PointInstancer Object Model

Introduction

Several years prior to developing general scene-level instancing in USD, at Pixar we were using a specialized point/array/table instancer consisting of a schema, optimized drawing support in Hydra, and plugin support in Katana (read only), Houdini, Presto, and Maya (export only). Today, even though scene-level instancing is broadly deployed in our pipeline, there are still scalability use cases for a vectorized instancer over having many prim-instances: when the number of instances grows to the tens or hundreds of thousands or more (largest instancer to-date in production had around nine million instances) and the need to interact with individual instances is small, an instancer will load faster and consume less memory than individual prim-instances.

Our Houdini plugins rely on pointInstancers as they map so closely to Houdini's instancing model; therefore to enable open-sourcing of those plugins, we are reformulating our internal pointInstancer - mostly simplifying, plus applying some lessons learned from earlier versions - for inclusion in UsdGeom.