hlod

Hierarchical Level of Detail (HLOD) is a computer graphics technique used to improve the rendering efficiency of large 3D scenes. By grouping many small objects into clusters and representing each cluster with a simplified proxy mesh, HLOD reduces the number of renderable primitives and the overall draw calls required when objects are distant from the camera. This helps maintain frame rates in complex environments such as open-world games and architectural visualizations.

The core idea of HLOD is to create multiple levels of detail for groups of objects rather than for individual objects. A scene is partitioned into clusters at different levels of the hierarchy, with each cluster having a progressively simpler representation. During rendering, the system selects the appropriate level of detail based on factors such as the camera’s distance, screen-space size, or importance, and may blend between levels to avoid noticeable popping. The approach often works in concert with culling, impostors, or billboards to further reduce rendering load.

Generation and integration typically involve a preprocessing step where objects are clustered, merged, and decimated to produce proxy meshes that preserve the overall silhouette and spatial extent of the original content. Bounding volumes are calculated to support efficient culling, and transitions between detail levels are managed to minimize visual disruption. Some systems support dynamic streaming or on-demand generation to adapt to memory constraints and loading bandwidth.

Benefits of HLOD include reduced draw calls, lower overdraw, and improved performance in large scenes. Limitations can include preprocessing time, memory overhead for proxy data, and potential quality loss if proxies do not accurately represent the finer geometry. HLOD remains a common tool in modern rendering pipelines for scalable, high-detail environments.