Early this year, NVIDIA released their new raytracing technology, RTX Mega Geometry, alongside an impressive Zorah demo. Distributed as a ~100 GB Unreal Engine scene, it showcased driver-exposed clustered raytracing combined with the Nanite clustered LOD pipeline. An open-source vk_lod_clusters update later featured the scene as a glTF file, leading to improved hierarchical clustered LOD support in meshoptimizer.

The task involves generating a hierarchical structure to represent a mesh at any level of detail, streaming parts appropriately, and rendering visible sections efficiently. The chosen structure is a graph of clusters; each represents a small patch with up to 128 triangles. Runtime code streams them to minimize visual error, replacing coarse clusters only if deviation stays under 1 pixel.

Building the structure splits the mesh into clusters, merges neighboring groups, simplifies them independently, and recurses until admissible clusters remain. Since Nanite launched in 2021, multiple engines adopted this paradigm. meshoptimizer now provides end-to-end examples combining these algorithms, enabling efficient processing of massive geometry while preventing cracks between clusters at varying detail levels.