic/CMakeLists.txt
ADD_SUBDIRECTORY( AbcMaterial )

To load an Alembic file into Maya, use the AbcImport command. This is the simplest method for importing an Alembic scene.

Note that AbcImport manages an AlembicNode. While an AlembicNode exists in the scene, you should use the AbcImport command to create and manage it rather than interacting with the node directly, especially if the scene contains animated data.

AbcImport "scene.abc";

The Alembic Python bindings are organized into several submodules that correspond to the core C++ library components. To use Alembic in Python, you must import the base alembic module and then import the specific submodules required for your task (e.g., Abc, AbcGeom, AbcCoreAbstract).

Note: The bindings depend on the imath module, which must be available in your Python environment.

import alembic
import alembic.Abc
import alembic.AbcGeom
import alembic.AbcCoreAbstract
import alembic.Util