================== Alembic USD Plugin

.. include:: rolesAndUtils.rst

.. admonition:: Configure Environment

The Alembic USD plugin is not built by default. To enable it, the :makevar:PXR_BUILD_ALEMBIC_PLUGIN option must be specified when running CMake. Check the 3rd Party Library and Application Versions <https://github.com/PixarAnimationStudios/OpenUSD/blob/release/VERSIONS.md>_ document for the Alembic library versions that have been used for testing.

For more information see our page on Advanced Build Configuration <https://github.com/PixarAnimationStudios/OpenUSD/blob/release/BUILDING.md>_.

As shipped, USD supports its own text (usda) and binary (usdc) file formats. However, it is possible for USD to support additional formats by providing it with a custom file format plugin. One of these plugins, usdAbc, which provides the ability to interact with Alembic files, is included in the :filename:pxr/usd/plugin directory of the USD distribution. In this example, we'll demonstrate the extended USD functionality using the existing USD tools.

Let's start by creating a simple USD file (save it as :filename:hello.usda):

.. code-block:: usda

#usda 1.0

def Xform "hello" { def Sphere "world" { } }

The previous snippet defined a simple sphere in the :filename:.usda file format. Now, let's use :ref:toolset:usdcat to convert it to an Alembic file!

.. code-block:: sh

$ usdcat hello.usda --out hello.abc

Now we can use :ref:toolset:usdview to view our new alembic file.

.. code-block:: sh

$ usdview hello.abc

.. image:: http://openusd.org/images/plugins_alembic_usdview.jpg

We can also convert this Alembic file back to USD using a similar call to usdcat.

.. code-block:: sh

$ usdcat hello.abc --out hello_converted.usda

Known Limitations #################

In general, Alembic files can be used in place of USD files. There are some caveats to our current Alembic support in usdAbc. For example, we translate AbcGeom Schemas <http://docs.alembic.io/reference/abcg.html>_ except for FaceSet, NuPatch and Light.

Also, we currently don't translate Alembic's notion of Component Ops, instead we currently flatten them into a 4x4 Matrix, this could be added in the future.

Finally, while we hope to achieve lossless translation from abc to usd, :ref:Alembic files will never perform as well as native USD binary files in composed scenes <maxperf:use binary ".usd" files for geometry and shading caches>