Introduction

The Alembic (.abc) file format is a widely adopted standard in 3D production pipelines for storing and exchanging complex animated scenes. It supports efficient handling of large datasets, including geometry, hierarchy, and animation data.

Starting with Viz Engine 5.4, sampled meshes (meshes with time-varying vertex data) are natively supported in the Viz Engine Renderer. This functionality is provided through the DynamicGeometry system and its associated DynamicGeometryOmoNode, enabling real-time playback of baked simulations such as cloth, fluids, or character deformations directly from Alembic files.

In addition, animated transformations (position, rotation, scale over time) are supported, allowing for dynamic and accurate scene playback.

Supported Features

  • Sampled Meshes (Time-Varying Geometry)

    • Supported via DynamicGeometry and DynamicGeometryOmoNode.

    • Meshes with vertex positions that change over time (for example, baked simulations or deformations) are imported and rendered correctly.

  • Scene Tree Hierarchy

    • Preserved from the Alembic file.

    • Parent-child relationships and groupings are maintained.

  • Static and Animated Transformations

    • Both static and time-varying transformations (position, rotation, scale) are supported.

    • Transform animations are correctly imported and evaluated during playback.

    • Hierarchical transformations are respected.

How Alembic Operates in Viz Engine

  • Importing Alembic Files

    • Alembic files are imported via the Import section of Viz Artist.

    • During import, the Alembic content is converted into a merged GEOMETRY object and stored in Graphic Hub.

  • Resulting Object

    • The imported Alembic file appears as a GEOMETRY asset in Graphic Hub.

    • All meshes and hierarchy are merged into a single geometry object for simplified handling.

  • Playback and Rendering

    • If the Alembic file contains sampled mesh data, it is handled by the DynamicGeometry system. A “OMO” Generator is added automatically.

    • To modify the animation, you can split the imported object.

      image-20250723-080351.png

Sample-to-Time Conversion

When importing animated data from Alembic scene files, each animation sample must be accurately mapped to a time value in seconds. This conversion is essential for ensuring temporal consistency across different digital content creation (DCC) tools and playback environments.

To convert sample indices to time values, the importer follows a prioritized strategy determining the frame rate (FPS):

  1. DCC FPS Metadata
    If the Alembic file contains embedded metadata specifying the frame rate used in the original DCC application, this value is honored as the authoritative source. This ensures fidelity to the original animation timing.

  2. Engine Output Format Frame Rate
    If no metadata is available, the importer falls back to the frame rate defined by the engine's output format settings. This allows for consistent integration with the target rendering or playback environment.

  3. Default Frame Rate (24 FPS)
    In cases where neither metadata nor engine settings provide a usable frame rate, a default of 24 frames per second is applied.