Instancing

Instancing is the process of creating identical occurrences (instances) of geometry, at render time. Where a single piece of geometry is used multiple times in a scene, it can be beneficial to use instances, rather than copies to reduce the memory overhead of the scene. Rather than individual copies, where each copy has its own geometry attributes, instances use the geometry of a source location. This means that the memory overhead of an instance can be greatly reduced compared to a copy. The overhead of the instance location is limited to bookkeeping, such as maintaining transformation matrices.

The greatest benefits from instancing are seen when rendering many instances of complex source geometry. As mentioned previously, there is a minor bookkeeping overhead with each instance location, so if the source geometry is very light (such as a single primitive sphere), the benefits of instancing likely doesn't outweigh the cost of that additional bookkeeping.

The differing approaches adopted by the available renderers also have an impact on the level of benefit gained from instancing.